In the latest issue of JCB, Strale et al. reveal that interactions between neighboring E-cadherin molecules help to strengthen their connection to the actin cytoskeleton and stabilize cell-cell contacts. As explained here, E-cadherin mutants unable to interact with other E-cadherin molecules in the same membrane can still form intercellular adherens junctions, but these junctions are weaker and cannot coordinate the movements of cells undergoing collective cell migration.
Donovan and Bretscher track the behavior of individual secretory vesicles in budding yeast in order to provide a timeline of the events involved in exocytosis. As detailed in this week’s In Focus, the researchers find that vesicles consistently tether to the bud cortex for 18 seconds before they fuse with the plasma membrane. This tethering period, which may allow cells to ensure vesicles are targeted to the right location, is regulated by the Rab GTPase Sec4p and the myosin motor Myo2p. The researchers also find that Myo2p dissociates from the vesicles about 4 seconds before fusion, in contrast to other components, such as the exocyst complex, that remain bound to vesicles until exocytosis is completed.
Nyathi and Pool describe how a chaperone complex called NAC helps ensure nascent polypeptides are correctly processed as they emerge from ribosomes. Many of the factors that modify, fold, or target nascent polypeptides bind to a particular region of ribosomes called the Universal Adaptor Site. As summarized here, Nyathi and Pool find that NAC regulates the competition between two processing factors: Map1, an enzyme that cleaves the N-terminal methionine off of most cytosolic proteins, and the SRP, which guides nascent secretory and membrane proteins to the ER. Moreover, NAC also prevents nascent secretory proteins from aggregating before they can be recognized by the SRP.
Yan et al. describe how the deubiquitinating enzyme complex BRISC regulates the mitotic spindle assembly factor NuMA. In the absence of BRISC, mitotic cells form disorganized, multipolar spindles because ubiquitinated NuMA shows an increased association with two of its regulators, importin-beta and dynein. More here.
Elsewhere, Bamidele et al. describe how cells regulate the endocytic trafficking and function of the CXCR4 chemokine receptor, and Treuner-Lange et al. explain how a small GTPase combines with bacterial actin to regulate bacterial focal adhesions and motility. You can hear the senior authors of both papers discuss their findings in this month’s biobytes podcast. Listen below or subscribe in iTunes!
As always, there are plenty of other interesting papers for you to discover in this week’s issue. You can find them all by visiting our table of contents page here.
Cover image showing the localization of NuMA (green) in monopolar spindles in the presence (bottom) or absence (top) of BRISC subunits © 2015 Yan et al.