Structure and expression of the mouse gene encoding the endozepine-like peptide from haploid male germ cells

The endozepine-like peptide (ELP) represents a testis-specific isoform of t he ubiquitous acyl-CoA binding protein (ACBP) and is highly expressed in la te haploid stages of male germ cell development. The genomic sequence of th e functional ELP gene as well as that of a pseudogene were analysed from in dependent bacteriophage clones of a 129sv mouse genomic library. Unlike the ACBP gene, which comprises four exons, the ELP gene has only a single intr on within the region of the 5' untranslated region, suggesting that, like s ome other haploid expressed genes, the ELP gene might have evolved by retro poson-mediated gene duplication. Primer extension analysis was used to defi ne the start site for transcription and hence the 5' promoter region. Elect rophoretic mobility shift analysis was carried out on this region comparing nuclear extracts from adult mouse testis with those from mouse liver. Seve ral testis-specific DNA-protein complexes were observed throughout 700 bp u pstream of the transcription start site. One of these could be identified a s corresponding to a steroidogenic factor-1 (SF-1) binding element. Further analysis using pure transcription factors showed that this element at posi tion -340 was able to bind specifically to both SF-1 and to the germ cell n uclear factor (GCNF). Immunohistochemical analysis using an ELP-specific an tibody showed that expression was very restricted within the testis to the postmeiotic germ cells, and in the ovary to interstitial/luteal cells, cell -types known to express GCNF and SF-1, respectively. Testes of CREM-tau kno ckout mice, lacking all spermatogenic stages later than round spermatids, w ere devoid of ELP immunoreactivity, whereas in RAD6 knockout mice the few r emaining elongated spermatids were clearly defined by this excellent late h aploid marker product. The ELP gene and its product thus offer an ideal sys tem with which to investigate the differentiation of late haploid stages of spermatogenesis.