Isolation and characterization of chicken TaxREB107, a putative DNA binding protein abundantly expressed in muscle

Myogenic regulatory factors (MRFs) are vital transcription factors that act at multiple points during development to establish the skeletal muscle phe notype. This class of muscle-restricted, basic helix-loop-helix (bHLH) prot eins acts in concert with additional transcriptional modulators to precisel y control muscle gene expression. We have isolated the chicken homologue of Tax responsive element binding protein 107 (TaxREB107). The cDNA is 83% ho mologous at the amino acid level to human and mouse TaxREB107 and contains a centrally located leucine zipper motif. Northern analysis demonstrated th at the gene is expressed in multiple tissues including skeletal muscle. Imm unofluorescent staining revealed that the cTaxREB107 protein is located in both the nuclear and cytoplasmic compartments. Distinct localization to the nucleoli supports the evidence that TaxREB107 is a ribosomal protein. Beca use TaxREB proteins also are implicated in transcriptional regulation, we o verexpressed cTaxREB107 in embryonic myoblasts. cTaxREB107 increased tropon in I reporter gene activity as well as MRF-directed transcription from a mu ltimerized skeletal muscle E-box reporter gene (4Rtk-luc). However, cotrans fection of expression plasmids coding for MyoD and cTaxREB107 did not produ ce an increase in 4Rtk-luc suggesting that cTaxREB107 enhances myogenic gen e transcription through a means independent of a physical association with MyoD. In conclusion, our results define a role for cTaxREB107 during avian myogenesis as a positive modulator of skeletal muscle gene expression. (C) 2001 Elsevier Science B.V. All rights reserved.