The mir-35 Family Links Maternal Germline Sex to Embryonic Viability in Caenorhabditis elegans

Abstract

The germline sex determination pathway in C. elegans determines whether germ cells develop as oocytes or sperm, with no previously known effect on viability. The mir-35 family of microRNAs are expressed in the C. elegans germline and embryo and are essential for both viability and normal hermaphroditic sex determination, preventing aberrant male gene expression in XX hermaphrodite embryos. Here we show that combining feminizing mutations with partial loss of function of the mir-35 family results in enhanced penetrance embryonic lethality that preferentially kills XO animals. This lethal phenotype is due to altered signaling through the germline sex determination pathway, and maternal germline feminization is sufficient to induce enhanced lethality. These findings reveal a surprising pleiotropy of sperm-fate promoting pathways on organismal viability. Overall, our results demonstrate an unexpectedly strong link between sex determination and embryonic viability, and suggest that in wild type animals, mir-35 family members buffer against misregulation of pathways outside the sex determination program, allowing for clean sex reversal rather than deleterious effects of perturbing sex determination genes.

In vivo CRISPR screening for phenotypic targets of themir-35-42family inC. elegans

“…Many other phenotypes have been characterized in the context of mir-35-41 deletion (leaving mir-42 intact), which allows for the bypass of lethality at low temperature. These additional roles for mir-35-41 include promoting germ cell proliferation and fecundity, resistance to radiation and hypoxia, proper sex determination, and dampening of RNA interference (Liu et al 2011;Massirer et al 2012;Ambros 2014, 2017;Kagias and Pocock 2015;Benner et al 2019;Doll et al 2019;Tran et al 2019). The lethal phenotype of mir-35 family mutants is still poorly understood: Deep forward mutagenesis screens failed to recover suppressors, suggesting that either multiple target genes contribute to lethality when derepressed or loss-of-function mutations of the critical target gene(s) is lethal (Alvarez-Saavedra and Horvitz 2010).…”

Widespread destabilization ofC. elegansmicroRNAs by the E3 ubiquitin ligase EBAX-1

“…2A)(Lau et al 2001). These miRNAs are redundantly required for viability and embryonic patterning (Alvarez-Saavedra and Horvitz 2010; Dexheimer et al 2020) and promote multiple aspects of postembryonic development (Liu et al 2011; Massirer et al 2012; McJunkin and Ambros 2014; McJunkin and Ambros 2017; Benner et al 2019; Tran et al 2019). Seven of the miR-35 family members (miR-35–41) are processed from the same primary transcript, whereas miR-42 originates from a different transcript, enabling differential transcriptional control (Martinez et al 2008; Alvarez-Saavedra and Horvitz 2010).…”