Shimaji Kouhei, Konishi Takahiro, Tanaka Shintaro, Yoshida Hideki, Kato Yasuko, Ohkawa Yasuyuki, Sato Tetsuya, Suyama Mikita, Kimura Hiroshi, Yamaguchi Masamitsu
Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan.
Insect Biomedical Research Center, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan.
Genes Cells. 2015 Nov;20(11):902-14. doi: 10.1111/gtc.12281. Epub 2015 Sep 3.
Post-translational modification of the histone plays important roles in epigenetic regulation of various biological processes. Among the identified histone methyltransferases (HMTases), G9a is a histone H3 Lys 9 (H3K9)-specific example active in euchromatic regions. Drosophila G9a (dG9a) has been reported to feature H3K9 dimethylation activity in vivo. Here, we show that the time required for hatching of a homozygous dG9a null mutant and heteroallelic combination of dG9a null mutants is delayed, suggesting that dG9a is at least partially responsible for progression of embryogenesis. Immunocytochemical analyses of the wild-type and the dG9a null mutant flies indicated that dG9a localizes in cytoplasm up to nuclear division cycle 7 where it is likely responsible for di-methylation of nucleosome-free H3K9. From cycles 8-11, dG9a moves into the nucleus and is responsible for di-methylating H3K9 in nucleosomes. RNA-sequence analysis utilizing early wild-type and dG9a mutant embryos showed that dG9a down-regulates expression of genes responsible for embryogenesis. RNA fluorescent in situ hybridization analysis further showed temporal and spatial expression patterns of these mRNAs did not significantly change in the dG9a mutant. These results indicate that dG9a controls transcription levels of some zygotic genes without changing temporal and spatial expression patterns of the transcripts of these genes.
组蛋白的翻译后修饰在各种生物过程的表观遗传调控中发挥着重要作用。在已鉴定的组蛋白甲基转移酶（HMTases）中，G9a是一种在常染色质区域具有活性的组蛋白H3赖氨酸9（H3K9）特异性酶。据报道，果蝇G9a（dG9a）在体内具有H3K9二甲基化活性。在此，我们表明纯合dG9a缺失突变体和dG9a缺失突变体的杂合等位基因组合的孵化时间延迟，这表明dG9a至少部分负责胚胎发育的进程。对野生型和dG9a缺失突变体果蝇的免疫细胞化学分析表明，dG9a在核分裂周期7之前定位于细胞质中，在那里它可能负责无核小体H3K9的二甲基化。从第8 - 11个周期开始，dG9a进入细胞核并负责核小体中H3K9的二甲基化。利用早期野生型和dG9a突变体胚胎进行的RNA序列分析表明，dG9a下调负责胚胎发育的基因的表达。RNA荧光原位杂交分析进一步表明，这些mRNA的时空表达模式在dG9a突变体中没有显著变化。这些结果表明，dG9a控制一些合子基因的转录水平，但不改变这些基因转录本的时空表达模式。
