Divergent patterns of ocular development and gene expression in the evolution of a subterranean salamander

Relatively few studies have focused on the evolution and development of divergent nervous systems. The salamander clade (Eurycea) from the karst regions of central Texas provide an ideal platform for comparing divergent nervous and sensory systems, since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes. We describe ocular development and examine early ocular protein expression (Pax6 and Shh), comparing between two salamander species representing two phenotypes: the surface dwelling Barton Springs salamander (E. sosorum) and the obligate subterranean Texas blind salamander (E. rathbuni). Between the two species, similarities during the development of ocular tissue (e.g. optic cup and lens vesicle) were observed during embryogenesis. However, during late stage embryogenesis the two species display markedly different patterns of Pax6 localization, which parallel patterns previously reported in a cavefish. A lens vesicle was observed in E. rathbuniembryos at stage 40, yet the lens is absent in adults, suggesting the regression of the lens during ontogeny. We also include adult histology of the surface dwelling San Marcos salamander (E. nana) and note similarities to E. sosorum. Adult E. rathbunilack major histological features associated with vision; however, eye morphology did not differ significantly between E. rathbuniand E. sosorumin early developmental stages, suggesting a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

Divergent patterns of ocular development and gene expression in the evolution of a subterranean salamander

Relatively few studies have focused on the evolution and development of divergent nervous systems. The salamander clade (Eurycea) from the karst regions of central Texas provide an ideal platform for comparing divergent nervous and sensory systems, since some species exhibit extreme phenotypes thought to be associated with inhabiting a subterranean environment, including highly reduced eyes. We describe ocular development and examine early ocular protein expression (Pax6 and Shh), comparing between two salamander species representing two phenotypes: the surface dwelling Barton Springs salamander (E. sosorum) and the obligate subterranean Texas blind salamander (E. rathbuni). Between the two species, similarities during the development of ocular tissue (e.g. optic cup and lens vesicle) were observed during embryogenesis. However, during late stage embryogenesis the two species display markedly different patterns of Pax6 localization, which parallel patterns previously reported in a cavefish. A lens vesicle was observed in E. rathbuniembryos at stage 40, yet the lens is absent in adults, suggesting the regression of the lens during ontogeny. We also include adult histology of the surface dwelling San Marcos salamander (E. nana) and note similarities to E. sosorum. Adult E. rathbunilack major histological features associated with vision; however, eye morphology did not differ significantly between E. rathbuniand E. sosorumin early developmental stages, suggesting a combination of underdevelopment and degeneration contribute to the reduced eyes of adult E. rathbuni.

Lens-specific deletion of the Msx2 gene increased apoptosis by enhancing the caspase-3/caspase-8 signaling pathway

Objective To investigate the influence of Msx2 conditional gene knockout during lens development in mice. Methods Lens-specific Msx2 knockout mice were generated using the Cre-loxP system. The eyes of Msx2 conditional knockout ( Msx2CKO) and wild-type ( Msx2WT) mice were examined during embryonic and early postnatal periods using histological, immunofluorescence, in situ hybridization, cell proliferation, apoptosis, and mRNA microarray analyses. Results Msx2CKO mice exhibited small lens formation and microphthalmia after birth, while Msx2CKO embryos exhibited a persistent lens stalk, small lens formation, and microphthalmia. Conditional deletion of Msx2 also led to an increased apoptosis rate, a significant reduction in FoxE3 expression, and an upregulation of Prox1 expression in the lens vesicle during the early embryonic period. Microarray comparison of Msx2CKO and Msx2WT lens transcriptomes identified a large number of differentially expressed genes. Real-time PCR showed that Casp8 and Casp3 expression was upregulated in Msx2CKO mice at post-natal day 1. Conclusion The activation of apoptosis through the caspase-8/caspase-3 signaling pathway, together with the downregulation of FoxE3 expression, appeared to account for the smaller lens formation in Msx2CKO mice.

Mechanics of Optic Cup Invagination in the Embryonic Chick Eye

Invagination of epithelia is an essential morphogenetic process that occurs in early eye development. The mechanics of the tissue forces necessary for eye invagination are not yet understood [1]. The eyes begin as two optic vesicles that grow outwards from the forebrain and adhere to the surface ectoderm. At this point of contact, both the surface ectoderm and optic vesicle thicken, forming the lens placode and retinal placode, respectively. The two placodes then bend inward to create the lens vesicle and bilayered optic cup (OC) [1, 2].