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The enigmatic rodlet cells (RCs) are characterized by conspicuous inclusions named "rodlets". They were discovered over 100 years ago and were considered as parasites but shortly afterward interpreted as endogenous cells. The RCs have been described in different tissues of marine and freshwater teleosts, but their origin and function remain unknown. This work was designed to an ultrastructural study on RCs development and distribution in intestinal epithelium of Dicentrarchus labrax. Three different stages of RCs development from early precursor cells to mature phase were observed, as well as a migration and finally an extrusion of their contents. In this study, the immature cells were found near the basal epithelium membrane. They were mainly identified by a rough endoplasmic reticulum with dilated cisternae, by developing rodlets and a thin fibrillar coat. The maturing RCs, localized in the middle zone of the epithelium, appeared to be undergoing a reorganization of the cell organelles. The mature RCs, placed near the free surface, showed a thick subplasmalemmar fibrillar coat. Most of the organelles were aggregated at the cell apex with a basally located nucleus. A cellular polarity was more evident. One of the most conspicuous features was the occurrence of mature rodlets club-sac in shape orientated toward the cell apex. Adhesive junctions between surface epithelial cells and RCs, while discharging their contents, were seen. We have connected morphological figures and distribution to different stages of development in RCs, supporting the hypothesis of their secretory function., (Copyright © 2012 Wiley Periodicals, Inc.)

The transient receptor potential (TRP) channels are involved in sensing mechanical/physical stimuli such as temperature, light, pressure, as well as chemical stimuli. Some TRP channels are present in the vertebrate retina, and the occurrence of the multifunctional channel TRP vanilloid 4 (TRPV4) has been reported in adult zebrafish. Here, we investigate the expression and distribution of TRPV4 in the retina of zebrafish during development using polymerase chain reaction (PCR), Western blot, and immunohistochemistry from 3 days post fertilization (dpf) until 100 dpf. TRPV4 was detected at the mRNA and protein levels in the eye of zebrafish at all ages sampled. Immunohistochemistry revealed the presence of TRPV4 in a population of the retinal cells identified as amacrine cells on the basis of their morphology and localization within the retina, as well as the co-localization of TRPV4 with calretinin. TRPV4 was first (3 dpf) found in the soma of cells localized in the inner nuclear and ganglion cell layers, and thereafter (10 dpf) also in the inner plexiform layer. The adult pattern of TRPV4 expression was achieved by 40 dpf the expression being restricted to the soma of some cells in the inner nuclear layer and ganglion cell layers. These data demonstrate the occurrence and developmental changes in the expression and localization of TRPV4 in the retina of zebrafish, and suggest a role of TRPV4 in the visual processing., (Copyright © 2012 Wiley Periodicals, Inc.)

The zebrafish pineal gland plays a fundamental role in the regulation of the circadian rhythm through the melatonin secretion. The pinealocytes, also called photoreceptive cells, are considered the morphofunctional unit of pineal gland. In literature, the anatomical features, the cellular characteristics, and the pinealocytes morphology of zebrafish pineal gland have not been previously described in detail. Therefore, this study was undertaken to analyze the structure and ultrastructure, as well as the immunohistochemical profile of the zebrafish pineal gland with particular reference to the pinealocytes. Here, we demonstrated, using RT-PCR, immunohistochemistry and transmission electron microscopy, the expression of the mRNA for rhodopsin in the pineal gland of zebrafish, as well as its cellular localization exclusively in the pinealocytes of adult zebrafish. Moreover, the ultrastructural observations demonstrated that the pinealocytes were constituted by an outer segment with numerous lamellar membranes, an inner segment with many mitochondria, and a basal pole with the synapses. Our results taken together demonstrated a central role of zebrafish pinealocytes in the control of pineal gland functions., (Copyright © 2011 Wiley Periodicals, Inc.)

TRPV4 is a nonselective cation channel that belongs to the vanilloid (V) subfamily of transient receptor potential (TRP) ion channels. While TRP channels have been found to be involved in sensing temperature, light, pressure, and chemical stimuli, TPRV4 is believed to be primarily a mechanosensor although it can also respond to warm temperatures, acidic pH, and several chemical compounds. In zebrafish, the expression of trpv4 has been studied during embryonic development, whereas its pattern of TPRV4 expression during the adult life has not been thoroughly analyzed. In this study, the occurrence of TRPV4 was addressed in the zebrafish sensory organs at the mRNA (RT-PCR) and protein (Westernblot) levels. Once the occurrence of TRPV4 was demonstrated, the TRPV4 positive cells were identified by using immunohistochemistry. TPRV4 was detected in mantle and sensory cells of neuromasts, in a subpopulation of hair sensory cells in the macula and in the cristae ampullaris of the inner ear, in sensory cells in the taste buds, in crypt neurons and ciliated sensory neurons of the olfactory epithelium, and in cells of the retina. These results demonstrate the presence of TRPV4 in all sensory organs of adult zebrafish and are consistent with the multiple physiological functions suspected for TRPV4 in mammals (mechanosensation, hearing, and temperature sensing), but furthermore suggest potential roles in olfaction and vision in zebrafish., (Copyright © 2011 Wiley Periodicals, Inc.)

The family of B1 Sox transcription factors plays critical roles in the early stages of development, including the central nervous system. It was demonstrated that Sox2 is expressed in repressed neural stem cells. Therefore, we decided to investigate the expression of Sox2 in the brain of zebrafish at different ages to identify potential neurogenic areas, and to establish the developmental changes they undergo. The brains were assessed by qRT-PCR, western blot, and immunohistochemistry. The maximal expression of Sox2 was found at 15 dpf progressively decreases up to 30 dpf, then increases up to 40 dpf and remains unchanged up to 180 dpf. By western blot three protein bands of 28 kDa, 34 kDa (main band), and 38 kDa were detected in the brain of 180 dpf animals. The immunolocalization of Sox2 revealed that by 15 dpf Sox2 was detected in cells of the olfactory bulb, the walls of the telencephalic and diencephalic ventricles, several nucleus in the diencephalons, and the tectum opticum; by 25-50 dpf the Sox2 positive areas were the same as above, and in the rhombencephalic ventricle and cerebellum. In adult animals Sox2 was restricted to the olfactory bulb and to cells of the telencephalic ventricle walls. Taken together present results demonstrate that the potential neurogenic areas in the brain of zebrafish are widespread than in mammals and change with development, but they are primarily concentrated around the ventricles and olfactory bulb in adults, following a similar localization as in mammals., (Copyright © 2010 Wiley-Liss, Inc.)

Neurotrophins acting through Trk signal-transducing receptors play essential roles in the nervous system, and probably in some nonneuronal tissues. In the present study we used Western-blot and immunohistochemistry to investigate the occurrence and cellular localization of TrkB in the mouse kidney. Furthermore, the structure and ultrastructure of the kidney in mice carrying a mutation in the trkB gene were analyzed. TrkB in the kidney was identical to the cerebral one (145 kDa). Since the antibody used recognize a sequence within the tyrosine-kinase domain of TrkB, the renal TrkB receptor identified here must be regarded as able to mediate biological effects of their ligands. TrkB immunoreactivity was restricted to the juxtaglomerular apparatus, including differentiated vascular cells and extaglomerular mesangial cells. In these cells, TrkB colocalized with renin. The structural analysis revealed no major changes in the kidney structure of TrkB-deficient mice, with the exception of a significant reduction of the glomerular area. Nevertheless, in these animals there was an apparent increase in the number of extraglomerular mesangial cells (which retain the ability to synthesize renin) and absence of the macula densa. Taken together, these results strongly suggest a role of TrkB and their ligands in the control of the normal development and maintenance of the juxtaglomerular apparatus., (Copyright (c) 2006 Wiley-Liss, Inc.)

The avian primary lymphoid organs, the thymus and the bursa of Fabricius, undergo age-dependent changes leading in some cases to the complete atrophy of the organ. Nevertheless, the timetable of the involutive process as well as the consequences in the structure and functionality of the organs vary largely in the time frame and structural changes among species. On the other hand, and in contrast with the large body of literature reporting the structural and functional changes in mammalian primary lymphoid organs, the age-dependent changes in avian thymus and bursa of Fabricius are scarce, fragmentary, and heterogeneous. This article reviews the current literature on this topic, and focuses primarily on the involution of the bursa of Fabricius., (Copyright 2003 Wiley-Liss, Inc.)