UC Berkeley

The phylum Arthropoda displays some of the most diverse and versatile body plans and appendages. To explore this diversity, the main focus of this thesis is on members of the arthropod clade, the Pancrustacea (crustaceans and hexapods), and the role that body patterning genes, Hox genes, have played in body plan evolution and limb identity. Specifically focusing on the expression boundaries and the role of Hox genes in two orders of crustaceans, Branchiopoda and Amphipoda. In Branchiopoda, the focus was to expand our understanding of the role of the posterior most Hox gene Abdominal-B (Abd-B) in the brine shrimp, Artemia franciscana, this was done through gene expression data and functional experiments. In our gene expression data, a temporal expression pattern was observed of Abd-B, that suggests that Abd-B does play a role in the limbless nature of the abdomen A. francsicana, while our functional experiments (RNAi) preliminarily suggests that Abd-B represses limb formation. In Amphipoda, the focus was to discern the potential causes of the highly reduced and strikingly different body plan of the skeleton shrimp, Caprella mutica. The first question approached was which mechanisms are used to reduce the abdomen, by exploring apoptosis (TUNEL assay) during embryogenesis. Observations through Scanning Electron Microscopy (SEM) were made to understand the sexually dimorphic appendages on the male abdomen. Once it was observed that C. mutica reduced the abdomen through apoptosis, the next question was to understand the limb identity along the Anteroposterior axis (A/P axis). To do this a transcriptome of 4 embryonic time points of C. mutica were used to discern the Hox gene expression boundaries, visualized through in situ Hybridization Chain Reaction (HCR). These Hox gene expression boundaries were then compared to another member of Amphipoda, Parhyale hawaiensis, which has a typical amphipod body plan. This comparison was to tease out the role the Hox genes had in limb identity along the A/P axis and explore the evolutionary relationship of the Hox gene expression pattern in limb identity.