Proteomic Characterization of Inbreeding-Related Cold Sensitivity in Drosophila melanogaster

Inbreeding depression is a widespread phenomenon of central importance to agriculture, medicine, conservation biology and evolutionary biology. Although the population genetic principles of inbreeding depression are well understood, we know little about its functional genomic causes. To provide insight into the molecular interplay between intrinsic stress responses, inbreeding depression and temperature tolerance, we performed a proteomic characterization of a well-defined conditional inbreeding effect in a single line of Drosophila melanogaster, which suffers from extreme cold sensitivity and lethality. We identified 48 differentially expressed proteins in a conditional lethal line as compared to two control lines. These proteins were enriched for proteins involved in hexose metabolism, in particular pyruvate metabolism, and many were found to be associated with lipid particles. These processes can be linked to known cold tolerance mechanisms, such as the production of cryoprotectants, membrane remodeling and the build-up of energy reserves. We checked mRNA-expression of seven genes with large differential protein expression. Although protein expression poorly correlated with gene expression, we found a single gene (CG18067) that, after cold shock, was upregulated in the conditional lethal line both at the mRNA and protein level. Expression of CG18067 also increased in control flies after cold shock, and has previously been linked to cold exposure and chill coma recovery time. Many differentially expressed proteins in our study appear to be involved in cold tolerance in non-inbred individuals. This suggest the conditional inbreeding effect to be caused by misregulation of physiological cold tolerance mechanisms.

近交衰退（Inbreeding depression）是一种广泛存在的现象，对农业、医学、保护生物学以及进化生物学均具有核心重要性。尽管近交衰退的群体遗传学原理已被充分阐释，但其功能基因组学层面的成因仍有待深入解析。为探究内在应激反应、近交衰退与温度耐受性之间的分子互作机制，我们针对一株表现出极端冷敏感性与致死性的黑腹果蝇（Drosophila melanogaster）品系，对其明确的条件性近交效应开展了蛋白质组学表征。相较于两个对照品系，我们在该条件致死品系中鉴定出48种差异表达蛋白。这些差异表达蛋白显著富集于己糖代谢通路，尤其是丙酮酸代谢通路，且其中多数与脂质颗粒相关联。上述代谢过程可与已知的冷耐受机制建立关联，例如抗冻保护剂的合成、细胞膜重塑以及能量储备的积累。我们针对7个蛋白表达差异显著的基因开展了mRNA表达水平检测。尽管蛋白表达水平与基因转录水平之间的相关性较弱，但我们发现基因CG18067在冷休克处理后，于该条件致死品系中在mRNA与蛋白两个层面均呈现上调表达。冷休克处理后，对照果蝇体内CG18067的表达量同样出现升高，且此前已有研究将该基因与冷暴露及冷昏迷恢复时间相关联。本研究鉴定的诸多差异表达蛋白，在非近交个体中似乎均参与冷耐受相关的生理过程。这表明该条件性近交效应是由生理冷耐受机制的调控失常所引发的。