PRICE, Alivia L.*; PATEL, Nipam H.; The Salk Institute; Univ. of California, Berkeley; Howard Hughes Medical Institute: Mesoderm development in arthropods: a view from crustaceans
The Arthropoda is a highly diverse group of organisms including the Chelicerata, Myriapoda, Crustacea, and Insecta. Studies of comparative development in arthropods can benefit from the vast amount of knowledge garnered from the fruitfly, Drosophila melanogaster. But how does mesoderm development of Drosophila, an insect, compare with other arthropod groups? We have developed a new arthropod system for studying development: the amphipod crustacean Parhyale hawaiensis. Using Parhyale, we have explored the cell lineage of mesoderm, molecular aspects of mesoderm patterning, and interactions between ectoderm and mesoderm in the formation of germ band segments. Cell lineage studies in amphipod crustaceans show that three cell lineages from the eight-cell stage contribute to the visceral mesoderm, somatic mesoderm of the head, and teloblast-derived somatic trunk mesoderm. Through ablation studies, we show cell lineages giving rise to the mesoderm have the ability to compensate for one another, suggesting a mesoderm equivalency group is established at the eight-cell stage. The genes twist, snail, and mef2 are involved in mesoderm development throughout the Metazoa. We characterized orthologs of these genes from Parhyale and find that expression implicates them in patterning, but not specification, of mesoderm. The majority of segmental mesoderm in malacostracan crustaceans is formed via the asymmetric division of eight mesoteloblasts in an anterior to posterior progression. Through ablation experiments, we have investigated the interaction between ectoderm and mesoderm during segmentation. We find that segmentation of the ectoderm is independent of the mesoderm, but segmentation of the mesoderm depends on the ectoderm for organization. These results will be discussed in relation to what is known about mesoderm development from other arthropod groups.
