Genetic Dissection of a Supergene Implicates Tfap2a in Craniofacial Evolution of Threespine Sticklebacks
Genetic Dissection of a Supergene Implicates Tfap2a in Craniofacial Evolution of Threespine Sticklebacks
复制标题
DOI：
10.1534/genetics.118.300760
复制
发表时间：
2018-06-01
期刊：
影响因子：
3.3
通讯作者：
Miller, Craig T.
中科院分区：
文献类型：
--
作者：
Erickson, Priscilla A.;Baek, Jiyeon;Miller, Craig T.
在自然界中，多种适应性表型通常共同进化，并且可以由称为超基因的紧密相连的遗传位点控制。剖析这些相关表型的遗传基础是进化遗传学的一个重大挑战。多个淡水种群的三刺刺鱼（Gasterosteus aculeatus）已经进化出两种结构性颅面特征：更长的鳃骨和更多的咽齿数量，这可能是为了适应海洋和淡水环境之间的饮食差异。先前的 QTL 作图表明，这两个性状部分受到 21 号染色体上重叠基因组区域的控制，并且 Bmp6 的调控变化可能是牙齿数量 QTL 的基础。在这里，我们将鳃骨长度 QTL 映射到一个 155 kb 的八基因间隔，该间隔与 Bmp6 的编码区紧密相连，但不包括包含候选基因 Tfap2a 的编码区。进一步的重组作图表明，该骨长度 QTL 可分为至少两个基因座。在胚胎和幼虫发育过程中，Tfap2a 在鳃骨原基中表达，其中等位基因特异性表达测定显示，相对于杂交鱼中的海洋等位基因，Tfap2a 的淡水等位基因的表达水平较低。 Tfap2a 诱导的功能丧失突变揭示了刺鱼颅面发育中的重要作用，并表明杂合子中骨长度对 Tfap2a 剂量敏感。综合起来，这些结果表明，Bmp6 和 Tfap2a 密切相关但在遗传上可分离的变化有助于多个淡水刺鱼种群进化骨骼增益的潜在超基因。
In nature, multiple adaptive phenotypes often coevolve and can be controlled by tightly linked genetic loci known as supergenes. Dissecting the genetic basis of these linked phenotypes is a major challenge in evolutionary genetics. Multiple freshwater populations of threespine stickleback fish (Gasterosteus aculeatus) have convergently evolved two constructive craniofacial traits, longer branchial bones and increased pharyngeal tooth number, likely as adaptations to dietary differences between marine and freshwater environments. Prior QTL mapping showed that both traits are partially controlled by overlapping genomic regions on chromosome 21 and that a regulatory change in Bmp6 likely underlies the tooth number QTL. Here, we mapped the branchial bone length QTL to a 155 kb, eight-gene interval tightly linked to, but excluding the coding regions of Bmp6 and containing the candidate gene Tfap2a. Further recombinant mapping revealed this bone length QTL is separable into at least two loci. During embryonic and larval development, Tfap2a was expressed in the branchial bone primordia, where allele specific expression assays revealed the freshwater allele of Tfap2a was expressed at lower levels relative to the marine allele in hybrid fish. Induced loss-of-function mutations in Tfap2a revealed an essential role in stickleback craniofacial development and show that bone length is sensitive to Tfap2a dosage in heterozygotes. Combined, these results suggest that closely linked but genetically separable changes in Bmp6 and Tfap2a contribute to a supergene underlying evolved skeletal gain in multiple freshwater stickleback populations.