Ivano Mocavini (@notquitesincere.bsky.social)

Probing RNA-protein interactions in the early mouse embryo The union of two germ cells to form a zygote, and subsequent early embryo development, are marked by radical remodeling of virtually every major class of biomolecules as the specialized germline states give way to the rapid and active growth that marks early development. In recent years, advances in ultra-low input genome-wide methods have enabled systematic analyses of mRNA abundance, and of chromatin organization, throughout early development in a variety of model systems. Here, we extend these efforts to the study of RNA binding protein (RBP) function in early mouse embryos, adapting REMORA 1 -- based on fusing an RNA-editing enzyme to an RBP of interest -- for use in early embryos. We benchmark our approach for several well-studied RBPs, successfully recovering expected features of their RNA cargos, and assayed the RNA cargos for 17 RBPs of interest for early gene regulation. Analysis of changes in mRNA metabolism following knockdowns of the RBPs surveyed here allowed us to identify direct regulatory functions for a subset of RBPs in the early mammalian embryo, including an unanticipated role for the RNA export adaptor Alyref in control of 3 prime polyadenylation sites. Together, our data provide a proof of concept resource for systematically exploring RBP functions in mammalian embryogenesis. ### Competing Interest Statement The authors have declared no competing interest. Eunice Kennedy Shriver National Institute of Child Health and Human Development, https://ror.org/04byxyr05, NIHR01HD099816 https://doi.org/10.64898/2026.04.30.721999