| Popis: |
This thesis compares developmental processes between two related organisms, the fruit fly Drosophila melanogaster and the locust Schistocerca gregaria. The aims of this approach are to define how genetic changes in development pathways have led to evolutionarily important morphological differences, and to distinguish basic, widely applicable developmental mechanisms from more derived, specialised ones. The Hox gene family of transcription factors are particularly suitable for this type of comparative analysis as they are known to control anteroposterior regional identity in a wide variety of animals. I have focused on one such gene: a Hox gene of the locust Schistocerca gregaria. The starting point for this study was a locust homeobox containing genomic fragment, Sg Dax, previously isolated by Iain Dawson. The Dax homeodomain clearly belongs to the Antennapedia class of Hox genes. However, no clear fly homologue could be identified on the basis of the homeodomain sequence. To establish the relationship of Dax to the fly Hox genes, I subcloned the genomic fragment, raised antibodies against the encoded protein, analysed Dax expression and isolated a Dax cDNA. This work shows Dax to be the locust homologue of the Drosophila segmentation gene fushi tarazu (ftz). Ftz is not a homeotic gene but both ftz and Dax contain homeoboxes of the homeotic gene class. Sequence analysis suggests that ftz and Dax belong to a family of genes that are diverging more rapidly than the homeotic Hox genes but may have derived from a canonical Hox cluster gene. Despite this sequence divergence, Dax and ftz have highly conserved patterns of expression in the nervous system, which may reflect conserved function. Surprisingly, however, their expression during segmentation is not conserved. |
