INTRINSIC POLARITY OF MAMMALIAN NEUROEPITHELIAL CELLS

Progenitor cells in the mammalian forebrain can undergo either symmetr ic or asymmetric cell divisions by varying their cleavage orientation. In asymmetric divisions, cells distribute apically and basally locali zed proteins differentially to their daughters. Here we explore the in trinsic polarity of neuroepithelial cells in the developing telencepha lon. Actin microfilaments are concentrated epically, forming beltlike structures that encircle spots of gamma-tubulin immunoreactivity. Stai ning for N-cadherin, beta-catenin, and the tyrosine kinase substrates pp120 and paxillin is also enriched at the lumenal surface, presumably due to the localization of these proteins at adherens junctions. Phos photyrosine immunoreactivity is concentrated apically in rings, sugges ting that adherens junctions are enriched for signaling molecules. In mitotic cells it appears that adherens junction proteins and phosphoty rosine immunoreactivity may be inherited either symmetrically or asymm etrically, depending on the cell's cleavage orientation during mitosis . The differential inheritance of junctional proteins may determine wh ether a daughter cell can respond to extrinsic signals after mitosis.