Meeting Abstract
31.4 Friday, Jan. 4 The cellular basis of pharyngeal skeleton growth and metamorphosis in frogs ROSE, C.S.*; SMITH, A.; TRACY, J.; James Madison University; James Madison University; James Madison University rosecs@jmu.edu
The Meckel�s cartilage (MC), ceratohyal (CH), and branchial arch cartilages (BA) of Xenopus laevis grow isometrically in pre- and prometamorphosis, and undergo distinct shape changes at climax metamorphosis. MC lengthens from a bow to a U, CH changes from short and broad to long and narrow, and BA disappear. We investigated how these growth and shape changes are accomplished at the level of cell division, cell size, cell shape, matrix secretion, and cell death. Cell behaviors were quantified by BrdU and TUNEL labeling and direct measurements from slides for NF stages 47-66. The three cartilages show different patterns and magnitudes of each cell behavior, but, with the exception of cell death in BA, no cartilage exhibits any regional variation in behaviors. MC has the highest BrdU labeling and the smallest cells. Also, MC cell size decreases and percentage matrix increases throughout pro- and climax metamorphosis. BA and CH have comparably large cells and little matrix until climax, when BA are lost to a wave of cell death, and CH exhibits a decrease in cell size and increase in percentage matrix. Levels of BrdU labeling are not strongly correlated among cartilages, suggesting asynchronous cell cycles. Interestingly, besides cell death in BA, no cell behavior exhibits a significant change at the transition from growth to shape change. This suggests that the transition is tied to changes in cell behavior rates and cell cycle length. Also, without regionalization, the measured cell behaviors do not explain isometric growth or shape changes such as elongation without increasing width (MC) or with decreasing width (CH). These questions are being addressed by efforts to measure cell cycle and examine the orientation and relative distribution of cell division and cell death within cartilages.
