RESUMO
The fish Astyanax mexicanus comes in two forms: the normal surface-dwelling (SF) and the blind depigmented cave-adapted (CF) morphs. Among many phenotypic differences, cavefish show enhanced olfactory sensitivity to detect amino-acid odors and they possess large olfactory sensory organs. Here, we questioned the relationship between the size of the olfactory organ and olfactory capacities. Comparing olfactory detection abilities of CF, SF and F1 hybrids with various olfactory epithelium (OE) sizes in behavioral tests, we concluded that OE size is not the only factor involved. Other possibilities were envisaged. First, olfactory behavior was tested in SF raised in the dark or after embryonic lens ablation, which leads to eye degeneration and mimics the CF condition. Both absence of visual function and absence of visual organs improved the SF olfactory detection capacities, without affecting the size of their OE. This suggested that developmental plasticity occurs between the visual and the olfactory modalities, and can be recruited in SF after visual deprivation. Second, the development of the olfactory epithelium was compared in SF and CF in their first month of life. Proliferation, cell death, neuronal lifespan, and olfactory progenitor cell cycling properties were identical in the two morphs. By contrast, the proportions of the three main olfactory sensory neurons subtypes (ciliated, microvillous and crypt) in their OE differed. OMP-positive ciliated neurons were more represented in SF, TRPC2-positive microvillous neurons were proportionately more abundant in CF, and S100-positive crypt cells were found in equal densities in the two morphs. Thus, general proliferative properties of olfactory progenitors are identical but neurogenic properties differ and lead to variations in the neuronal composition of the OE in SF and CF. Together, these experiments suggest that there are at least two components in the evolution of cavefish olfactory skills: (1) one part of eye-dependent developmental phenotypic plasticity, which does not depend on the size of the olfactory organ, and (2) one part of developmental evolution of the OE, which may stem from embryonic specification of olfactory neurons progenitor pools.
Assuntos
Comportamento Animal/fisiologia , Caraciformes/embriologia , Células-Tronco Neurais/metabolismo , Mucosa Olfatória/embriologia , Percepção Olfatória/fisiologia , Olfato/fisiologia , Animais , Morte Celular/fisiologia , Proliferação de Células/fisiologia , Células-Tronco Neurais/citologia , Mucosa Olfatória/citologiaRESUMO
In the last years several studies have shown that vascular endothelial growth factor (VEGF) is present in neural stem cells and mature neurons from different neural tissues where it may play an important role as a neuroproliferative and/or antiapoptotic factor. The olfactory neuroepithelium has the capability to replace dying neurons with new neurons formed by cell division from stem cells in the basal region of the epithelium. The present study demonstrates, for the first time, that VEGF is present in the olfactory epithelium, nerves and bulbs (both main and accessory) during the development of the toad Bufo arenarum. In this report, we detected VEGF immunoreactivity in mature olfactory neurons from early larval stages until the beginning of the metamorphic climax. VEGF expression decreases dramatically after metamorphosis. VEGF receptor Flk-1 was localized by immunohistochemistry, from premetamorphic larval stages until the climax in the neurons of the olfactory epithelium with a more intense labeling in the basal cell layer. Double-label immunofluorescence studies localized VEGF to the cytoplasm and the nucleus of mature neurons whereas Flk-1 was expressed in cell membranes. Flk-1 was present in neurons of both the main and accessory olfactory bulbs. After the end of metamorphosis, Flk-1 expression was limited to basal cells in the olfactory epithelium and Bowman's glands. The main and accessory olfactory bulbs showed the same pattern of Flk-1 immunostaining before and after the end of metamorphosis. The presence of VEGF and its receptor in the olfactory system suggests that VEGF may play an important role during neural development.
Assuntos
Bufo arenarum/embriologia , Mucosa Olfatória/embriologia , Mucosa Olfatória/metabolismo , Fator A de Crescimento do Endotélio Vascular/metabolismo , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/metabolismo , Animais , Western Blotting , Diferenciação Celular , Imuno-Histoquímica , Larva/metabolismo , Mucosa Olfatória/citologiaRESUMO
The expression of 9-O-acetylated gangliosides recognized by the Jones monoclonal antibody (mAb) correlates with cell migration and axonal outgrowth in the developing rat nervous system. We studied the expression of these gangliosides during the development and maturation of the rat olfactory system. Beginning on embryonic day 13 (E13) the olfactory epithelium and the migratory mass were intensely stained with Jones mAb. However, though this immunoreactivity disappeared from the olfactory epithelium at E19, it remained in a few fascicles and some glomeruli of the newborn and adult olfactory bulbs. We concluded that the expression of 9-O-acetylated gangliosides by olfactory axons and/or migrating cells may facilitate axonal outgrowth during development and might be involved in the formation of new glomeruli in the mature olfactory bulb.