title: Doublecortin is widely expressed in the developing and adult retina of sharks.
abstract: Doublecortin (DCX) is a microtubule-associated protein that has been considered a marker for neuronal precursors and young migrating neurons during the development of the central nervous system and in adult neurogenic niches. The retina of fishes represents an accessible, continuously growing and highly structured (layered) part of the central nervous system and, therefore, offers an exceptional model to extend our knowledge on the possible role of DCX in promoting neurogenesis and migration to appropriate layers. We have analyzed the distribution of DCX in the embryonic and postembryonic retina of a small shark, the lesser spotted dogfish Scyliorhinus canicula, by means of immunohistochemistry. We investigated the relationship between DCX expression and the neurogenic state of DCX-labeled cells by exploring its co-localization with the proliferation marker PCNA (proliferating cell nuclear antigen) and the marker of neuronal differentiation HuC/D. Since radially migrating neurons use radial glial fibers as substrate, we explored the possible correlation between DCX expression and cell migration along radial glia by comparing its expression with that of the glial marker GFAP (glial fibrillary acidic protein). Additionally, we characterized DCX-expressing cells by double immunocytochemistry using antibodies against Calbindin (a marker for mature bipolar and horizontal cells in this species) and Pax6, which has been proposed as a regulator of cell proliferation, cell differentiation, and neuron diversification in the neural retina of sharks. Strong DCX immunoreactivity was observed in immature cells and cell processes, at a time when retinal cells were not yet organized into different laminae. DCX was also found in subsets of mature ganglion, amacrine, bipolar and horizontal cells long after they had exited the cell cycle, a pattern that was maintained in juveniles and adults. Our results on DCX expression in the retina are compatible with a role for DCX in cell migration within the immature retina, and in dynamic neuronal plasticity in the mature retina. We also provide evidence of DCX expression in discrete cells in the retinal pigment epithelium of prehatching embryos and juveniles, which suggest that retinal pigmented epithelial cells in sharks, as in mammals, have an intrinsic capacity to proliferate and differentiate into cells with neural identity.
authors: Department of Cell Biology and Ecology, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain. Electronic address: nuria.sanchez@usc.es.
authors: Nuria
authors: N
authors: Sánchez-Farías
authors: Department of Cell Biology and Ecology, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain. Electronic address: eva.candal@usc.es.
authors: Eva
authors: E
authors: Candal
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002465:Cell Movement; D049109:Cell Proliferation / Q000502:physiology; D004284:Dogfish; D000089622:Doublecortin Domain Proteins; D019084:Fluorescent Antibody Technique, Indirect; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D055495:Neurogenesis / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D009479:Neuropeptides / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D012160:Retina / Q000196:embryology* / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D000089622:Doublecortin Domain Proteins; D005904:Glial Fibrillary Acidic Protein; D008869:Microtubule-Associated Proteins; D009479:Neuropeptides; D018809:Proliferating Cell Nuclear Antigen
keywords: Cell migration; DCX; Development; Elasmobranch fish; Neural plasticity; Neurogenesis; Retinal pigment epithelium