Involvement of a Basic Helix-Loop-Helix Gene BHLHE40 in Specification of Chicken Retinal Pigment Epithelium

Abstract

The first event of differentiation and morphogenesis in the optic vesicle (OV) is specification of the neural retina (NR) and retinal pigment epithelium (RPE), separating the inner and outer layers of the optic cup, respectively. Here, we focus on a basic helix-loop-helix gene, BHLHE40, which has been shown to be expressed by the developing RPE in mice and zebrafish. Firstly, we examined the expression pattern of BHLHE40 in the developing chicken eye primordia by in situ hybridization. Secondly, BHLHE40 overexpression was performed with in ovo electroporation and its effects on optic cup morphology and expression of NR and RPE marker genes were examined. Thirdly, we examined the expression pattern of BHLHE40 in LHX1-overexpressed optic cup. BHLHE40 expression emerged in a subset of cells of the OV at Hamburger and Hamilton stage 14 and became confined to the outer layer of the OV and the ciliary marginal zone of the retina by stage 17. BHLHE40 overexpression in the prospective NR resulted in ectopic induction of OTX2 and repression of VSX2. Conversely, BHLHE40 was repressed in the second NR after LHX1 overexpression. These results suggest that emergence of BHLHE40 expression in the OV is involved in initial RPE specification and that BHLHE40 plays a role in separation of the early OV domains by maintaining OTX2 expression and antagonizing an NR developmental program.

Scientific Papers by Developmental Biologists in Japan

“…We believe that these manuscripts represent a valuable contribution to the specific field of developmental biology. This Special Issue contains six research articles [ 1 , 2 , 3 , 4 , 5 , 6 ] and four reviews [ 7 , 8 , 9 , 10 ].…”

“…Kinuhata et al [ 4 ] studied the role of a basic helix-loop-helix (bHLH) transcription factor, Bhlhe40, in chicken eye development, focusing on the stage of optic vesicle morphogenesis, when two retinal domains, the neural retina (NR) and retinal pigment epithelium (RPE), emerge to separate. They reported that Bhlhe40 is expressed in the prospective and definitive RPE and that its overexpression represses an NR gene, Vsx2 , while maintaining an RPE gene, Otx2 .…”