RETINOIC ACID MEDIATES PAX6 EXPRESSION DURING IN-VITRO DIFFERENTIATION OF EMBRYONIC STEM-CELLS

Neural cells are found rarely during differentiation of embryonic stem (ES) cells in vitro. To increase the yield of neuronal and glial cell s from ES cells, we de signed a differentiation procedure in which emb ryoid bodies were grown in medium containing retinoic acid (RA) and a low level (1%) of fetal calf serum. Using this procedure we were able to obtain neurofilament or glial fibrillary acidic protein-positive ce lls in 90% of outgrowths of embryonic bodies. Differentiation was depe ndent on the RA concentration, whereas depletion of RA favored the app earance of cardiac muscle cells. Differentiation of ES cells correlate d with increased activity of Pax6, a transcription factor involved in central nervous system development. Pax6 was not expressed in undiffer entiated ES cells, nor after differentiation by depletion of leukemia inhibitory factor or by overgrowth. After embryoid body formation and subsequent attachment, only infrequently did a few cells express Pax6. Addition of RA resulted in the appearance of Pax6-expressing cells in a concentration-dependent manner, with a peak at 100 nM RA. The prese nted differentiation procedure can be used for studying the molecular biology of neurogenesis in vitro.