EARLY POSTMITOTIC NEURONS TRANSIENTLY EXPRESS TOAD-64, A NEURAL-SPECIFIC PROTEIN

To identify proteins involved in the early development of the mammalia n cerebral cortex, we previously used two-dimensional gels to compare proteins synthesized at different stages in corticogenesis in the embr yonic rat at embryonic day 14 (E14), E17, and E21. During this period, the cortex develops from a morphologically homogeneous population of proliferative precursor cells into a complex structure containing a di verse array of terminally differentiated neurons. Several proteins are up-regulated coincident with the generation of postmitotic neurons. H ere we describe the purification, partial amino acid sequencing, and c haracterization of one of these proteins, TOAD-64 (Turned On After Div ision; 64 MDa), using polyclonal antisera to two synthetic peptides fr om the protein. This analysis reveals that TOAD-64 is a 64,000 Da prot ein that increases in abundance over the period of corticogenesis and then subsequently decreases to very low levels in the adult. The prote in is neural specific and is expressed by postmitotic neurons as they begin their migration out of the ventricular zone into the developing cortical plate. It is expressed in advance of most other neuronal prot eins. Progenitor cells do not express TOAD-64. Therefore, this protein is a marker for postmitotic cells that have made a commitment to a ne uronal phenotype. The extremely early expression, the relative abundan ce in newly born neurons, as well as the restriction in expression to the period of initial neuronal differentiation suggest that TOAD-64 ma y be a key structural protein for early neuronal function. (C) 1995 Wi ley-Liss, Inc.