Renfree Marilyn B, Hore Timothy A, Shaw Geoffrey, Graves Jennifer A Marshall, Pask Andrew J
ARC Center of Excellence for Kangaroo Genomics, Melbourne, Victoria 3010, Australia.
Annu Rev Genomics Hum Genet. 2009;10:241-62. doi: 10.1146/annurev-genom-082908-150026.
Parent-of-origin gene expression (genomic imprinting) is widespread among eutherian mammals and also occurs in marsupials. Most imprinted genes are expressed in the placenta, but the brain is also a favored site. Although imprinting evolved in therian mammals before the marsupial-eutherian split, the mechanisms have continued to evolve in each lineage to produce differences between the two groups in terms of the number and regulation of imprinted genes. As yet there is no evidence for genomic imprinting in the egg-laying monotreme mammals, although these mammals also form a placenta (albeit short-lived) and transfer nutrients from mother to embryo. Therefore, imprinting was not essential for the evolution of the placenta and its importance in nutrient transfer but the elaboration of imprinted genes in marsupials and eutherians is associated with viviparity. Here we review the recent analyses of imprinted gene clusters in marsupials and monotremes, which have served to shed light on the origin and evolution of imprinting mechanisms in mammals.
亲本来源基因表达（基因组印记）在真兽类哺乳动物中广泛存在，在有袋类动物中也有发生。大多数印记基因在胎盘中表达，但大脑也是一个常见的表达部位。尽管印记现象在有袋类和真兽类分化之前的兽亚纲哺乳动物中就已演化出现，但在每个谱系中其机制仍在不断演变，导致两组动物在印记基因的数量和调控方面存在差异。尽管产卵的单孔目哺乳动物也形成胎盘（尽管寿命短暂）并将营养物质从母体转移到胚胎，但目前尚无证据表明其存在基因组印记现象。因此，印记对于胎盘的演化及其在营养物质转移中的重要性并非必不可少，但有袋类和真兽类中印记基因的细化与胎生有关。在此，我们综述了近期对有袋类和单孔目动物印记基因簇的分析，这些分析有助于阐明哺乳动物印记机制的起源和演化。
