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Jeffrey Welch1 , Randy Barbee1 , Naomi Roberts1 , Gary Klinefelter1 *
U.S. EPA, Reproductive Toxicology Division, Research Triangle Park, NC. 1
SP22, a protein correlated with the fertilizing ability of rat spermatozoa, was recently shown to belong to a conserved gene family expressed in organisms as varied as bacteria (thiJ), rat (SP22), mouse (DJ-1), and human (DJ-1) (Welch et al., J. Androl. 19:385, 1998). In the rat, SP22 is represented by a 1kb transcript in somatic tissues, but is encoded by an additional 1.5kb mRNA in the testis. Cloning of testicular SP22 transcripts produced three SP22 cDNA sequences which were designated SP22A, SP22B, and SP22C. SP22C has subsequently been shown to be an artifactual sequence. The SP22A and SP22B sequences differed only in their 5' untranslated regions (UTRs). Northern blotting with a SP22A-specific probe detected a ~1.5 kb mRNA in the testis, but not in somatic tissues. During rat testis development, the SP22A mRNA was first detected in postnatal day 15 testis, coinciding with the appearance of early pachytene spermatocytes. The amount of SP22A mRNA increased until day 33, reaching maximal levels coincident with the appearance of post-meiotic germ cells. GenBank searches with the SP22A-specific sequence identified a single matching entry designated as CAP1. Although isolated from rat testis, CAP1 appears to represent a fusion of SP22A and rat hepatoma derived growth factor sequences. A similar database search with the SP22B-specific 5' UTR identified 18 rat and mouse sequences from various somatic tissues which matched the SP22B-specific 5' UTR sequence, suggesting that SP22B represents a somatic cell transcript. This was confirmed by Northern blotting with a SP22B-specific probe which detected a single band in all tissues examined, including all stages of testicular development. These results indicate that while the SP22 gene is expressed in both the testis and somatic tissues, SP22 is encoded by an additional 1.5kb transcript only in the testis.
This abstract is being presented on Monday, August 2 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.