Transposon expression kinetics in Dnmt3L-/- developing testes [RNA-seq]

We examined the kinetics of production of mRNAs and small RNAs derived from transposable elements during mouse spermatogenesis, in whole gonads of wildtype and DNA methylation-deficient males (Dnmt3L and Miwi2 mutants). We found that in absence of DNA methylation, transposon reactivation is not constitutive but rather occurs in a class- and development-specific manner : both the intensity of reactivation and the number of reactivated transposon classes increased as germ cells progress in meiosis. Moreover, we observed that transposon silencing before meiosis is not due to increased cleavage by the piRNA machinery. In contrast, the burst of transposon transcripts occurring at meiosis in the absence of DNA methylation serve as substrates for increased piRNA production Six whole testis samples were analyzed, corresponding to three time points (16.5dpc, 10dpp and 20dpp) each for Dnamt3L-/- animals and control littermates. For 16.5dpc, testes from 7/8 mice were pooled per genotype. For the other stages, three mice were pooled per genotype.本研究探究了小鼠精子发生过程中，源自转座元件（transposable element）的信使RNA（mRNA）与小RNA（small RNA）的生成动力学，实验材料为野生型及DNA甲基化缺陷雄性小鼠的全生殖腺，涵盖Dnmt3L与Miwi2基因突变体。研究发现，在DNA甲基化缺失的条件下，转座元件的重新激活并非组成型表达，而是呈现出类别特异性与发育阶段特异性：随着生殖细胞推进至减数分裂进程，转座元件重新激活的强度与被激活的转座元件类别数量均会升高。此外，本研究观察到，减数分裂前的转座元件沉默并非由piRNA（PIWI-interacting RNA）介导的剪切增强所引发。与之相反，DNA甲基化缺失时减数分裂阶段出现的转座元件转录本爆发，可作为piRNA生成增强的底物。本研究共分析6份全睾丸样本，分别对应Dnmt3L基因敲除（Dnmt3L^-/-）小鼠与同窝对照小鼠的三个时间节点：16.5dpc、10dpp与20dpp。针对16.5dpc时间节点，每种基因型的睾丸样本均由7~8只小鼠的睾丸混合制备；其余阶段则每种基因型取3只小鼠的睾丸进行混合。