Nuclear envelope budding: Getting large macromolecular complexes out of the nucleus.

Transport of macromolecules from the nucleus to the cytoplasm is essential for nearly all cellular and developmental events, and when mis-regulated, is associated with diseases, tumor formation/growth, and cancer progression. Nuclear Envelope (NE)-budding is a newly appreciated nuclear export pathway for large macromolecular machineries, including those assembled to allow co-regulation of functionally related components, that bypasses canonical nuclear export through nuclear pores. In this pathway, large macromolecular complexes are enveloped by the inner nuclear membrane, transverse the perinuclear space, and then exit through the outer nuclear membrane to release its contents into the cytoplasm. NE-budding is a conserved process and shares many features with nuclear egress mechanisms used by herpesviruses. Despite its biological importance and clinical relevance, little is yet known about the regulatory and structural machineries that allow NE-budding to occur in any system. Here we summarize what is currently known or proposed for this intriguing nuclear export process.

Centralspindlin is required for thorax development during Drosophila metamorphosis.

Epithelial morphogenesis is an essential process in all metazoans during both normal development and pathological processes such as wound healing. The coordinated regulation of cell shape, cell size, and cell adhesion during the migration of epithelial sheets ultimately gives rise to the diversity of body plans among different organisms as well as the diversity of cellular structures and tissues within an organism. Metamorphosis of the Drosophila pupa is an excellent system to study these transformative events. During pupal development, the cells of the wing imaginal discs migrate dorsally and fuse to form the adult thorax. Here I show centralspindlin, a protein complex well known for its role in cytokinesis, is essential for migration of wing disc cells and proper thorax closure. I show the subcellular localization of centralspindlin is important for its function in thorax development. This study demonstrates the emerging role of centralspindlin in regulating cell migration and cell adhesion in addition to its previously known function during cytokinesis.

Ser/Thr kinase Trc controls neurite outgrowth in Drosophila by modulating microtubule-microtubule sliding.

Correct neuronal development requires tailored neurite outgrowth. Neurite outgrowth is driven in part by microtubule-sliding - the transport of microtubules along each other. We have recently demonstrated that a 'mitotic' kinesin-6 (Pavarotti in Drosophila) effectively inhibits microtubule-sliding and neurite outgrowth. However, mechanisms regulating Pavarotti itself in interphase cells and specifically in neurite outgrowth are unknown. Here, we use a combination of live imaging and biochemical methods to show that the inhibition of microtubule-sliding by Pavarotti is controlled by phosphorylation. We identify the Ser/Thr NDR kinase Tricornered (Trc) as a Pavarotti-dependent regulator of microtubule sliding in neurons. Further, we show that Trc-mediated phosphorylation of Pavarotti promotes its interaction with 14-3-3 proteins. Loss of 14-3-3 prevents Pavarotti from associating with microtubules. Thus, we propose a pathway by which microtubule-sliding can be up- or downregulated in neurons to control neurite outgrowth, and establish parallels between microtubule-sliding in mitosis and post-mitotic neurons.

Centralspindlin Recruits ALIX to the Midbody during Cytokinetic Abscission in Drosophila via a Mechanism Analogous to Virus Budding.

Abscission, the final step of cytokinesis, cleaves the thin intercellular bridge connecting the two daughter cells [1-6]. The scaffold protein ALIX is a core component of the abscission machinery with an evolutionarily conserved role in midbody recruitment of ESCRT-III [7-11], which mediates the final cut [1-5, 8-10, 12-14]. In mammalian cells, the centralspindlin complex recruits the major midbody organizer CEP55 that directly binds and recruits ALIX and ESCRT-I [7-9, 15-17], which in turn cooperatively recruit ESCRT-III [8, 9, 18]. However, CEP55 is missing in Drosophila melanogaster and other invertebrates [6, 9, 19], and it is unknown how the abscission machinery is recruited to the midbody in the absence of CEP55. Here, we address how Drosophila ALIX is recruited to the midbody. Surprisingly, ALIX localizes to the midbody via its V-domain, independently of the GPPX3Y motif in the proline-rich region that recruits human ALIX [8, 9]. We elucidate that the centralspindlin component Pavarotti (H.s.MKLP1) interacts with the V-domain of ALIX to recruit it to the midbody. Specifically, our results indicate that an LxxLF motif in Pavarotti directly interacts with a conserved hydrophobic pocket in the ALIX V-domain, which in human ALIX binds (L)YPXnL/LxxLF motifs of virus proteins [20-28]. Thus, our study identifies that ALIX is recruited by an analogous mechanism during abscission in Drosophila as during virus budding in mammalian cells and an ancestral role for centralspindlin in recruiting the abscission machinery to the midbody.