Deakin Janine E, Koina Edda, Waters Paul D, Doherty Ruth, Patel Vidushi S, Delbridge Margaret L, Dobson Bianca, Fong James, Hu Yanqiu, van den Hurk Cecilia, Pask Andrew J, Shaw Geoff, Smith Carly, Thompson Katherine, Wakefield Matthew J, Yu Hongshi, Renfree Marilyn B, Graves Jennifer A Marshall
ARC Centre of Excellence for Kangaroo Genomics, Research School of Biological Sciences, The Australian National University, Canberra, ACT 0200, Australia.
Chromosome Res. 2008;16(8):1159-75. doi: 10.1007/s10577-008-1266-y. Epub 2008 Nov 8.
Marsupials are especially valuable for comparative genomic studies of mammals. Two distantly related model marsupials have been sequenced: the South American opossum (Monodelphis domestica) and the tammar wallaby (Macropus eugenii), which last shared a common ancestor about 70 Mya. The six-fold opossum genome sequence has been assembled and assigned to chromosomes with the help of a cytogenetic map. A good cytogenetic map will be even more essential for assembly and anchoring of the two-fold wallaby genome. As a start to generating a physical map of gene locations on wallaby chromosomes, we focused on two chromosomes sharing homology with the human X, wallaby chromosomes X and 5. We devised an efficient strategy for mapping large conserved synteny blocks in non-model mammals, and applied this to generate dense maps of the X and 'neo-X' regions and to determine the arrangement of large conserved synteny blocks on chromosome 5. Comparisons between the wallaby and opossum chromosome maps revealed many rearrangements, highlighting the need for comparative gene mapping between South American and Australian marsupials. Frequent rearrangement of the X, along with the absence of a marsupial XIST gene, suggests that inactivation of the marsupial X chromosome does not depend on a whole-chromosome repression by a control locus.
有袋类动物对于哺乳动物的比较基因组研究尤为重要。已经对两种亲缘关系较远的有袋类动物模型进行了测序：南美负鼠（Monodelphis domestica）和帚尾袋貂（Macropus eugenii），它们在大约7000万年前拥有共同的祖先。在细胞遗传图谱的帮助下，已经完成了六倍体负鼠基因组序列的组装并将其定位到染色体上。对于二倍体袋貂基因组的组装和定位而言，一张良好的细胞遗传图谱将更为关键。作为构建袋貂染色体上基因位置物理图谱的开端，我们聚焦于与人类X染色体具有同源性的两条染色体，即袋貂的X染色体和5号染色体。我们设计了一种高效策略来绘制非模式哺乳动物中大型保守同线基因块图谱，并将其应用于生成X染色体和“新X染色体”区域的密集图谱，以及确定5号染色体上大型保守同线基因块的排列。袋貂和负鼠染色体图谱之间的比较揭示了许多重排现象，凸显了对南美和澳大利亚有袋类动物进行比较基因图谱绘制的必要性。X染色体频繁重排，加之有袋类动物缺乏XIST基因，这表明有袋类动物X染色体的失活并不依赖于一个控制位点对整条染色体的抑制作用。
