New genetic regulators question relevance of abundant yolk protein production in C. elegans.

Liesbeth Van Rompay,Isabel Beets,Charline Borghgraef,Jelle Caers,Liesbet Temmerman

doi:10.1038/srep16381

Abstract

Vitellogenesis or maternal yolk formation is considered critical to the reproduction of egg-laying animals. In invertebrates, however, most of its regulatory genes are still unknown. Via a combined mapping and whole-genome sequencing strategy, we performed a forward genetic screen to isolate novel regulators of yolk production in the nematode model system Caenorhabditis elegans. In addition to isolating new alleles of rab-35, rab-10 and M04F3.2, we identified five mutant alleles corresponding to three novel regulatory genes potently suppressing the expression of a GFP-based yolk reporter. We confirmed that mutations in vrp-1, ceh-60 and lrp-2 disrupt endogenous yolk protein synthesis at the transcriptional and translational level. In contrast to current beliefs, our discovered set of mutants with strongly reduced yolk proteins did not show serious reproduction defects. This raises questions as to whether yolk proteins per se are needed for ultimate reproductive success.

Highlights

2(lst464) mutant populations display incomplete vit-2-gfp expression, unlike their siblings, which display complete loss. bWe isolated the exact same gk2294 allele as earlier isolated113. cThe obvious ‘bag of worms’
The C. elegans genome harbours six vit genes, all encoding yolk proteins[14,15]. These are subdivided into two classes - YP170 and YP88/115 - named according to their approximate molecular weight[15,16,17]
We created a reporter strain expressing a functional fluorescent VIT-2(YP170B)::GFP fusion protein which is, like endogenous yolk, transported from the intestine into the growing oocytes[6,18,19,20,21]. Starting from this strain, roughly 7,500 ethyl methanesulfonate (EMS)-mutagenized haploid genomes were manually analysed during a phenotypic selection step based on aberrant gfp expression

Summary

Introduction

2(lst464) mutant populations display incomplete vit-2-gfp expression, unlike their siblings, which display complete loss. bWe isolated the exact same gk2294 allele as earlier isolated113. cThe obvious ‘bag of worms’. Novel causal protein-changing variants of two genes could be pinpointed in the corresponding mutants by rescuing vit-2::gfp expression with genomic wild-type copies of these candidates (Supplementary Fig. S1). Having obtained novel regulators of vit-2 gene expression, it can be asked whether the allelic variants emerging from our screen have a more general impact on yolk protein production (i.e. YP170 and YP88/YP115) in C. elegans.

Results

Conclusion