Costa-Richene Ana Beatriz P, Almeida Bruno R R, Tavares Flávia S, Frade Luan F S, Sá André L A, Nascimento Luís A S, Nagamachi Cleusa Y, Pieczarka Julio C, Sampaio Maria I C, R Filho Geraldo N, Cardoso Adauto L, Martins Cesar, Noronha Renata C R
Genetics and Cellular Biology Laboratory, Center for Biodiversity Studies, Federal University of Pará, Belém 66075-110, Pará, Brazil.
University of the State of Pará, Cametá 68400-000, Pará, Brazil.
ACS Omega. 2025 Aug 18;10(34):39263-39271. doi: 10.1021/acsomega.5c05643. eCollection 2025 Sep 2.
Histone genes contain sequences responsible for coding five types of proteins (H1, H2A, H2B, H3, and H4) that are of great importance for chromatin organization. Their transcriptional regulation through DNA methylation has been little studied. Testudines are ancient reptiles with high cytogenetic diversity (2 = 26-68), with a large number of histone gene loci in their karyotype. The aim of this study was to analyze the physical location of the histone genes H2A, H2B, and H4 and the regions rich in 5-methylcytosine (5mC) and 5-hydroxy-methylcytosine (5hmC) in the karyotypes of and . The results showed that and have a diploid number of 2 = 28, NF = 50 and 46, respectively. Fluorescence hybridization (FISH) showed clusters of histone genes in both species, with histone H2A, H2B, and H4 sequences located in the pericentromeric region of several pairs of karyotypes. Interstitial clusters of histone H2A and histone H4 genes were observed in the chromosome arms of and . Immunolocalization of 5mC in and showed that highly methylated regions are distributed mainly in the centromeres, coinciding with many loci H2A, H2B, and H4 genes, as well as markings observed along chromosome arms and distal regions. In relation to 5hmc, it was observed that most of this epigenetic mark has a dispersed distribution along the chromatids and in the distal regions in and . Our findings suggest that ectopic recombination and inversion-type rearrangements may contribute to the dispersion of histone genes in and that DNA hypermethylation may be an important mechanism for the inactivation of these multigens during the cell cycle in the turtles studied.
组蛋白基因包含负责编码五种蛋白质（H1、H2A、H2B、H3和H4）的序列，这些蛋白质对染色质组织非常重要。它们通过DNA甲基化的转录调控研究较少。龟鳖目是具有高细胞遗传学多样性（2n = 26 - 68）的古老爬行动物，其核型中有大量组蛋白基因位点。本研究的目的是分析组蛋白基因H2A、H2B和H4以及富含5 - 甲基胞嘧啶（5mC）和5 - 羟甲基胞嘧啶（5hmC）的区域在[物种名称1]和[物种名称2]核型中的物理位置。结果表明，[物种名称1]和[物种名称2]的二倍体数目分别为2n = 28，NF = 50和2n = 46，NF = 46。荧光原位杂交（FISH）显示这两个物种中都有组蛋白基因簇，组蛋白H2A、H2B和H4序列位于几对核型的着丝粒周围区域。在[物种名称1]和[物种名称2]的染色体臂中观察到组蛋白H2A和组蛋白H4基因的间质簇。[物种名称1]和[物种名称2]中5mC的免疫定位表明，高度甲基化区域主要分布在着丝粒中，与许多H2A、H2B和H4基因位点重合，以及沿染色体臂和远端区域观察到的标记。关于5hmC，观察到这种表观遗传标记在[物种名称1]和[物种名称2]中大多沿染色单体和远端区域呈分散分布。我们的研究结果表明，异位重组和倒位型重排可能有助于组蛋白基因在[物种名称1]和[物种名称2]中的分散，并且DNA高甲基化可能是所研究龟类细胞周期中这些多基因失活的重要机制。
