51.1 Saturday, Jan. 5 The Cellular Basis of Cartilage Growth and Shape Change in Frogs ROSE, C.S.; James Madison University, Harrisonburg, Va firstname.lastname@example.org
Unlike bone, skeleton that is comprised entirely of cartilage grows and changes shape as a result of cell behaviors inside the tissue as well as on its surface. The pharyngeal arch skeleton of the frog Xenopus laevis offers an excellent model for studying how cartilage growth and shape change are controlled at the cell level because the three ventral elements (Meckel’s cartilage or MC, ceratohyal or CH, and branchial arch cartilages or BA) are not replaced by bone and their cell behaviors are not localized to specific regions, yet they grow isometrically at tadpole stages and undergo diverse shape changes at metamorphosis. MC lengthens and increases its curvature, CH transforms from a broad plate into a narrow cylinder, and BA is resorbed. Our goal is to understand how these growth and shape changes are accomplished at the level of cell division, enlargement, shape change, matrix secretion, and death. We used BrdU to label dividing cells, DAPI to stain dying cells, and Cell Profiler to quantify cell size, shape and orientation in frontal and transverse sections through MC and CH at early, mid and late tadpole and metamorphic stages. BrdU pulse labeling was used to estimate the duration of chondrocyte cell cycles at mid and late tadpole stages. MC and CH have different ontogenetic profiles of cell division, death, size, shape and matrix secretion. However, with the exception of cell death in CH, no cartilage exhibits a dramatic change in frequency or spatial pattern of any behavior going from growth to shape change. Most cells that complete S phase do not complete mitosis, and only a small percentage complete a second mitosis. These data will be used to generate rules of cell behavior for cartilage growth and shape change and to test multiple models for their developmental regulation.