RESUMEN
The retinal development of the gilthead seabream Sparus aurata has been analysed from late embryonic development to juvenile stages using classical histological and immunohistological methods. Five significant phases were established. Phases 1 and 2 comprise the late embryonic and hatching stages, respectively. The results indicate that during these early stages the retina is composed of a single neuroblastic layer that consists of undifferentiated retinal progenitor cells. Phase 3 (late prolarval stage) is characterized by the emergence of the retinal layers and the appearance of neurochemical profiles in differentiating photoreceptors, amacrine and ganglion cells. Phases 4 and 5 comprise the late larval and juvenile stages. In these stages, all the retinal cell types can be detected immunohistochemically. All the maturational events described are first detected in the central retina and, as development progresses, spread to the rest of the retina following a central-to-peripheral gradient. The results of this study suggest that S. aurata is an altricial teleost species that hatches with a morphologically undifferentiated retina. The most relevant processes involved in retinogenesis occur during the late prolarval stage (phase 3).
Asunto(s)
Retina/crecimiento & desarrollo , Dorada/crecimiento & desarrollo , Animales , Larva/crecimiento & desarrollo , Neuronas/citología , Organogénesis , Retina/embriología , Epitelio Pigmentado de la Retina/citología , Epitelio Pigmentado de la Retina/embriología , Epitelio Pigmentado de la Retina/crecimiento & desarrollo , Dorada/embriologíaRESUMEN
We investigated patterns of cell death in the turtle retina that could potentially be associated with the innervation of the optic tectum, and looked for mechanisms of retinal development that might be common to reptilian and homeotherm vertebrates. We used retinas of turtle embryos between the 23rd day of incubation (E23) (before the first optic fibres reach the optic tectum) and hatching (when all the optic fibres have established synaptic connections). Dying retinal neurons were identified in paraffin sections by the TUNEL technique, which specifically labels fragmented DNA. Apoptotic cells were found in the ganglion cell layer (GCL), the inner nuclear layer (INL), and the outer nuclear layer (ONL). Cell death in the GCL was intense between E29 and E47, and had disappeared by the day of hatching. In the INL, dead and dying cells were most abundant between E31 and E34, and progressively disappeared. The temporal pattern in the ONL was similar to the INL although the density was very low. In all the nuclear layers cell death spread from the dorso-temporal area of the central retina to the periphery. Additional dorsal to ventral and temporal to nasal gradients were distinguishable in a quantitative TUNEL analysis. The patterns of cell death observed in the developing turtle retina were thus similar to those found in birds and mammals. This process could be under the control of differentiation gradients in all the vertebrate classes.