Extraocular dorsal signal affects the developmental fate of the optic vesicle and patterns the optic neuroepithelium

Abstract

Dorsal-ventral (DV) specification in the early optic vesicle plays a crucial role in the proper development of the eye. To address the questions of how DV specification is determined and how it affects fate determination of the optic vesicle, isolated optic vesicles were cultured either in vitro or in ovo. The dorsal and ventral halves of the optic vesicle were fated to develop into retinal pigment epithelium (RPE) and neural retina, respectively, when they were separated from each other and cultured. In optic vesicles treated with collagenase to remove the surrounding tissues, the neuroepithelium gave rise to cRax expression but not Mitf, suggesting that surrounding tissues are necessary for RPE specification. This was also confirmed in in ovo explant cultures. Combination cultures of collagenase-treated optic vesicles with either the dorsal or ventral part of the head indicated that head-derived factors have an important role in the fate determination of the optic vesicle: in the optic vesicles co-cultured with the dorsal part of the head Mitf expression was induced in the neuroepithelium, while the ventral head portion did not have this effect. The dorsal head also suppressed Pax2 expression in the optic vesicle. These observations indicate that factors from the dorsal head portion have important roles in the establishment of DV polarity within the optic vesicle, which in turn induces the patterning and differentiation of the neural retina and pigment epithelium.

Bone morphogenetic proteins specify the retinal pigment epithelium in the chick embryo

“…A signal released from the mesenchyme is thought to be the primary inducer of Mitf expression in the chick and mouse optic vesicle (Fuhrmann et al, 2000;Kagiyama et al, 2005). At stage 9, Mitf expression was seen to be strongest in the distal part of the optic vesicle that is covered by the surface ectoderm (Fig.…”

“…Embryonic transplantations and in ovo explant cultures of the chick optic vesicle have shown that the dorsoventral polarity of the eye is already specified by stage 10 ( Uemonsa et al, 2002;Kagiyama et al, 2005). At this time point, the dorsal half of the optic vesicle is fated to develop mainly into RPE, whereas the ventral portion develops mainly into NR (Kagiyama et al, 2005).…”

“…For example, fibroblast growth factors (FGFs) expressed in the surface ectoderm and/or distal optic vesicle appear to be involved in NR induction and differentiation (Pittack et al, 1997;Hyer et al, 1998;Nguyen and Arnheiter, 2000;Vogel-Höpker et al, 2000;Martinez-Morales et al, 2005). Embryonic transplantations and in ovo explant cultures of the chick optic vesicle have shown that the dorsoventral polarity of the eye is already specified by stage 10 ( Uemonsa et al, 2002;Kagiyama et al, 2005). At this time point, the dorsal half of the optic vesicle is fated to develop mainly into RPE, whereas the ventral portion develops mainly into NR (Kagiyama et al, 2005).…”

RPE specification in the chick is mediated by surface ectoderm-derived BMP and Wnt signalling

“…Antisense RNA probes specific for chicken Rx (T. Ogura, Tohoku University, Aoba, Japan), Mitf (M. Mochii, University of Hyogo, Japan), Vsx2 and Wnt3a,Wnt4,Wnt5,Wnt5b,Wnt7b,Wnt8b (D. Schulte, Goethe University of Frankfurt/M., Germany) and Wnt2b (H. Roelink, University of Washington, Seattle, WA), were used. In explant cultures of ov, MITF expression was carried out as previously described (Kagiyama et al, 2005;Kobayashi et al, 2010). Human MITF antibody (Sigma-Aldrich, HPA003259), PY489-β-catenin (DSHB), pSmad1/5, pSMAD1/5/8 (Cell Signaling, 9516, 9511S), Retinal pigment epithelial-specific protein 65 kDa (Novus Biologicals, 4018BD113D9) and mouse Pax7 (MAB1675) were used on cryostat sections.…”

“…Once NR specification has occurred in the distal ov, Mitf expression becomes restricted to the dorsal ov (Nguyen and Arnheiter, 2000;Nakayama et al, 1998;Müller et al, 2007;Ishii et al, 2009). At this stage, the chick ov is divided into a dorsal RPE and ventral NR domain (Kagiyama et al, 2005;Hirashima et al, 2008;Kobayashi et al, 2010).…”