Ectopic expression of Msx2 in chick retinal pigmented epithelium cultures suggests a role in patterning the optic vesicle

During the initial stages of vertebrate retinogenesis, cells of the optic v esicle adopt one of two alternate cell fates. Cells in the distal-most part of the vesicle, immediately beneath the surface ectoderm, undergo neural d ifferentiation; cells in the proximal part differentiate into retinal pigme nted epithelial cells. The mechanisms that establish this pattern of differ entiation are poorly understood. In the mouse embryo, Msx2, a homeobox-cont aining transcription factor, is expressed in cells of the optic vesicle tha t will form the neural retina, whilst the developing retinal pigmented epit helium (RPE) does not express this gene. Msx2 could therefore be involved i n patterning the optic vesicle into neural and pigmented domains. To explor e this possibility we ectopically expressed mouse Msx2 in cultures of chick RPE cells. Compared with cultures transfected with a control construct. Ms x2-transfected cultures contained fewer cells expressing the RPE marker, Mi tf, and more cells expressing class III P-tubulin, a neuronal marker. In ad dition a small proportion of Msx2-transfected cells acquired a neural-like morphology. These results show that Msx2 can suppress the differentiated st ate of RPE cells and promote their differentiation into neural cell types. We suggest that Msx2 may pattern the optic vesicle into neural and pigmente d domains by affecting the balance between RPE and neural retina differenti ation. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.