Abstract
Segmentation is an essential process during the early development of the three major phyla of Bilateria: Chordata, Annelida, and Arthropoda, yet little is known about the genes responsible for achieving this process. There are two main forms of segmentation, Notch-controlled and insect-like segmentation. It is not known how segmentation has evolved into the two forms we see today. Our current understanding of segmentation is mostly focused on the fruit fly Drosophila melanogaster that uses insect-like segmentation, which is a highly derived form only present in distal groups of Arthropoda. Notch-controlled segmentation is more prevalent in the basal subphyla of Arthropoda and is also shared among vertebrates and an annelid, suggesting Notchcontrolled segmentation is the ancestral form. The crustacean Artemia franciscana lies between the Notch-controlled and insect-like segmentation within Arthropoda and may answer how forms of segmentation transition during evolution. Understanding how changes in the genes controlling the interactions between segmentation genes can show us the mechanisms of the evolution of development. To further understand the expression and function of segmentation genes in A. franciscana, several existing and newly-developed methodologies were used. Transcriptomics were used to identify segmentation genes and understand relationships between A. franciscana genes and other arthropod segmentation genes. In-situ hybridisation was used to find expression patterns of the identified segmentation genes to compare to expected patterns in Notch-controlled and insectlike segmentation. Finally, new protocols were developed to investigate functional knockdown impacts on Artemia during segmentation. Using these techniques, we show how A. franciscana uses aspects of both Notch-controlled and Insect-like segmentation, possibly indicating that it uses a transitory form of segmentation. This project furthers our understanding of the evolution of development and describes A. franciscana as a model for studying the changes in segmentation genetics.