La cinétique cellulaire au cours de la segmentation du germe d’Axolotl: proposition d’un modèle statistique

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ABSTRACT The present work is based on the study of individual cell cycle times for a given category of cells. The material considered in detail is the Axolotl embryo during the eleventh cleavage cycle. In spite of the exceptional homogeneity of this population, individual cycle times show a remarkable variation from cell to cell, coinciding with a characteristic statistical distribution. To describe the kinetics of cell proliferation, we propose a model for which the theoretical distribution of cycle times fits with the distribution observed in our material. Numerous observations allow us to generalize the model to other types of populations. According to this concept the notion of cell cycle time disappears in favour of the notion of a statistical distribution of individual cycle times. This variability is integral to the cell division process itself. We suggest that in the cycle there is a particular event the probability of occurrence of which is constant beginning with a critical state. The cells would therefore remain a certain time in this state, overcoming it at a characteristic rate. To this exponential distribution variability would be added the variability of other events whose cumulative effects would result in a normal distribution. The resultant of both factors conforms to the frequency distribution implicated in our kinetic model. Discussing in a more general way the distributions of the cycle times of each cell division during cleavage, we propose the following interpretation of this development. The introduction of new events in the cyclic process would imply the switching on of certain essential genetic activities. The final consequences would be the desynchronization and the lengthening of the cycles observed at the blastula stage. Thus considered, this period of embryonic development would be eminently suitable for the study of the factors of cell division control.