Muscle Segmentation in Xenopus tropicalis and Xenopus laevis
By: Sophia Huang
Department: Cellular & Molecular Biology
Faculty Advisors: Dr. Carmen Domingo and Dr. Julio Ramirez
In vertebrates, the paraxial mesoderm will give rise to segmented structures referred to as somites. These embryonic structures will differentiate to form the dermis, cartilage, skeletal muscles, and tendons in the adult. Somite formation in the African clawed frog, Xenopus laevis, begins with segmentation of the presomitic mesoderm (PSM) to generate bilateral pairs of somites. During this process, individual muscle progenitors in the PSM will first mediolaterally elongate before undergoing a 90-degree rotation to become elongated muscle fibers that are aligned parallel to the notochord. Unlike Xenopus laevis, a tetraploid species, the general steps of somitogenesis have not been well documented in a closely related diploid species, Xenopus tropicalis. Embryos are injected with gap43GFP, which is expressed in the cell membrane, and immunostained with an antibody against fibronectin to observe how cells interact with the extracellular matrix and visualize cell shapes. Using image analysis tools, we have characterized the general steps of muscle formation in X. tropicalis by measuring the length, surface area, and cell bending in X. tropicalis at late tadpole stages. Imaris was used to create three-dimensional models that allowed us to better visualize the cells in the transition zone. Our observations show that the general sequence of cellular morphological changes in X. tropicalis is very similar to X. laevis. However, the timing of events appears to be accelerated in X. tropicalis due to the smaller size difference between these species. Given that X. tropicalis is diploid, we will be able to more easily determine the molecular underpinnings that control muscle formation in the Xenopus genus and its evolutionary significance to other vertebrates species.