Supplementary Material for: Interaction Study of the Male Specific Lethal (MSL) Complex and Trans-Acting Dosage Effects in Metafemales of <i>Drosophila melanogaster</i>

The effect of ectopic expression of male specific lethal 2 <i>(msl2)</i> on chromatin modification and gene expression was studied in Drosophila diploid females and metafemales (3X;2A). Results show that ectopic expression of MSL2 in transgenic <i>msl2</i> females and metafemales sequesters the MOF histone acetylase to the X, which occurs concordantly with an increase of histone acetylation. Gene expression studies indicate that the X-linked genes are not affected by direct targeting of the MSL complex and the resulting increased H4Lys16 acetylation on the X chromosomes, suggesting one function of the MSL complex is to nullify the effect of a high level of histone acetylation. These results are not consistent with the hypothesis that the presence of the MSL complex conditions a two-fold upregulation. Autosomal gene expression is generally decreased in ectopically expressed MSL2 females, which correlates with the reduced autosomal histone acetylation. Metafemales show dosage compensation of X-linked genes with some autosomal reductions in expression. Interestingly, in metafemales with ectopically expressed MSL2, the autosomal expression is returned to a more normal level. There is a lower autosomal level of histone acetylation compared to the normal metafemales, suggesting a nullifying effect on the negative dosage effect of the X chromosome as previously hypothesized to occur in normal males.

本研究以果蝇二倍体雌性与超雌果蝇（3X;2A）为实验材料，探究雄性特异致死2（male specific lethal 2，msl2）异位表达对染色质修饰与基因表达的影响。结果显示，在转基因msl2雌性果蝇与超雌果蝇中，异位表达的MSL2会将MOF组蛋白乙酰转移酶（MOF histone acetylase）招募至X染色体，这一过程与组蛋白乙酰化水平的升高同步发生。基因表达研究表明，X连锁基因（X-linked genes）并未因MSL复合物（MSL complex）的直接靶向以及X染色体上H4Lys16位组蛋白乙酰化（H4Lys16 acetylation）水平的升高而受到影响，这提示MSL复合物的功能之一是抵消高水平组蛋白乙酰化所带来的效应。上述结果与"MSL复合物的存在可介导两倍上调（two-fold upregulation）"的假说并不相符。异位表达MSL2的雌性果蝇中，常染色体基因表达普遍下调，这与常染色体组蛋白乙酰化水平降低呈相关性。超雌果蝇的X连锁基因呈现剂量补偿（dosage compensation）效应，同时伴随部分常染色体基因表达下调。值得注意的是，在异位表达MSL2的超雌果蝇中，常染色体基因表达恢复至更为正常的水平；其常染色体组蛋白乙酰化水平相较于正常超雌果蝇更低，这表明该过程可抵消X染色体的负剂量效应（negative dosage effect），正如此前假说中所述的正常雄性个体中存在的现象。

搜集汇总

背景与挑战

背景概述

该数据集是果蝇研究中关于MSL复合物和剂量效应的补充材料，聚焦于msl2基因异位表达对染色质修饰和基因表达的影响。关键发现包括：异位表达导致X染色体组蛋白乙酰化增加但未直接影响X连锁基因，同时常染色体基因表达降低；超雌性中观察到X连锁基因的剂量补偿和MSL2对常染色体表达的调节作用，支持MSL复合物在否定高乙酰化效应中的功能假设。