Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna, Austria.
Genes Dev. 2012 Aug 1;26(15):1729-42. doi: 10.1101/gad.196493.112.
The ciliated protozoan Tetrahymena undergoes extensive programmed DNA elimination when the germline micronucleus produces the new macronucleus during sexual reproduction. DNA elimination is epigenetically controlled by DNA sequences of the parental macronuclear genome, and this epigenetic regulation is mediated by small RNAs (scan RNAs [scnRNAs]) of ∼28-30 nucleotides that are produced and function by an RNAi-related mechanism. Here, we examine scnRNA production and turnover by deep sequencing. scnRNAs are produced exclusively from the micronucleus and nonhomogeneously from a variety of chromosomal locations. scnRNAs are preferentially derived from the eliminated sequences, and this preference is mainly determined at the level of transcription. Despite this bias, a significant fraction of scnRNAs is also derived from the macronuclear-destined sequences, and these scnRNAs are degraded during the course of sexual reproduction. These results indicate that the pattern of DNA elimination in the new macronucleus is shaped by the biased transcription in the micronucleus and the selective degradation of scnRNAs in the parental macronucleus.
纤毛虫四膜虫在有性生殖过程中，当生殖系小核产生新的大核时，会经历广泛的程序性 DNA 消除。DNA 消除受亲代大核基因组 DNA 序列的表观遗传控制，这种表观遗传调控是由约 28-30 个核苷酸的小 RNA（扫描 RNA [scnRNA]）介导的，这些小 RNA 通过 RNAi 相关机制产生并发挥作用。在这里，我们通过深度测序检查 scnRNA 的产生和周转。scnRNA 仅从小核产生，并且从各种染色体位置不均匀产生。scnRNA 优先从已消除的序列中衍生，这种偏好主要在转录水平上决定。尽管存在这种偏差，但相当一部分 scnRNA 也来自大核定向序列，并且这些 scnRNA 在有性生殖过程中被降解。这些结果表明，新大核中的 DNA 消除模式是由小核中的偏转录和亲代大核中 scnRNA 的选择性降解共同决定的。
