HELIX-LOOP-HELIX PROTEINS IN SCHWANN-CELLS - A STUDY OF REGULATION AND SUBCELLULAR-LOCALIZATION OF IDS, REB, AND E12 47 DURING EMBRYONIC AND POSTNATAL-DEVELOPMENT/

Although basic helix-loop-helix (bHLH) proteins play an important role in transcriptional control in many cell types, the role of HLH protei ns in Schwann cells has yet to be assessed, In this study, we have ana lyzed the expression of the dominant negative HLH genes, Id1 to Id4 an d the class A gene REB, during Schwann cell development, We found that mRNA derived from these genes was present in the Schwann cell lineage throughout development including embryonic precursors and mature cell s, The mRNA levels were not significantly regulated during development , Nevertheless, by using antibodies against the four different Id prot eins, we found clear regulation of some of these genes at the protein level, in particular Id 2, 4, and REB, both in amount and nuclear/cyto plasmic localization, All these proteins are found in the nuclei of Sc hwann cell precursors but are not seen in nuclei of Schwann cells of n ewborn nerves, We observed extensive overlap in Id expression, especia lly in Schwann cell precursors that co-expressed all four Id proteins and REB, We also showed that Id 1 and 2 were up-regulated as Schwann c ells progressed through the cell cycle, These data indicate that HLH t ranscription factors act as regulators of Schwann cell development and point to the existence of as yet unidentified cell type-specific bHLH proteins in these cells. (C) 1997 Wiley-Liss, Inc.