Comparative Transcriptomics of Malaria Mosquito Testes: Function, Evolution, and Linkage

Abstract

Testes-biased genes evolve rapidly and are important in the establishment, solidification, and maintenance of reproductive isolation between incipient species. The Anopheles gambiae complex, a group of at least eight isomorphic mosquito species endemic to Sub-Saharan Africa, is an excellent system to explore the evolution of testes-biased genes. Within this group, the testes are an important tissue in the diversification process because hybridization between species results in sterile hybrid males, but fully fertile females. We conducted RNA sequencing of A. gambiae and A. merus carcass and testes to explore tissue- and species-specific patterns of gene expression. Our data provides support for transcriptional repression of X-linked genes in the male germline, which likely drives demasculinization of the X chromosome. Testes-biased genes predominately function in cellular differentiation and show a number of interesting patterns indicative of their rapid evolution, including elevated dN/dS values, low evolutionary conservation, poor annotation in existing reference genomes, and a high likelihood of differential expression between species.

High-resolution transcriptional profiling of Anopheles gambiae spermatogenesis reveals mechanisms of sex chromosome regulation

“…Further studies will be required to clarify possible correlations between chromosomal pairing and transcription at these specific loci. On the other hand, our data also confirm unequivocally that dosage compensation does not act on the X chromosome in diploid germline cells as indicated by previous analysis of whole testes and in contrast to somatic tissues where dosage compensation is present 27–29 .…”

Rapid genome shrinkage in a self-fertile nematode reveals sperm competition proteins

“…In cases where their chromosomal loci can be identified, mss and msrp genes are autosomal; this linkage fits a general pattern in heterogametic male species of male-biased genes being autosomal rather than X-chromosomal (ref. (26) and references therein).…”

Rapid Evolution of Ovarian-Biased Genes in the Yellow Fever Mosquito (Aedes aegypti)

“…It is worth noting that a recent study in preprint for four species of Anopheles, a related mosquito from the same family as Aedes (Culicidae), has indicated that female-biased genes identified after blood feeding evolve faster than male-biased genes in that genus (Papa et al 2016) [see also a recent study by of testis vs. male carcass genes (Cassone et al 2017)]. Both female carcass-(excluding the gonads) and ovary-biased genes showed elevated dN/dS as compared to their male counterparts (Papa et al 2016).…”