Unexpected conservation of the X-linked color vision gene in nocturnal prosimians: evidence from two bush babies.
Unexpected conservation of the X-linked color vision gene in nocturnal prosimians: evidence from two bush babies.
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夜间活动的原猴中 X 连锁色觉基因的意外保守：来自两个丛林婴儿的证据。
DOI：
10.1007/pl00006265
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发表时间：
1997
影响因子：
3.9
通讯作者：
Li,WH
中科院分区：
文献类型：
--
作者：
Zhou,YH;Hewett-Emmett,D;Ward,JP;Li,WH
布什婴儿有着悠久的夜生活历史，了解他们的色觉基因是否已经退化将会很有趣。因此，我们利用PCR技术对这两种夜行性原猿的X连锁色素基因进行了测序：Galago senegalensis和Otolemur garnettii。Galago基因组DNA的Southern杂交。塞内加尔人显示出单个X连锁色素基因。有趣的是，推断出的两个丛林婴儿的色素序列是相同的。通过比较丛林婴儿、人类、松鼠猴和狨猴的 X 连锁色素，确定了 38 个可变位置。在那些可能导致光谱偏移的位置，灌木婴儿色素具有与狨猴锥体色素相同或生化相似的残留物，光谱峰值为 543 nm。这一结果与对与Otolemur garnettii密切相关的Otolemur crassicaudatus X连锁色素的光谱峰544-545 nm的估计一致。哺乳动物X连锁色素的邻接树在灌木幼崽谱系中显示出比其他灵长类谱系中明显更短的分支。相对率测试表明，灌木丛婴儿X连锁色素基因的非同义取代率比人类红色素基因慢约三倍，尽管这两个基因的同义取代率相似。丛林宝宝谱系中较慢的非同义率表明，尽管丛林宝宝是夜间生活，但X连锁色素基因受到功能限制。在丛林婴儿的 X 连锁锥体色素中观察到在盘内表面靠近第六跨膜结构域的位置处的两个根本性变化，但在其他灵长类动物中没有观察到。它们是从Ala到Ser以及从Asn到His的变化，其功能与视紫红质中相应残基的功能相似。这两个变化可能对弱光敏感性很重要，这与我们的假设一致，即布什婴儿X连锁色素基因的进化处于选择压力下。此外，两个灌木丛幼崽之间 X 连锁色素基因内含子 2 和 5 的 2.5% 差异支持它们分为两个不同的属。
Bush babies have had a long history of nocturnal life and it would be interesting to know whether their color vision genes have become degenerate. Therefore, we used PCR techniques to sequence the X-linked pigment gene of two of these nocturnal prosimians:Galago senegalensisandOtolemur garnettii.Southern hybridization of genomic DNA ofG. senegalensisshowed a single X-linked pigment gene. Interestingly, the deduced pigment sequences of the two bush babies are identical. By comparing the X-linked pigments of bush baby, human, squirrel monkey, and marmoset, 38 variable positions were identified. At those positions that may cause a spectral shift, the bush baby pigment has identical or biochemically similar residues to those of the marmoset cone pigment with a spectral peak of 543 nm. This result is consistent with the estimate of 544–545 nm for the spectral peak of the X-linked pigment ofOtolemur crassicaudatus,which is closely related toOtolemur garnettii.The neighbor-joining tree of mammalian X-linked pigments showed a significantly shorter branch in the bush baby lineage than in other primate lineages. A relative rate test showed that the nonsynonymous substitution rate of the bush baby X-linked pigment gene is about three times slower than that of the human red pigment gene, though the synonymous substitution rates of the two genes are similar. The slower nonsynonymous rate in the bush baby lineage suggests that the bush baby X-linked pigment gene is under functional constraints, in spite of its nocturnal life. Two radical changes at positions in the intradiskal surface next to the sixth transmembrane domain were observed in the X-linked cone pigment of bush babies but not in other primates. They are changes from Ala to Ser and from Asn to His, which are similar in function to the corresponding residues in rhodopsins. These two changes may be of importance for dim light sensitivity, which is consistent with our proposal that the evolution of the bush baby X-linked pigment gene is under selective pressure. In addition, the 2.5% divergence in introns 2 and 5 of the X-linked pigment gene between the two bush babies supports their classification into two separate genera.