Kriener K, O'hUigin C, Klein J
Max-Planck-Institut für Biologie, Abteilung Immungenetik, D-72076 Tübingen, Germany.
Genome Res. 2000 May;10(5):634-43. doi: 10.1101/gr.10.5.634.
The primate major histocompatibility complex (Mhc) genes fall into two classes and each of the classes into several families. Of the class II families, the DRB family has a long and complex evolutionary history marked by gene turnover, rearrangement, and molecular convergence. Because the history is not easily decipherable from sequences alone, Alu element insertions were used as cladistic markers to support the surmised phylogenetic relationships among the DRB genes. Intron 1 segments of 24 DRB genes from five platyrrhine species and five DRB genes from three prosimian species were amplified by PCR and cloned, and the amplification products were sequenced or PCR-typed for Alu repeats. Three Alu elements were identified in the platyrrhine and four in the prosimian DRB genes. One of the platyrrhine elements (Alu50J) is also found in the Catarrhini, whereas the other two (Alu62Sc, Alu63Sc) are restricted to the New World monkeys. Similarly, the four prosimian elements are found only in this taxon. This distribution of Alu elements is consistent with the phylogeny of the DRB genes as determined from their intron 1 sequences in an earlier and the present study. It contradicts the exon 2-based phylogeny and thus corroborates the conclusion that the evolution of DRB exon 2 sequences is, to some extent, shaped by molecular convergence. Taken together, the data indicate that each of the assemblages of DRB genes in prosimians, platyrrhines, and catarrhines is derived from a separate ancestral gene.
灵长类主要组织相容性复合体（Mhc）基因分为两类，每一类又包含几个家族。在II类家族中，DRB家族有着漫长而复杂的进化史，其特征为基因更替、重排和分子趋同。由于仅从序列难以解读这段历史，因此使用Alu元件插入作为分支标记，以支持DRB基因之间推测的系统发育关系。通过PCR扩增并克隆了来自5种阔鼻猴物种的24个DRB基因的内含子1片段以及来自3种原猴亚目物种的5个DRB基因，对扩增产物进行测序或PCR分型以检测Alu重复序列。在阔鼻猴的DRB基因中鉴定出3个Alu元件，在原猴亚目的DRB基因中鉴定出4个。阔鼻猴的一个元件（Alu50J）也存在于狭鼻猴中，而另外两个（Alu62Sc、Alu63Sc）仅存在于新大陆猴中。同样，这4个原猴亚目的元件仅在该分类单元中发现。Alu元件的这种分布与根据早期和本研究中DRB基因内含子1序列确定的系统发育一致。它与基于外显子2的系统发育相矛盾，从而证实了DRB外显子2序列的进化在某种程度上受到分子趋同影响的结论。综上所述，数据表明原猴亚目、阔鼻猴和狭鼻猴中DRB基因的每个组合都源自一个独立的祖先基因。
