What Drives Positive Selection in the Drosophila piRNA Machinery? The Genomic Autoimmunity Hypothesis

• Published in: The Yale journal of biology & medicine Vol. 89; no. 4; pp. 499 - 512
• Main Authors: Blumenstiel, Justin P, Erwin, Alexandra A, Hemmer, Lucas W
• Format: Journal Article
• Language: English
• Published: United States YJBM 01-12-2016
• Series: Focus: Epigenetics
• Subjects: Animals; Autoimmunity - genetics; Autoimmunity - physiology; DNA Transposable Elements - genetics; Drosophila; Epigenesis, Genetic - genetics; Review; RNA, Small Interfering - genetics; positive selection; Red Queen; host-parasite; transposable element; piRNA; selfish elements
• ISSN: 0044-0086; 1551-4056

In animals, PIWI-interacting RNAs (piRNAs) play a crucial role in genome defense. Moreover, because piRNAs can be maternally transmitted, they contribute to the epigenetic profile of inheritance. Multiple studies, especially in
, have demonstrated that the machinery of piRNA biogenesis is often the target of positive selection. Because transposable elements (TEs) are a form of genetic parasite, positive selection in the piRNA machinery is often explained by analogy to the signatures of positive selection commonly observed in genes that play a role in host-parasite dynamics. However, the precise mechanisms that drive positive selection in the piRNA machinery are not known. In this review, we outline several mechanistic models that might explain pervasive positive selection in the piRNA machinery of
species. We propose that recurrent positive selection in the piRNA machinery can be partly explained by an ongoing tension between selection for sensitivity required by genome defense and selection for specificity to avoid the off-target effects of maladaptive genic silencing by piRNA.