Multiscale diffusion in the mitotic Drosophila melanogaster syncytial blastoderm

Abstract

Despite the fundamental importance of diffusion for embryonic morphogen gradient formation in the early Drosophila melano-gasterembryo, there remains controversy regarding both the extent and the rate of diffusion ofwell-characterizedmorphogens. Furthermore, the recent observation of diffusional "compartmentalization"has suggested that diffusion may in fact be nonideal and mediated by an as-yet-unidentified mechanism. Here, we characterize the effects of the geometry of the early syncytial Drosophila embryo on the effective diffusivity of cytoplasmic proteins. Our results demonstrate that the presence of transient mitotic membrane furrows results in amultiscale diffusion effect that has a significant impact on effective diffusion rates across the embryo. Using a combination of live-cell experiments and computational modeling, we characterize these effects and relate effective bulk diffusion rates to instantaneous diffusion coefficients throughout the syncytial blastoderm nuclear cycle phase of the early embryo. This multiscale effect may be related to the effect of interphase nuclei on effective diffusion, and thus we propose that an as-yet-unidentified role of syncytial membrane furrows is to temporally regulate bulk embryonic diffusion rates to balance themultiscale effect of interphase nuclei,which ultimately stabilizes the shapes of various morphogen gradients.