Maternal Control of Embryonic Development in Zebrafish

Patterning of embryos is dependent on both maternal and zygotic gene products. Maternal transcripts of the zebrafishNodal-related factor, Squint (Sqt), are localized to future embryonic dorsal, via microtubule mediated transport.We showed that maternal squint RNA has a non-coding function, independent of the signaling functions of the protein, in specification of dorsal cell fates.  We have identifiedan essential role for maternal control of Nodal signaling via the conserved Y box-binding protein 1 (Ybx1). We identified Ybx1in a proteomics screen for sqt RNA-binding proteins.  Ybx1 recognizes the dorsal localization element (DLE) in the sqt 3’ un-translated region (3’UTR), and prevents premature Sqt translation and Nodal signaling. Maternal effect mutations in ybx1 lead to deregulated Nodal signaling, gastrulation failure and embryonic lethality.  Implantation of beads coated with Nodal protein can phenocopyMybx1 mutant defects.  Our findings show that maternal Ybx1 prevents ectopic Nodal activity by translational repression of maternal sqt RNA, and reveal a new paradigm in regulation of Nodal signaling, which is likely to be conserved.