Cechmanek, P.B., McFarlane, S. (2017) Retinal pigment epithelium expansion around the neural retina occurs in two separate phases with distinct mechanisms. Developmental dynamics : an official publication of the American Association of Anatomists. 246(8):598-609.
Background The retinal pigment epithelium (RPE) is a specialized monolayer of epithelial cells that forms a tight barrier surrounding the neural retina. RPE cells are indispensible for mature photoreceptor renewal and survival, yet how the initial RPE cell population expands around the neural retina during eye development is poorly understood.
Results Here we characterize the differentiation, proliferation and movements of RPE progenitors in the zebrafish embryo over the period of optic cup morphogenesis. RPE progenitors are present in the dorso-medial eye vesicle shortly after eye vesicle evagination. We define two separate phases that allow for full RPE expansion. The first phase involves a previously uncharacterized antero-wards expansion of the RPE progenitor domain in the inner eye vesicle leaflet, driven largely by an increase in cell number. During this phase, RPE progenitors start to express differentiation markers. In the second phase the progenitor domain stretches in the dorso-ventral and posterior axes, involving cell movements and shape changes, and coinciding with optic cup morphogenesis. Significantly, cell division is not required for RPE expansion.
Conclusions RPE development to produce the monolayer epithelium that covers the back of the neural retina occurs in two distinct phases driven by distinct mechanisms.