View Program - 63rd Annual Drosophila Research Conference

Meiotic drivers are selfish genetic elements that promote their own transmission to the gametes. Sex-ratio (SR) meiotic drive occurs when a selfish genetic element on the X chromosome manipulates gametogenesis to prevent the maturation of Y-bearing sperm in males, resulting in the production of predominant female progeny. The spread of SR meiotic drive can affect host genetic diversity, sex chromosome evolution, and even cause host extinction if it reaches high enough frequency. SR meiotic drivers have evolved independently several times, however, the underlying genetic mechanism is only known in few cases. In this study we use a combination of genomics, transcriptomics, single nuclei RNA-seq (snRNA-seq), and CRISPR-Cas9 to identify the genetic mechanism responsible for the SR meiotic drive in Drosophila affinis. We found X chromosome is enriched for differentially expressed (DE) transcripts and that many DE genes had elevated Ka/Ks values between SR and ST. We identified top DE candidate genes, including two X-linked duplicate and testis-specific: encoding a chromosomal protein involved in spermatogenesis (tHMG2), and encoding the regulator of chromatin condensation (RCC1). We used CRISPR-Cas9 knockout experiments to test whether these genes were involved in the sex ratio phenotype. Lastly, snRNA-seq analysis recapitulates transcriptional patterns associated with gene expression changes during spermatogenesis between ST and SR testes. Our results suggest the two candidate genes’ significant role involving in the drive in this species, providing evidence that rapid evolution of genes disrupting spermatogenesis is important source of intragenomic conflict.

The evolution and genetic mechanism of sex-ratio meiotic drive in Drosophila affinis