TEMPORAL AND SPATIAL PATTERN OF MASH-1 EXPRESSION IN THE DEVELOPING RAT RETINA DEMONSTRATES PROGENITOR-CELL HETEROGENEITY

The temporal and spatial pattern of mammalian achaete-scute homolog 1 (MASH-I) expression in the developing rat retina was examined in an ef fort to correlate achaete-scute homolog expression with the generation of particular cell classes. The expression of MASH-I was restricted t o the latter portion of retinal neurogenesis and was most closely corr elated with the appearance of bipolar cells and Muller glia, two cell classes that are generated late in retinogenesis. We also examined the proliferative nature of the MASH-1-expressing cell type to confirm th at MASH-I is expressed by progenitor cells and to determine the propor tion of the proliferating population that expresses MASH-1. MASH-I was expressed by only 10-30% of the total proliferating population, depen ding on the age examined. Thus, MASH-I expression provides a molecular marker of heterogeneity among retinal progenitor cells and may play a role in the commitment and/or differentiation of one or more of the l ate-appearing retinal phenotypes. (C) 1996 Wiley-Liss, Inc.