Expression data from testes and abdomen in fertile and sterile introgression males. Drosophila simulans

Postmating reproductive isolation is often manifested as hybrid male sterility, for which X-linked genes are over-represented. In contrast, X-linked gene are significantly under-represented among testis-expressing gene.This seeming contradiction may be germane to the X:autosome imbalance hypothesis on hybrid sterility ,in which the X-linked effect is mediated mainly through the misexpression of autosomal genes. We compared gene expression in fertile and sterile males in the hybrids between two Drosophila species. These hybrid males differ only in a small region of the X chromosome containing the OdsH locus of hybrid sterility. Of genes expressed in the testis, autosomal genes were indeed more likely to be misexpressed than X-linked genes under the steriizing action of OdsH. Overall design: We compared gene expression between D. simulans males that carried either a fertile or sterile introgression (referred to as F or S males, respectively) from D. mauritiana. The introgressions span approximately 1/10 of the X chromosome, but the difference between the two introgressions is only about 3 Kb which contains exons 3 – 4 of OdsH. In short, F and S males have the same genetic background with respect to species origin, except the source of a portion of the OdsH gene. Three separate extractions and hybridizations were carried out for the RNA samples derived from testes and abdomens in each of two introgression lines.

交配后生殖隔离（Postmating Reproductive Isolation）通常表现为杂交雄性不育，该表型中X连锁基因（X-linked genes）显著富集。与之形成鲜明对比的是，睾丸表达基因（testis-expressing gene）中X连锁基因却明显匮乏。这一表观矛盾或许与杂交雄性不育的X染色体-常染色体失衡假说（X:autosome imbalance hypothesis）密切相关，该假说指出X连锁效应主要通过常染色体基因的表达异常（misexpression）介导。我们对两个果蝇（Drosophila）物种间杂交子代的可育与不育雄性个体的基因表达谱进行了比较。这些杂交雄性个体仅在包含杂交雄性不育OdsH基因座（OdsH locus）的X染色体小区域存在差异。在睾丸表达的基因中，受OdsH的不育效应作用时，常染色体基因确实比X连锁基因更易出现表达异常。

整体实验设计：我们比较了拟暗果蝇（D. simulans）雄性中携带来自毛里求斯果蝇（D. mauritiana）可育或不育渐渗片段（introgression）的个体（分别记为F雄性与S雄性）的基因表达差异。上述渐渗片段覆盖约1/10的X染色体，但二者的序列差异仅为约3kb的区域，该区域包含OdsH基因的外显子3至4。简言之，F与S雄性除OdsH基因部分区段的来源不同外，其余与物种起源相关的遗传背景完全一致。针对每个渐渗品系的睾丸与腹部组织提取的RNA样本，我们均开展了3次独立的提取与杂交实验。