Tau is an abundant microtubule-associated protein in neurons. Tau aggregation into insoluble fibrils is a hallmark of Alzheimer's disease and other dementias 1 , yet the physiological state of tau molecules within cells remains unclear. Using single molecule imaging, we directly observe that the microtubule lattice regulates reversible tau self-association, leading to localized, dynamic condensation of tau molecules on the microtubule surface. Tau condensates form selectively permissible barriers, spatially regulating the activity of microtubule severing enzymes and the movement of molecular motors through their boundaries. We propose that reversible selfassociation of tau molecules, gated by the microtubule lattice, is an important mechanism of tau's biological functions, and that oligomerization of tau is a common property shared between the physiological and disease forms of the molecule.

Background Type-2 diabetes and obesity independently increases the risk of heart failure via incompletely understood mechanisms. We propose that hyperinsulinemia might promote adverse consequences in hearts of subjects with type-2 diabetes and obesity. Methods High fat diet feeding was used to induce obesity and diabetes in wild type mice or mice lacking β2-adrenergic receptor (β2AR) or β-arrestin2. Wild type mice fed with high fat diet were treated with β-blocker carvedilol or G-protein receptor kinase 2 (GRK2) inhibitor. We examined the signaling and cardiac contractile function. Results High fat diet feeding selectively increases the expression of phosphodiesterase 4D (PDE4D) in mouse hearts, in concert with reduced PKA phosphorylation of phospholamban, which contributes to systolic and diastolic dysfunction. The expression of PDE4D is also elevated in human hearts with diabetes. The induction of PDE4D expression is mediated by an insulin receptor, insulin receptor substrate, and (GRK2) and β-arrestin2-dependent transactivation of a β2AR-ERK signaling cascade. Thus pharmacological inhibition of β2AR or GRK2, or genetic deletion of β2AR or β-arrestin2, all significantly attenuate insulin-induced phosphorylation of ERK and PDE4D induction, to prevent diabetes-related contractile dysfunction. Conclusions These studies elucidate a novel mechanism by which hyperinsulinemia contributes to heart failure by increasing PDE4D expression and identify β2AR or GRK2 as plausible therapeutic targets for preventing or treating heart failure in subjects with type-2 diabetes.

Tau is an abundant microtubule-associated protein in neurons. Tau aggregation into insoluble fibrils is a hallmark of Alzheimer's disease and other dementias, yet the physiological state of tau molecules within cells remains unclear. Using single molecule imaging, we directly observe that the microtubule lattice regulates reversible tau selfassociation, leading to dynamic condensation of tau molecules on the microtubule surface. Tau condensates form selectively permissible barriers, spatially regulating the activity of MT severing enzymes and the movement of molecular motors through their boundaries. We propose that reversible self-association of tau molecules, controlled by the microtubule, is an important mechanism of tau's biological functions, and that oligomerization of tau is a common property shared between the physiological and disease forms of the molecule.

Dyneins make up a family of AAA+ motors that move toward the minus end of microtubules. Cytoplasmic dynein is responsible for transporting intracellular cargos in interphase cells and mediating spindle assembly and chromosome positioning during cell division. Other dynein isoforms transport cargos in cilia and power ciliary beating. Dyneins were the least studied of the cytoskeletal motors due to challenges in the reconstitution of active dynein complexes in vitro and the scarcity of high-resolution methods for in-depth structural and biophysical characterization of these motors. These challenges have been recently addressed, and there have been major advances in our understanding of the activation, mechanism, and regulation of dyneins. This review synthesizes the results of structural and biophysical studies for each class of dynein motors. We highlight several outstanding questions about the regulation of bidirectional transport along microtubules and the mechanisms that sustain self-coordinated oscillations within motile cilia.