UBIQUITOUS, BUT VARIABLE, EXPRESSION OF 2 ALTERNATIVELY SPLICED MESSENGER-RNAS ENCODING MOUSE HOMOLOGS OF TRANSCRIPTION FACTORS E47 AND E12

Two basic helix-loop-helix (bHLH) transcription factors, E47 and E12, are involved in cell-specific gene expression as part of dimeric compl exes which interact with the cis-acting motif E-box. Although both gen erated from a single gene (E2A) by means of alternative splicing, the structural difference in these bHLH regions between the two suggests t hat the two bHLH proteins may differ in some of their functions. As a step toward elucidating the individual implications of E47 and E12, we investigated the mRNA expression ratios of their homologues (A1 and k A1, respectively) in mouse tissues and cell lines. Both the A1 and kA1 mRNAs were ubiquitously expressed in all tissues examined. However, t heir ratios varied: e.g., skeletal muscle, 2.2+/-0.3 (mean+/-SE); sple en, 2.0+/-0.2; pancreatic islet cells, 1.2+/-0.2. The A1/kA1 ratios in the cell lines investigated were similar to those of their original t issues. In conclusion, the ubiquity in mRNA expression observed for bo th the E47 and E12 homologues in mouse provides support for their invo lvement in a broad range of transcriptional regulation. The variation in the A1/kA1 expression ratios, on the other hand, supports the idea that A1 (E47) and kA1 (E12) each have some unique roles in the functio ns of these E2A gene-encoded bHLH proteins.