在长达30多亿年的生命进化史上，生命何时出现雌雄之分？这个问题一直困扰着科学家，在2008年最后一期的世界著名杂志《基因组研究》上，中外科学家发表了《番木瓜原始Y染色体的雄性特异区中DNA甲基化和异染色质化》的研究论文，初步揭示了性染色体的起源变化机制。番木瓜的雄性区域很有可能和人类2亿至3亿年前的Y染色体相似。这种水果Y染色体基因为人类性染色体起源和进化的初始阶段所发生的事件提供了间接证据。
论文作者之一，南京农业大学作物遗传与种质创新国家重点实验室王秀娥教授说，番木瓜这种植物不同寻常，因为它有三性——雄株、雌株和雌雄同株。代表它还正处于性别分化的起始阶段。通过它或许能够找到“性别起源”的秘密。
专家在一株雌雄同株的番木瓜身上发现了一条刚刚处于起源阶段的原始性染色体，雄性区域很小，约占该条染色体的10%，说明它是一条初始的性染色体，同时这个雄性区域似乎已经丢失了一些编码蛋白的DNA。这种丢失通常被认为是Y染色体从X染色体中分化的一个步骤。专家说，这样的雄性区域与两亿年到三亿年前人类的Y染色体的进化状况有相似之处。
专家们通过DNA分子原位杂交和免疫荧光分析直观地研究了这条初始性染色体的重组抑制过程后发现，在番木瓜的雄性区域，大约占到Y染色体的13%，而与X染色体相对应的区域相比，番木瓜的这段雄性区域积累了更多的DNA，导致了该区域的X和Y染色体配对异常。而通过NDA的分子原位杂交，专家在番木瓜的雄性区域发现了该区域有4个特异的异染色质疖，免疫荧光分析则揭示出这个区域与X染色体的相应区域发生了较大的分化，具有高度的甲基化。
这些研究结果为人类性染色体起源和进化的初始阶段所发生的事件，提供了一个直接的证据。（生物谷Bioon.com）
生物谷推荐原始出处：
Genome Research Published in Advance July 1, 2008, doi:10.1101/gr.078808.108 Genome Res. 2008. 18: 1938-1943
DNA methylation and heterochromatinization in the male-specific region of the primitive Y chromosome of papaya
Wenli Zhang1,5, Xiue Wang1,2,5, Qingyi Yu3, Ray Ming4, and Jiming Jiang1,6
1 Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706, USA;2 State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, Jiangsu 210095, People’s Republic of China;3 Hawaii Agriculture Research Center, Aiea, Hawaii 96701, USA;4 Department of Plant Biology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, USA5 These authors contributed equally to this work.
Abstract
Sex chromosomes evolved from autosomes. Recombination suppression in the sex-determining region and accumulation of deleterious mutations lead to degeneration of the Y chromosomes in many species with heteromorphic X/Y chromosomes. However, how the recombination suppressed domain expands from the sex-determining locus to the entire Y chromosome remains elusive. The Y chromosome of papaya (Carica papaya) diverged from the X chromosome approximately 2–3 million years ago and represents one of the most recently emerged Y chromosomes. Here, we report that the male-specific region of the Y chromosome (MSY) spans ～13% of the papaya Y chromosome. Interestingly, the centromere of the Y chromosome is embedded in the MSY. The centromeric domain within the MSY has accumulated significantly more DNA than the corresponding X chromosomal domain, which leads to abnormal chromosome pairing. We observed four knob-like heterochromatin structures specific to the MSY. Fluorescence in situ hybridization and immunofluorescence assay revealed that the DNA sequences associated with the heterochromatic knobs are highly divergent and heavily methylated compared with the sequences in the corresponding X chromosomal domains. These results suggest that DNA methylation and heterochromatinization play an important role in the early stage of sex chromosome evolution.
论文作者之一，南京农业大学作物遗传与种质创新国家重点实验室王秀娥教授说，番木瓜这种植物不同寻常，因为它有三性——雄株、雌株和雌雄同株。代表它还正处于性别分化的起始阶段。通过它或许能够找到“性别起源”的秘密。
专家在一株雌雄同株的番木瓜身上发现了一条刚刚处于起源阶段的原始性染色体，雄性区域很小，约占该条染色体的10%，说明它是一条初始的性染色体，同时这个雄性区域似乎已经丢失了一些编码蛋白的DNA。这种丢失通常被认为是Y染色体从X染色体中分化的一个步骤。专家说，这样的雄性区域与两亿年到三亿年前人类的Y染色体的进化状况有相似之处。
专家们通过DNA分子原位杂交和免疫荧光分析直观地研究了这条初始性染色体的重组抑制过程后发现，在番木瓜的雄性区域，大约占到Y染色体的13%，而与X染色体相对应的区域相比，番木瓜的这段雄性区域积累了更多的DNA，导致了该区域的X和Y染色体配对异常。而通过NDA的分子原位杂交，专家在番木瓜的雄性区域发现了该区域有4个特异的异染色质疖，免疫荧光分析则揭示出这个区域与X染色体的相应区域发生了较大的分化，具有高度的甲基化。
这些研究结果为人类性染色体起源和进化的初始阶段所发生的事件，提供了一个直接的证据。（生物谷Bioon.com）
生物谷推荐原始出处：
Genome Research Published in Advance July 1, 2008, doi:10.1101/gr.078808.108 Genome Res. 2008. 18: 1938-1943
DNA methylation and heterochromatinization in the male-specific region of the primitive Y chromosome of papaya
Wenli Zhang1,5, Xiue Wang1,2,5, Qingyi Yu3, Ray Ming4, and Jiming Jiang1,6
1 Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706, USA;2 State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, Jiangsu 210095, People’s Republic of China;3 Hawaii Agriculture Research Center, Aiea, Hawaii 96701, USA;4 Department of Plant Biology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, USA5 These authors contributed equally to this work.
Abstract
Sex chromosomes evolved from autosomes. Recombination suppression in the sex-determining region and accumulation of deleterious mutations lead to degeneration of the Y chromosomes in many species with heteromorphic X/Y chromosomes. However, how the recombination suppressed domain expands from the sex-determining locus to the entire Y chromosome remains elusive. The Y chromosome of papaya (Carica papaya) diverged from the X chromosome approximately 2–3 million years ago and represents one of the most recently emerged Y chromosomes. Here, we report that the male-specific region of the Y chromosome (MSY) spans ～13% of the papaya Y chromosome. Interestingly, the centromere of the Y chromosome is embedded in the MSY. The centromeric domain within the MSY has accumulated significantly more DNA than the corresponding X chromosomal domain, which leads to abnormal chromosome pairing. We observed four knob-like heterochromatin structures specific to the MSY. Fluorescence in situ hybridization and immunofluorescence assay revealed that the DNA sequences associated with the heterochromatic knobs are highly divergent and heavily methylated compared with the sequences in the corresponding X chromosomal domains. These results suggest that DNA methylation and heterochromatinization play an important role in the early stage of sex chromosome evolution.
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