[Modelling of Drosophila gap gene network under Bcd morphogen variation].

Expression patterns of segmentation genes are formed under the influence of maternal transcription factor gradients, which initiate spatially localized expression in the cascade of segmentation genes. Bcd is one of these activators. We have studied one model of regulation in the gap gene network by varying the concentration of this protein. We have shown that the known gap gene network topology is not sufficient to explain experimental data on the shifts exhibited by the hb anterior expression domain by change in Bcd concentration in the embryo. As the result of modeling with these experimental data taken into account, a new topology is obtained that determines the correct shifts of the hb expression domain. These results suggest that interactions among the three hb, Kr and gt genes are key regulatory factors for the valid behaviour of the hb expression pattern with Bcd concentration changes. This study made it possible to specify the limits of validity for phenomenological models of gene networks.