Bifurcation of the amphibian embryo's axis: analysis of variation in response to egg centrifugation

Xenopus embryos have been reported to vary widely in their developmental response to centrifugation. Variation in response to centrifugation, as measured by embryo survival and twinning of axial structures, was monitored different spawnings of Xenopus laevis eggs. A convenient method for quantifying the egg cytoplasm's potential for displacement in a centrifugal field was employed. It involved testing small batches of eggs from each spawn under carefully controlled conditions for displacement of the cytoplasm while held in an inverted orientation. The cytoplasmic immobility (CIM) values thus measured in samples from each spawn were correlated with the spawning's developmental success (survival of embryos) and the twinning frequency after centrifugation. Those spawnings with high CIM values (i.e. a rigid or stiff cytoplasm) had the highest survival rates and the lowest frequency and severity of twinning in centrifuged eggs. Variations in CIM account for the broad variation in response to centrifugation previously noted in several reports and further emphasize the role cytoplasmic compartments play vis-à-vis egg organization and early embryonic pattern formation.