A new translational repression element and unusual transcriptional control regulate expression of don juan during Drosophila spermatogenesis

Abstract

The Drosophila don juan (dj) gene encodes a basic protein that is expressed solely in the male germline and shows structural similarities to the linker histone H1. Don Juan is located in two different subcellular structures: in the nucleus during the phase of chromatin condensation and later in the mitochondrial derivatives starting with spermatid individualization. The don juan gene is transcribed in primary spermatocytes under the control of 23 bp upstream in combination with downstream sequences. During meiotic stages and in early spermatid stages don juan mRNA is translationally repressed for several days. Analysis of male sterile mutants which fail to undergo meiosis shows that release of dj mRNA from translational repression is independent of meiosis. In gel retardation assays 60 nucleotides at the end of the dj leader form four major complexes with proteins that were extracted from testes but not with protein extracts from ovaries. Transformation studies prove that in vivo 35 bp within that region of the dj mRNA is essential to confer translational repression. UV cross-linking studies show that a 62 kDa protein specifically binds to the same region within the 5' untranslated region. The dj translational repression element, TRE, is distinct from the translational control element, TCE, described earlier for all members of the Mst(3)CGP gene family. Moreover, expression studies in several male sterile mutants reveal that don juan mRNA is translated in earlier developmental stages during sperm morphogenesis than the Mst(3)CGP mRNAs. This proves that translational activation of dormant mRNAs in spermatogenesis occurs at different time-points which are characteristic for each gene, an essential feature for coordinated sperm morphogenesis.