Selfish meiotic drive and the role of RNAi in defending intragenomic conflict

Selfish meiotic drive systems (SMDs) that cheat Mendel's law of segregation during gametogenesis are ubiquitous in nature. The wildtype activities of these selfish genes have negative fitness effects, such as distortion of sex-ratio (SR) or sterility. Therefore, SMDs are catalysts for intragenomic conflicts and place strong pressure to innovate host suppression mechanisms. Despite their ubiquity, the molecular mechanisms by which SMDs emerge, operate, and are silenced, generally remain poorly understood. A significant contribution from my postdoctoral work revealed a crucial role for hairpin RNA (hpRNA)-class siRNA loci in suppressing Dox family meiotic drivers on the X-chromosome in Drosophila simulans (Dsim). Furthermore, transcriptome profiling from RNAi mutants (Ago2 and Dcr2) in Dsim revealed an array of de novo hpRNAs that were born in the simulans clade and preferentially target X-chromosome genes, suggesting sex chromosomes as a breeding ground for intragenomic conflicts. I hypothesize that the surprising role(s) of RNAi in resolving intragenomic conflicts may be widespread across taxa, and untamed meiotic drive can propel speciation. The proposed work expands on my discoveries utilizing a multidisciplinary approach. First, in Specific Aim 1, using clues to the origin, and their provocative similarity to sperm packaging proteins, I will study how the Dox family drivers impair spermatogenesis, employing cutting-edge molecular biology and genomics. Based on conserved themes in genetic conflicts, I suspect a role for RNAi in resolving intragenomic conflict in mice, analogous to flies, and in Specific Aim 2, I will test this hypothesis with the proprietary Ago-2 catalytic dead (Ago2-CD) mutant mice generated in Dr. Eric Lai's lab. The proposed work in SA2 will be performed in collaboration with Dr. Scott Keeney, an expert in mouse meiosis and spermatogenesis. Finally, in Specific Aim 3, I will build upon the exciting discovery in Dsim that several cryptic SMDs can be uncovered by ablating the RNAi pathway. I propose to employ RNAi mutants as a versatile "tool" to unmask cryptic SMDs in non-model insects, which otherwise take years of laborious genetics to identify and characterize SMDs.