The evolution and development of the eye has intrigued developmental biologists for centuries. Aside from partial or complete loss, few vertebrates display substantial modifications to the eye morphology. One example is the Four-eyed fish (Anableps anableps). This species is commonly found from Gulf of Paria in Venezuela to Delta of Parnaíba and reproduces throughout the year. The four-eyed fish consists in a unique model system to study eye Evo-Devo due to its distinctive feature of having divided eye structures, such as pupils and cornea. The retina is a unique structure divided into two regions, dorsal (receives aquatic luminous information) and ventral (receives aerial luminous information). The aim of this study was to describe larval stages of this species, and morphological and molecular description of the retina during eye development. Six larval stages were described. The two earlier stages did not split the cornea and pupil, and from stage three, it is possible to observe this division. It was also described the development and expansion of the frontal bone. The appearance of the frontal bone begins at stage three of development. It has been identified the appearance of an inter-orbital septum cartilaginous, starting four stage of the ocular development. It was observed that the early development of the retinal cellular layers are disorganized and is not possible to distinguish between them, but later during development, these layers become organized, with ventral outer nuclear layer thicker than the dorsal one, and the dorsal inner nuclear layer is thinner than the ventral. The pattern of retinal cell proliferation has been described in three stages of development, before and during ocular division. It was observed that the proliferation is greater at the beginning of the larval development and decreases on later stages. The result of this study will shed light on the molecular basis of this innovative feature.
|
