Apoptosis and differentiation in presumptive neural retina and presumptive retinal pigmented epithelium during early eye development in toad, Bufo raddei strauch

Apoptosis and differentiation in presumptive neural retina (PNR) and presumptive retinal pigmented epithelium (PRPE) were investigated during early retina development of toad, Bufo raddei Strauch. TUNEL staining was used to evaluate apoptotic cells and the immunohistochemistry was used to assess the expression levels of glial fibrillary acidic protein (GFAP), RT97 and tyrosinase (Tyr) during early eye development respectively. The density of apoptotic cells and protein expression were quantitated with Image-Pro Plus 6.0. Apoptosis was found in both PNR and PRPE and the density of apoptotic profiles in PRPE was higher than that in PNR (most P < 0.01) at the same stage during early eye development. The expression levels of GFAP and RT97 changed from low to high in PNR, but from high to low in PRPE, whereas the expression level of Tyr, was contrary to those of GFAP and RT97 in both PNR and PRPE. The point of intersection of these, increase and decrease respectively was found at 5–6 h after formation of optic vesicle (FOV). PRPE becomes thinner than PNR, one of the reasons might be due to higher density of apoptosis in PRPE than that in PNR during early eye development. Molecular differentiation, however, occurred after the contact of the optic vesicle outer wall with the overlying ectoderm which promotes the expression of specific molecules and inhibits the expression of non-specific molecules in PNR and PRPE respectively.