VandeBerg J L, Johnston P G, Cooper D W, Robinson E S
Isozymes Curr Top Biol Med Res. 1983;9:201-18.
Sex chromosome dosage compensation in Australian marsupials exhibits several characteristics not ordinarily manifested in eutherian mammals. They are: 1) preferential inactivation of the paternally derived X-chromosome in somatic tissues; 2) a state of partial inactivity at some paternally derived X-linked gene loci in some cells; 3) absence of dosage compensation in some cell types; 4) absence of nuclear sex dimorphism at interphase; 5) discordance between late DNA replication and gene inactivation in some cell types; 6) failure of the X-chromosome to behave as a single unit. Despite these seemingly major differences between the dosage compensation systems of Australian marsupials and eutherians, there are also many underlying similarities. We propose that the two systems arose from a common ancestral mechanism in which the X-chromosome was regulated in a piecemeal fashion, rather than as a whole. To determine more precisely the sequence and timing of evolutionary events, we have initiated an investigation of dosage compensation in American marsupials, which diverged from Australian marsupials soon after the divergence of marsupials from eutherian mammals.
澳大利亚有袋类动物的性染色体剂量补偿表现出一些在真兽类哺乳动物中通常未表现出的特征。它们是：1）体细胞组织中父源X染色体的优先失活；2）某些细胞中一些父源X连锁基因座处于部分无活性状态；3）某些细胞类型中不存在剂量补偿；4）间期不存在核性别二态性；5）某些细胞类型中DNA复制后期与基因失活不一致；6）X染色体不能作为一个单一单元起作用。尽管澳大利亚有袋类动物和真兽类动物的剂量补偿系统之间存在这些看似主要的差异，但也有许多潜在的相似之处。我们提出，这两种系统起源于一种共同的祖先机制，其中X染色体是以零碎的方式调控的，而不是作为一个整体。为了更精确地确定进化事件的顺序和时间，我们已经开始对美洲有袋类动物的剂量补偿进行研究，美洲有袋类动物在有袋类动物与真兽类哺乳动物分化后不久就与澳大利亚有袋类动物分道扬镳了。
