Mouse Leydig insulin-like (Ley I-L) gene: structure and expression during testis and ovary development.

Leydig insulin-like protein (Ley I-L) is a novel member of the insulin-like hormone superfamily. We report here the isolation and expression of the mouse Ley I-L gene. The gene encodes a polypeptide of 122 amino acids that shows a relatively weak homology (54%) to human and porcine prepro-Ley I-L. However, the predicted B and A chain of the mature mouse Ley I-L exhibit similarities of 73% and 71% with human and porcine Ley I-L, respectively. Alignment of the 5' flanking region of the mouse gene with those of human and porcine did not exhibit any significant sequence homology. However, it contains the conserved sequence of the Ad4 binding site that is present in all promoter regions of steroidogenic P-450 genes and the Müllerian inhibitor substance gene and is recognized by steroidogenic factor 1. The Ley I-L gene is expressed at a high level in the testis and at a much lower level in the ovary. No transcripts could be detected in placenta prepared between days 10 and 19 of pregnancy. Ley I-L transcripts were first detected in fetal testis at 13.5 dpc. After birth, transcript levels remain constant during the following 3 weeks, increasing at the stage in which the first wave of round spermatids undergo spermiogenesis suggesting a functional role of the Ley I-L in early stages of spermatogenesis and germ-cell maturation. In the ovary, the expression of Ley I-L was first detected at day 6 after birth. The pattern of Ley I-L expression at various stages of the estrous cycle and during pregnancy showed a correlation with follicle development.