Not all nuclei are regular spheres as is often shown in textbooks. For example, in Drosophila embryos, nuclei are initially spherical but they elongate and acquire an irregular lobulated morphology during cellularisation. These morphological changes coincide with transcriptional activation of the zygotic genome and reflect poorly understood changes in nuclear envelope (NE) mechanics. Here (see ), Thomas Lecuit and co-workers provide new insights into NE morphogenesis in early Drosophila embryos. Microtubule (MT) polymerisation events produce the forces necessary for NE dynamics, they report, and the large-scale NE deformations associated with lobulation require both a concentration of MT polymerisation in bundles that are organised by dynein and the presence of the farnesylated inner nuclear membrane protein Kugelkern. The researchers also show that MT-induced NE deformations control the dynamics of chromatin and its organisation at steady state. They suggest, therefore, that the mechanical regulation of chromatin dynamics by MT-induced NE fluctuations might be important for gene regulation in Drosophila embryos.
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