The homeobox gene superfamily is highly conserved during evolution. These genes act as transcription factors during several important developmental processes through their 60 amino acid homeodomains that recognize and bind to the regulatory region of their target genes. We isolated a novel homeobox gene designated Tex1 from a mouse testis cDNA library by degenerate oligonucleotide polymerase chain reaction (PCR) screening. Three extra amino acid residues, AYP, are inserted between the first and second helices of the homeodomain, which makes Tex1 a TGIF subclass homeobox gene. Tex1 was expressed specifically in the testis as seen by both Northern blot and RT-PCR analysis. Tex1 expression is initiated at around day 20 of testes. Furthermore, the results of in situ hybridization analysis reveal that the expression of Tex1 in testis is restricted in the germ cells at spermatid stage. Based on these data, it is suggested that Tex1, a novel testis homeobox gene, may play a crucial role during spermatogenesis.
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