Crx is necessary but not sufficient to generate fully differentiated photoreceptors

GARELLI A., ROTSTEIN N. AND POLITI L.

Pinamar, Bs. As., Argentina

Congreso; Reunión conjunta de PABMB, SAIB y SAN; 2005

PABMB, SAIB, SAN

CRX IS NECESSARY BUT NOT SUFFICIENT TO gENERATe FULLY DIFFERENTIATED  PHOTORECEPTORS Garelli, Andrés; Rotstein, Nora P. and Politi Luis E. INIBIBB (UNS-CONICET) CC857 B8000FWB – Bahía Blanca, Argentina-. E-mail: agarelli@criba.edu.ar  Pax6 is necessary for eye development and Crx for the generation of photoreceptor cells. To understand the role of Crx on photoreceptor differentiation we studied its expression in vivo and in vitro during rat eye development along with that of Pax6, as well as the effects of docosahexaenoic acid (DHA), a photoreceptor trophic factor. Progenitor cells labeled with BrdU in vivo expressed Pax6 during retina differentiation at every embryonic stage analyzed. On the contrary, Crx was expressed at embryonic day 20 and only in postmitotic photoreceptors, preceding the onset of opsin expression. Similar results were found in vitro, when retinal cells were cultured in chemically defined media, pulsed with BrdU and fixed at different time points. Progenitor cells in culture initially expressed Pax6 and nestin, even during mitosis. Pax6 and nestin expression were downregulated and Crx upregulated as progenitors left cell cycle. However, only a small percentage of Crx-positive cells also expressed opsin. Interestingly, addition of DHA promoted neurite elongation, outer segment development and opsin expression. Hence, Crx is necessary to initiate photoreceptor differentiation, but not sufficient for photoreceptor development, and DHA is required to promote further differentiation in these cells.