Rat transition nuclear protein 2 regulatory region directs haploid expression of reporter gene in male germ cells of transgenic mice

During spermiogenesis, the successive replacement of somatic histones by ba sic proteins, the transition nuclear proteins and protamines, allows normal sperm condensation. Transition nuclear protein 2( TNP2) is transcribed pos tmeiotically in round spermatids. In order to determine regulatory flanking sequences responsible for stage specific expression of TNP2 gene, differen t transgenic mice were generated by microinjection of fertilized eggs. We d emonstrate here that 525 bp of 5'- and 920 bp of 3'-flanking sequences of r at TNP2 gene could properly and efficiently direct chloramphenicol acetyltr ansferase gene expression to the postmeiotic male germ cells of transgenic mice. During male germ cell differentiation the first transgene transcripts were observed in round spermatids and translation started 6 days later in elongating spermatids, which is an evidence for posttranscriptional regulat ion of transgene expression. In contrast, transgenic mice bearing only the 525 bp 5'-flanking sequences of rat transition protein 2 gene and 3'-flanki ng sequences of the simian virus 40 large T antigen showed low levels of tr ansgene expression in testis. From these results, it can be concluded that the 525 bp 5'-flanking sequences regulate the cell specific expression and the sequences located in 920 bp 3'- Ranking region either enhance the trans gene expression in the male germ cells or may have a posttranscriptional ro le in stabilizing the mRNA in addition to its function in delaying the mRNA translation, Using comparative alignment of 5'-flanking of TNP2 genes from different species, the putative regulatory sequences are identified. (C) 2 001 Wiley-Liss, Inc.