Functional aspects of hybrid genome interaction : sex determination and gene expression regulation in the Squalius alburnoides complex

Tese de doutoramento em Biologia (Biologia Evolutiva) apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2009.Hybrid polyploidy success has been extensively reported in plant species and more restrictedly in animals, but the regulatory changes that contribute to genome stabilization and regulation in the presence of distinct chromosome sets are still elusive. Due to its unique features among polyploidy taxa, the Squalius alburnoides complex of hybrid fish is a very desirable system to address these questions. It is considered an example of polyploid viability and evolutionary success, thus making it more interesting as a model to assess whether such features could be the result of an underlying specific gene regulatory basis. The aim of this dissertation was to assess whether hybridisation and polyploidy could have a functional effect over gene expression regulation: at the level of sex determination, a more strictly regulated process of gene interactions that apparently could be disrupted in the hybrids, as well as in a broader context regarding the contribution of each genome to the overall gene expression patterns. Six conserved elements of sex determination cascades (vasa, amh, dmrt1, wt1, dax1 e figla) were isolated, and their expression patterns and potential contributions were characterized in the adult gonads of S. alburnoides and the parental species S. pyrenaicus. Transcripts of four of these genes were shown to be present during early stages of S. alburnoides male development, suggesting their involvement, at least in the process of hybrid gonad differentiation. The participation of genome-specific gene copies in the global gene expression patterns was assessed by the analysis of six housekeeping and tissue specific genes, revealing the occurrence of a mechanism of non-additive gene expression and allele silencing acting in S. alburnoides triploids, described for the first time in a polyploid vertebrate. Further examination of the evolutionary consequences of the observed patterns of gene expression and the extension of the analysis to representative populati