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キーワード:
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要旨:
Developmental plasticity and polyphenisms, the ability of a single genotype to form multiple phenotypes in response to environmental variation, have been proposed to represent a major facilitator of evolutionary divergence and novelty. While still contentious after a long time of neglect, the role of plasticity is gaining popular support through the development of various model systems that provide molecular and epigenetic insight into associated processes. Such studies are increasingly coupled with organismal work indicating ecological relevance and evolutionary significance of developmental plasticity. We will review the current understanding of mouth-form plasticity in the nematode Pristionchus pacificus that exhibits a mouth dimorphism with the eurystomatous (Eu) form being a potential predator on nematodes, whereas the stenostomatous (St) form is a strict bacterial feeder. After working on the genetic and epigenetic regulation of P. pacificus mouth-form plasticity for more than a decade, we recently started to use long-term environmental induction experiments to study the influence of shifts in microbial diet. Using a wild isolate of P. pacificus that is preferentially St on E. coli OP50, we performed long-term environmental induction experiments of 110 genetically identical lines for 101 generations on a Novosphingobium diet. We found immediate and systemic diet-induced plasticity, resulting exclusively in the formation of the Eu morph. Strikingly, periodic diet-reversals to OP50 starting in F15, F25 etc revealed transgenerational memory that entails multigenerational plasticity. We combined these long-term induction experiments with unbiased forward genetic screens and found a role of the ubiquitin ligase EBAX-1/ZSWIM8 in memory transmission. Subsequent studies revealed a repressive role of a microRNA cluster, the first demonstration of a role of microRNAs in transgenerational inheritance. We will review our current understanding of these processes and their potential role for evolution.
