Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, Iowa 50011, USA. nvalenzu @ iastate.edu
Sex Dev. 2010;4(1-2):39-49. doi: 10.1159/000277935. Epub 2010 Jan 22.
Sexual development has long been the target of study and despite great advances in our understanding of the composition and regulation of the gene network underlying gonadogenesis, our knowledge remains incomplete. Of particular interest is the relative role that the environment and the genome play in directing gonadal formation, especially the effect of environmental temperature in directing this process in vertebrates. Comparative analyses in closely related taxa with contrasting sex-determining mechanisms should help fill this gap. Here I present a multivariate study of the regulation of the gene network underlying sexual development in turtles with temperature-dependent (TSD; Chrysemys picta) and genotypic sex determination (GSD; Apalone mutica). I combine novel data on SOX9 and DMRT1 from these species with contrasting sex-determining mechanisms for the first time with previously reported data on DAX1, SF-1 (NR5A1), WT1, and aromatase (CYP19A1) from these same taxa. Comparative expression analyses of SOX9 and DMRT1 from these and other species indicate additional elements whose expression has diverged among TSD taxa, further supporting the notion that significant evolutionary changes have accrued in the regulation of the TSD gene network in reptiles. A non-parametric MANOVA revealed that temperature had a significant effect in multivariate gene expression in C. picta that varied during embryonic development, whereas the covariation of gene expression in A. mutica was insensitive to temperature. A phenotypic trajectory analysis (PTA) of gene expression comparing both species directly indicated that the relative covariation in gene expression varied between temperatures in C. picta. Furthermore, the 25 degrees C trajectory of C. picta differed from that of A. mutica in the magnitude of gene expression change. Additional analyses revealed a stronger covariation in gene expression and a more interconnected regulatory network in A. mutica, consistent with the hypothesis that sexual development is a more canalized process in A. mutica, as would be expected if GSD evolved in this lineage through directional selection from its TSD ancestor.
性发育一直是研究的目标，尽管我们在理解性腺发生的基因网络组成和调控方面取得了重大进展，但我们的知识仍然不完整。特别感兴趣的是环境和基因组在指导性腺形成中的相对作用，特别是环境温度在脊椎动物中指导这一过程的作用。对具有相反性别决定机制的密切相关类群进行比较分析应该有助于填补这一空白。在这里，我介绍了一项关于温度依赖性（TSD；Chrysemys picta）和基因型性别决定（GSD；Apalone mutica）的海龟性发育相关基因网络调控的多变量研究。我首次将这些物种中与温度相关的 SOX9 和 DMRT1 的新数据与之前从这些相同分类群中报告的 DAX1、SF-1（NR5A1）、WT1 和芳香酶（CYP19A1）的数据相结合。来自这些和其他物种的 SOX9 和 DMRT1 的比较表达分析表明，表达已经在 TSD 分类群中分化的其他元素进一步支持了这样的观点，即爬行动物 TSD 基因网络的调控发生了重大进化变化。非参数 MANOVA 表明，温度对 C. picta 胚胎发育过程中多基因表达有显著影响，而 A. mutica 中基因表达的协变对温度不敏感。对两种物种进行直接比较的表型轨迹分析（PTA）表明，C. picta 中基因表达的相对协变因温度而异。此外，C. picta 的 25 度轨迹与 A. mutica 的不同，表现在基因表达变化的幅度上。进一步的分析显示，A. mutica 中的基因表达具有更强的协变和更相互关联的调控网络，这与性发育在 A. mutica 中是一个更加定型的过程的假设一致，如果 GSD 是通过从其 TSD 祖先的定向选择在这条线系中进化而来的，那么这是可以预期的。
