Nuclear morphogenesis: forming a heterogeneous nucleus during embryogenesis

An embryo experiences progressively complex spatial and temporal patterns of gene expression that guide the morphogenesis of its body plan as it matures. Using super-resolution fluorescence microscopy in Drosophila melanogaster embryos, we observed a similar increase in complexity in the nucleus: the spatial distributions of transcription factors became increasingly heterogeneous as the embryo matured. We also observed a similar trend in chromatin conformation with the establishment of specific histone modification patterns. However, transcription sites of specific genes had distinct local preferences for histone marks separate from the average nuclear trend, depending on the time and location of their expression. These results suggest that reconfiguring the nuclear environment is an integral part of embryogenesis and that the physical organization of the nucleus is a key element in developmental gene regulation. Summary statement We observed spatial rearrangements in the nucleus during embryo development, progressively forming a heterogeneous nuclear environment, paralleling the increasing complexity of the embryo body as morphogenesis progresses.