CLONING OF TCFL5 ENCODING A NOVEL HUMAN BASIC HELIX-LOOP-HELIX MOTIF PROTEIN THAT IS SPECIFICALLY EXPRESSED IN PRIMARY SPERMATOCYTES AT THEPACHYTENE STAGE

We have isolated a novel human gene that is expressed specifically in primary spermatocytes in the testis. The cDNA contains an open reading frame of 1356 bp, encoding a 452-amino-acid protein that includes a b asic Helix-Loop-Helix (bHLH) motif. The gene, which was mapped to chro mosome region 20ql 3.3-->qter by fluorescence in situ hybridization, c onsists of six exons and spans approximately 24 kb of genomic DNA. Imm unohistochemical staining located the gene product exclusively in cell nuclei of primary spermatocytes at the pachytene stage, but not in th ose at the leptonema stage. We named this gene TCFL5 (transcription fa ctor-like 5, basic helix-loop-helix). The cell-type and stage-specific expression of TCFL5 indicates that this protein may function in a cru cial role in spermatogenesis as a transcription factor by regulating c ell proliferation or differentiation of cells through binding to a spe cific DNA sequence like other bHLH molecules.