Microtubules under mechanical pressure can breach dense actin networks.

The crosstalk between the actin network and microtubules is essential for cell polarity. It orchestrates microtubule organization within the cell, driven by the asymmetry of actin architecture along the cell periphery. The physical intertwining of these networks regulates spatial organization and force distribution in the microtubule network. Although their biochemical interactions are becoming clearer, the mechanical aspects remain less understood. To explore this mechanical interplay, we developed an in vitro reconstitution assay to investigate how dynamic microtubules interact with various actin filament structures. Our findings revealed that microtubules can align and move along linear actin filament bundles through polymerization force. However, they are unable to pass through when encountering dense branched actin meshworks, similar to those present in the lamellipodium along the periphery of the cell. Interestingly, immobilizing microtubules through crosslinking with actin or other means allow the buildup of pressure, enabling them to breach these dense actin barriers. This mechanism offers insights into microtubule progression towards the cell periphery, with them overcoming obstacles within the denser parts of the actin network and ultimately contributing to cell polarity establishment.

Noninvasive Respiratory Support as an Alternative to Tracheostomy in Severe Laryngomalacia.

OBJECTIVES/HYPOTHESIS: To analyze the role of noninvasive respiratory support (NRS) as an alternative to tracheostomy in the management of severe laryngomalacia. STUDY DESIGN: We conducted a monocentric retrospective study in a tertiary pediatric care center. METHODS: All children under the age of 3 years with severe laryngomalacia, treated between January 2014 and December 2019, were included. Patient demographics, medical history, nutrition, surgery, NRS, and outcome were reviewed. Predictors for NRS were analyzed. RESULTS: One hundred and eighty-eight patients were included. Mean age was 4 ± 5 months and mean weight was 4,925 ± 1,933 g. An endoscopic bilateral supraglottoplasty was performed in 183 (97%) patients and successful in 159 (87%). NRS was initiated in 29 (15%) patients at a mean age of 3 ± 2 months (1-11 months): 15 (52%) patients were treated with NRS after surgical failure, 9 (31%) were treated with NRS initiated prior to surgery because of abnormal overnight gas exchange, and 5 (17%) were treated exclusively with NRS due to comorbidities contraindicating an endoscopic procedure. NRS was successfully performed in all patients with a mean duration of 6 ± 11 months. No patient required a tracheostomy. Univariate analysis identified the following predictors of NRS: neonatal respiratory distress (P = .003), neurological comorbidity (P < .001), associated laryngeal abnormality (P < .001), cardiac surgery (P = .039), surgical endoscopic revision (P = .007), and nutritional support (P < .001). CONCLUSION: NRS is a safe procedure, which may avoid a tracheostomy in severe laryngomalacia, in particular, in case of endoscopic surgery failure, respiratory failure before surgery, and/or severe co-morbidity. LEVEL OF EVIDENCE: 3 Laryngoscope, 132:1861-1868, 2022.

Kinesin-6 Klp9 orchestrates spindle elongation by regulating microtubule sliding and growth.

Mitotic spindle function depends on the precise regulation of microtubule dynamics and microtubule sliding. Throughout mitosis, both processes have to be orchestrated to establish and maintain spindle stability. We show that during anaphase B spindle elongation in Schizosaccharomyces pombe, the sliding motor Klp9 (kinesin-6) also promotes microtubule growth in vivo. In vitro, Klp9 can enhance and dampen microtubule growth, depending on the tubulin concentration. This indicates that the motor is able to promote and block tubulin subunit incorporation into the microtubule lattice in order to set a well-defined microtubule growth velocity. Moreover, Klp9 recruitment to spindle microtubules is dependent on its dephosphorylation mediated by XMAP215/Dis1, a microtubule polymerase, creating a link between the regulation of spindle length and spindle elongation velocity. Collectively, we unravel the mechanism of anaphase B, from Klp9 recruitment to the motors dual-function in regulating microtubule sliding and microtubule growth, allowing an inherent coordination of both processes.