Measurement of Tensile Forces in Xenopus laevis Neural Tissue
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Neurulation is critical for the proper development of the central nervous system during embryogenesis. This process requires coordinated morphogenetic movements driven by localized cell movements. The key morphogenetic process responsible for lengthening the neural plate is convergent extension. During convergent extension medially oriented cell polarity, protrusive activity, and motility are thought to generate forces through cell intercalation resulting in stiffer elongating tissues. My research determines that forces that help shape the neural plate arise from morphogenetic movements in the neural tissue and determines PCP signaling regulates tissue stiffness in the neural ectoderm. We have established an experimental system sensitive enough to evaluate the stiffness of Xenopus neural tissue. Stiffness is measured by gluing two fine wires onto neural explants from an early gastrula stage Xenopus laevis embryo. The wires stretch the tissue at a constant strain rate using a real-time image-based feedback system and stiffness is determined by measuring the deflection of one wire. Measurements obtained from control embryos prior to neurulation estimate tissue stiffness at approximately 12.7 ± 0.53 mN/m in both mediolateral and anteroposterior directions. Stiffness measurements double in early neurula embryos (P < 0.05). Mediolateral stiffness, 24.9 ±6.2 mN/m, is significantly greater than anteroposterior stiffness, 21.4 ±5.3 mN/m (P < 0.05). These trends are strengthened in normalized data to reduce clutch-to-clutch variation. Expressions of dominant-negative Wnt11, Fz7, and Dsh constructs successfully disrupt neurulation by interfering with the PCP pathway. Changes in stiffness of the neural plate were measured and show reduced stiffness at early neurula stage in both mediolateral and anteroposterior directions suggesting mechanical forces are generated within the neural plate.