Sass G L, Henikoff S
Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
Genetics. 1999 Jun;152(2):595-604. doi: 10.1093/genetics/152.2.595.
We describe the precise positioning of a reporter gene within heterochromatin where it may be silenced. A transposition of the 59E-60A region into pericentric heterochromatin ensnares distal 59E-60A via somatic pairing. The frequency with which a brown (bw) reporter gene in 59E is silenced is influenced by chromosomal configurations. Silencing occurs only when the bw+ reporter is unpaired due to heterozygosity with a deficiency, where the frequency of bw+ reporter expression is correlated with the extent of bw gene and flanking sequence present. Surprisingly, the frequency of pairing between the transposition in heterochromatin and distal 59E observed cytologically is indistinguishable from the frequency of pairing of homologous chromosomes at 59E in wild-type larval brains, regardless of configuration. Therefore, bringing a susceptible reporter gene into close proximity with heterochromatin does not necessarily affect its expression, but local pairing changes resulting from altered chromosomal configurations can lead to silencing. We also find that an ensnared distal copy of bw that is interrupted by a heterochromatic insertion enhances silencing. This demonstrates that bw can be simultaneously acted upon by pericentric and distal blocks of heterochromatin.
我们描述了报告基因在异染色质内的精确定位，在该位置它可能会被沉默。59E - 60A区域向着丝粒周围异染色质的转座通过体细胞配对捕获了远端的59E - 60A。59E中棕色（bw）报告基因被沉默的频率受染色体构型影响。只有当bw +报告基因由于与缺失杂合而未配对时才会发生沉默，此时bw +报告基因表达的频率与存在的bw基因及侧翼序列的范围相关。令人惊讶的是，无论构型如何，在细胞学上观察到的异染色质中转座与远端59E之间的配对频率与野生型幼虫大脑中59E处同源染色体的配对频率没有区别。因此，将一个易感报告基因与异染色质紧密靠近不一定会影响其表达，但染色体构型改变导致的局部配对变化可导致沉默。我们还发现，被异染色质插入中断的被困住的远端bw拷贝会增强沉默。这表明bw可同时受到着丝粒周围和远端异染色质区域的作用。
