Department of Biological Sciences, Smith College, Northampton, Massachusetts, USA.
J Eukaryot Microbiol. 2022 Sep;69(5):e12891. doi: 10.1111/jeu.12891. Epub 2022 Feb 19.
Mobile genetic elements (MGEs) are transient genetic material that can move either within a single organism's genome or between individuals or species. While historically considered "junk" DNA (i.e., deleterious or at best neutral), more recent studies reveal the potential adaptive advantages MGEs provide in lineages across the tree of life. Ciliates, a group of single-celled microbial eukaryotes characterized by nuclear dimorphism, exemplify how epigenetic influences from MGEs shape genome architecture and patterns of molecular evolution. Ciliate nuclear dimorphism may have evolved as a response to transposon invasion and ciliates have since co-opted transposons to carry out programmed DNA deletion. Another example of the effect of MGEs is in providing mechanisms for lateral gene transfer (LGT) from bacteria, which introduces genetic diversity and, in several cases, may drive ecological specialization in ciliates. As a third example, the integration of viral DNA, likely through transduction, provides new genetic materials and can change the way host cells defend themselves against other viral pathogens. We argue that the acquisition of MGEs through non-Mendelian patterns of inheritance, coupled with their effects on ciliate genome architecture and persistence throughout evolutionary history, exemplify how the transmission of mobile elements should be considered a mechanism of transgenerational epigenetic inheritance.
移动遗传元件（MGEs）是可在单个生物体的基因组内或个体之间或物种之间移动的短暂遗传物质。虽然它们在历史上被认为是“垃圾”DNA（即有害或充其量是中性的），但最近的研究揭示了 MGEs 在生命之树上的各个谱系中提供潜在适应性优势。纤毛虫是一类具有核二态性的单细胞微生物真核生物，它们是 MGEs 如何影响表观遗传并塑造基因组结构和分子进化模式的典型例子。纤毛虫核二态性可能是作为转座子入侵的反应而进化的，并且纤毛虫已经将转座子用于进行程序性 DNA 缺失。MGEs 影响的另一个例子是提供从细菌进行横向基因转移（LGT）的机制，这引入了遗传多样性，并且在几种情况下，可能导致纤毛虫的生态特化。作为第三个例子，病毒 DNA 的整合，可能通过转导，提供了新的遗传物质，并可以改变宿主细胞抵御其他病毒病原体的方式。我们认为，通过非孟德尔遗传模式获得 MGEs，以及它们对纤毛虫基因组结构和在整个进化历史中的持久性的影响，说明了应该如何将移动元件的传递视为跨代表观遗传遗传的一种机制。
