Uncharacterized bacterial structures revealed by electron cryotomography

Electron cryotomography (ECT) can reveal the native structure and arrangement of macromolecular complexes inside intact cells. This technique has greatly advanced our understanding of the ultrastructure of bacterial cells. We now view bacteria as structurally complex assemblies of macromolecular machines rather than as undifferentiated bags of enzymes. To date, our group has applied ECT to nearly 90 different bacterial species, collecting more than 15,000 cryotomograms. In addition to known structures, we have observed, to our knowledge, several uncharacterized features in these tomograms. Some are completely novel structures; others expand the features or species range of known structure types. Here, we present a survey of these uncharacterized bacterial structures in the hopes of accelerating their identification and study, and furthering our understanding of the structural complexity of bacterial cells

Loss of Navβ4-Mediated Regulation of Sodium Currents in Adult Purkinje Neurons Disrupts Firing and Impairs Motor Coordination and Balance

Summary: The resurgent component of voltage-gated Na+ (Nav) currents, INaR, has been suggested to provide the depolarizing drive for high-frequency firing and to be generated by voltage-dependent Nav channel block (at depolarized potentials) and unblock (at hyperpolarized potentials) by the accessory Navβ4 subunit. To test these hypotheses, we examined the effects of the targeted deletion of Scn4b (Navβ4) on INaR and on repetitive firing in cerebellar Purkinje neurons. We show here that Scn4b−/− animals have deficits in motor coordination and balance and that firing rates in Scn4b−/− Purkinje neurons are markedly attenuated. Acute, in vivo short hairpin RNA (shRNA)-mediated “knockdown” of Navβ4 in adult Purkinje neurons also reduced spontaneous and evoked firing rates. Dynamic clamp-mediated addition of INaR partially rescued firing in Scn4b−/− Purkinje neurons. Voltage-clamp experiments revealed that INaR was reduced (by ∼50%), but not eliminated, in Scn4b−/− Purkinje neurons, revealing that additional mechanisms contribute to generation of INaR. : Loss of Navβ4 attenuates, but does not eliminate, the resurgent sodium current (INaR) in cerebellar Purkinje neurons, revealing that additional mechanism(s) contribute to the generation of INaR. Ransdell et al. also find that INaR magnitude tunes the firing rate of Purkinje neurons and that Navβ4−/− animals display balance and motor deficits. Keywords: cerebellum, resurgent sodium current, Scn4b−/−, Scn4b-targeted shRNA, dynamic clam