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Recent studies of border cells in the Drosophila melanogaster ovary have identified a novel mechanism that is involved in cell migration. Binding of the minus-end-directed motor, Myosin VI, to the cell adhesion molecule, DE-Cadherin, stabilizes the cadherin–catenin complex. This interaction might promote the formation of long cellular extensions (LCEs) at the leading edge of migrating border cells.
Using sophisticated fluorescence microscopy, polymerization of single actin filaments can now be observed directly. Recent experiments show that the ends of actin filaments grow and shorten more rapidly than would be predicted from measured rate constants for monomer association and dissociation. This suggests that actin filaments may undergo a type of dynamic instability, similar to microtubules, or even use a previously uncharacterized mechanism to drive filament turnover.
Guanine nucleotide-exchange factors (GEFs) interact with and activate members of the Rho family of small GTPases through Dbl homology (DH) domains. A new domain has been found in DOCK180 and shown to specifically activate Rho proteins. Interestingly, this module does not contain any homology to Dbl sequences.
Specification of one neurite as the axon is the first milestone achieved as neuronal polarity is established. It is clear that regional changes in the cytoskeleton underlie axonal differentiation, but is one cytoskeletal element any more crucial than the others? Although early studies implicated microtubules, more recent studies have focused on the actin cytoskeleton as the potential hub for factors that influence axonal differentiation. Now, studies on a novel protein called CRMP-2 have shifted attention back to microtubules.
Modulating the cell cycle is essential for viral replication and infection. HIV is an expert at manipulating these processes. New work now shows how apoptosis of CD4/CXCR4-expressing T cells during the course of HIV-infection is intimately connected to aberrant cell-cycle regulation.
Extracellular stimuli transmit information to cells by activating receptor-dependent signal-transduction cascades, most typically involving tyrosine and serine/threonine kinases. The cell's response to the activation of these kinases depends on the duration of their signals. New work now shows how cells sense the duration of an ERK signal in the G1 phase of the cell cycle. The study suggests that a common mechanism for sensing ERK signal duration may be involved in diverse cellular functions.
To move between different parts of their hosts, most plant viruses exploit the phloem. Plants exposed to subtoxic levels of cadmium ions can resist this viral highjacking of their transportation network. New work in this issue of Nature Cell Biology has identified a novel, chemically induced, glycine-rich protein that is responsible for inhibiting the long-distance movement of turnip vein clearing tobamovirus (TVCV) in tobacco plants.
Engulfment of pathogens by phagocytosis requires the coordination of actin assembly and progressive 'zippering' of pseudopodial membranes around the particle. Recent work shows that Myosin-X, which binds phosphatidylinositol-3-OH kinase (PI(3)K) products through its pleckstrin homology (PH) domains, is required for phagocytosis, thereby providing a molecular basis for the function of PI(3)K in pseudopod extension.
Inhibitor of apoptosis proteins (IAPs) are critical regulators of apoptosis. Recent evidence suggests that in some situations, induction of apoptosis initiates general repression of translation, as well as the targeted ubiquitination and degradation of IAPs.
The tumour suppressor protein p53 is stabilized by the de-ubiquitination enzyme herpes-virus-associated ubiquitin-specific protease (HAUSP), which localizes to the promyelocytic leukaemia nuclear body (PML-NB). The pro-apoptotic activity of p53 is also induced by HAUSP. Therefore, p53 ubiquitination is a dynamic process, and HAUSP might function as a tumour suppressor by enhancing p53 stabilization.
The link between hearing and reproduction has been made before, as in William Shakespeare's Twelfth Night1. Now, a paper in the current issue of Nature Cell Biology demonstrates that these two processes have an unforeseen degree of structural similarities2.
The Par-1/MARK kinases have a conserved role in cell polarization and are required to establish the anterior–posterior axis of Caenorhabditis elegans and Drosophila melanogaster. Now, elegant studies in Drosophila uncover the posterior patterning molecule Oskar (Osk) as a direct target of Par-1. Phosphorylation of Oskar at the posterior pole stabilizes the protein and contributes to its localized accumulation at high levels.
