Department of Biology and Biochemistry, University of Houston, Texas 77204-5001.
Institute of Molecular Life Sciences, University of Zurich, Switzerland CH-8057.
Genetics. 2019 Sep;213(1):313-327. doi: 10.1534/genetics.119.302441. Epub 2019 Jul 17.
Sex determination, the developmental process by which organismal sex is established, evolves fast, often due to changes in the master regulators at the top of the pathway. Additionally, in species with polygenic sex determination, multiple different master regulators segregate as polymorphisms. Understanding the forces that maintain polygenic sex determination can be informative of the factors that drive the evolution of sex determination. The house fly, , is a well-suited model to those ends because natural populations harbor male-determining loci on each of the six chromosomes and a biallelic female determiner. To investigate how natural selection maintains polygenic sex determination in the house fly, we assayed the phenotypic effects of proto- chromosomes by performing mRNA-sequencing experiments to measure gene expression in house fly males carrying different proto- chromosomes. We find that the proto- chromosomes have similar effects as a nonsex-determining autosome. In addition, we created sex-reversed males without any proto- chromosomes and they had nearly identical gene expression profiles as genotypic males. Therefore, the proto- chromosomes have a minor effect on male gene expression, consistent with previously described minimal - sequence differences. Despite these minimal differences, we find evidence for a disproportionate effect of one proto- chromosome on male-biased expression, which could be partially responsible for fitness differences between males with different proto- chromosome genotypes. Therefore our results suggest that, if natural selection maintains polygenic sex determination in house fly via gene expression differences, the phenotypes under selection likely depend on a small number of genetic targets.
性别决定是生物体性别建立的发育过程，它进化迅速，通常是由于途径顶端的主调控因子发生变化。此外，在具有多基因性别决定的物种中，多个不同的主调控因子作为多态性分离。了解维持多基因性别决定的力量，可以为驱动性别决定进化的因素提供信息。家蝇是一个很好的模型，因为其自然种群在每一条染色体上都有决定雄性的基因座，以及一个双等位的雌性决定基因。为了研究自然选择如何在家蝇中维持多基因性别决定，我们通过进行 mRNA 测序实验来测量携带不同原染色体的雄性家蝇中的基因表达，来检测原染色体的表型效应。我们发现原染色体的作用与非性别决定的常染色体相似。此外，我们还创建了没有任何原染色体的性反转雄性，它们与基因型雄性具有几乎相同的基因表达谱。因此，原染色体对雄性基因表达的影响很小，与先前描述的最小序列差异一致。尽管存在这些微小差异，但我们发现有证据表明，一条原染色体对雄性偏向表达的影响不成比例，这可能部分解释了具有不同原染色体基因型的雄性之间的适应度差异。因此，我们的结果表明，如果自然选择通过基因表达差异来维持家蝇的多基因性别决定，那么受选择的表型可能取决于少数几个遗传靶标。
