We present evidence for the association of DAZL1 with actively translating polyribosomes in testes. Our results suggest a role for DAZL1 in translational regulation of a subset of mRNAs in germ cells. Germ cell-specific translational regulation is well documented for transition proteins and protamines. Their mRNAs are synthesized in round spermatids and stored as cytoplasmic mRNP particles for up to a week before being translated in elongated spermatids. Premature translation of Prm-1 mRNA in transgenic mice leads to dominant male sterility.
Translational repression of protamine mRNAs requires sequences within the 3′ untranslated region, and several RNA-binding proteins that bind to the region have been isolated. Among them PRBP (Prm-1 RNA-binding protein, encoded by the Tarbp2 gene) and TB-RBP (testis brain RNA-binding protein) were shown to repress protamine mRNA translation in vitro, and TB-RBP was found to be associated with translationally dormant free mRNP particles. However, a recent study on the expression of protamines in the testes of Tarbp2 knock-out mice indicated unexpectedly that PRBP is required for proper translational activation, but not repression, of protamine mRNA. How PRBP activates the translation of protamine mRNA and whether it is associated with polyribosomes remain to be determined.