Martins Juliana R, Pinheiro Daniel G, Ahmed Amy C C, Giuliatti Silvana, Mizzen Craig A, Bitondi Márcia M G
Faculdade de Medicina de Ribeirão Preto, Departamento de Genética, Ribeirão Preto, Brazil.
Departamento de Biotecnologia Agropecuária e Ambiental, Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil.
Insect Mol Biol. 2023 Jun;32(3):277-304. doi: 10.1111/imb.12830. Epub 2023 Feb 14.
Hexamerins, the proteins massively stored in the larval haemolymph of insects, are gradually used throughout metamorphosis as a source of raw material and energy for the development of adult tissues. Such behaviour defined hexamerins as storage proteins. Immunofluorescence experiments coupled with confocal microscopy show a hexamerin, HEX 70a, in the nucleus of the brain and fat body cells from honeybee workers, an unexpected localization for a storage protein. HEX 70a colocalizes with fibrillarin, a nucleolar-specific protein and H3 histone, thus suggesting a potential role as a chromatin-binding protein. This was investigated through chromatin immunoprecipitation and high-throughput DNA sequencing (ChIP-seq). The significant HEX 70a-DNA binding sites were mainly localized at the intergenic, promoter and intronic regions. HEX 70a targeted DNA stretches mapped to the genomic regions encompassing genes with relevant functional attributes. Several HEX 70a targeted genes were associated with H3K27ac or/and H3K27me3, known as active and repressive histone marks. Brain and fat body tissues shared a fraction of the HEX 70 targeted genes, and tissue-specific targets were also detected. The presence of overrepresented DNA motifs in the binding sites is consistent with specific HEX 70a-chromatin association. In addition, a search for HEX 70a targets in RNA-seq public libraries of fat bodies from nurses and foragers revealed differentially expressed targets displaying hex 70a-correlated developmental expression, thus supporting a regulatory activity for HEX 70a. Our results support the premise that HEX 70a is a moonlighting protein that binds chromatin and has roles in the brain and fat body cell nuclei, apart from its canonical role as a storage protein.
六聚体蛋白是大量储存在昆虫幼虫血淋巴中的蛋白质，在整个变态过程中逐渐被用作成年组织发育的原材料和能量来源。这种行为将六聚体蛋白定义为储存蛋白。免疫荧光实验结合共聚焦显微镜显示，在蜜蜂工蜂的大脑和脂肪体细胞的细胞核中存在一种六聚体蛋白HEX 70a，这对于一种储存蛋白来说是意外的定位。HEX 70a与核仁特异性蛋白纤维蛋白原和H3组蛋白共定位，因此表明其具有作为染色质结合蛋白的潜在作用。通过染色质免疫沉淀和高通量DNA测序（ChIP-seq）对此进行了研究。显著的HEX 70a-DNA结合位点主要位于基因间、启动子和内含子区域。HEX 70a靶向的DNA片段映射到包含具有相关功能属性基因的基因组区域。几个HEX 70a靶向基因与H3K27ac或/和H3K27me3相关，它们分别是已知的活性和抑制性组蛋白标记。大脑和脂肪体组织共享一部分HEX 70靶向基因，同时也检测到了组织特异性靶点。结合位点中过度代表的DNA基序的存在与特定的HEX 70a-染色质关联一致。此外，在护士蜂和觅食蜂脂肪体的RNA-seq公共文库中搜索HEX 70a靶点，发现差异表达的靶点显示出与hex 70a相关的发育表达，从而支持了HEX 70a的调节活性。我们的结果支持这样一个前提，即HEX 70a是一种兼性蛋白，除了作为储存蛋白的典型作用外，还能结合染色质并在大脑和脂肪体细胞核中发挥作用。
