Convergent evolution of antifreeze glycoproteins in Antarctic notothenioid fish and Arctic cod
Convergent evolution of antifreeze glycoproteins in Antarctic notothenioid fish and Arctic cod
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DOI：
10.1073/pnas.94.8.3817
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发表时间：
1997-04-15
影响因子：
11.1
通讯作者：
Cheng, CHC
中科院分区：
文献类型：
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作者：
Chen, LB;DeVries, AL;Cheng, CHC
南极鳕鱼和几种北方鳕鱼在系统发育上相距很远(在不同的目和超级目中)，但它们产生的抗冻糖蛋白(AFGP)几乎相同，以在各自的冰冻环境中生存。这两种鱼的AFGP都是由一个简单的糖三肽单体重复组成的离散大小的聚合物家族。对北鳕科鱼类和北极鳕鱼AFGP基因的研究表明，它们的AFGP都是由一个多蛋白基因家族编码的，每个基因编码多个AFGP分子，这些分子通过小的可切割间隔区串联在一起。尽管有这些明显的相似之处，但对AFGP基因序列和亚结构的详细分析提供了强有力的证据，表明这两种极地鱼类的AFGP实际上是独立进化的。首先，虽然南极类NOTTHENNIZE AFGP基因已被证明起源于胰酶原，但北极鳕鱼AFGP基因与胰酶原基因没有序列上的同源性，这表明胰酶原不是胰酶原的前体。其次，两种鱼的AFGP基因具有不同的内含子-外显子组织和不同的间隔区序列，因此对多蛋白前体的加工也不同，这与不同的基因组来源是一致的。第三，重复的AFGP三肽(Thr-Ala/Pro-Ala)编码序列在两组基因中有很大的不同，这表明它们是由两个不同的短祖先序列重复产生的，同一三肽有三个密码子的不同排列。分离祖先的分子证据得到了形态、古生物和古气候证据的支持，这些证据共同表明，这两种极地鱼类各自独立地进化出各自的AFGP，从而通过趋同进化达到相同的AFGP。
Antarctic notothenioid fishes and several northern cods are phylogenetically distant (in different orders and superorders), yet produce near-identical antifreeze glycoproteins (AFGPs) to survive in their respective freezing environments. AFGPs in both fishes are made as a family of discretely sized polymers composed of a simple glycotripeptide monomeric repeat. Characterizations of the AFGP genes from notothenioids and the Arctic cod show that their AFGPs are both encoded by a family of polyprotein genes, with each gene encoding multiple AFGP molecules linked in tandem by small cleavable spacers. Despite these apparent similarities, detailed analyses of the AFGP gene sequences and substructures provide strong evidence that AFGPs in these two polar fishes in fact evolved independently. First, although Antarctic notothenioid AFGP genes have been shown to originate from a pancreatic trypsinogen, Arctic cod AFGP genes share no sequence identity with the trypsinogen gene, indicating trypsinogen is not the progenitor. Second, the AFGP genes of the two fish have different intron-exon organizations and different spacer sequences and, thus, different processing of the polyprotein precursors, consistent with separate genomic origins. Third, the repetitive AFGP tripeptide (Thr-Ala/Pro-Ala) coding sequences are drastically different in the two groups of genes, suggesting that they arose from duplications of two distinct, short ancestral sequences with a different permutation of three codons for the same tripeptide. The molecular evidence for separate ancestry is supported by morphological, paleontological, and paleoclimatic evidence, which collectively indicate that these two polar fishes evolved their respective AFGPs separately and thus arrived at the same AFGPs through convergent evolution.