National Centre for Biosystematics, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway.
Mutat Res. 2011 Mar 15;708(1-2):37-43. doi: 10.1016/j.mrfmmm.2011.01.006. Epub 2011 Feb 1.
Microsatellites mutate frequently by replication slippage. Empirical evidence shows that the probability of such slippage mutations may increase with the length of the repeat region as well as exposure to environmental mutagens, but the mutation rate can also differ between the male and female germline. It has been hypothesized that more intense sexual selection or sperm competition can also lead to elevated mutation rates, but the empirical evidence is inconclusive. Here, we analyzed the occurrence of germline slippage mutations in the hypervariable pentanucleotide microsatellite locus HrU10 across six species of swallow (Aves: Hirundinidae). These species exhibit marked differences in the length range of the microsatellite, as well as differences in the intensity of sperm competition. We found a strong effect of microsatellite length on the probability of mutation, but no residual effect of species or their level of sperm competition when the length effect was accounted for. Neither could we detect any difference in mutation rate between tree swallows (Tachycineta bicolor) breeding in Hamilton Harbour, Ontario, an industrial site with previous documentation of elevated mutation rates for minisatellite DNA, and a rural reference population. However, our cross-species analysis revealed two significant patterns of sex differences in HrU10 germline mutations: (1) mutations in longer alleles occurred typically in the male germline, those in shorter alleles in the female germline, and (2) male germline mutations were more often expansions than contractions, whereas no directional bias was evident in the female germline. These results indicate some fundamental differences in male and female gametogenesis affecting the probability of slippage mutations. Our study also reflects the value of a comparative, multi-species approach for locus-specific mutation analyses, through which a wider range of influential factors can be assessed than in single-species studies.
微卫星通过复制滑动频繁发生突变。经验证据表明，这种滑动突变的概率可能随着重复区域的长度以及暴露于环境诱变剂而增加，但突变率也可能在雄性和雌性生殖细胞之间有所不同。有人假设，更强烈的性选择或精子竞争也可能导致突变率升高，但经验证据尚无定论。在这里，我们分析了六种燕子（雀形目：燕科）中高度可变的五核苷酸微卫星 HRU10 生殖细胞滑动突变的发生情况。这些物种在微卫星的长度范围以及精子竞争强度方面存在显著差异。我们发现微卫星长度对突变概率有强烈影响，但在考虑长度效应时，物种或其精子竞争水平没有剩余影响。当我们在安大略省汉密尔顿港繁殖的树燕（Tachycineta bicolor）与之前记录有微卫星 DNA 突变率升高的工业地点和农村参考人群进行比较时，也无法检测到突变率在两者之间存在差异。然而，我们的跨物种分析揭示了 HRU10 生殖细胞突变中存在两种性别差异的显著模式：（1）较长等位基因的突变通常发生在雄性生殖细胞中，较短等位基因的突变发生在雌性生殖细胞中，（2）雄性生殖细胞突变通常是扩张而不是收缩，而在雌性生殖细胞中没有明显的定向偏差。这些结果表明，在影响滑动突变概率的雄性和雌性配子发生方面存在一些根本差异。我们的研究还反映了比较多物种方法对于特定基因座突变分析的价值，通过这种方法可以评估比单一物种研究更广泛的影响因素。
