Biology subjects

Falk, B. L.

Publications and source records attributed to Falk, B. L..

3 recordsLinked to original sources

bioRxiv2026

In Step, the sole Drosophila TENT5 poly(A) polymerase, is required for spermatid elongation and individualization

Cytoplasmic poly(A) tail length is a key regulator of mRNA translation and stability, controlled in part by non-canonical poly(A) polymerases of the TENT5 family, which are required for gametogenesis in mice. We characterize the sole Drosophila melanogaster TENT5 ortholog, which we name in step (isep). Although identified as a candidate target of the eye specification factor Eyeless, isep mutants have normal eyes; instead, isep is essential for male fertility. The isep gene and its protein are expressed in spermatocytes and in elongating spermatids and are concentrated at the distal end of spermatid cysts. Mutant spermatids fail to elongate normally and to individualize. Whole-testis poly(A) tail sequencing revealed that, unexpectedly for the loss of a poly(A) polymerase, median tail length increased in mutants, with lengthened transcripts enriched for roles in axoneme assembly. Both wild-type and a predicted catalytically inactive Isep rescued sterility. We propose that Isep controls localized translation of axonemal transcripts at the spermatid tip, largely independently of its poly(A) polymerase activity.

developmental biology↗

bioRxiv2025

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.

genetics↗

bioRxiv2021

Eukaryotic translation initiation factor eIF4E-5 is required for spermiogenesis in Drosophila melanogaster

Drosophila sperm development is characterized by extensive post-transcriptional regulation whereby thousands of transcripts are preserved for translation during later stages. A key step in translation initiation is the binding of eukaryotic initiation factor 4E (eIF4E) to the 5 mRNA cap. Drosophila has multiple paralogs of eIF4E, including four (eIF4E-3, -4, -5, and -7) that are highly expressed in the testis. Other than eIF4E-3, none of these has been characterized genetically. Here, using CRISPR/Cas9 mutagenesis, we determined that eIF4E-5 is essential for male fertility. eIF4E-5 mutants exhibit defects during post-meiotic stages, including a fully penetrant defect in individualization, resulting in failure to produce mature sperm. eIF4E-5 protein localizes to the distal ends of elongated spermatid cysts, where it regulates non-apoptotic caspase activity during individualization by promoting local accumulation of the E3 ubiquitin ligase inhibitor Soti. eIF4E-5 mutants also have mild defects in spermatid cyst polarization, similar to mutants affecting the cytoplasmic polyadenylation-element binding protein Orb2 and atypical protein kinase C (aPKC). Our results further extend the diversity of non-canonical eIF4Es that carry out distinct spatiotemporal roles during spermatogenesis. Summary StatementThe testis-enriched translation initiation factor eIF4E-5 is needed for spermatid cyst polarization, individualization of mature sperm and male fertility in Drosophila.

developmental biology↗