Cloning of a cDNA for a novel insulin-like peptide of the testicular Leydig cells.

We have isolated complementary DNA clones coding for a novel member of the insulin-like hormone super-family from a boar testis cDNA library. Northern blot analysis and in situ hybridization revealed that the gene is expressed exclusively in prenatal and postnatal Leydig cells. We have tentatively proposed the name Leydig insulin-like (Ley I-L) for the gene and its encoded protein. The Leydig insulin-like protein is synthesized as a 131-amino acid preproprotein, which contains a 24-amino acid signal peptide. Comparison of the deduced amino acid sequence of pro-Leydig insulin-like protein with members of the insulin-like hormone superfamily predicts that the biologically active protein, after proteolytic processing of the C-peptide, consists of a 32-residue-long B-chain and a 26-residue-long A-chain and has a molecular size of 6.25 kDa.