THE TRANSCRIPTIONAL AND TRANSLATIONAL CONTROL OF DIAZEPAM-BINDING INHIBITOR EXPRESSION IN RAT MALE GERM-LINE CELLS

The diazepam binding inhibitor [DBI, also known as acyl-CoA-binding pr otein, (ACBP), or endozepine] is a 10-kD protein that has been suggest ed to be involved in the regulation of several biological processes su ch as acyl-CoA metabolism, steroidogenesis, insulin secretion, and gam ma-aminobutyric acid type A (GABA(A))/benzodiazepine receptor modulati on. DBI has been cloned from vertebrates, insects, plants, and yeasts, In mammals, DBI is expressed in almost all the tissues studied, Never theless, DBI expression is restricted to specific cell types, Here we have studied DBI gene expression in the germ-line cells of rat testis, The DBI gene was intensively transcribed in postmeiotic round spermat ids from stages VI to Vm of the seminiferous epithelial cycle, A promi nent, spermatid-specific upstream transcription initiation site was id entified in addition to the multiple common transcriptional initiation sites found in the somatic tissues, However, no DBI protein was detec ted in round spermatids, suggesting that the DBI transcripts were tran slationally arrested, The DBI protein was detected in the late spermat ogenic stages starting from elongating spermatids from step 18 (stage VI) onward. The DBI protein was also detected in mature spermatozoa an d in ejaculated human sperms, The majority of DBI was located at the m iddle piece of the spermatozoons tail enriched with mitochondria, On t he basis of this observation and the well-established role of DBI in a cyl-CoA metabolism, we propose that DBI expression in spermatozoa refl ects the usage of fatty acids as a primary energy source by spermatozo a, The biological function of DBI in spermatozoa could thus be related to the motility function of sperm.