Hodson Christina N, Hamilton Phineas T, Dilworth Dave, Nelson Chris J, Curtis Caitlin I, Perlman Steve J
Department of Biology, University of Victoria, V8P 5C2, Canada
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3JG, United Kingdom.
Genetics. 2017 Jun;206(2):1091-1100. doi: 10.1534/genetics.117.199786. Epub 2017 Mar 14.
How sex is determined in insects is diverse and dynamic, and includes male heterogamety, female heterogamety, and haplodiploidy. In many insect lineages, sex determination is either completely unknown or poorly studied. We studied sex determination in Psocodea-a species-rich order of insects that includes parasitic lice, barklice, and booklice. We focus on a recently discovered species of booklice (Psocodea: Troctomorpha), which are among the closest free-living relatives of parasitic lice. Using genetic, genomic, and immunohistochemical approaches, we show that this group exhibits paternal genome elimination (PGE), an unusual mode of sex determination that involves genomic imprinting. Controlled crosses, following a genetic marker over multiple generations, demonstrated that males only transmit to offspring genes they inherited from their mother. Immunofluorescence microscopy revealed densely packed chromocenters associated with H3K9me3-a conserved marker for heterochromatin-in males, but not in females, suggesting silencing of chromosomes in males. Genome assembly and comparison of read coverage in male and female libraries showed no evidence for differentiated sex chromosomes. We also found that females produce more sons early in life, consistent with facultative sex allocation. It is likely that PGE is widespread in Psocodea, including human lice. This order represents a promising model for studying this enigmatic mode of sex determination.
昆虫的性别决定方式多样且具有动态性，包括雄性异配、雌性异配和单双倍体。在许多昆虫谱系中，性别决定要么完全未知，要么研究较少。我们研究了啮目昆虫的性别决定，啮目是一个物种丰富的昆虫目，包括寄生虱、树虱和书虱。我们重点研究了最近发现的一种书虱（啮目：啮亚目），它们是寄生虱最亲近的自由生活亲属之一。通过遗传、基因组和免疫组织化学方法，我们发现这个群体表现出父本基因组消除（PGE），这是一种涉及基因组印记的不寻常性别决定模式。通过多代追踪遗传标记进行的受控杂交表明，雄性只将从母亲那里继承的基因传递给后代。免疫荧光显微镜显示，雄性中存在与H3K9me3（一种异染色质的保守标记）相关的密集堆积的染色中心，而雌性中没有，这表明雄性染色体发生了沉默。基因组组装以及对雄性和雌性文库中读取覆盖率的比较没有发现性染色体分化的证据。我们还发现，雌性在生命早期会产生更多儿子，这与兼性性别分配一致。父本基因组消除很可能在包括人虱在内的啮目中广泛存在。这个目是研究这种神秘性别决定模式的一个很有前景的模型。
