A PROCESSED HOMEOBOX GENE EXPRESSED IN A STAGE-SPECIFIC, TISSUE-SPECIFIC AND REGION-SPECIFIC MANNER IN EPIDIDYMIS

Processed genes are generated by reverse transcription of mRNA and int egration at a novel site in the genome and are typically transcription ally silent. Here, we report that a processed gene on rat chromosome 4 that is highly related to the X chromosome-encoded rat Pem (r.Pem) ho meobox gene is transcriptionally active. This processed gene, r.Pem2, is expressed at high levels in epididymis but not in any other tissues that express the r.Pem gene, including testis. Although r.Pem2 lacks all the introns present in the r.Pem gene, it contains splice donor an d acceptor sequences within the coding region, permitting it to be spl iced and to potentially encode a 57 amino acid polypeptide, r.Pem2 tra nscripts accumulate in the caput and cauda regions of the epididymis b ut not in the initial segment. The r.Pem2 gene exhibits different regu lation from the r.Pem gene; its expression is induced later during pre pubertal development (between days 23 and 30 post partum) and independ ently of the presence of testosterone. Although the functional signifi cance of r.Pem2 is unknown, its developmental regulation and its appar ent acquisition of splicing sites during evolution are unique.