Wolbachiainfection at least partially rescues the fertility and ovary defects of several newDrosophila melanogaster bag of marblesprotein-coding mutants

Abstract

AbstractTheD. melanogasterprotein coding genebag of marbles(bam) plays a key role in early male and female reproduction by forming complexes with partner proteins to promote differentiation in gametogenesis. Like another germline gene,Sex lethal,bamgenetically interacts with the endosymbiontWolbachia, asWolbachiarescues the reduced fertility of abamhypomorphic mutant. Here, we explored the specificity of thebam-Wolbachiainteraction by generating 22 newbammutants, with ten mutants displaying fertility defects. Nine of these mutants trend towards rescue by thewMelWolbachiavariant, with eight statistically significant at the fertility and/or cytological level. In some cases, fertility was increased a striking 20-fold. There is no specificity between the rescue and the known binding regions ofbam, suggestingwMel does not interact with one singularbampartner to rescue the reproductive phenotype. We further tested ifwMel interacts withbamin a non-specific way, by increasingbamtranscript levels or acting upstream in germline stem cells. A fertility assessment of abamRNAi knockdown mutant reveals thatwMel rescue is specific to functionally mutantbamalleles and we find no obvious evidence ofwMel interaction with germline stem cells inbammutants.Author SummaryReproduction in theDrosophila melanogasterfruit fly is dependent on thebag of marbles(bam) gene, which acts early in the process of generating eggs and sperm. Mutations to this gene negatively impact the fertility of the fly, causing it to be sterile or have fewer progeny. Interestingly, we find that the bacteriaWolbachia, which resides within reproductive cells across a wide range of insects, partially restores the fertility and ovary phenotype of severalbammutants of which the resultant Bam protein is altered from wildtype. The protein function of Bam is further suggested to be important by the lack of rescue for a fly that has a fertility defect due to low expression of a non-mutatedbamgene. Previous work makes similar conclusions aboutWolbachiawith another reproductive gene,Sex lethal(Sxl), highlighting the potential for rescue of fertility mutants to occur in a similar way across different genes. An understanding of the ways in whichWolbachiacan affect host reproduction provides us with context with which to frameWolbachia’s impact on host genes, such asbamandSxl,and consider the evolutionary implications ofWolbachia’s infection inD. melanogasterfruit flies.