A testicular form of hormone-sensitive lipase (HSL tes ), a triacylglycerol lipase, and cholesterol esterase, is expressed in male germ cells. Northern blot analysis showed HSL tes mRNA expression in early spermatids. Immunolocalization of the protein in human and rodent seminiferous tubules indicated that the highest level of expression occurred in elongated spermatids. We have previously shown that 0.5 kilobase pairs of the human HSL tes promoter directs testis-specific expression of a chloramphenicol acetyltransferase reporter gene in transgenic mice and determined regions binding nuclear proteins expressed in testis but not in liver (Blaise, R., Grober, J., Rouet, P., Tavernier, G., Daegelen, D., and Langin, D. (1999) J. Biol. Chem. 274, 9327-9334). Mutation of a SRY/Sox-binding site in one of the regions did not impair in vivo testis-specific expression of the reporter gene. Further transgenic analyses established that 95 base pairs upstream of the transcription start site were sufficient for correct testis expression. In gel retardation assays using early spermatid nuclear extracts, a germ cell-specific DNA-protein interaction was mapped between ؊46 and ؊29 base pairs. The DNA binding nuclear protein showed properties of zinc finger transcription factors. Mutation of the region abolished reporter gene activity in transgenic mice, showing that it is necessary for testis expression of HSL tes .
Hormone-sensitive lipase (HSL)1 hydrolyzes triacylglycerol and, cholesterol and retinyl esters (1, 2). In adipose tissue, HSL catalyzes the rate-limiting step in lipolysis, the catabolic pathway that mobilizes fatty acids from triacylglycerol stored in the lipid droplet. HSL is also expressed in rodent and human testis (3-5). In situ hybridization experiments performed in rat testis showed strong labeling of cells in the adluminal parts of the seminiferous tubules at stages X-XIV and sparsely distributed grains in the basal parts (6). Immunohistochemistry experiments showed an HSL-like immunoreactivity in the adluminal part of the rat seminiferous tubules at stages XIII-VIII (5). The data suggested that rodent HSL mRNA and protein are expressed in haploid germ cells with a lag between mRNA and protein appearance. However, the precise germ cell type(s) expressing HSL was not determined in rat and it was not possible to rule out HSL expression in Sertoli cells. Moreover, the expression of HSL in germ cells of other mammalian species, including man, has not been documented. The effects of HSL gene disruption in mice have recently been reported (7). The most striking feature of the phenotype is male sterility due to oligospermia. Degenerated spermatocytes and spermatids were observed in HSL-deficient testis with a lack of mature spermatozoa. The data clearly demonstrate that HSL is required for spermatogenesis.The human adipose tissue form of HSL is encoded by 9 exons spanning 11 kb (8). The transcription start site was mapped in a short 5Ј-noncoding exon located 1.5 kb upstream of the first coding exon (9). The 2.8-kb mR...
