Meyer E, Duharcourt S
Laboratoire de Génétique Moléculaire, Ecole Normale Superieure, Paris, France.
J Eukaryot Microbiol. 1996 Nov-Dec;43(6):453-61. doi: 10.1111/j.1550-7408.1996.tb04504.x.
In ciliates, development of the polyploid somatic macronucleus after sexual events involves extensive and reproducible rearrangements of the germ-line genome, including chromosome fragmentation and precise excision of numerous internal sequence elements. In Paramecium aurelia, alternative macronuclear versions of the same germ-line genome can be maternally inherited across sexual generations, showing that rearrangement patterns are not strictly determined by the germ-line sequence. Homology-dependent maternal effects can be evidenced by transformation of the vegetative macronucleus with cloned macronuclear sequences: new fragmentation patterns or internal deletions are specifically induced during differentiation of a new macronucleus, in sexual progeny of transformed clones. Furthermore, transformation of the maternal macronucleus with germ-line sequences containing internal eliminated sequences (short single-copy elements) can result in a specific inhibition of the excision of the same elements in the zygotic macronucleus. These experiments show that the processing of many germ-line sequences in the developing macronucleus is sensitive to the structure and copy number of homologous sequences in the maternal macronucleus. The generality and sequence specificity of this trans-nuclear, epigenetic regulation of rearrangements suggest that it is mediated by pairing interactions between germ-line sequences and sequences imported from the maternal macronucleus.
在纤毛虫中，有性生殖后多倍体体细胞大核的发育涉及种系基因组广泛且可重复的重排，包括染色体片段化以及众多内部序列元件的精确切除。在双小核草履虫中，同一套种系基因组的不同大核版本能够通过母系遗传跨越有性生殖世代，这表明重排模式并非严格由种系序列决定。同源依赖的母体效应可以通过用克隆的大核序列转化营养性大核来证明：在转化克隆的有性子代中，新的大核分化过程中会特异性地诱导出新的片段化模式或内部缺失。此外，用含有内部消除序列（短单拷贝元件）的种系序列转化母体大核，可导致合子大核中相同元件的切除受到特异性抑制。这些实验表明，发育中的大核中许多种系序列的加工对母体大核中同源序列的结构和拷贝数敏感。这种跨核的、重排的表观遗传调控的普遍性和序列特异性表明，它是由种系序列与从母体大核导入的序列之间的配对相互作用介导的。
