Imp and Syp in vivo temporal RNA interactomes uncover networks of temporal regulators of Drosophila brain development

Temporal patterning of neural progenitors is an evolutionarily conserved mechanism generating neural diversity. In Drosophila , post-embryonic neurogenesis requires the RNA-binding proteins (RBPs) Imp/IGF2BP and Syp/SYNCRIP. However, how they co-achieve their function is not well understood. Here, we elucidate the in vivo temporal RNA interactome landscapes of Imp and Syp during larval brain development. Imp and Syp bind a highly overlapping set of conserved mRNAs encoding proteins involved in neurodevelopment. We identify transcripts differentially occupied by Imp/Syp over time, featuring a network of known and novel candidate temporal regulators that are post-transcriptionally regulated by Imp/Syp. Furthermore, the physical and co-evolutionary relationships between Imp and Syp binding sites reveal a combinatorial, rather than competitive, mode of molecular interplay. Our study establishes a new in vivo framework for dissecting the temporal co-regulation of RBP networks as well as providing a resource for understanding neural fate specification.