2 NOVEL ODORANT RECEPTOR FAMILIES EXPRESSED IN SPERMATIDS UNDERGO 5'-SPLICING

We report the identification of two novel families of odorant receptor (OdR)-like proteins, termed spermatid chemoreceptors (SCRs), in rat s permatids of the testis. The full-length genomic clones encode seven t ransmembrane domain receptors that share 35-40% identity with certain OdRs and are among the most divergent members of the OdR superfamily b ased on phylogenetic analysis. RNase protection assays and in situ hyb ridization studies confirmed the expression of SCRs in spermatids, the post meiotic, differentiating cell population in the testis. SCR tran scripts were undetectable in the prepubertal testis but were readily i dentified in spermatids of sexually maturing and mature testis. Rapid amplification of cDNA end-polymerase chain reaction and genomic clone sequencing led to the discovery that SCRs are spliced upstream of thei r presumptive starting methionines. 5'-Splicing of OdRs may regulate t he expression of functional chemoreceptors.