Transvection is an epigenetic phenomenon wherein regulatory elements communicate between different chromosomes in trans, and is thereby dependent upon the three-dimensional organization of the genome. Transvection is best understood in Drosophila, where homologous chromosomes are closely paired in most somatic nuclei, although similar phenomena have been observed in other species. Previous data have supported that the Drosophila genome is generally permissive to enhancer action in trans, a form of transvection where an enhancer on one homolog activates gene expression from a promoter on a paired homolog. However, the capacity of different genomic positions to influence the quantitative output of transvection has yet to be addressed. To investigate this question, we employed a transgenic system that assesses and compares enhancer action in cis and in trans at defined chromosomal locations. Using the strong synthetic eye-specific enhancer GMR, we show that loci supporting strong cis-expression tend to support robust enhancer action in trans, whereas locations with weaker cis-expression show reduced transvection in a fluorescent reporter assay. Our subsequent analysis is consistent with a model wherein the chromatin state of the transgenic insertion site is a primary determinant of the degree to which enhancer action in trans will be supported, whereas other factors such as locus-specific variation in somatic homolog pairing are of less importance in influencing position effects on transvection.

中文翻译：

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位置效应影响果蝇的横传。

横传是一种表观遗传现象，其中调控元件在不同染色体之间进行反式通讯，因此依赖于基因组的三维组织。横传在果蝇中得到了最好的理解，其中同源染色体在大多数体细胞核中紧密配对，尽管在其他物种中也观察到了类似的现象。先前的数据支持果蝇基因组通常允许反式增强子作用，反式是一种反式传输形式，其中一个同源物上的增强子激活配对同源物上的启动子的基因表达。然而，不同基因组位置影响横转定量输出的能力尚未得到解决。为了研究这个问题，我们采用了一个转基因系统来评估和比较特定染色体位置的顺式和反式增强子作用。使用强合成眼特异性增强子GMR，我们发现支持强顺式表达的位点往往支持反式中强大的增强子作用，而顺式表达较弱的位置在荧光报告基因测定中显示出横传减少。我们随后的分析与模型一致，其中转基因插入位点的染色质状态是支持反式增强子作用程度的主要决定因素，而其他因素（例如体细胞同源配对中的位点特异性变异）的影响较小。影响横穿位置效应的重要性。