simultaneous-visualization-dynamics-crosslinked-single-microtubules

Simultaneous Visualization of the Dynamics of Crosslinked and Single Microtubules <em>In Vitro</em> by TIRF Microscopy

Microtubules are polymers of &#945;&#946;-tubulin heterodimers that organize into distinct structures in cells. Microtubule-based architectures and ...

Massachusetts General Hospital

Harvard Medical School

Social networks are increasingly recognized as important determinants of many chronic diseases, yet little data exist regarding the influence of social networks on diabetes. We surveyed diabetic patients to determine how social networks affect their overall level of concern regarding diabetes and its complications. We adapted a previously published instrument and surveyed 240 diabetic patients at two primary care practices. Patients recorded the number of family and friends who had diabetes and rated their level of concern about diabetes on a scale of 0% (no concern) to 100% (extremely concerned). Our primary outcome variable was patients' level of concern (<75% or ≥75%). We developed logistic regression models to determine the effect of disease burden in patients' social networks on expressed level of concern about diabetes. We received 154 surveys (64% response rate). We found that for each additional family member with diabetes, patients expressed a greater level of concern about diabetes (AOR 1.5; 95% CI 1.2-2.0) and its potential complications (AOR 1.4; 95% CI 1.1-1.7). Similarly, patients with an increased number of friends with diabetes expressed greater concern about diabetes (AOR 1.5; 95% CI 1.2-1.9) and its complications (AOR 1.3; 95% CI 1.1-1.7). Patients with a higher prevalence of diabetes within their social networks expressed greater concern about diabetes and diabetic complications. Determining disease burden within patients' social networks may allow physicians to better understand patients' perspectives on their disease and ultimately help them achieve meaningful behavioral change.

The influence of social networks on patients' attitudes toward type II diabetes.

The correct localization of Hedgehog effectors to the tip of primary cilia is critical for proper signal transduction. The conserved non-motile kinesin Kif7 defines a "cilium-tip compartment" by localizing to the distal ends of axonemal microtubules. How Kif7 recognizes microtubule ends remains unknown. We find that Kif7 preferentially binds GTP-tubulin at microtubule ends over GDP-tubulin in the mature microtubule lattice, and ATP hydrolysis by Kif7 enhances this discrimination. Cryo-electron microscopy (cryo-EM) structures suggest that a rotated microtubule footprint and conformational changes in the ATP-binding pocket underlie Kif7's atypical microtubule-binding properties. Finally, Kif7 not only recognizes but also stabilizes a GTP-form of tubulin to promote its own microtubule-end localization. Thus, unlike the characteristic microtubule-regulated ATPase activity of kinesins, Kif7 modulates the tubulin mechanochemical cycle. We propose that the ubiquitous kinesin fold has been repurposed in Kif7 to facilitate organization of a spatially restricted platform for localization of Hedgehog effectors at the cilium tip.

Interplay between the Kinesin and Tubulin Mechanochemical Cycles Underlies Microtubule Tip Tracking by the Non-motile Ciliary Kinesin Kif7.

A remarkable feature of the microtubule cytoskeleton is the coexistence of subpopulations having different dynamic properties. A prominent example is the anaphase spindle, where stable antiparallel bundles exist alongside dynamic microtubules and provide spatial cues for cytokinesis. How are the dynamics of spatially proximal arrays differentially regulated? We reconstitute a minimal system of three midzone proteins: microtubule-crosslinker PRC1 and its interactors CLASP1 and Kif4A, proteins that promote and suppress microtubule elongation, respectively. We find that their collective activity promotes elongation of single microtubules while simultaneously stalling polymerization of crosslinked bundles. This differentiation arises from (1) strong rescue activity of CLASP1, which overcomes the weaker effects of Kif4A on single microtubules, and (2) lower microtubule- and PRC1-binding affinity of CLASP1, which permits the dominance of Kif4A at overlaps. In addition to canonical mechanisms where antagonistic regulators set microtubule length, our findings illuminate design principles by which collective regulator activity creates microenvironments of arrays with distinct dynamic properties.

Differential regulation of single microtubules and bundles by a three-protein module.

The organization of micron-sized, multi-microtubule arrays from individual microtubules is essential for diverse cellular functions. The microtubule polymer is largely viewed as a passive building block during the organization process. An exception is the 'tubulin code' where alterations to tubulin at the amino acid level can influence the activity of microtubule-associated proteins. Recent studies reveal that micron-scale geometrical features of individual microtubules and polymer networks, such as microtubule length, overlap length, contact angle, and lattice defects, can also regulate the activity of microtubule-associated proteins and modulate polymer dynamics. We discuss how the interplay between such geometrical properties of the microtubule lattice and the activity of associated proteins direct multiple aspects of array organization, from microtubule nucleation and coalignment to specification of array dimensions and remodeling of dynamic networks. The mechanisms reviewed here highlight micron-sized features of microtubules as critical parameters to be routinely investigated in the study of microtubule self-organization.

Micron-scale geometrical features of microtubules as regulators of microtubule organization.

The C-terminal tail of tubulin influences microtubule assembly and stability. In this issue of Developmental Cell, Chen et al. combine in vitro experiments using recombinant tubulin with molecular dynamics simulations to provide molecular-level insights into the importance of α-tubulin tail and its post-translational modifications in microtubule assembly and stability.

Article	Year
The influence of social networks on patients' attitudes toward type II diabetes. Journal of community health\| PubMed ID: 21298473	2011
Interplay between the Kinesin and Tubulin Mechanochemical Cycles Underlies Microtubule Tip Tracking by the Non-motile Ciliary Kinesin Kif7. Developmental cell\| PubMed ID: 31031197	2019
Differential regulation of single microtubules and bundles by a three-protein module. Nature chemical biology\| PubMed ID: 34083810	2021
Micron-scale geometrical features of microtubules as regulators of microtubule organization. eLife\| PubMed ID: 34114950	2021
The tail wags the tubulin. Developmental cell\| PubMed ID: 34314694	2021

Nandini Mani

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