Pala Irene, Schartl Manfred, Thorsteinsdóttir Sólveig, Coelho Maria Manuela
Centro de Biologia Ambiental, Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, Lisbon, Portugal.
PLoS One. 2009 Jul 28;4(7):e6401. doi: 10.1371/journal.pone.0006401.
Sex determination processes vary widely among different vertebrate taxa, but no group offers as much diversity for the study of the evolution of sex determination as teleost fish. However, the knowledge about sex determination gene cascades is scarce in this species-rich group and further difficulties arise when considering hybrid fish taxa, in which mechanisms exhibited by parental species are often disrupted. Even though hybridisation is frequent among teleosts, gene based approaches on sex determination have seldom been conducted in hybrid fish. The hybrid polyploid complex of Squalius alburnoides was used as a model to address this question.
METHODOLOGY/PRINCIPAL FINDINGS: We have initiated the isolation and characterization of regulatory elements (dmrt1, wt1, dax1 and figla) potentially involved in sex determination in S. alburnoides and in the parental species S. pyrenaicus and analysed their expression patterns by in situ hybridisation. In adults, an overall conservation in the cellular localization of the gene transcripts was observed between the hybrids and parental species. Some novel features emerged, such as dmrt1 expression in adult ovaries, and the non-dimorphic expression of figla, an ovarian marker in other species, in gonads of both sexes in S. alburnoides and S. pyrenaicus. The potential contribution of each gene to the sex determination process was assessed based on the timing and location of expression. Dmrt1 and wt1 transcripts were found at early stages of male development in S. alburnoides and are most likely implicated in the process of gonad development.
CONCLUSIONS/SIGNIFICANCE: For the first time in the study of this hybrid complex, it was possible to directly compare the gene expression patterns between the bisexual parental species and the various hybrid forms, for an extended set of genes. The contribution of these genes to gonad integrity maintenance and functionality is apparently unaltered in the hybrids, suggesting that no abrupt shifts in gene expression occurred as a result of hybridisation.
性别决定过程在不同脊椎动物类群中差异很大，但没有哪个类群能像硬骨鱼那样为性别决定进化研究提供如此丰富的多样性。然而，在这个物种丰富的类群中，关于性别决定基因级联的知识却很匮乏，当考虑杂交鱼类类群时，问题变得更加复杂，其中亲本物种所表现出的机制常常受到干扰。尽管硬骨鱼之间杂交频繁，但基于基因的性别决定方法在杂交鱼中却很少进行。阿尔巴尼亚鲤杂交多倍体复合体被用作模型来解决这个问题。
方法/主要发现：我们开始分离和鉴定可能参与阿尔巴尼亚鲤及其亲本物种比利牛斯鲤性别决定的调控元件（dmrt1、wt1、dax1和figla），并通过原位杂交分析它们的表达模式。在成体中，杂交种和亲本物种之间基因转录本的细胞定位总体上是保守的。出现了一些新特征，比如dmrt1在成年卵巢中的表达，以及figla（在其他物种中是卵巢标记物）在阿尔巴尼亚鲤和比利牛斯鲤两性性腺中的非二态性表达。根据表达的时间和位置评估了每个基因对性别决定过程的潜在贡献。在阿尔巴尼亚鲤雄性发育早期发现了dmrt1和wt1转录本，它们很可能参与性腺发育过程。
结论/意义：在这个杂交复合体的研究中，首次能够直接比较双性亲本物种和各种杂交形式之间一系列基因的基因表达模式。这些基因对性腺完整性维持和功能的贡献在杂交种中显然未改变，这表明杂交并未导致基因表达发生突然变化。
