Institute of Evolutionary Biology, University of Edinburgh, United Kingdom.
Genome Biol Evol. 2021 Jun 8;13(6). doi: 10.1093/gbe/evab072.
In some eukaryotes, germline soma differentiation involves elimination of parts of the genome from somatic cells. The portions of the genome restricted to the germline often contain genes that play a role in development and function of the germline. Lineages with germline-restricted DNA are taxonomically diverse, and the size of the germline-restricted genome varies substantially. Unfortunately, few of these lineages have been studied in detail. As a result, we understand little about the general evolutionary forces that drive the origin and maintenance of germline-restricted DNA. One of the taxonomic groups where germline-restricted DNA has been poorly studied are the flies (Diptera). In three Dipteran families, Chironomidae, Cecidomyiidae, and Sciaridae, entire chromosomes are eliminated from somatic cells early in embryonic development. Germline-restricted chromosomes are thought to have evolved independently in the Dipteran families and their size, number, and transmission patterns vary between families. Although there is a wealth of cytological studies on these chromosomes in flies, almost no genomic studies have been undertaken. As a result, very little is known about how and why they evolved and what genes they encode. This review summarizes the literature on germline-restricted chromosomes in Diptera, discusses hypotheses for their origin and function, and compares germline-restricted DNA in Diptera to other eukaryotes. Finally, we discuss why Dipteran lineages represent a promising system for the study of germline-restricted chromosomes and propose future avenues of research on this topic.
在一些真核生物中，生殖细胞体的分化涉及到从体细胞中消除基因组的部分。限制在生殖细胞中的基因组部分通常包含在生殖细胞发育和功能中起作用的基因。具有生殖细胞限制 DNA 的谱系在分类上是多种多样的，生殖细胞限制基因组的大小也有很大的差异。不幸的是，这些谱系中的少数得到了详细研究。因此，我们对驱动生殖细胞限制 DNA 的起源和维持的一般进化力量知之甚少。生殖细胞限制 DNA 研究不足的分类群之一是苍蝇（双翅目）。在三个双翅目科中，摇蚊科、瘿蚊科和丝虫科，整个染色体在胚胎发育早期从体细胞中消除。生殖细胞限制染色体被认为是在双翅目科中独立进化的，它们的大小、数量和传递模式在科之间有所不同。尽管在这些苍蝇的染色体上有大量的细胞学研究，但几乎没有进行基因组研究。因此，关于它们是如何以及为什么进化的，以及它们编码哪些基因，我们知之甚少。这篇综述总结了双翅目生殖细胞限制染色体的文献，讨论了它们起源和功能的假说，并将双翅目生殖细胞限制 DNA 与其他真核生物进行了比较。最后，我们讨论了为什么双翅目谱系是研究生殖细胞限制染色体的一个很有前途的系统，并提出了该主题未来的研究方向。
