The evolution of bicoid regulated genes in insects

A network of interactions between transcription factors and cis-regulatory sequences controls the expression of developmental genes. Changes in either the cis- or trans acting components of a developmental interaction can have consequences for both the output of the interaction and for the greater network of interactions. Thus, the evolution of regulation is considered to be a major force in the evolution of morphological diversity. To investigate the evolution of an interaction, this thesis has compared the Bicoid-dependent regulation of hunchback and orthodenticle expression in the Dipterans, Drosophila melanogaster, Musca domestica, Calliphora vicina, Lucilia sericata and Megaselia abdita. hb genes were isolated from Calliphora and Lucilia and these encode a number of domains that are conserved in hb from other species such as Drosophila, Musca and Tribolium. In contrast to the coding sequences, the hb promoters from Calliphora and Lucilia differ from each other and from the Drosophila and Musca hb promoters in terms of the number, sequence, orientation and spacing of Bed-binding sites that they contain. Analysis of intra-specific variation in the M. domestica hb gene demonstrated that both coding and non-coding sequences are subject to slippage generated turnover of simple motifs and that the extent of this turnover is dependent upon region specific constraints. This suggests that mechanisms of turnover are responsible for the different hb promoter configurations observed in the Dipterans. To investigate any functional consequences of the differences in both bed and hb between Drosophila, Musca and Megaselia, transcription assays were carried out using homogeneous and heterogeneous combinations of these two components in yeast. The results of these assays suggest that differences in Bed and the hb promoters between these species may have co-evolved to maintain the interaction. Therefore, to investigate how other Bed-regulated genes have evolved in Musca, the expression patterns and coding sequences of the otd gene were characterized in Musca and compared to those of Drosophila otd.