13.5 Wednesday, Jan. 4 Does temperature dependence of morphogenesis require fine control of tissue mechanics? VON DASSOW, M*; DAVIDSON, LA; Univ. of Pittsburgh; Univ. of Pittsburgh firstname.lastname@example.org
Understanding morphogenesis requires deciphering how organisms withstand environmental perturbations. Environmental temperature strongly affects developmental rates but previous studies suggest that temperature does not affect the relative timing of developmental stages. Rates of morphogenetic movements should depend on both the viscoelastic properties of the embryo and the timing and magnitude of the driving forces. A simple model based on these conditions suggests tight constraints on how tissue mechanics should change with temperature to allow normal morphogenesis. We tested this model in gastrulating Xenopus laevis embryos, using micro-aspiration and electrically stimulated contractions. Tissue viscoelasticity was independent of temperature, consistent with our model when formulated for power-law time-dependence of compliance. Changes in contraction kinematics (~2.4-fold increase in speed from 16 to 26°C) appear similar to changes in whole embryo morphogenetic rates (2- to 3-fold increase). However, contraction magnitudes were ~40% smaller at high temperature than at low temperature, contrary to predictions. When investigated at a fine scale, temperature caused heterochronic shifts in morphogenesis. As temperature rose, the speed of blastopore closure increased more slowly than the speed of dorsal-to-ventral progression of involution. While there was only a ~25% shift from 16 to 26°C, this invalidates an assumption of our model. We conclude that the ability of morphogenetic rates to vary by more than three-fold with temperature depends on tolerance of variation in morphogenetic movements, rather than on fine control of tissue mechanics. The viscoelasticity of the tissue and the time-dependence of morphogenetic forces may account for the observed heterochronic shifts.