Investigation of Hox gene expression and Wnt-signalling in basally branching ecdysozoans

Sammanfattning: One of the most important processes in the development of an animal is the determination and patterning of the primary body axis, the anterior-posterior (AP) axis. After the AP axis has been established the embryo grows and elongates through posterior elongation.Several evolutionary conserved sets of genes and signalling pathways are involved in AP axis formation and posterior elongation, including Wnt-signalling. Wnt-signalling was involved in AP axis determination and posterior elongation even before the evolution of the Bilateria. In segmented animals, Wnt-signalling is also involved in maintaining segmental boundaries and in giving each segment its polarity. Hox genes, conversely, play a significant role in the regionalisation of the AP axis in Bilateria. This role as regionalisation factors probably emerged within the bilaterian in stem-group and it has been speculated that Wnt genes may have had this function prior to the rise of the Hox genes.The goal of this work is to shed light on the expression and function of Wnt-signalling and Hox gene patterning in basally branching ecdysozoans, Priapulida and Onychophora, two phyla that are underrepresented in current research, but represent key phyla for the understanding of ecdysozoan evolution.Wnt genes are likely to have retained a prominent function in posterior regionalisation and elongation in Priapulida. Investigation of Hox gene expression patterns proved to be difficult in Priapulida, but preliminary results suggest partially conserved function in AP axis patterning.In Onychophora, Wnt-signalling appears to be involved in segment formation, intrasegmental patterning and segment/parasegment border maintenance. Some of the onychophoran Wnt genes are expressed in Hox-like patterns suggesting a role in AP-axis patterning, a function that Wnt genes may thus have retained throughout their evolution.Finally, I have also investigated some of the factors involved in Wnt-signalling (or morphogen processing in general). These genes, the morphogen-interfering factors (MIFs), have been poorly investigated in general. I studied their expression in an onychophoran and a number of other emerging arthropod model organisms in order to obtain a more solid basis for comparison. These data, although difficult to interpret, suggest that the interaction of Wnts and MIFs is diverse and complex among Panarthropoda.