Cerutti H, Johnson A M, Gillham N W, Boynton J E
Department of Botany, Duke University, Durham, North Carolina 27708-1000, USA.
Plant Cell. 1997 Jun;9(6):925-45. doi: 10.1105/tpc.9.6.925.
The unstable expression of introduced genes poses a serious problem for the application of transgenic technology in plants. In transformants of the unicellular green alga Chlamydomonas reinhardtii, expression of a eubacterial aadA gene, conferring spectinomycin resistance, is transcriptionally suppressed by a reversible epigenetic mechanism(s). Variations in the size and frequency of colonies surviving on different concentrations of spectinomycin as well as the levels of transcriptional activity of the introduced transgene(s) suggest the existence of intermediate expression states in genetically identical cells. Gene silencing does not correlate with methylation of the integrated DNA and does not involve large alterations in its chromatin structure, as revealed by digestion with restriction endonucleases and DNase I. Transgene repression is enhanced by lower temperatures, similar to position effect variegation in Drosophila. By analogy to epigenetic phenomena in several eukaryotes, our results suggest a possible role for (hetero)chromatic chromosomal domains in transcriptional inactivation.
导入基因的不稳定表达给转基因技术在植物中的应用带来了严重问题。在单细胞绿藻莱茵衣藻的转化体中，赋予壮观霉素抗性的真细菌aadA基因的表达通过一种可逆的表观遗传机制被转录抑制。在不同浓度壮观霉素上存活的菌落大小和频率的变化以及导入转基因的转录活性水平表明，在基因相同的细胞中存在中间表达状态。基因沉默与整合DNA的甲基化无关，并且如用限制性内切酶和DNase I消化所揭示的，不涉及染色质结构的大的改变。转基因抑制在较低温度下增强，类似于果蝇中的位置效应斑驳。类比几种真核生物中的表观遗传现象，我们的结果表明（异）染色质染色体结构域在转录失活中可能起作用。
