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Fish exhibit a broad spectrum of colors and patterns facilitated by specialized cells known as chromatophores. The vibrant coloration of fish, controlled by complex genetic and environmental interactions, serves critical roles in ecological functions such as mating, predation, and camouflage. This diversity not only makes fish an invaluable model for exploring the molecular mechanisms of pigmentation but also significantly impacts their economic value within the aquaculture industry, where color traits can drive marketability and breeding choices. This review delves into the sophisticated biological processes governing fish pigmentation and discusses their applications in enhancing aquaculture practices. By exploring the intersection of genetic regulation, environmental influences, and advanced breeding techniques, this review highlights both the scientific understanding and practical applications of fish coloration, providing a bridge between basic biological research and its application in commercial aquaculture. [ABSTRACT FROM AUTHOR]

How complex organs coordinate cellular morphogenetic events to achieve three-dimensional (3D) form is a central question in development. The question is uniquely tractable in the late Drosophila pupal retina, where cells maintain stereotyped contacts as they elaborate the specialized cytoskeletal structures that pattern the apical, basal and longitudinal planes of the epithelium. In this study, we combined cell type-specific genetic manipulation of the cytoskeletal regulator Abelson (Abl) with 3D imaging to explore how the distinct cellular morphogenetic programs of photoreceptors and interommatidial pigment cells (IOPCs) organize tissue pattern to support retinal integrity. Our experiments show that photoreceptor and IOPC terminal differentiation is unexpectedly interdependent, connected by an intercellular feedback mechanism that coordinates and promotes morphogenetic change across orthogonal tissue planes to ensure correct 3D retinal pattern. We propose that genetic regulation of specialized cellular differentiation programs combined with inter-plane mechanical feedback confers spatial coordination to achieve robust 3D tissue morphogenesis. [ABSTRACT FROM AUTHOR]

This study investigated the significance of aldh3a2a in zebrafish pigment cell development and its impact on aldehyde metabolism and liver health. Using CRISPR/Cas9 technology, we successfully generated aldh3a2a knockout homozygous mutant lineages, resulting in reduced numbers of melanocytes, xanthophores and iridophores, csf1ra, pnp4a and itk were downregulated, and key genes in the melanin synthesis pathway, including mitfa, tyrp1b and kita, were also downregulated. Transcriptome analysis revealed changes in gene expression profiles, with downregulation of differential genes scd, lpla and aox5 in the steroid biosynthesis pathway, indicating the critical role of aldh3a2a in steroid biosynthesis. Transcriptomic analysis and qPCR combined study on the retinol metabolism pathway revealed that aldh3a2a can regulate raldh2, rxrab and aox5, indicating its certain influence on the signaling transduction of retinoic acid receptors. Additionally, aldh3a2a can regulate potassium channel protein kcns3b, suggesting its association with melanocyte function and potassium ion signaling. GO and KEGG enrichment analysis found widespread effects on pathways such as the cell cycle, homologous recombination, RNA degradation, RNA transport, p53 signaling pathway, eukaryotic ribosome biogenesis, DNA replication, base excision repair, aminoacyl-tRNA biosynthesis, cytoplasmic DNA sensing pathway, steroid biosynthesis, mismatch repair, steroid hormone biosynthesis, and aldarate metabolism in the mutant. Moreover, knockout of the aldh3a2a gene leads to significant accumulation of aldehydes in the body, causing cytotoxicity and resulting in abnormal enlargement of the liver, appearance of vacuoles within the liver, and characteristic weight gain, resembling symptoms of Sjögren-Larsson syndrome. This reveals the role of aldh3a2a in zebrafish and its relevance to human genetic diseases, which will contribute to a deeper understanding of its function and potential therapeutic targets in both zebrafish and humans. [ABSTRACT FROM AUTHOR]

Teleost fish of the genus Danio are excellent models to study the genetic and cellular bases of pigment pattern variation in vertebrates. The two sister species Danio rerio and Danio aesculapii showdivergent patterns of horizontal stripes and vertical bars that are partly caused by the divergence of the potassium channel gene kcnj13. Here, we show that kcnj13 is required only in melanophores for interactions with xanthophores and iridophores, which cause location-specific pigment cell shapes and thereby influence colour pattern and contrast in D. rerio. Cis-regulatory rather than protein coding changes underlie kcnj13 divergence between the two Danio species. Our results suggest that homotypic and heterotypic interactions between the pigment cells and their shapes diverged between species by quantitative changes in kcnj13 expression during pigment pattern diversification. [ABSTRACT FROM AUTHOR]

The decreased antioxidant capacity in the retinal pigment epithelium (RPE) is the hallmark of retinal degenerative diseases including age-related macular degeneration (AMD). Nevertheless, the exact regulatory mechanisms underlying the pathogenesis of retinal degenerations remain largely unknown. Here we show in mice that deficiencies in Dapl1, a susceptibility gene for human AMD, impair the antioxidant capacity of the RPE and lead to age-related retinal degeneration in the 18-month-old mice homozygous for a partial deletion of Dapl1. Dapl1-deficiency is associated with a reduction of the RPE's antioxidant capacity, and experimental re-expression of Dapl1 reverses this reduction and protects the retina from oxidative damage. Mechanistically, DAPL1 directly binds the transcription factor E2F4 and inhibits the expression of MYC, leading to upregulation of the transcription factor MITF and its targets NRF2 and PGC1α, both of which regulate the RPE's antioxidant function. When MITF is experimentally overexpressed in the RPE of DAPL1 deficient mice, antioxidation is restored and retinas are protected from degeneration. These findings suggest that the DAPL1-MITF axis functions as a novel regulator of the antioxidant defense system of the RPE and may play a critical role in the pathogenesis of age-related retinal degenerative diseases.

Abstract Background A congenital melanocytic naevus (CMN) is a rare skin condition that can be associated with abnormalities of the central nervous system (CNS). These anomalies can sometimes cause severe complications, and rarely death. Adequate information about aetiology and management is therefore crucial. To identify how to monitor patients with CMN, we aimed to estimate the prevalence of neurological involvement in patients with CMN and to summarize what specific neurological signs and symptoms and MRI abnormalities are reported in the medical literature. In addition, we summarized and evaluated the recommendations regarding MRI-screening reported in the medical literature. Methods This review was registered in PROSPERO and reported according to the MOOSE checklist. A search was conducted in EMBASE (Ovid), PubMed, and the Cochrane Library. We included studies with 10 or more patients with CMN, reporting on neurological signs and symptoms or CNS MRI. Study selection, data extraction and methodological quality assessment were performed by two independent reviewers. A meta-analysis was used to assess the prevalence of neurological signs and symptoms. Results Out of 1287 studies, fourteen studies were eligible for inclusion of which eight were included in the meta-analysis. Neurological signs and symptoms prevalence was 7.04% (CI 95% 4.47–10.93%) in the meta-analysis group and 6.26% (95% CI 3.85–10%) in a subgroup of patients with a CMN > 6 cm, evaluated in seven studies. Neurodevelopmental delay and seizures were the most frequently reported signs and symptoms. CNS melanocytosis and hydrocephalus were the most frequently reported MRI abnormalities. It was not possible to estimate the increased risk of neurological involvement in patients with CMN due to low quality of evidence and clinical heterogeneity. Conclusion Standardization in CMN studies and a multi-centre prospective study are needed to evaluate neurological involvement. Based on current literature, it is not possible to make strong recommendations on routine MRI-screening. For now, every clinical centre should decide on its own policy and weigh the advantages and disadvantages of routine MRI.

Abstract Over the past years, Human Amnion Epithelial Cells (hAECs), a placental stem cell, are gaining higher attention from the scientific community as they showed several advantages over other types of stem cells, including availability, easy accessibility, reduced rejection rate, non-tumorigenicity, and minimal legal constraint. Recently, natural compounds are used to stimulate stem cell differentiation and proliferation and to enhance their disease-treating potential. A polyphenolic compound 3,4,5-Tri-O-Caffeoylquinic Acid (TCQA) has been previously reported to induce human neural stem cell differentiation and may affect melanocyte stem cell differentiation as well. In this study, TCQA was tested on 3D cultured hAECs after seven days of treatment, and then, microarray gene expression profiling was conducted of TCQA-treated and untreated control cells on day 0 and day 7. Analyses revealed that TCQA treatment significantly enriched pigment and neural cells sets; besides, genes linked with neurogenesis, oxidation–reduction process, epidermal development, and metabolism were positively regulated. Interestingly, TCQA stimulated cell cycle arrest-related pathways and differentiation signaling. On the other hand, TCQA decreased interleukins and cytokines expression and this due to its anti-inflammatory properties as a polyphenolic compound. Results were validated to highlight the main activities of TCQA on hAECs, including differentiation, cell cycle arrest, and anti-inflammatory. This study highlights the important role of hAECs in regenerative medicine and the use of natural compounds to regulate their fate. Video abstract

The eye, the pineal complex and the skin are important photosensitive organs. The African clawed frog, Xenopus laevis, senses light from the environment and adjusts skin color accordingly. For example, light reflected from the surface induces camouflage through background adaptation while light from above produces circadian variation in skin pigmentation. During embryogenesis, background adaptation, and circadian skin variation are segregated responses regulated by the secretion of α-melanocyte-stimulating hormone (α-MSH) and melatonin through the photosensitivity of the eye and pineal complex, respectively. Changes in the color of skin pigmentation have been used as a readout of biochemical and physiological processes since the initial purification of pineal melatonin from pigs, and more recently have been employed to better understand the neuroendocrine circuit that regulates background adaptation. The identification of 37 type II opsin genes in the genome of the allotetraploid X. laevis, combined with analysis of their expression in the eye, pineal complex and skin, is contributing to the elucidation of the role of opsins in the different photosensitive organs, but also brings new questions and challenges. In this review, we analyze new findings regarding the anatomical localization and functions of type II opsins in sensing light. The contribution of X. laevis in revealing the neuroendocrine circuits that regulate background adaptation and circadian light variation through changes in skin pigmentation is discussed. Finally, the presence of opsins in X. laevis skin melanophores is presented and compared with the secretory melanocytes of birds and mammals.

Objective: To explore the clinical efficacy of a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with different parameters in the treatment of chloasma. Methods: In this study, 30 patients with chloasma, symmetrically distributed on the left and right sides of the face and who were treated with a Fayton Q-switched 1064 nm Nd:YAG laser, were recruited. The patients were randomly selected for the treatment of facial lesions on the left and right sides of the face using a spot diameter of 9mm and an energy density of 0.8 J/cm² on one side, and, on the opposite side, a spot diameter of 6mm with an energy density of 1.2 J/cm². The laser frequency was 5Hz and treatment was conducted once every 7-10 days and repeated eight times as a course of treatment. At the end of the course of treatment, as well as 1, 3, and 6 months after treatment, front-facing images and 45° left- and right-side images were taken, respectively. The curative effect of the treatment was evaluated using the Melasma Area Severity Index (MASI) score. Results: The results of this study showed that the total effective rate of a Fayton Q-switched 1064 nm Nd:YAG laser in the treatment of chloasma was 60%. Conclusions: Using a Q-switched 1064 nmNd:YAG laser represents a safe and effective approach for the treatment of chloasma. The therapeutic effects of the parameter sets, that is, a spot diameter of 9mm and an energy density of 0.8 J/cm², and a spot diameter of 6mm with an energy density of 1.2 J/cm², were similar. The treatment time and average effective times of the latter were relatively shortened. Clinical Trial Registration number researchregistry6799. [ABSTRACT FROM AUTHOR]

Background: A congenital melanocytic naevus (CMN) is a rare skin condition that can be associated with abnormalities of the central nervous system (CNS). These anomalies can sometimes cause severe complications, and rarely death. Adequate information about aetiology and management is therefore crucial. To identify how to monitor patients with CMN, we aimed to estimate the prevalence of neurological involvement in patients with CMN and to summarize what specific neurological signs and symptoms and MRI abnormalities are reported in the medical literature. In addition, we summarized and evaluated the recommendations regarding MRI-screening reported in the medical literature.Methods: This review was registered in PROSPERO and reported according to the MOOSE checklist. A search was conducted in EMBASE (Ovid), PubMed, and the Cochrane Library. We included studies with 10 or more patients with CMN, reporting on neurological signs and symptoms or CNS MRI. Study selection, data extraction and methodological quality assessment were performed by two independent reviewers. A meta-analysis was used to assess the prevalence of neurological signs and symptoms.Results: Out of 1287 studies, fourteen studies were eligible for inclusion of which eight were included in the meta-analysis. Neurological signs and symptoms prevalence was 7.04% (CI 95% 4.47-10.93%) in the meta-analysis group and 6.26% (95% CI 3.85-10%) in a subgroup of patients with a CMN > 6 cm, evaluated in seven studies. Neurodevelopmental delay and seizures were the most frequently reported signs and symptoms. CNS melanocytosis and hydrocephalus were the most frequently reported MRI abnormalities. It was not possible to estimate the increased risk of neurological involvement in patients with CMN due to low quality of evidence and clinical heterogeneity.Conclusion: Standardization in CMN studies and a multi-centre prospective study are needed to evaluate neurological involvement. Based on current literature, it is not possible to make strong recommendations on routine MRI-screening. For now, every clinical centre should decide on its own policy and weigh the advantages and disadvantages of routine MRI. [ABSTRACT FROM AUTHOR]

Pigment cell composition, pigment content, tyrosinase content and activity analysis were investigated on three kinds of loaches Misgurnus anguillicaudatus: big blackspot loaches (BBL), small blackspot loaches (SBL) and non-blackspot loaches (NBL), from Poyang Lake. Results showed that there were three types of skin pigment cells, namely melanophores, xanthophores and iridophores. Melanophores in dorsum were more than those in abdomen. Melanophore cytosomes in BBL were larger than those in SBL and NBL, and melanosomes were the largest in stage four. The melanophores in dorsal skin of SBL or NBL were small cell bodies, spindle-like and in chain distribution. There was an extremely significant difference in melanin content in BBL between the dorsum and abdomen (P < 0.01). There were no significant differences in melanin abdominal content, lutein and carotenoid contents among three kinds of loaches (P > 0.05). In dorsal skin, tyrosinase content was the highest in BBL, and it was significantly lower in NBL than in BBL and SBL (P < 0.01). This study reveals the differences in pigment and tyrosinase content in three kinds of loaches and provides a theoretical basis for further study of the mechanism of black spot formation. [ABSTRACT FROM AUTHOR]

Background: Recent phylogenomic studies have revealed a robust, new hypothesis of annelid phylogeny. Most surprisingly, a few early branching lineages formed a basal grade, whereas the majority of taxa were categorized as monophyletic Pleistoannelida. Members of these basal groups show a comparatively simple organization lacking certain characters regarded to be annelid specific. Thus, the evolution of organ systems and the characteristics probably present in the last common annelid ancestor require reevaluation. With respect to light-sensitive organs, a pair of simple larval eyes is regarded as being present in their last common ancestor. However, the evolutionary origin and structure of adult eyes remain obscure. Typically, adult eyes are multicellular pigment cups or pinhole eyes with or without a lens comprising rhabdomeric photoreceptor cells (PRCs) and pigmented supportive cells (PSCs) in converse design. However, in the most basal lineages, eyes are only present in a few taxa, and thus far, their ultrastructure is unknown. Results: Ultrastructural investigations of members of Oweniidae and Chaetopteridae reveal a corresponding design of adult cerebral eyes and PRCs. The eyes in species of these groups are simple pigment spot eyes, either forming a flat patch or embedded in a tube-like invagination. They are part of the epidermis and comprise two cell types, PSCs and rhabdomeric PRCs. Both cell types bear microvilli and one more or less reduced cilium. However, the PRCs showed only a moderate increase in the apical membrane surface in the form of irregularly arranged microvilli intermingling with those of the PSCs; a densely arranged brush border of rhabdomeric microvilli was absent. Additionally, both cell types show certain characteristics elsewhere observable in typical epidermal supportive cells. Conclusions: These findings shed new light on the evolutionary history of adult eyes in Annelida. Most likely, the adult eye of the annelid stem species was a pair of simple pigment spot eyes with only slightly specialized PSCs and PRCs being an integrative part of the epidermis. As is the case for the nuchal organs, typical pigment cup adult eyes presumably evolved later in the annelid phylogeny, namely, in the stem lineages of Amphinomida and Pleistoannelida. [ABSTRACT FROM AUTHOR]

The eye, the pineal complex and the skin are important photosensitive organs. The African clawed frog, Xenopus laevis , senses light from the environment and adjusts skin color accordingly. For example, light reflected from the surface induces camouflage through background adaptation while light from above produces circadian variation in skin pigmentation. During embryogenesis, background adaptation, and circadian skin variation are segregated responses regulated by the secretion of α-melanocyte-stimulating hormone (α-MSH) and melatonin through the photosensitivity of the eye and pineal complex, respectively. Changes in the color of skin pigmentation have been used as a readout of biochemical and physiological processes since the initial purification of pineal melatonin from pigs, and more recently have been employed to better understand the neuroendocrine circuit that regulates background adaptation. The identification of 37 type II opsin genes in the genome of the allotetraploid X. laevis , combined with analysis of their expression in the eye, pineal complex and skin, is contributing to the elucidation of the role of opsins in the different photosensitive organs, but also brings new questions and challenges. In this review, we analyze new findings regarding the anatomical localization and functions of type II opsins in sensing light. The contribution of X. laevis in revealing the neuroendocrine circuits that regulate background adaptation and circadian light variation through changes in skin pigmentation is discussed. Finally, the presence of opsins in X. laevis skin melanophores is presented and compared with the secretory melanocytes of birds and mammals. [ABSTRACT FROM AUTHOR]

Neural crest cells are crucial in development, not least because of their remarkable multipotency. Early findings stimulated two hypotheses for how fate specification and commitment from fully multipotent neural crest cells might occur, progressive fate restriction (PFR) and direct fate restriction, differing in whether partially restricted intermediates were involved. Initially hotly debated, they remain unreconciled, although PFR has become favoured. However, testing of a PFR hypothesis of zebrafish pigment cell development refutes this view. We propose a novel 'cyclical fate restriction' hypothesis, based upon a more dynamic view of transcriptional states, reconciling the experimental evidence underpinning the traditional hypotheses. [ABSTRACT FROM AUTHOR]

Abstract Background Enormous variability in skin colour and patterning is a characteristic of teleost fish, including Salmonidae fishes, which present themselves as a suitable model for studying mechanisms of pigment patterning. In order to screen for candidate genes potentially involved in the specific skin pigment pattern in marble trout (labyrinthine skin pattern) and brown trout (spotted skin pattern), we conducted comparative transcriptome analysis between differently pigmented dermis sections of the adult skin of the two species. Results Differentially expressed genes (DEGs) possibly associated with skin pigment pattern were identified. The expression profile of 27 DEGs was further tested with quantitative real-time PCR on a larger number of samples. Expression of a subset of ten of these genes was analysed in hybrid (marble x brown) trout individuals and compared with the complexity of their skin pigment pattern. A correlation between the phenotype and the expression profile assessed for hybrid individuals was detected for four (gja5, clcn2, cdkn1a and tjp1) of the ten candidate genes tested. The potential role of these genes in skin pigment pattern maintenance is discussed. Conclusions Our results indicate that the maintenance of different pigment patterns in trout is dependent upon specific communication—involving gap junctions, tight junctions and ion channels—between chromatophores present in differentially pigmented skin regions.

Mastigias papua, known as the golden (or spotted) jellyfish, is an epipelagic jellyfish widely distributed in the warm waters of the West Pacific. This jellyfish has a brownish body, owing to zooxanthellae, and white spots. We measured the maximum force to pierce the umbrella, which averaged 94-144 mm in diameter, to evaluate the hardness of M. papua, and returned a range of 0.14-0.45 N. Correlation analyses indicate that when the M. papua medusa grows (i.e., becomes heavier), the umbrella becomes larger in diameter, as well as thicker and harder within the size range we examined. However, a significant relationship between the hardness of the umbrellar apex and the thickness of the umbrella was not obtained. White spots are comprised of loose aggregates of mesogleal cells containing reflective granules. Since the white spots and the transparent parts were not significantly different in hardness, the spots were unlikely to strengthen the umbrella. The primary function of the spots may be the shading of solar radiation. Most of the zooxanthellae are located in mesogleal cells, and often beneath the exumbrellar epidermis. Therefore, light shading by white spots may be unnecessary for the zooxanthellae in mesogleal cells. [ABSTRACT FROM AUTHOR]

Background: Zebrafish display a striped skin pattern on their body; two types of connexins, namely, Connexin39.4 (Cx39.4) and Connexin41.8 (Cx41.8), are involved in stripe pattern formation. Herein, we investigated the role of the C-terminal (CT) domains of Cx39.4 and Cx41.8 in vivo and in vitro. Methods: To investigate the role of CT domains in vivo, we established transgenic zebrafish lines expressing the CT-domain-modified connexin series in pigmented cells and observed skin patterns in fish. To investigate the role of the CT domains in vitro, we expressed the CT-domain modified connexin series in Neuro-2a (N2a) cells and calculated the plaque formation frequency. Results: The overexpression of Cx39.4 lacking a CT domain produced skin patterns similar to that produced by full-length Cx39.4 in the cx39.4−/− mutant and in cx39.4 and cx41.8 double-knockout mutant zebrafish. Fluorescence-protein-fused CT-domain-modified Cx39.4 formed gap junction plaques between N2a cells. The overexpression of CT-truncated Cx41.8 rescued the mutant phenotype in the cx41.8−/− mutant but did not function in the double knockout zebrafish. Fluorescence-protein-fused CT-truncated Cx41.8 hardly formed plaques between N2a cells without Cx39.4 but formed gap junction plaques when co-expressed with Cx39.4. Conclusions: The CT domain of Cx39.4 is not required for protein function, at least in the pigment cells of zebrafish. However, the need for the CT domain of Cx41.8 depends on Cx39.4 expression. General significance: These results provide evidence for the interactions between Cx39.4 and Cx41.8 in pigment cells of zebrafish and suggest that at least one connexin must have a CT domain.

Magnetic field affects many living organisms, fishes included. The fish reactions are observed from the early stage of development, during embryogenesis and larval period, and into adult stage. Magnetic field affects, among other processes, water exchange in the eggs, embryo heart rate and respiration, directional reactions and spatial orientation. The few papers in this field published so far present melanophores morphology and development. Melanophores developing in embryos and in newly hatched sea trout (Salmo trutta m. trutta L.) larvae which had been incubated and kept under optimal conditions constituted the material for the study. The effect of static, generated magnetic field of intensity of 1, 3 and 5 mT on melanophores of sea trout embryos and larvae was studied. The control setting was kept under geomagnetic field. The appearance of melanophores in the trout embryos exposed to magnetic field was delayed. The number of melanophores was smaller, and the movement of melanin within the melanophores, visible as aggregation of pigment in the cells. Static magnetic field of relatively low intensity influences the reaction of melanophores of developing trout embryos and newly hatched larvae. Most probably, magnetite (Fe3O4) compounds, detected in many fish species, mainly migratory fishes such as trout, are responsible for such behaviour of melanophores.Highlights Static magnetic field delays the appearance of melanophores in the trout embryos and larvae. The largest aggregation of melanin in melanophores was found in larvae incubated in a 5 mT magnetic field. The largest number of melanophores was found in the embryos incubated in the geomagnetic field.

Over the past years, Human Amnion Epithelial Cells (hAECs), a placental stem cell, are gaining higher attention from the scientific community as they showed several advantages over other types of stem cells, including availability, easy accessibility, reduced rejection rate, non-tumorigenicity, and minimal legal constraint. Recently, natural compounds are used to stimulate stem cell differentiation and proliferation and to enhance their disease-treating potential. A polyphenolic compound 3,4,5-Tri-O-Caffeoylquinic Acid (TCQA) has been previously reported to induce human neural stem cell differentiation and may affect melanocyte stem cell differentiation as well. In this study, TCQA was tested on 3D cultured hAECs after seven days of treatment, and then, microarray gene expression profiling was conducted of TCQA-treated and untreated control cells on day 0 and day 7. Analyses revealed that TCQA treatment significantly enriched pigment and neural cells sets; besides, genes linked with neurogenesis, oxidation–reduction process, epidermal development, and metabolism were positively regulated. Interestingly, TCQA stimulated cell cycle arrest-related pathways and differentiation signaling. On the other hand, TCQA decreased interleukins and cytokines expression and this due to its anti-inflammatory properties as a polyphenolic compound. Results were validated to highlight the main activities of TCQA on hAECs, including differentiation, cell cycle arrest, and anti-inflammatory. This study highlights the important role of hAECs in regenerative medicine and the use of natural compounds to regulate their fate. 4ntr2z8GsC-Lz3nsa9SfYx Video abstract [ABSTRACT FROM AUTHOR]

To investigate the spatiotemporal dynamics of skin pattern formation, we developed a simple method for artificially disarranging the placement of all three pigment cell types in the body trunk of zebrafish (Danio rerio). We generated transgenic fish with melanophores that ectopically expressed a variant of channelrhodopsin-2 (ChR2). Blue light (BL) irradiation induced melanophore depolarization and random migration; the latter resulted in the disarrangement of the two other pigment cell types (xanthophores and iridophores). This BL disarrangement (BLD) method was effective in both young and adult fish, but it did not affect the initial placement of pigment cells in juvenile fish (approximately 5 weeks post-fertilization). Irradiation with BL was not harmful to cells, and the patterning process immediately resumed when BL was switched off. Using the BLD method, we demonstrated that interactions between pigment cells determined stripe width in the absence of any pre-set positional cues, while the initial horizontal alignment of iridophores determined their directionality. The BLD method can be adapted to any zebrafish skin-pattern mutant, providing a novel tool for analyzing pattern formation mechanisms under a variety of conditions and facilitating further study in this field. • Using optogenetics, we constructed a method to noninvasively disarrange the skin pattern of zebrafish. • This method provides a new procedure to analyze the mechanism of skin pattern formation. • The initial positional cue just determines the stripe directionality, and the width of stripes is autonomously determined. [ABSTRACT FROM AUTHOR]

Abstract Background Crucian carp is a popular ornamental strain in Asia with variants in body color. To further explore the genetic mechanisms underlying gray and red body color formation in crucian carp, the skin transcriptomes and partial DNA methylation sites were obtained from red crucian carp (RCC) and white crucian carp (WCC). Here, we show significant differences in mRNA expression and DNA methylation sites between skin tissues of RCC and WCC. Results Totals of 3434 and 3683 unigenes had significantly lower and higher expression in WCC, respectively, compared with unigenes expressed in RCC. Some potential genes for body color development were further identified by quantitative polymerase chain reaction, such as mitfa, tyr, tyrp1, and dct, which were down-regulated, and foxd3, hpda, ptps, and gch1, which were up-regulated. A KEGG pathway analysis indicated that the differentially expressed genes were mainly related to mitogen activated protein kinase (MAPK), Wnt, cell cycle, and endocytosis signaling pathways, as well as variations in melanogenesis in crucian carp. In addition, some differentially expressed DNA methylation site genes were related to pigmentation, including mitfa, tyr, dct, foxd3, and hpda. The differentially expressed DNA methylation sites were mainly involved in signaling pathways, including MAPK, cAMP, endocytosis, melanogenesis, and Hippo. Conclusions Our study provides the results of comparative transcriptome and DNA methylation analyses between RCC and WCC skin tissues and reveals that the molecular mechanism of body color variation in crucian carp is strongly related to disruptions in gene expression and DNA methylation during pigmentation.

Connexin 39.4 (Cx39.4) and connexin 41.8 (Cx41.8), two gap-junction proteins expressed in both melanophores and xanthophores, are crucial for the intercellular communication among pigment cells that is necessary for generating the stripe pigment pattern of zebrafish. We have previously characterized the gap-junction properties of Cx39.4 and Cx41.8, but how these proteins contribute to stripe formation remains unclear; this is because distinct types of connexins potentially form heteromeric gap junctions, which precludes accurate elucidation of individual connexin functions in vivo. Here, by arranging Cx39.4 and Cx41.8 expression in pigment cells, we have identified the simplest gap-junction network required for stripe generation: Cx39.4 expression in melanophores is required but expression in xanthophores is not necessary for stripe patterning, whereas Cx41.8 expression in xanthophores is sufficient for the patterning, and Cx41.8 expression in melanophores might stabilize the stripes. Moreover, patch-clamp recordings revealed that Cx39.4 gap junctions exhibit spermidine-dependent rectification property. Our results suggest that Cx39.4 facilitates the crucial cell-cell interactions between melanophores and xanthophores that mediate a unidirectional activation-signal transfer from xanthophores to melanophores, which is essential for melanophore survival. [ABSTRACT FROM AUTHOR]

Pigmentation is closely associated with various behaviors, and it is also an important feature that influences the popularity and price of ornamental fish. However, the molecular mechanism that regulates the pigmentation of fish is barely understood. There are two clearly different pigmentation phenotypes, i.e. light and dark phenotypes, in the same natural population of Leptobotia taeniops. Type and distribution of chromatophores is the cellular basis of the pigmentation. To analyze the composition of chromatophores in the light and dark phenotypes of L. taeniops and the correlation of the pigmentation to the expressions of pigment synthesis genes, we studied the pigment cell types and distribution in the skin of L. taeniops by microscope, and analyzed the expressions of genes that regulate melanin production using real-time qRT-PCR. Our results showed that the amount of melanophores in the skin was the major factor that caused the pigment deviation of L. taeniops living in the same habitat. The expressions of TYR, Tyrp1, and Dct genes were significantly higher in the skin of the dark phenotype than those in the light phenotype. This result implied that the amount of melanophores was influenced by the expression of these genes in the skin of L. taeniops. [ABSTRACT FROM AUTHOR]

For this Special Issue “Zebrafish-A Model System for Developmental Biology Study,” we present a collection of studies, including original research papers and review articles, that focus on advances in developmental biology research and that take advantage of the zebrafish model organism [...]

Background To treat skin color disorders, such as vitiligo or burns, melanocytes are transplanted for tissue regeneration. However, melanocyte distribution in the human body varies with age and location, making it difficult to select the optimal donor skin to achieve a desired color match. Determining the correlations with the desired skin color measurement based on CIELAB color, epidermal melanocyte numbers, and melanin content of individual melanocytes is critical for clinical application. Method Fifteen foreskin samples from Asian young adults were analyzed for skin color, melanocyte ratio (melanocyte proportion in the epidermis), and melanin concentration. Furthermore, an equation was developed based on CIELAB color with melanocyte ratio, melanin concentration, and the product of melanocyte ratio and melanin concentration. The equation was validated by seeding different ratios of keratinocytes and melanocytes in tissue-engineered skin substitutes, and the degree of fitness in expected skin color was confirmed. Results Linear regression analysis revealed a significant strong negative correlation (r = − 0.847, R2 = 0.717) between CIELAB L* value and the product of the epidermal melanocyte ratio and cell-based melanin concentration. Furthermore, the results showed that an optimal skin color match was achieved by the formula. Discussion We found that L* value was correlated with the value obtained from multiplying the epidermal melanocyte ratio (R) and melanin content (M) and that this correlation was more significant than either L* vs M or L* vs R. This suggests that more accurate prediction of skin color can be achieved by considering both R and M. Therefore, precise skin color match in treating vitiligo or burn patients would be potentially achievable based on extensive collection of skin data from people of Asian descent.

Magnetic field affects many living organisms, fishes included. The fish reactions are observed from the early stage of development, during embryogenesis and larval period, and into adult stage. Magnetic field affects, among other processes, water exchange in the eggs, embryo heart rate and respiration, directional reactions and spatial orientation. The few papers in this field published so far present melanophores morphology and development. Melanophores developing in embryos and in newly hatched sea trout (Salmo trutta m. trutta L.) larvae which had been incubated and kept under optimal conditions constituted the material for the study. The effect of static, generated magnetic field of intensity of 1, 3 and 5 mT on melanophores of sea trout embryos and larvae was studied. The control setting was kept under geomagnetic field. The appearance of melanophores in the trout embryos exposed to magnetic field was delayed. The number of melanophores was smaller, and the movement of melanin within the melanophores, visible as aggregation of pigment in the cells. Static magnetic field of relatively low intensity influences the reaction of melanophores of developing trout embryos and newly hatched larvae. Most probably, magnetite (Fe3O4) compounds, detected in many fish species, mainly migratory fishes such as trout, are responsible for such behaviour of melanophores. Static magnetic field delays the appearance of melanophores in the trout embryos and larvae. The largest aggregation of melanin in melanophores was found in larvae incubated in a 5 mT magnetic field. The largest number of melanophores was found in the embryos incubated in the geomagnetic field. [ABSTRACT FROM AUTHOR]

In order to determine the function of pigment cell types in different pigment pattern of skin, we have applied the laser capture microdissection method (LCM) for isolation of different pigment cell types from skin sections of marble trout (Salmo marmoratus) and brown trout (S. trutta), characterized with labyrinthine and spotted skin pattern, respectively. RNA was isolated from dissected pigment cell populations and used for expression analysis. Expression profiles of candidate genes, potentially involved in pigmentation, in LCM isolated pigment cell population, were more specific compared to differently pigmented skin regions, containing a heterogeneous mixture of cells, including more types of chromatophores. Moreover, they could provide important information about particular pigment cell type function and its contribution to different pigment pattern. Protocol of combined LCM and genomic approach to study single pigment cell populations can be applied in the future, but needs to be further optimized in order to yield RNA of sufficient quantity and quality required for i.e. transcriptomic analyses. [ABSTRACT FROM AUTHOR]

Abstract: The periodic albino mutant of Xenopus laevis has been used to study the development of pigment cells because both the retinal pigment epithelium (RPE) and melanophores are affected. In this mutant, “white pigment cells” containing both melanophore‐specific and iridophore‐specific pigment organelles appear. The present experiments were designed to investigate the structural organization and expression of microphthalmia‐associated transcription factor (Mitf) in the mutant since Mitf is known to regulate the development of melanocytes and RPE. The exon structures of X. laevis mitf genes (mitf.L and mitf.S) were defined using newly obtained Mitf transcripts and X. laevis genomic data. Compared to mouse mitf, exons 3 and 6a were absent in X. laevis mitf. The four exons between exons 4 and 6b in X. laevis mitf were named 5α, 5β, 5γ, and 5δ. Exons 5α and 5δ were specific to X. laevis mitf, whereas the continuous exons 5β/γ were identical to exon 5 of mouse mitf. A wide variety of A‐Mitf and M‐Mitf transcript variants lacking one or more exons were found in X. laevis; however, different types of Mitf transcripts were expressed in the mutant. In addition, white pigment cells and melanophores expressed both the mitf and dopachrome tautomerase (dct) genes. [ABSTRACT FROM AUTHOR]

Many industrial activities release Nickel (Ni) in the environment with harmful effects for terrestrial and marine organisms. Despite many studies on the mechanisms of Ni toxicity are available, the understanding about its toxic effects on marine organisms is more limited. We used Paracentrotus lividus as a model to analyze the effects on the stress pathways in embryos continuously exposed to different Ni doses, ranging from 0.03 to 0.5 mM. We deeply examined the altered embryonic morphologies at 24 and 48 h after Ni exposure. Some different phenotypes have been classified, showing alterations at the expenses of the dorso-ventral axis as well as the skeleton and/or the pigment cells. At the lowest dose used, Ni mainly induced a multi-spicule phenotype observed at 24 h after treatment. On the contrary, at the highest dose of Ni (0.5 mM), 90% of embryos showed no skeleton and no pigment cells. Therefore, we focused on this dose to study protein and gene expression patterns at 24 and 48 h after exposure. Among the proteins analyzed, i.e. p38MAPK, Grp78 and Mn-SOD, only p38MAPK was induced by Ni treatment. Moreover, we analyzed the mRNA profiles of a pool of genes that are involved in stress response and in development mechanisms, i.e. the transcription factors Pl - NFkB and Pl - FOXO ; a marker of DNA repair, Pl -XPB/ ERCC3 ; a mitogen-activated protein kinase (MAPK), Pl - p38 ; an ER stress gene, Pl - grp78 ; an adapter protein, Pl - 14-3-3ε ; two markers of pigment cells, Pl - PKS1 and Pl-gcm . The spatial expression of mesenchymal marker genes has been evaluated in Ni-treated embryos at both 24 and 48 h after exposure. Our results indicated that Ni acts at several levels in P. lividus sea urchin, by affecting embryo development, influencing the embryonic immune response and activating stress response pathways to counteract the suffered injury and to promote embryos surviving. [ABSTRACT FROM AUTHOR]

Abstract: The striped pigmentation pattern of zebrafish is determined by the interaction between pigment cells with different colors. Recent studies show the behaviors of pigment cells are substantially different according to the environment. Interestingly, the resulting patterns are almost identical, suggesting a robustness of the patterning mechanism. To know how this robustness originates, we investigated the behavior of melanophores in various environments including different developmental stages, different body positions, and different genetic backgrounds. Normally, when embryonic melanophores are excluded from the yellow stripe region in the body trunk, two different cellular behaviors are observed. Melanophores migrate to join the black stripe or disappear (die) in the position. In environments where melanophore migration was restricted, we observed that most melanophores disappeared in their position, resulting in the complete exclusion of melanophores from the yellow stripe. In environments where melanophore cell death was restricted, most melanophores migrated to join the black stripes, also resulting in complete exclusion. When both migration and cell death were restricted, melanophores remained alive in the yellow stripes. These results show that migration and cell death complement each other to achieve the exclusion of melanophores. This flexibility may be the basis of the mechanistic robustness of skin pattern formation. [ABSTRACT FROM AUTHOR]

Summary: Vertebrate eye development and homoeostasis critically depend on the regulation of proliferation of cells forming the retinal pigment epithelium (RPE). Previous results indicated that the death‐associated protein like‐1 DAPL1 cell autonomously suppresses RPE proliferation in vivo and in vitro. Here, we show in human RPE cell lines that the pigment cell transcription factor MITF regulates RPE cell proliferation by upregulating DAPL1 expression. DAPL1 regulation by MITF is, however, mediated predominantly by (−) MITF, one of two alternative splice isoforms of MITF that lacks six residues located upstream of the DNA‐binding basic domain. Furthermore, we find that the regulation of DAPL1 by MITF is indirect in that (−) MITF stimulates the transcription of Musashi homolog‐2 (MSI2), which negatively regulates the processing of the anti‐DAPL1 microRNA miR‐7. Our results provide molecular insights into the regulation of RPE cell proliferation and quiescence and may help us understand the mechanisms of normal RPE maintenance and of eye diseases associated with either RPE hyperproliferation or the lack of regenerative proliferation. [ABSTRACT FROM AUTHOR]

Migratory species experience morphological and physiological changes during transitions between different life stages. In particular, modification of sensory systems is critical for animals to adapt to new environments. For example, to prepare for entry into seawater, salmonids undergo smoltification with dramatic changes in ultraviolet photoreceptors and polarized vision, which are important for orientation and foraging behaviours. Extraretinal organs are also involved in photoreception; however, the ontogenetic development of extraretinal photoreceptors is not well known, especially in migratory species. Here, we investigated whether rainbow trout dermal photoreceptors, melanophores, undergo change in spectral sensitivity during smoltification and which candidate molecules may account for this ontogenetic alteration. Our results showed that, contrary to parr melanophores which are insensitive to light, smolt melanophores displayed chromatic photoresponses with the emergence of cryptochrome and melanopsin expression. We suggest that these modifications may benefit the active foraging behaviour of smolts and enable adaptation to variable environments.