Browsing by Author "Francisco-Morcillo, Javier"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Histological and scanning electron microscope observations on the developing retina of the cuttlefish (Sepia officinalis Linnaeus, 1758)Publication . Arias-Montecino, Alejandro; Álvarez-Hernán, Guadalupe; Mera-Rodríguez, José Antonio de; Calle-Guisado, Violeta; Martín-Partido, Gervasio; Rodríguez-León, Joaquín; Francisco-Morcillo, Javier; Sykes, AntónioIn this work we present a detailed study of the major events during retinal histogenesis of the cuttlefish Sepia officinalis from early embryos to newly hatched animals and juveniles. For this purpose, we carried out morphometric and histological analyses using light and scanning electron microscopy. From St19, the first embryonic stage analysed, to St23/24 the embryonic retina is composed of a pseudostratified epithelium showing abundant mitotic figures in the more internal surface. At St24 the first photoreceptor nuclei appear in the presumptive inner segment layer, while an incipient layer of apical processes of the future rhabdomeric layer become visible at St25. From this stage onwards, both the rhabdomeric layer and the inner segment layer increase in size until postnatal ages. In contrast, the width of the supporting cell layer progressively decreases from St25/26 until postnatal ages. S. officinalis embryos hatched in a morphologically advanced state, showing a differentiated retina even in the last stages of the embryonic period. However, features of immaturity are still observable in the retinal tissue during the first postnatal weeks of life, such as the existence of mitotic figures in the apical region of the supporting cell layer and migrating nuclei of differentiating photoreceptors crossing the basal membrane to reach their final location in the inner segment layer. Therefore, postnatal retinal neurogenesis is present in juvenile specimens of S. officinalis.
- Retinal differentiation in syngnathids: comparison in the developmental rate and acquisition of retinal structures in altricial and precocial fish speciesPublication . Alvarez-Hernan, Guadalupe; Andrade, José Pedro; Escarabajal-Blazquez, Laura; Blasco, Manuel; Solana-Fajardo, Jorge; Martin-Partido, Gervasio; Francisco-Morcillo, JavierThe altricial-precocial spectrum describes the degree of morphological maturation of offspring at the moment of hatching. In fishes, precocial species develop all their structures at early stages of embryogenesis and larvae hatch at an advanced stage of development, while altricial species hatch at a less developed stage. The timing of retinal development also varies significantly between precocial and altricial fish species. Thus, retinal development is completed before hatching in precocial species. In contrast, a relatively simple retina is observed in altricial newborns and the acquisition of the adult retinal features extends until late in larval life. Therefore, retinal maturation at hatching could be considered as a morphological character to describe the developmental mode of fish newborns. Syngnathids fishes hatch with well-developed sensory systems, jaws, and feeding structures and, therefore, they are considered as precocial fish species. Using as a model the retina of two species of syngnathids (Syngnathus typhle and Hippocampus guttulatus), we describe the retinal maturity during different embryological stages and compare the results with previous studies in the retina of other altricial and precocial fish species. This will be done through a review of the pertinent literature, as well as by drawing on our own experience gathered through recent studies on fish retinogenesis. These differences in the maturity of the visual system have implications for the vision-based survival skills during the early life stages after hatching and for the overall ecology and fitness of the species.