Lambert Max R, Skelly David K, Ezaz Tariq
School of Forestry and Environmental Studies, Yale University, Greeley Memorial Lab, 370 Prospect St, New Haven, CT, 06511, USA.
Institute for Applied Ecology, University of Canberra, Canberra, ACT, Australia.
BMC Genomics. 2016 Oct 28;17(1):844. doi: 10.1186/s12864-016-3209-x.
The extent to which sex reversal is associated with transitions in sex determining systems (XX-XY, ZZ-ZW, etc.) or abnormal sexual differentiation is predominantly unexplored in amphibians. This is in large part because most amphibian taxa have homomorphic sex chromosomes, which has traditionally made it challenging to identify discordance between phenotypic and genetic sex in amphibians, despite all amphibians having a genetic component to sex determination. Recent advances in molecular techniques such as genome complexity reduction and high throughput sequencing present a valuable avenue for furthering our understanding of sex determination in amphibians and other taxa with homomorphic sex chromosomes like many fish and reptiles.
We use DArTseq as a novel approach to identify sex-linked markers in the North American green frog (Rana clamitans melanota) using lab-reared tadpoles as well as wild-caught adults from seven ponds either in undeveloped, forested habitats or suburban ponds known to be subject to contamination by anthropogenic chemicals. The DArTseq methodology identified 13 sex-linked SNP loci and eight presence-absence loci associated with males, indicating an XX-XY system. Both alleles from a single locus show partial high sequence homology to Dmrt1, a gene linked to sex determination and differentiation throughout Metazoa. Two other loci have sequence similarities to regions of the chimpanzee and human X-chromosome as well as the chicken Z-chromosome. Several loci also show geographic variation in sex-linkage, possibly indicating sex chromosome recombination. While all loci are statistically sex-linked, they show varying degrees of female heterozygosity and male homozygosity, providing further evidence that some markers are on regions of the sex chromosomes undergoing higher rates of recombination and therefore further apart from the putative sex determining locus.
The ease of the DArTseq platform provides a useful avenue for future research on sex reversal and sex chromosome evolution in vertebrates, particularly for non-model species with homomorphic or cryptic or nascent sex chromosomes.
在两栖动物中，性反转与性别决定系统转变（XX - XY、ZZ - ZW等）或异常性别分化之间的关联程度在很大程度上尚未得到探索。这主要是因为大多数两栖类群具有同型性染色体，传统上，尽管所有两栖动物的性别决定都有遗传成分，但要识别两栖动物表型性别与遗传性别之间的不一致仍具有挑战性。诸如基因组复杂性降低和高通量测序等分子技术的最新进展为增进我们对两栖动物以及许多鱼类和爬行动物等具有同型性染色体的其他类群的性别决定的理解提供了一条宝贵途径。
我们使用DArTseq作为一种新方法，利用实验室饲养的蝌蚪以及从七个池塘捕获的野生成年北美绿蛙（Rana clamitans melanota）来鉴定性连锁标记，这些池塘要么位于未开发的森林栖息地，要么是已知受到人为化学物质污染的郊区池塘。DArTseq方法鉴定出13个与雄性相关的性连锁单核苷酸多态性（SNP）位点和8个存在/缺失位点，表明这是一个XX - XY系统。单个位点的两个等位基因与Dmrt1显示出部分高度序列同源性，Dmrt1是一个与后生动物性别决定和分化相关的基因。另外两个位点与黑猩猩和人类X染色体以及鸡Z染色体的区域具有序列相似性。几个位点在性连锁方面也表现出地理变异，这可能表明性染色体发生了重组。虽然所有位点在统计学上都是性连锁的，但它们表现出不同程度的雌性杂合性和雄性纯合性，这进一步证明一些标记位于性染色体上重组率较高的区域，因此与假定的性别决定位点距离更远。
DArTseq平台的简便性为未来脊椎动物性反转和性染色体进化的研究提供了一条有用途径，特别是对于具有同型、隐蔽或新生性染色体的非模式物种。
