Expression of the phosphomimetic Travel E protein caused a marked increase in the number of multinucleated cells compared with WT or unphosphorylatable Travel F proteins (Fig. abscission. GNE-6640 Control of abscission requires Eph kinase activity, and Src and citron kinase (CitK) are downstream effectors in the Eph-induced signal transduction cascade. CitK is usually phosphorylated on tyrosines in neural progenitors in vivo, and Src kinase directly phosphorylates CitK. We have recognized the specific tyrosine residues of CitK that NS1 are phosphorylated and show that tyrosine phosphorylation of CitK impairs cytokinesis. Finally, we show that, much like CitK, Ephrin/Eph signaling controls neuronal ploidy in the developing neocortex. Our study indicates that CitK integrates intracellular and extracellular signals provided by the local environment to coordinate completion of cytokinesis. Introduction Cytokinesis is the last step of cell division, allowing physical separation of the two child cells and faithful partitioning of genetic and cytoplasmic material (Green et al., 2012; Mierzwa and Gerlich, GNE-6640 2014). Tight control of cytokinesis completion is essential because cytokinesis failure has been associated with carcinogenesis (Sagona and Stenmark, 2010), but also because incomplete cytokinesis is an evolutionarily conserved physiological event required for development and homeostasis of several tissues harboring polyploid cells (Davoli and GNE-6640 de Lange, 2011; Haglund et al., 2011). Cytokinesis begins with the assembly of an equatorial contractile ring whose constriction allows the formation of a thin intercellular bridge (ICB) between the nascent child cells. Physical separation of the two daughter cells, also called abscission, ends cytokinesis. Completion of abscission requires the coordination of several cellular functions such as membrane trafficking, lipid turnover, cytoskeletal rearrangements, and orderly recruitment of molecular complexes to the midbody (Agromayor and Martin-Serrano, 2013; Mierzwa and Gerlich, 2014; Cauvin and Echard, 2015). One of the grasp regulators of cytokinesis is the small GTPase RhoA, whose accumulation at the equatorial cell cortex is the first event of cytokinesis, participating in specifying the position and promoting assembly and contraction of the actomyosin ring (Bement et al., 2005). After cleavage furrow ingression, active RhoA participates in the stabilization of the ICB by recruiting other proteins to the midbody, including Anillin and citron kinase (CitK; Madaule et al., 1998; Hickson and OFarrell, 2008). At late GNE-6640 stages of cytokinesis, the cytoskeleton is usually cleared from your ICB; disassembly of actin filaments requires inactivation of RhoA and changes in lipid composition of the plasma membrane (Emoto et al., 2005; Saurin et al., 2008; Dambournet et al., 2011), whereas microtubule severing is usually accomplished by spastins (Connell et al., 2009). Lastly, components of the ESCRT (endosomal sorting complexes required for transport) complex are recruited to the ICB, and membrane abscission ensues (Morita et al., 2007). A key player in the maintenance of RhoA at the midbody is usually CitK, a protein that itself localizes to the midbody (Madaule et al., 1998; Naim et al., 2004; Bassi et al., 2011, 2013; Gai et al., 2011). Although CitK was first thought to be important for contraction of the equatorial actomyosin ring via phosphorylation of MLC2, it has more recently emerged that CitK is in fact dispensable for these actions and that its role is usually primarily to act as a scaffold protein during late cytokinesis and abscission (Naim et al., 2004; Gai et al., 2011; Serres et al., 2012; Watanabe et al., 2013). Indeed, CitK loss of function causes abscission defects with frequent reopening of the ICB, causing multinucleation (Echard et al., 2004; Gai et al., 2011; Watanabe et al., 2013). In mammals, CitK is usually purely required for cytokinesis of a limited quantity of cell types, including neural progenitors of the developing neocortex. Accordingly, loss of CitK impairs cytokinesis of these cells, leading to an increase in the number of binucleated and polyploid neurons as well as neuronal cell death (Di Cunto et al., 2000; Sarkisian et al., 2002; LoTurco et al., 2003; Sgro et al., 2016). In solid organs, dividing cells are a part of tissues, and recent studies suggest that in addition to intracellular events, successful cytokinesis requires coordination with extracellular processes (Herszterg et al., 2014; Le Bras and Le Borgne, 2014). For instance, cooperation between dividing cells and their neighbors is necessary to remodel cell adhesion.
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