Multiple RNA regulatory pathways coordinate the activity and expression pattern of a conserved germline RNA-binding protein

RNA regulation is essential to successful reproduction. Messenger RNAs delivered from parent to progeny govern early embryonic development. RNA-binding proteins (RBPs) are the key effectors of this process, controlling the translation and stability of parental transcripts to control cell fate specification events prior to zygotic gene activation. The KH-domain RBP MEX-3 is conserved from nematode to human. It was first discovered in Caenorhabditis elegans, where it is essential for anterior cell fate and embryo viability. Here, we show that mex-3 mRNA is itself regulated by several RBPs to define its unique germline spatiotemporal expression pattern. We also show that both poly(A) tail length control and translational regulation contribute to this expression pattern. Though the 3UTR is sufficient to establish the germline expression pattern, we show that it is not essential for reproduction. An allelic series of 3UTR deletion variants identifies repressing regions of the UTR and show that the expression pattern is not precisely coupled to reproductive health. Together, our results define the pathways that govern the spatiotemporal regulation of this highly conserved germline RBP and suggest that redundant mechanisms control MEX-3 function when RNA regulation is compromised.