An optogenetic tool to study asymmetric cell division

It has been shown that two different pathways - the spindle and the polarity pathways- co-regulate the asymmetric division of neuroblasts (NBs). Moreover, it has recently been demonstrated that the spatio-temporal distribution and activation of Myosin is key to the establishment of sibling cell size asymmetry and the positioning of a basally shifted cleavage furrow. Before being enriched at the cleavage furrow, Myosin is initially cleared from the apical pole of the NB and subsequently from the basal pole.
In this context, polarity proteins and spindle cues appear to be key to the asymmetric distribution of Myosin. In particular, the apical polarity protein Pins plays a key role in controlling biased Myosin distribution. Additionally, the centralspindle cue Tumbleweed (Tum) has been reported to be required for the cortical flow of Myosin from the basal side towards the apical side. On the basal pole, the localization of the cargo protein Miranda, which segregates cell fate determinant into the GMC, has recently been shown to be actomyosin-dependent.
In this project, I sought to understand how physical asymmetry is established by manipulating spindle cue (Tum), polarity proteins (Pins and Miranda) and Myosin in vivo by using optogenetics. By using cellular optogenetics I found that: neither cortical recruitment of endogenous Tum nor cortical recruitment of a minimal photorecruitable spindle cue (generated by deletion analysis) resulted in premature induced furrowing at the site of activation; changing Pins dynamics by trapping it apically limited mitotic progression in a spindle assembly checkpoint-dependent manner and mitotic delay could be relieved by Cdk1 partial inhibition; neither ectopic localization of Myo activators (Rho kinase catalytic domain, Pebble DH catalytic domain (RhoGE-DHF in mammals), RhoAV14 (active RhoA) nor deactivators (Pp1-87B, Flapwing phosphatase domain), induced a phenotypic change during asymmetric cell division; cortical recruitment of a fully photorecruitable version of Mira induced ectopic furrowing after endogenous furrow closure; and cortical recruitment of Myo in a wt background but not in a mutant background induced changes in Myo dynamics.
In summary, I have developed an optogenetic toolbox to dissect in vivo asymmetric cell division. Using this toolbox, I found a novel link between polarity and cell cycle regulation and a surprising spatiotemporal limited capacity of centralspindle cue to induce furrowing. At this stage, further investigations are required to consolidate these conclusions.