A critical role for the optic vesicle in lens development; a reinvestigation of free lens formation in Cynops pyrrhogaster.

The role of the optic vesicle in lens development was reinvestigated in Cynops pyrrhogaster. To study the necessity for the optic vesicle in early lens development, the optic anlages of stage 17-27 embryos were ablated and the frequency of free lens formation was examined with lens specific markers. Free lens formation was not observed when operations were performed prior to contact between the head surface epidermis and the optic vesicle (stages 17-18). On the contrary, free lens formation occurred in all cases where the optic vesicles were removed after the initiation of lens placode formation in the head surface epidermis (stage 27). However, no lens fiber formation was observed in these free lenses as judged by the absence of lens fiber specific gene expression, namely gamma-crystallin, at stages when secondary lens fiber formation could be found in the control lenses of the unoperated sides. The pattern of expression of alpha A-crystallin in the developing free lens also differed from that of the normally developing lens. This paper is the first report to indicate that the coordinated and sequential expression of crystallin genes are influenced by the optic vesicle; the optic vesicle is required for proper regulation of the alpha A- and gamma-crystallin but not beta B1-crystallin genes.