Asymmetric nuclear division in neural stem cells generates sibling nuclei with different Identities
Invited by : Roland Le Borgne
Although nuclei are defining features of eukaryotes, we still do not fully understand how the nuclear compartment is duplicated and partitioned during division. This is important, as the mechanism of nuclear division differs profoundly across systems. In studying this process in Drosophila neural stem cells, we recently found that the nuclear compartment persists during mitosis due to the maintenance of a mitotic nuclear lamina. This bounding spindle envelope is then asymmetrically remodelled and partitioned at division, giving rise to two daughter nuclei that profoundly differ in size (physical asymmetry) and envelope composition (molecular asymmetry).The asymmetry in the size of daughter nuclei following division results from: i) an asymmetric nuclear envelope resealing at mitotic exit that depends on the central spindle, and ii) a differential nuclear growth in early G1 that depends on the availability of ER/nuclear membranes reservoir in the cytoplasm. Furthermore, my data show that asymmetric nuclear division in this system is associated with a different chromatin organization between the two daughter nuclei as well as with an asymmetric distribution of several histone marks, before the cortical release of cell fate determinants. This suggests that the asymmetric remodelling of the nuclear envelope has profound functional consequences for these stem cell divisions. Taken together, these data make clear the importance of considering the path of nuclear re-modelling when investigating how a stem cell division generates two distinct sibling cells with different identities/fates.