rbm24a is an organizer component of germ plasm to determine germ cell fate

The formation of germ cells is a critical issue for the continuation of species. A large group of animals follow a preformation strategy to generate their primordial germ cells (PGCs). They produce a set of localized maternal mRNAs and proteins to form phase-separated germ plasm that functions as the PGC determinants, but the mechanisms underlying the assembly of germ plasm is poorly understood. This study identifies Rbm24a as an enssential localized germ plasm protein component that controls the formation of large and functional germ plasm granules. Rbm24a is complexed with Buc and interacts with germ plasm mRNAs, which determines the specific grasp of germ plasm mRNAs into the phase-separated aggregates. Rbm24a-absent granules fail to undergo kinesin-dependent transport towards the cleavage furrows, where small particles fuse into large ones. The loss of maternal rbm24a causes the complete degradation of germ plasm components and the disappearance of PGCs, resulting in totally sterile animals. Our work establishes that Rbm24 is a critical nucleating organizer component of germ plasm, highlighting an emerging common mechanism to read and recruit RNA component into phase-separated condensates. Overall design: We performed single-cell RNA-seq (scRNA-seq) for shield-stage embryos to compare gene expression between Mrbm24a and sibling embryos. Another purpose of this omic analysis is to examine possible cell populations that can be affected by the loss of maternal Rbm24a.