Palate morphogenesis: II. Contraction of cytoplasmic processes in ATP-induced palate rotation in glycerinated mouse heads

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Abstract
It has been previously shown that non‐muscle contractile system(s) exist in mouse palate mesenchyme underlying the palate epithelium before shelf rotation. In order to obtain evidence that the non‐muscle contractile system(s) function to elevate the palate, glycerinated heads have been incubated with ATP. It was shown that 5 mM ATP and a 30 min incubation at 25°C stimulated palate rotation optimally. Elevation of the anterior end of the palate was nearly complete (PSI = 3.90, p−6). Although rotation of the posterior end was significant (p<0.02), movement was limited (PSI = 1.70). Light microscopy of the palate revealed that ATP caused a marked condensation of the cytoplasmic processes of the mesenchymal cells. The contraction of the processes of the mesenchymal cells induced by ATP increased roughly with increased palate shelf rotation and was greater at the peripheral than at the internal mesenchyme. Cytochalasin B pre‐treatment at 40 μM completely blocked the ATP‐induced rotation at the anterior end. The effect of other nucleotides on palate rotation was tested. GTP caused a significant stimulation of anterior shelf rotation (p<0.005), which was less than ATP, while ADP and CTP were ineffective. Low temperature (6°C) prevented the ATP‐induced shelf rotation. These results suggest that the non‐muscle contractile cells in the mesenchyme play a role in palate elevation and that contraction of the actomyosin containing microfilaments supplies the motive force.