Debenham P, Brzezinski M A, Foltz K R
Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
J Mol Evol. 2000 Nov;51(5):481-90. doi: 10.1007/s002390010111.
Recent evidence suggests that gamete recognition proteins may be subjected to directed evolutionary pressure that enhances sequence variability. We evaluated whether diversity enhancing selection is operating on a marine invertebrate fertilization protein by examining the intraspecific DNA sequence variation of a 273-base pair region located at the 5' end of the sperm bindin locus in 134 adult red sea urchins (Strongylocentrotus franciscanus). Bindin is a sperm recognition protein that mediates species-specific gamete interactions in sea urchins. The region of the bindin locus examined was found to be polymorphic with 14 alleles. Mean pairwise comparison of the 14 alleles indicates moderate sequence diversity (p-distance = 1.06). No evidence of diversity enhancing selection was found. It was not possible to reject the null hypothesis that the sequence variation observed in S. franciscanus bindin is a result of neutral evolution. Statistical evaluation of expected proportions of replacement and silent nucleotide substitutions, observed versus expected proportions of radical replacement substitutions, and conformance to the McDonald and Kreitman test of neutral evolution all indicate that random mutation followed by genetic drift created the polymorphisms observed in bindin. Observed frequencies were also highly similar to results expected for a neutrally evolving locus, suggesting that the polymorphism observed in the 5' region of S. franciscanus bindin is a result of neutral evolution.
最近的证据表明，配子识别蛋白可能受到定向进化压力，从而增强序列变异性。我们通过检测134只成年红海胆（强壮拟球海胆）精子结合蛋白基因座5'端一个273碱基对区域的种内DNA序列变异，评估了增强多样性的选择是否作用于一种海洋无脊椎动物的受精蛋白。结合蛋白是一种精子识别蛋白，介导海胆中物种特异性的配子相互作用。所检测的结合蛋白基因座区域具有多态性，有14个等位基因。对这14个等位基因的平均成对比较表明序列多样性适中（p距离 = 1.06）。未发现增强多样性选择的证据。无法拒绝这样的零假设，即强壮拟球海胆结合蛋白中观察到的序列变异是中性进化的结果。对替换和沉默核苷酸替换的预期比例、观察到的与预期的激进替换替换比例以及符合中性进化的麦克唐纳和克瑞特曼检验的统计评估均表明，随机突变后接着遗传漂变产生了结合蛋白中观察到的多态性。观察到的频率也与中性进化基因座预期的结果高度相似，表明强壮拟球海胆结合蛋白5'区域观察到的多态性是中性进化的结果。
