The C-terminal ZZ domain of the Drosophila ORB2 RNA-binding protein is required for spermatid individualization

ORB2 is the Drosophila ortholog of the human CPEB2-4 family of RNA-binding proteins, which include a conserved C-terminal Zinc-binding ( ZZ) domain. We have recently shown that this domain interacts with several translation co-repressors in the early embryo, and that deletion of this domain from the endogenous orb2 gene results in derepression of its target mRNAs (LOW et al. 2025). Here we assess the effect of deletion of the ZZ domain on spermatogenesis. We find that ORB2{Delta}ZZ protein is no longer localized to the distal tip of spermatids; that in orb2{Delta}ZZ testes, additional proteins known to play a role in spermatid individualization - ORB, IMP, SOTI - are mislocalized; that the SOTI-dependent Cleaved Caspase 3 gradient no longer forms; that individualization complexes are defective; and that orb2{Delta}ZZ flies are sterile and lack mature sperm.