Conservation of sequence motifs suggests that the nonclassical MHC class I lineages CD1/PROCR and UT were established before the emergence of tetrapod species
Conservation of sequence motifs suggests that the nonclassical MHC class I lineages CD1/PROCR and UT were established before the emergence of tetrapod species
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DOI：
10.1007/s00251-017-1050-2
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发表时间：
2018-07-01
期刊：
影响因子：
3.2
通讯作者：
Grimholt, Unni
中科院分区：
文献类型：
--
作者：
Dijkstra, Johannes M.;Yamaguchi, Takuya;Grimholt, Unni
人类有许多非经典主要组织相容性复合体（MHC） I类分子，这些分子与经典分子大相径庭，可能在前哺乳动物时代就与经典谱系分离了。为了估计在进化过程中各自的非经典谱系与经典谱系分离的时间，我们首先在经典MHC I类的进化中确定了“系统发育标记基序”；所选择的基序是相当特定的，并且在物种的分支中相当稳定地遗传。这些基序在非经典MHC I类分子中的分布表明，包括非经典MHC I类分子CD1和PROCR在内的谱系在四足动物出现之前就从经典谱系中分离出来，而人类非经典MHC I类分子FCGRT、MIC/ULBP/RAET、HFE、MR1和ZAG在鸟类/爬行动物水平上与经典MHC I类具有相似性。在海龟中发现了一个mr1样α 1外显子序列。我们的系统进一步表明，迄今为止仅在非真足哺乳动物中发现的UT谱系早于四足动物的存在，我们在爬行动物中发现了UT基因。如果只接受在现存物种中广泛分布的谱系作为古老的真实证据，那么最古老的已确定的非经典MHC I类谱系仍然是鱼特有的谱系Z，这在本研究中得到了证实，在原始鱼类bichir中发现了Z和经典型MHC I类序列。简而言之，我们对经典MHC I类基序的进化和非经典MHC I类谱系的可能起源时间获得了重要的新见解。
Humans have a number of nonclassical major histocompatibility complex (MHC) class I molecules that are quite divergent from the classical ones, and that may have separated from the classical lineage in pre-mammalian times. To estimate when in evolution the respective nonclassical lineages separated from the classical lineage, we first identified "phylogenetic marker motifs" within the evolution of classical MHC class I; the selected motifs are rather specific for and rather stably inherited within clades of species. Distribution of these motifs in nonclassical MHC class I molecules indicates that the lineage including the nonclassical MHC class I molecules CD1 and PROCR separated from the classical lineage before the emergence of tetrapod species, and that the human nonclassical MHC class I molecules FCGRT, MIC/ULBP/RAET, HFE, MR1, and ZAG show similarity with classical MHC class I at the avian/reptilian level. An MR1-like alpha 1 exon sequence was identified in turtle. Our system furthermore indicates that the lineage UT, hitherto only found in non-eutherian mammals, predates tetrapod existence, and we identified UT genes in reptiles. If only accepting wide distribution of a lineage among extant species as true evidence for ancientness, the oldest identified nonclassical MHC class I lineage remains the fish-specific lineage Z, which was corroborated in the present study by finding both Z and classical-type MHC class I sequences in a primitive fish, the bichir. In short, we gained important new insights into the evolution of classical MHC class I motifs and the probable time of origin of nonclassical MHC class I lineages.