Evsikov Alexei V, Marín de Evsikova Caralina
Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL.
Yale J Biol Med. 2016 Dec 23;89(4):487-497. eCollection 2016 Dec.
Epigenetics is the study of phenotypic variation arising from developmental and environmental factors regulating gene transcription at molecular, cellular, and physiological levels. A naturally occurring biological process driven by epigenetics is the egg-to-embryo developmental transition when two fully differentiated adult cells - egg and sperm - revert to an early stem cell type with totipotency but subsequently differentiates into pluripotent embryonic stem cells that give rise to any cell type. Transposable elements (TEs) are active in mammalian oocytes and early embryos, and this activity, albeit counterintuitive because TEs can lead to genomic instability in somatic cells, correlates to successful development. TEs bridge genetic and epigenetic landscapes because TEs are genetic elements whose silencing and de-repression are regulated by epigenetic mechanisms that are sensitive to environmental factors. Ultimately, transposition events can change size, content, and function of mammalian genomes. Thus, TEs act beyond mutagenic agents reshuffling the genomes, and epigenetic regulation of TEs may act as a proximate mechanism by which evolutionary forces increase a species' hidden reserve of epigenetic and phenotypic variability facilitating the adaptation of genomes to their environment.
表观遗传学是对由发育和环境因素在分子、细胞和生理水平上调控基因转录所产生的表型变异的研究。由表观遗传学驱动的一个自然发生的生物学过程是从卵子到胚胎的发育转变，即当两个完全分化的成年细胞——卵子和精子——恢复到具有全能性的早期干细胞类型，但随后分化为能产生任何细胞类型的多能胚胎干细胞。转座元件（TEs）在哺乳动物卵母细胞和早期胚胎中具有活性，尽管这种活性看似有悖常理，因为转座元件会导致体细胞基因组不稳定，但它与成功发育相关。转座元件连接了遗传和表观遗传景观，因为转座元件是遗传元件，其沉默和去抑制受对环境因素敏感的表观遗传机制调控。最终，转座事件可以改变哺乳动物基因组的大小、内容和功能。因此，转座元件的作用不仅仅是像诱变剂那样重新排列基因组，转座元件的表观遗传调控可能是一种直接机制，通过这种机制，进化力量增加了一个物种表观遗传和表型变异的隐藏储备，促进基因组适应其环境。
