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A comparative overview is provided of Ca2+ signaling and its potential mechanistic roles during development in tunicates. As background, the review presents an introduction to tunicate taxonomy, and then a general overview of Ca2+ signaling and methods for recording and measuring Ca2+ signals. It then covers the dynamics and implicated mechanisms of Ca2+ signals during different phases of development from oocyte to larva. These include signals arising in the unfertilized oocyte, signals associated with fertilization and meiosis, intercellular signals occurring from early cleavage stages through gastrulation, intercellular signals during organogenesis, and signals associated with early behavior. Comparisons are made among different tunicate species and where relevant to other chordate species. In many tunicate species, Ca2+ currents across the oocyte membrane are present prior to fertilization, and in the appendicularian Oikopleura dioica regular Ca2+ transients have been recorded optically prior to fertilization. Ca2+ signals at this stage have been implicated in pre-fertilization oocyte maturation events. The fertilization transient is the most well-studied Ca2+ signal and is triggered by factors from the sperm, including pivotally a phospholipase C (PLC) isoform that catalyzes the generation of IP3, which elicits release of Ca2+ from the endoplasmic reticulum. Post-fertilization signals are similarly dependent on IP3 signaling and are regulated by cyclin-dependent kinase 1 (Cdk1), and thereby linked to the meiotic divisions required for zygote formation. Ca2+ signals associated with early cleavages through gastrulation arise in blastomeres of the muscle lineage and spread from these in a coordinated fashion to other blastomeres through gap junctions. Post-gastrulation Ca2+ signals begin to show tissue-specificity in their temporal pattern as organogenesis proceeds, likely associated with loss of general gap junction transmission. Once neurulation has occurred, Ca2+ signals arise first in the nervous system and are transmitted synaptically to muscle, while Ca2+ signals arising spontaneously in the epidermis follow a separate temporal pattern. Species differences in the spatiotemporal characteristics of pre- and postgastrulation Ca+2 signals are discussed. [ABSTRACT FROM AUTHOR]

Copyright of Acta Zoologica Lilloana is the property of Fundacion Miguel Lillo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A comparative overview is provided of Ca2+ signaling and its potential mechanistic roles during development in tunicates. As background, the review presents an introduction to tunicate taxonomy, and then a general overview of Ca2+ signaling and methods for recording and measuring Ca2+ signals. It then covers the dynamics and implicated mechanisms of Ca2+ signals during different phases of development from oocyte to larva. These include signals arising in the unfertilized oocyte, signals associated with fertilization and meiosis, intercellular signals occurring from early cleavage stages through gastrulation, intercellular signals during organogenesis, and signals associated with early behavior. Comparisons are made among different tunicate species and where relevant to other chordate species. In many tunicate species, Ca2+ currents across the oocyte membrane are present prior to fertilization, and in the appendicularian Oikopleura dioica regular Ca2+ transients have been recorded optically prior to fertilization. Ca2+ signals at this stage have been implicated in pre-fertilization oocyte maturation events. The fertilization transient is the most well-studied Ca2+ signal and is triggered by factors from the sperm, including pivotally a phospholipase C (PLC) isoform that catalyzes the generation of IP3, which elicits release of Ca2+ from the endoplasmic reticulum. Post-fertilization signals are similarly dependent on IP3 signaling and are regulated by cyclin-dependent kinase 1 (Cdk1), and thereby linked to the meiotic divisions required for zygote formation. Ca2+ signals associated with early cleavages through gastrulation arise in blastomeres of the muscle lineage and spread from these in a coordinated fashion to other blastomeres through gap junctions. Post-gastrulation Ca2+ signals begin to show tissue-specificity in their temporal pattern as organogenesis proceeds, likely associated with loss of general gap junction transmission. Once neurulation has occurred, Ca2+ signals arise first in the nervous system and are transmitted synaptically to muscle, while Ca2+ signals arising spontaneously in the epidermis follow a separate temporal pattern. Species differences in the spatiotemporal characteristics of pre- and postgastrulation Ca+2 signals are discussed.

Se reportan nuevos registros de zooplancton en el Pacífico tropical mexicano, con un énfasis particular en apendicularias. Las muestras se recolectaron entre enero de 2023 y junio de 2024 en diversas localidades utilizando redes de plancton, así como técnicas de ADN ambiental y filogenia molecular para la identificación precisa de ciertas especies. Se determinó un total de 12 nuevos registros para el Pacífico mexicano y tres registros específicos en ciertas áreas, incluyendo especies de los géneros Pseudevadne, Penilia, Appendicularia, Fritillaria y Oikopleura. Entre los hallazgos, destaca la primera caracterización molecular de Oikopleura dioica en México, revelando alta similitud genética con poblaciones japonesas, lo que subraya la distribución compartida entre la parte nororiental y noroccidental del Océano Pacífico. El nuevo registro de dos subespecies del género Fritillaria para México y el hallazgo de preferencias entre aguas oceánicas y costeras de los géneros Oikolpeura y Fritillaria. Este estudio no solo amplía el conocimiento sobre la riqueza y distribución de estos organismos en el Pacífico tropical mexicano, también proporciona una base sólida para futuras investigaciones en taxonomía, ecología y biogeografía de apendicularias y otros zoopláncteres, así como enfatizar en las posibles limitantes en el conocimiento de estos grupos. Los resultados obtenidos subrayan la necesidad de realizar estudios específicos con mayor esfuerzo de muestreo en diferentes escalas espaciales y temporales para entender mejor la biodiversidad marina de esta región. Asimismo, se recomienda el uso de técnicas moleculares para mejorar la precisión en la identificación y comprensión de la dinámica de las comunidades zooplanctónicas.

Stem cell division contributes to the generation of various cell types during animal development, especially a diverse pool of neural cells in the nervous system. One example is reiterated unequal stem cell divisions, in which a large stem cell undergoes a series of oriented unequal divisions to produce a chain of small daughter cells that differentiate. We show that reiterated unequal stem cell divisions are involved in the formation of the brain in simple chordate appendicularians (larvaceans). Two large neuroblasts in the anterior and middle of the brain-forming region of hatched larvae were observed. They produced at least 30 neural cells out of 96 total brain cells before completion of brain formation at 10 hours after fertilization by reiterated unequal stem cell divisions. The daughter cells of the anterior neuroblast were postmitotic, and the number was at least 19. The neuroblast produced small daughter neural cells posteriorly every 20 min. The neural cells first moved toward the dorsal side, turned in the anterior direction, aligned in a single line according to their birth order, and showed collective movement to accumulate in the anterior part of the brain. The anterior neuroblast originated from the right-anterior blastomeres of the eight-cell embryos and the right a222 blastomere of the 64-cell embryo. The posterior neuroblast also showed reiterated unequal stem cell divisions, and generated at least 11 neural cells. Sequential unequal stem cell divisions without stem cell growth have been observed in protostomes, such as insects and annelids. The results provide the first examples of this kind of stem cell division during brain formation in non-vertebrate deuterostomes. [ABSTRACT FROM AUTHOR]

Significance of larvaceans (class Appendicularia) for plankton community and feeding of nekton in the Far-Eastern Seas and North Pacific is underestimated, this group of species is poorly represented in scientific literature. The total biomass of larvaceans is below the stocks of dominant groups in the large-sized zooplankton, as copepods, euphausiids, arrowworms, amphipods, and coelenterates, but accounted together with their shells (called «houses») they form a comparable stock. In the studied area, the class Appendicularia is represented by four species: widely distributed Oikopleura vanhoeffeni, O. labradoriensis, and Fritillaria borealis and F. sp. (perhaps F. pacifica) in the southern periphery of this area. Larger and more numerous oikopleurids dominate by both abundance and biomass and are presented in all size fractions of zooplankton, whereas fritillarids are presented mostly in the small-sized fraction. Larvaceans distribute mainly in the upper epipelagic layer (55–97 %), i.e. in the layer of their prey concentration; their density is the highest in the coastal zone with the depth < 50 m and decreases in deeper areas. They are a significant portion in the diet of many nekton species (41 out of 151 species in the Trofology database of TINRO), including basic commercial fishes, as pollock, salmons, herring, polar cod, mackerels, sardine and some others. Their mucus houses glowing at night, with the animal inside, whose tail vibrates constantly providing movement and nutrition, are attractive for many plankton-eaters. Appendicularia have a high occurrence in the food of all size-classes of nekton, though it decreases for larger-sized fish of such mass fish species, as walleye pollock and pink and chum salmons.

The significance of larvaceans (class Appendicularia) for plankton community and feeding of nekton in the Far-Eastern Seas and North Pacific is underestimated, this group of species is poorly represented in scientific literature. The total biomass of larvaceans is below the stocks of dominant groups in the large zooplankton, as copepods, euphausiids, arrowworms, amphipods, and coelenterates, but counted together with their shells (called "houses") they form a comparable stock. In the studied area, the class Appendicularia is represented by four species: widely distributed Oikopleura vanhoeffeni, O. labradoriensis, and Fritillaria borealis and F. sp. (perhaps F. pacifica) in the southern periphery of this area. Larger and more numerous oikopleurids dominate by both abundance and biomass and are presented in all size fractions of zooplankton, whereas fritillarids are presented mostly in the small fraction. Larvaceans are distributed mainly in the upper epipelagic layer (55–97%), i.e., in the layer of their prey concentration; their density is the highest in the coastal zone with the depth less than 50 m and decreases in deeper areas. They are a significant portion in the diet of many nekton species (41 out of 151 species in the Trophology database of TINRO), including basic commercial fishes, such as pollock, salmons, herring, polar cod, mackerels, sardine and others. Their mucus houses that glow at night, with the animal inside, whose tail vibrates constantly providing movement and nutrition, are attractive for many plankton eaters. Appendicularia have a high occurrence in the food of all size-classes of nekton, although it decreases for larger fish of such mass fish species, as walleye pollock and pink and chum salmons. [ABSTRACT FROM AUTHOR]

Germ cells develop into eggs and sperms and represent a lineage that survives through multiple generations. Germ cell specification during embryogenesis proceeds through one of two basic modes: either the cell-autonomous mode or the inductive mode. In the cell-autonomous mode, specification of germ cell fate involves asymmetric partitioning of the specialized maternal cytoplasm, known as the germplasm. Oikopleura dioica is a larvacean (class Appendicularia) and a chordate. It is regarded as a promising animal model for studying chordate development because of its short life cycle (5 days) and small genome size (∼60 ​Mb). We show that their embryos possess germplasm, as observed in ascidians (class Ascidiacea). The vegetal cytoplasm shifted towards the future posterior pole before the first cleavage occurred. A bilateral pair of primordial germ cells (PGC, B11 ​cells) was formed at the posterior pole at the 32-cell stage through two rounds of unequal cleavage. These B11 ​cells did not undergo further division before hatching of the tadpole-shaped larvae. The centrosome-attracting body (CAB) is a subcellular structure that contains the germplasm and plays crucial roles in germ cell development in ascidians. The presence of CAB with germplasm was observed in the germline lineage cells of larvaceans via electron microscopy and using extracted embryos. The CAB appeared at the 8-cell stage and persisted until the middle stage of embryogenesis. The antigen for the phosphorylated histone 3 antibody was localized to the CAB and persisted in the PGC until hatching after the CAB disappeared. Maternal snail mRNA, which encodes a transcription factor, was co-localized with the antigen for the H3S28p antibody. Furthermore, we found a novel PGC-specific subcellular structure that we call the germ body (GB). This study thus highlights the conserved and non-conserved features of germline development between ascidians and larvaceans. The rapid development and short life cycle (five days) of O. dioica would open the way to genetically analyze germ cell development in the future. [Display omitted] • The vegetal ooplasm of larvaceans shifted towards the future posterior pole. • Primordial germ cells (PGCs) were formed at the 32-cell stage and never divided up to hatching. • Centrosome-attracting body (CAB) promoted unequal cell divisions and contained germplasm. • Snail mRNA and antigen for the phospho-histone antibody was localized to the CAB. • A PGC-specific subcellular structure that we call the germ body was observed. [ABSTRACT FROM AUTHOR]

Oikopleura dioica is a ubiquitous marine zooplankton of biological interest owing to features that include dioecious reproduction, a short life cycle, conserved chordate body plan, and a compact genome. It is an important tunicate model for evolutionary and developmental research, as well as investigations into marine ecosystems. The genome of north Atlantic O. dioica comprises three chromosomes. However, comparisons with the genomes of O. dioica sampled from mainland and southern Japan revealed extensive sequence differences. Moreover, historical studies have reported widely varying chromosome counts. We recently initiated a project to study the genomes of O. dioica individuals collected from the coastline of the Ryukyu (Okinawa) Islands in southern Japan. Given the potentially large extent of genomic diversity, we employed karyological techniques to count individual animals’ chromosomes in situ using centromere-specific antibodies directed against H3S28P, a prophase-metaphase cell cycle-specific marker of histone H3. Epifluorescence and confocal images were obtained of embryos and oocytes stained with two commercial anti-H3S28P antibodies (Abcam ab10543 and Thermo Fisher 07-145). The data lead us to conclude that diploid cells from Okinawan O. dioica contain three pairs of chromosomes, in line with the north Atlantic populations. The finding facilitates the telomere-to-telomere assembly of Okinawan O. dioica genome sequences and gives insight into the genomic diversity of O. dioica from different geographical locations. The data deposited in the EBI BioImage Archive provide representative images of the antibodies’ staining properties for use in epifluorescent and confocal based fluorescent microscopy.

Oikopleura dioica is a ubiquitous marine tunicate of biological interest due to features that include dioecious reproduction, short life cycle, and vertebrate-like dorsal notochord while possessing a relatively compact genome. The use of tunicates as model organisms, particularly with these characteristics, offers the advantage of facilitating studies in evolutionary development and furthering understanding of enduring attributes found in the more complex vertebrates. At present, we are undertaking an initiative to sequence the genomes of Oikopleura individuals in populations found among the seas surrounding the Ryukyu Islands in southern Japan. To facilitate and validate genome assemblies, karyotyping was employed to count individual animals’ chromosomes in situ using centromere-specific antibodies directed against H3S28P, a prophase-metaphase cell cycle-specific marker of histone H3. New imaging data of embryos and oocytes stained with two different antibodies were obtained; interpretation of these data lead us to conclude that the Okinawan Oikopleura dioica has three pairs of chromosomes, akin to previous results from genomic assemblies in Atlantic populations. The imaging data have been deposited to the open-access EBI BioImage Archive for reuse while additionally providing representative images of two commercially available anti-H3S28P antibodies’ staining properties for use in epifluorescent and confocal based fluorescent microscopy.

Background: Ascidians, a tunicate class, use a mitochondrial genetic code that is distinct from vertebrates and other invertebrates. Though it has been used to translate the coding sequences from other tunicate species on a case-by-case basis, it is has not been investigated whether this can be done systematically. This is an important because a) some tunicate mitochondrial sequences are currently translated with the invertebrate code by repositories such as NCBI GenBank, and b) uncertainties about the genetic code to use can complicate or introduce errors in phylogenetic studies based on translated mitochondrial protein sequences. Methods: We collected publicly available nucleotide sequences for non-ascidian tunicates including appendicularians such as Oikopleura dioica, translated them using the ascidian mitochondrial code, and built multiple sequence alignments covering all tunicate classes. Results: All tunicates studied here appear to translate AGR codons to glycine instead of serine (invertebrates) or as a stop codon (vertebrates), as initially described in ascidians. Among Oikopleuridae, we suggest further possible changes in the use of the ATA (Ile → Met) and TGA (Trp → Arg) codons. Conclusions: We recommend using the ascidian mitochondrial code in automatic translation pipelines of mitochondrial sequences for all tunicates. Further investigation is required for additional species-specific differences.

Mouth formation involves the processes of mouth opening, formation of the oral cavity, and the development of associated sensory organs. In deuterostomes, the surface ectoderm and the anterior part of the archenteron are reconfigured and reconnected to make a mouth opening. This study of the larval development of the larvacean, Oikopleura dioica, investigates the cellular organization of the oral region, the developmental processes of the mouth, and the formation of associated sensory cells. O. dioica is a simple chordate whose larvae are transparent and have a small number of constituent cells. It completes organ morphogenesis in 7 h, between hatching 3 h after fertilization and the juvenile stage at 10 h, when it attains adult form and starts to feed. It has two types of mechanosensory cell embedded in the oral epithelium, which is a single layer of cells. There are twenty coronal sensory cells in the circumoral nerve ring and two dorsal sensory organ cells. Two bilateral lip precursor cells (LPCs), facing the anterior surface, divide dorsoventrally and make a wedge-shaped cleft between the two daughter cells named the dorsal lip cell (DLC) and the ventral lip cell (VLC). Eventually, the DLC and VLC become detached and separated into dorsal and ventral lips, triggering mouth opening. This is an intriguing example of cell division itself contributing to morphogenesis. The boundary between the ectoderm and endoderm is present between the lip cells and coronal sensory cells. All oral sensory cells, including dorsal sensory organ cells, were of endodermal origin and were not derived from the ectodermal placode. These observations on mouth formation provide a cellular basis for further studies at a molecular level, in this simple chordate. [ABSTRACT FROM AUTHOR]

Background: Ascidians, a tunicate class, use a mitochondrial genetic code that is distinct from vertebrates and other invertebrates. Though it has been used to translate the coding sequences from other tunicate species on a case-by-case basis, it is has not been investigated whether this can be done systematically. This is an important because a) some tunicate mitochondrial sequences are currently translated with the invertebrate code by repositories such as NCBI GenBank, and b) uncertainties about the genetic code to use can complicate or introduce errors in phylogenetic studies based on translated mitochondrial protein sequences. Methods: We collected publicly available nucleotide sequences for non-ascidian tunicates including appendicularians such as Oikopleura dioica, translated them using the ascidian mitochondrial code, and built multiple sequence alignments covering all tunicate classes. Results: All tunicates studied here appear to translate AGR codons to glycine instead of serine (invertebrates) or as a stop codon (vertebrates), as initially described in ascidians. Among Oikopleuridae, we suggest further possible changes in the use of the ATA (Ile → Met) and TGA (Trp → Arg) codons. Conclusions: We recommend using the ascidian mitochondrial code in automatic translation pipelines of mitochondrial sequences for all tunicates. Further investigation is required for additional species-specific differences.

Abstract The mechanisms driving innovations that distinguish large taxons are poorly known and essentially accessible via a candidate gene approach. A spectacular acquisition by tunicate larvaceans is the house, a complex extracellular filtration device. Its components are secreted by the oikoplastic epithelium which covers the animal trunk. Here we describe the development of this epithelium in larvae through the formation of specific cellular territories known to produce distinct sets of house proteins (Oikosins). It involves cell divisions and morphological differentiation but very limited cell migration. A diverse set of homeobox genes, most often duplicated in the genome, are transiently and site-specifically expressed in the trunk epithelium at early larval stages. Using RNA interference, we show that two prop duplicates are involved in the differentiation of a region on and around the dorsal midline, regulating morphology and the production of a specific oikosin. Our observations favor a scenario in which multiple homeobox genes and most likely other developmental transcription factors were recruited for this innovation. Their frequent duplications probably predated, but were not required for the emergence of the house. Highlights • It shows how the uniform epithelium of the embryo is quickly transformed into a highly regionalized epithelium of the larva. • RNA interference confirmed the contribution of homeobox genes, often duplicated, to the epithelium transformation. • Gene duplications probably did not allow the emergence of the house but may have contributed to its later complexification. [ABSTRACT FROM AUTHOR]

The appendicularian Oikopleura dioica is a planktonic chordate that retains a tadpole shape throughout its life. Its simple and transparent body, invariant cell lineages, fast development and available genome and transcriptome resources make it a promising model organism for research in developmental biology. However, large-scale analysis of gene expression in O. dioica is limited owing to the laborious and time-consuming process of manual removal of the vitelline membrane, because devitellinisation of pre-hatching embryos causes failure of normal development. Therefore, in this study, modified procedures were developed for whole-mount in situ hybridisation (WISH) and immunohistochemistry (WIHC). This protocol enables rapid mRNA or protein detection without a manual devitellination step for each specimen. The critical procedure is brief treatment of the vitelline membrane of living embryos with 0.05% actinase E before fixation. Two minutes of treatment was optimal for the penetration of antisense RNA probes and antibodies through the vitelline membrane. This WISH protocol was applicable for chromogenic and fluorescent tyramide signal amplification reactions. Using the new protocol, we found eight genes with tissue-specific expression in the tail muscle, trunk epidermis, heart, pharynx, oesophagus, stomach or gill openings of developing larvae. This procedure also allowed for the detection of exogenous FLAG-tagged histone-enhanced green fluorescent protein by WIHC using anti-FLAG antibody. This study provides a useful and convenient tool for studying spatial and temporal gene expression patterns in this simple chordate model and should facilitate handling large amounts of genetic data from transcriptome-based approaches and other techniques such as treatments with chemical inhibitors. [ABSTRACT FROM AUTHOR]

In a previous report, we analyzed the stomach contents of juvenile chum salmon Oncorhynchus keta by morphological observation and also by molecular identification using the mitochondrial cytochrome c oxidase subunit I (COI) region. However, one of the most frequently detected COI sequences could not be assigned to any specific taxon, even at the phylum level. In the present study, we conducted in situ hybridization (ISH) on the stomach contents of juvenile chum salmon using the COI sequence and polymerase chain reaction amplification of a 18S ribosomal RNA gene from the tissue sections where ISH signals were detected. As a result, the organism that was enigmatic at the phylum level was found to be an appendicularian. Moreover, Oikopleura longicauda collected from the bay where the juvenile chum salmon samples were obtained was shown to have the same COI sequences as this taxonomic 'orphan' COI sequence from the stomach contents. The present results suggest that the COI sequences previously deposited in public databases for ' Oikopleura' are actually derived from taxonomic groups other than appendicularians, and that this may have hampered our understanding of prey richness in the stomach or gut of certain marine animals based on DNA barcoding. [ABSTRACT FROM AUTHOR]

To gain insight into the evolution of motor control systems at the origin of vertebrates, we have investigated higher-order motor circuitry in the protochordate Oikopleura dioica. We have identified a highly miniaturized circuit in Oikopleura with a projection from a single pair of dopaminergic neurons to a small set of synaptically coupled GABAergic neurons, which in turn exert a disinhibitory descending projection onto the locomotor central pattern generator. The circuit is reminiscent of the nigrostriatopallidal system in the vertebrate basal ganglia, in which disinhibitory circuits release specific movements under the modulatory control of dopamine. We demonstrate further that dopamine is required to optimize locomotor performance in Oikopleura , mirroring its role in vertebrates. A dopamine-regulated disinhibitory locomotor control circuit reminiscent of the vertebrate nigrostriatopallidal system was thus already present at the origin of ancestral chordates and has been maintained in the face of extreme nervous system miniaturization in the urochordate lineage. [Display omitted] • Oikopleura 's miniaturized brain contains only 2 dopaminergic neurons • Dopamine receptor expression reveals GABAergic neurons as principal synaptic targets • GABAergic neurons comprise a disinhibitory projection to the locomotor CPG • Dopamine regulates locomotor efficiency by adjusting the idling/swimming ratio Tolstenkov et al. show that locomotion in a urochordate is regulated by a highly miniaturized, dopamine-modulated disinhibitory circuit, similar and likely homologous to the vertebrate nigrostriatopallidal system. This form of motor control thus predates vertebrates and has been maintained in the face of extreme evolutionary CNS miniaturization. [ABSTRACT FROM AUTHOR]

Copyright of Iheringia. Série Zoologia is the property of Fundacao Zoobotanica do Rio Grande do Sul and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Larvacean (=appendicularian) and pteropod (Limacina helicina) composition and abundance were studied with physical variables each May and late summer across 11 years (2001–2011), along a transect that crosses the continental shelf of the sub-Arctic Gulf of Alaska (GoA) and five stations within Prince William Sound (PWS). Collection with 53-µm plankton nets allowed the identification of larvaceans to species: five occurred in the study area. Temperature was the driving variable in determining larvacean community composition, yielding pronounced differences between spring and late summer, while individual species were also affected differentially by salinity and chlorophyll-a concentration. During the spring Oikopleura labradoriensis and Fritillaria borealis were most abundant, being present at all stations. Late summer had highest abundances of Oikopleura dioica at nearshore stations, while F. borealis dominated numerically at outer stations. The 53-µm plankton nets collected higher abundances of Oikopleura spp., Fritillaria spp. and L. helicina than coarser 150- and 505-µm plankton nets. Limacina helicina abundance had a significant interaction effect among years, seasons and station location. Limacina helicina abundance in nearby PWS explained 30% of the variability in pink salmon survival; however, no significant correlations existed with larvacean or L. helicina abundances from the GoA stations. [ABSTRACT FROM PUBLISHER]

Appendicularians are planktonic tunicates (urochordates), and retain a swimming tadpole shape throughout their life. Together with ascidians, they are the closest relatives of the vertebrates. Oikopleura dioica is characterized by its simplified life habit and anatomical organization. It has a tiny genome, the smallest ever found in a chordate. Its life cycle is extremely short – about 5 days – and it can be maintained in the laboratory over many generations. Embryos and adults are transparent and consist of a small number of cells. The anatomy of juveniles and adults has been described in detail. Cleavage pattern, cell lineages, and morphogenetic movements during embryogenesis have also been comprehensively documented. A draft genome sequence is now available. These features make this organism a suitable experimental model animal in which genetic manipulations would be feasible, as in Drosophila and Caenorhabditis elegans. In this review, I summarize a hundred years’ knowledge on the development throughout the life cycle of this organism. Oikopleura is an attractive organism for developmental and evolutionary studies of chordates. It offers considerable promise for future genetic approaches. [ABSTRACT FROM AUTHOR]

Abstract: Developmental signaling by retinoic acid (RA) is thought to be an innovation essential for the origin of the chordate body plan. The larvacean urochordate Oikopleura dioica maintains a chordate body plan throughout life, and yet its genome appears to lack genes for RA synthesis, degradation, and reception. This suggests the hypothesis that the RA-machinery was lost during larvacean evolution, and predicts that Oikopleura development has become independent of RA-signaling. This prediction raises the problem that the anterior–posterior organization of a chordate body plan can be developed without the classical morphogenetic role of RA. To address this problem, we performed pharmacological treatments and analyses of developmental molecular markers to investigate whether RA acts in anterior–posterior axial patterning in Oikopleura embryos. Results revealed that RA does not cause homeotic posteriorization in Oikopleura as it does in vertebrates and cephalochordates, and showed that a chordate can develop the phylotypic body plan in the absence of the classical morphogenetic role of RA. A comparison of Oikopleura and ascidian evidence suggests that the lack of RA-induced homeotic posteriorization is a shared derived feature of urochordates. We discuss possible relationships of altered roles of RA in urochordate development to genomic events, such as rupture of the Hox-cluster, in the context of a new understanding of chordate phylogeny. [Copyright &y& Elsevier]

To clarify the feeding strategy of pelagic larvae of stone flounder in Mutsu Bay, the dietary composition and prey size was investigated from February to April during 1989–1999. Diets were compared with the numerical and volumetric compositions and frequency of occurrence of each prey species. Mensuration formulae were applied to estimate individual prey volume in the diet, while the length of planktonic species was measured from net and water samples. Prey shapes were assumed as sphere, cylinder, ellipsoid, pyramid, two elliptical cones, or a combination of ellipsoid and cylinder. Prey-size range increased as the larvae grew. Preflexion larvae fed mainly on copepod nauplii. Flexion and postflexion larvae ingested primarily appendicularians, with a suggestion that these larvae might depend on some parts of the microbial food web. Low frequencies of flexion and postflexion larvae with empty guts (1.7 and 1.4%, respectively) might be derived from feeding on slow-swimming appendicularians. From a size comparison between ‘house’-like organ length and trunk length of the appendicularian Oikopleura sp., almost all house-like organs with trunks in the larval diet were nonexpanded ‘house rudiments’, not expanded ‘houses’. Thus, stone flounder larvae may not chew the houses, but swallow the house rudiments with trunks. [ABSTRACT FROM AUTHOR]

Abstract: Three POU domain containing transcription factors have been cloned from the urochordate Oikopleura dioica. Phylogenetic analysis showed that two of these (OctA1 and OctA2) are closely related members of the class II POU domain family, and one (OctB) is a member of the class III POU domain family. All three transcription factors contained a highly conserved bipartite DNA-binding POU domain with POU specific and POU homeodomains, separated by a linker region. All three proteins were shown to bind specifically to the canonical octamer motif, ATGCAAAT. The ability of these factors to drive transcription from an octamer-containing reporter construct was assessed in vertebrate B lymphocyte cell lines. Both OctA1 and OctA2 drove transcription in murine and catfish B cell lines, however, OctB did not increase the level of transcription above background levels. It is concluded that Oct transcription factors capable of functioning in a similar fashion to vertebrate Oct1/2 were present at the phylogenetic level of the urochordates. [Copyright &y& Elsevier]

Abstract: Chromophoric dissolved organic matter (CDOM) can play an important role in regulating biological production in coastal environments. Fluorescent dissolved organic matter (FDOM) is a subset of the larger CDOM pool that can be used to look at sources of CDOM. Experiments were conducted with copepods and the pelagic larvacean, Oikopleura dioica to determine if these two types of zooplankton excrete FDOM. Shipboard bottle experiments were conducted with copepods in the Gulf of Mexico, in the Mississippi River Plume in April 2001 and laboratory experiments with the pelagic larvacean, O. dioica were conducted in Oviedo, Spain in June 2001. Both copepods and O. dioica were found to excrete FDOM. Excitation/emission matrices revealed that both animals contributed to fluorescent protein pools (ex/em 275/315–350 nm) and to humic-like material (maximum ex/em 300/420 nm). The humic-like material excreted by the copepods and larvaceans was shifted toward shorter wavelengths, providing a possible unique fluorescent signature for zooplankton. Using a ratio of the humic-like fluorescence excreted by the animals (ex/em 300/420) to the humic-like fluorescence maximum in controls (ex/em 320/420 nm) showed the zooplankton could contribute nearly 50% of the Peak M fluorescence. Molecular weight analysis of the CDOM in an O. dioica excretion study showed that O. dioica excreted CDOM was primarily <30 kDa. Both copepods and larvaceans are sources of marine FDOM and CDOM and can potentially influence the amount and type of CDOM present in coastal waters. [Copyright &y& Elsevier]

Oikopleura dioicais a pelagic tunicate with a very small genome and a very short life cycle. In order to investigate the intron-exon organizations inOikopleura, we have isolated and characterized ribosomal protein EF-1a, Hox, and a-tubulin genes. Their intron positions have been compared with those of the same genes from various invertebrates and vertebrates, including four species with entirely sequenced genomes.Oikopleuragenes, likeCaenorhabditis genes, have introns at a large number of nonconserved positions, which must originate from late insertions or intron sliding of ancient insertions. Both species exhibit hypervariable intron-exon organization within their a-tubulin gene family. This is due to localization of most nonconserved intron positions in single members of this gene family. The hypervariability and divergence of intron positions inOikopleuraandCaenorhabditismay be related to the predominance of short introns, the processing of which is not very dependent upon the exonic environment compared to large introns. Also, both species have an undermethylated genome, and the control of methylation-induced point mutations imposes a control on exon size, at least in vertebrate genes. That introns placed at such variable positions inOikopleuraorC. elegansmay serve a specific purpose is not easy to infer from our current knowledge and hypotheses on intron functions. We propose that new introns are retained in species with very short life cycles, because illegitimate exchanges including gene conversion are repressed. We also speculate that introns placed at gene-specific positions may contribute to suppressing these exchanges and thereby favor their own persistence. [ABSTRACT FROM AUTHOR]