Promotion of vesicular zinc efflux by ZIP13 and its implications for spondylocheiro dysplastic Ehlers–Danlos syndrome
Jeeyon Jeong, Joel M. Walker, Fudi Wang, J. Genevieve Park, Amy E. Palmer, Cecilia Giunta, Marianne Rohrbach, Beat Steinmann, and David J. Eide
Intracellular zinc is tightly controlled because zinc is essential but potentially toxic. Many organisms regulate zinc using storage vesicles/organelles, but whether mammals do so is unknown. Here, we show that human ZIP13 releases zinc from vesicular stores (pp. E3530–E3538). Previous studies found that mutations in the ZIP13 gene, SLC39A13, cause the spondylocheiro dysplastic form of Ehlers-Danlos syndrome (SCD-EDS) and speculated that ZIP13 exports zinc from the early secretory pathway and that zinc overload in the endoplasmic reticulum causes SCD-EDS. In contrast, our study suggests that SCD-EDS results from zinc deficiency in the endoplasmic reticulum resulting from zinc trapping in vesicular stores.
Orai-STIM–mediated Ca2+ release from secretory granules revealed by a targeted Ca2+ and pH probe
Eamonn J. Dickson, Joseph G. Duman, Mark W. Moody, Liangyi Chen, and Bertil Hille
Elevated cytoplasmic calcium modulates many cellular responses. Two Ca2+ sources feed most cytoplasmic Ca2+ elevations, the extracellular space and the endoplasmic reticulum. We found (pp. E3539–E3548) that secretory granules represent another Ca2+ source that releases Ca2+ in a physiologically interesting way. We developed a targeted probe for monitoring Ca2+ in secretory granules. It revealed a unique receptor-stimulated mechanism of Ca2+ release from secretory granules apparently involving “store-operated” Orai channels in the secretory granule membrane. The channels open when reticular stores are depleted. Such Ca2+ release from granules might elevate local Ca2+ concentrations and aid in the refilling of other cytoplasmic Ca2+ stores.
Use of biotinylated plasmid DNA as a surrogate for HSV DNA to identify proteins that repress or activate viral gene expression
Stephen Mallon, Bassam T. Wakim, and Bernard Roizman
DNA introduced into cells by infection or transfection is immediately coated by repressive histones and repressors. Viruses have evolved mechanisms to derepress their genes. What we know of these events is based on ChIP analyses that help identify the proteins involved in these processes, provided their identity is suspected and reagents are available. We report a procedure (pp. E3549–E3557) that enables identification of proteins hitherto not linked to these processes, based on the observation that HSV derepresses both viral DNA and DNAs introduced concurrently by transfection by using the transfected DNA as the surrogate for viral DNA.
Forward transport of proteins in the plasma membrane of migrating cerebellar granule cells
Dong Wang, Liang She, Ya-nan Sui, Xiao-bing Yuan, Yunqing Wen, and Mu-ming Poo
Newly differentiated neurons migrate over long distances to reach their proper destination in the developing brain. The mechanisms by which neurons accomplish this translocation remain to be clarified. By analyzing the trajectories of antibody-coated single quantum dots bound to specific plasma membrane proteins, we found (pp. E3558–E3567) that membrane proteins of migrating cultured cerebellar granule cells exhibited net forward translocation in a form of biased drift, which is superimposed upon Brownian motion, and that this biased drift appears to be driven by myosin II-dependent active transport processes. Thus, plasma membrane proteins undergo forward translocation in unison with cytoplasmic components in migrating neurons.