Depolymerizing kinesins Kip3 and MCAK shape cellular microtubule architecture by differential control of catastrophe.

Microtubules are dynamic filaments whose ends alternate between periods of slow growth and rapid shortening as they explore intracellular space and move organelles. A key question is how regulatory proteins modulate catastrophe, the conversion from growth to shortening. To study this process, we reconstituted microtubule dynamics in the absence and presence of the kinesin-8 Kip3 and the kinesin-13 MCAK. Surprisingly, we found that, even in the absence of the kinesins, the microtubule catastrophe frequency depends on the age of the microtubule, indicating that catastrophe is a multistep process. Kip3 slowed microtubule growth in a length-dependent manner and increased the rate of aging. In contrast, MCAK eliminated the aging process. Thus, both kinesins are catastrophe factors; Kip3 mediates fine control of microtubule length by narrowing the distribution of maximum lengths prior to catastrophe, whereas MCAK promotes rapid restructuring of the microtubule cytoskeleton by making catastrophe a first-order random process.

Rapid microtubule self-assembly kinetics.

Microtubule assembly is vital for many fundamental cellular processes. Current models for microtubule assembly kinetics assume that the subunit dissociation rate from a microtubule tip is independent of free subunit concentration. Total-Internal-Reflection-Fluorescence (TIRF) microscopy experiments and data from a laser tweezers assay that measures in vitro microtubule assembly with nanometer resolution, provides evidence that the subunit dissociation rate from a microtubule tip increases as the free subunit concentration increases. These data are consistent with a two-dimensional model for microtubule assembly, and are explained by a shift in microtubule tip structure from a relatively blunt shape at low free concentrations to relatively tapered at high free concentrations. We find that because both the association and the dissociation rates increase at higher free subunit concentrations, the kinetics of microtubule assembly are an order-of-magnitude higher than currently estimated in the literature.

Low tension recruits the yeast Aurora B protein Ipl1 to centromeres in metaphase.

Accurate genome segregation in mitosis requires that all chromosomes are bioriented on the spindle. Cells monitor biorientation by sensing tension across sister centromeres. Chromosomes that are not bioriented have low centromere tension, which allows Aurora B (yeast Ipl1) to perform error correction that locally loosens kinetochore-microtubule attachments to allow detachment of microtubules and fresh attempts at achieving biorientation. However, it is not known whether low tension recruits Aurora B to centromeres or, alternatively, whether low tension directly activates Aurora B already localized at centromeres. In this work, we experimentally induced low tension in metaphase Saccharomyces cerevisiae yeast cells, then monitored Ipl1 localization. We find low tension recruits Ipl1 to centromeres. Furthermore, low tension-induced Ipl1 recruitment depended on Bub1, which is known to provide a binding site for Ipl1. In contrast, Top2, which can also recruit Ipl1 to centromeres, was not required. Our results demonstrate cells are sensitive to low tension at centromeres and respond by actively recruiting Ip1l for error correction.

Kinesin-14 motors participate in a force balance at microtubule plus-ends to regulate dynamic instability.

Kinesin-14 molecular motors represent an essential class of proteins that bind microtubules and walk toward their minus-ends. Previous studies have described important roles for Kinesin-14 motors at microtubule minus-ends, but their role in regulating plus-end dynamics remains controversial. Kinesin-14 motors have been shown to bind the EB family of microtubule plus-end binding proteins, suggesting that these minus-end-directed motors could interact with growing microtubule plus-ends. In this work, we explored the role of minus-end-directed Kinesin-14 motor forces in controlling plus-end microtubule dynamics. In cells, a Kinesin-14 mutant with reduced affinity to EB proteins led to increased microtubule lengths. Cell-free biophysical microscopy assays were performed using Kinesin-14 motors and an EB family marker of growing microtubule plus-ends, Mal3, which revealed that when Kinesin-14 motors bound to Mal3 at growing microtubule plus-ends, the motors subsequently walked toward the minus-end, and Mal3 was pulled away from the growing microtubule tip. Strikingly, these interactions resulted in an approximately twofold decrease in the expected postinteraction microtubule lifetime. Furthermore, generic minus-end-directed tension forces, generated by tethering growing plus-ends to the coverslip using λ-DNA, led to an approximately sevenfold decrease in the expected postinteraction microtubule growth length. In contrast, the inhibition of Kinesin-14 minus-end-directed motility led to extended tip interactions and to an increase in the expected postinteraction microtubule lifetime, indicating that plus-ends were stabilized by nonmotile Kinesin-14 motors. Together, we find that Kinesin-14 motors participate in a force balance at microtubule plus-ends to regulate microtubule lengths in cells.

Recommendations for 46,XY Disorders/Differences of Sex Development Across Two Decades: Insights from North American Pediatric Endocrinologists and Urologists.

Clinical decision-making for individuals with 46,XY disorders/differences of sex development (DSD) remains unsettled and controversial. The North American DSD Clinician Survey examines the recommendations of a large group of clinical specialists over the last two decades. Active members of the (Lawson Wilkins) Pediatric Endocrine Society and the Societies for Pediatric Urology were invited to respond to a web-based survey at three different timepoints: 2003-2004 (T1), 2010-2011 (T2), and 2019-2020 (T3). Data from 429 participants in T1, 435 in T2, and 264 in T3 were included in this study. The participants were presented with three XY newborn clinical case scenarios-micropenis, partial androgen insensitivity syndrome, and iatrogenic penile ablation-and asked for clinical management recommendations. The main outcomes assessed included the recommended gender of rearing, surgical decision-maker (parent or patient), timing of genital surgery, and age at which to disclose medical details and surgical history to the patient. For all scenarios, the overwhelming majority recommended rearing as male, including a significant increase across timepoints in those recommending a male gender of rearing for the infant with penile ablation. The proportions recommending female gender of rearing declined significantly across timepoints. In general, most recommended parents (in consultation with the physician) serve as surgical decision-makers, but these proportions declined significantly across timepoints. Recommendations on the timing of surgery varied based on the patient's gender and type of surgery. There has been a shift in recommendations away from the "optimal gender policy" regarding gender of rearing and surgical interventions for patients with XY DSD.

Recommendations for 46,XX Congenital Adrenal Hyperplasia Across Two Decades: Insights from the North American Differences of Sex Development Clinician Survey.

Several aspects of clinical management of 46,XX congenital adrenal hyperplasia (CAH) remain unsettled and controversial. The North American Disorders/Differences of Sex Development (DSD) Clinician Survey investigated changes, over the last two decades, in clinical recommendations by specialists involved in the management of newborns with DSD. Members of the (Lawson Wilkins) Pediatric Endocrine Society and the Societies for Pediatric Urology participated in a web-based survey at three timepoints: 2003-2004 (T1, n = 432), 2010-2011 (T2, n = 441), and 2020 (T3, n = 272). Participants were presented with two clinical case scenarios-newborns with 46,XX CAH and either mild-to-moderate or severe genital masculinization-and asked for clinical recommendations. Across timepoints, most participants recommended rearing the newborn as a girl, that parents (in consultation with physicians) should make surgical decisions, performing early genitoplasty, and disclosing surgical history at younger ages. Several trends were identified: a small, but significant shift toward recommending a gender other than girl; recommending that adolescent patients serve as the genital surgery decision maker; performing genital surgery at later ages; and disclosing surgical details at younger ages. This is the first study assessing physician recommendations across two decades. Despite variability in the recommendations, most experts followed CAH clinical practice guidelines. The observation that some of the emerging trends do not align with expert opinion or empirical evidence should serve as both a cautionary note and a call for prospective studies examining patient outcomes associated with these changes.

UNC-45A breaks the microtubule lattice independently of its effects on non-muscle myosin II.

In invertebrates, UNC-45 regulates myosin stability and functions. Vertebrates have two distinct isoforms of the protein: UNC-45B, expressed in muscle cells only, and UNC-45A, expressed in all cells and implicated in regulating both non-muscle myosin II (NMII)- and microtubule (MT)-associated functions. Here, we show that, in vitro and in human and rat cells, UNC-45A binds to the MT lattice, leading to MT bending, breakage and depolymerization. Furthermore, we show that UNC-45A destabilizes MTs independent of its C-terminal NMII-binding domain and even in the presence of the NMII inhibitor blebbistatin. These findings identified UNC-45A as a novel type of MT-severing protein with a dual non-mutually exclusive role in regulating NMII activity and MT stability. Because many human diseases, from cancer to neurodegenerative diseases, are caused by or associated with deregulation of MT stability, our findings have profound implications in the biology of MTs, as well as the biology of human diseases and possible therapeutic implications for their treatment.This article has an associated First Person interview with the joint first authors of the paper.

Chromosome congression by Kinesin-5 motor-mediated disassembly of longer kinetochore microtubules.

During mitosis, sister chromatids congress to the spindle equator and are subsequently segregated via attachment to dynamic kinetochore microtubule (kMT) plus ends. A major question is how kMT plus-end assembly is spatially regulated to achieve chromosome congression. Here we find in budding yeast that the widely conserved kinesin-5 sliding motor proteins, Cin8p and Kip1p, mediate chromosome congression by suppressing kMT plus-end assembly of longer kMTs. Of the two, Cin8p is the major effector and its activity requires a functional motor domain. In contrast, the depolymerizing kinesin-8 motor Kip3p plays a minor role in spatial regulation of yeast kMT assembly. Our analysis identified a model where kinesin-5 motors bind to kMTs, move to kMT plus ends, and upon arrival at a growing plus end promote net kMT plus-end disassembly. In conclusion, we find that length-dependent control of net kMT assembly by kinesin-5 motors yields a simple and stable self-organizing mechanism for chromosome congression.

Mitigating Radiotoxicity in the Central Nervous System: Role of Proton Therapy.

OPINION STATEMENT: Central nervous system (CNS) radiotoxicity remains a challenge in neuro-oncology. Dose distribution advantages of protons over photons have prompted increased use of brain-directed proton therapy. While well-recognized among pediatric populations, the benefit of proton therapy among adults with CNS malignancies remains controversial. We herein discuss the role of protons in mitigating late CNS radiotoxicities in adult patients. Despite limited clinical trials, evidence suggests toxicity profile advantages of protons over conventional radiotherapy, including retention of neurocognitive function and brain volume. Modelling studies predict superior dose conformality of protons versus state-of-the-art photon techniques reduces late radiogenic vasculopathies, endocrinopathies, and malignancies. Conversely, potentially higher brain tissue necrosis rates following proton therapy highlight a need to resolve uncertainties surrounding the impact of variable biological effectiveness of protons on dose distribution. Clinical trials comparing best photon and particle-based therapy are underway to establish whether protons substantially improve long-term treatment-related outcomes in adults with CNS malignancies.

Examining the Effectiveness of an Intensive Telemental Health Treatment for Pediatric Anxiety and OCD During the COVID-19 Pandemic and Pediatric Mental Health Crisis.

Despite research supporting the efficacy of weekly outpatient videoconferencing-based cognitive behavioral therapy (VCBT), limited evidence exists about the benefits of leveraging VCBT for brief intensive formats. We examined the effectiveness of an intensive outpatient VCBT targeting pediatric anxiety and OCD. Quasi-experimental design was used to compare outcomes of intensive, in-person, group-based cognitive-behavioral therapy with medication management and caregiver guidance pre-pandemic, to a similar VCBT peri-pandemic (n = 130). Pretreatment and posttreatment assessments included patient- and caregiver-report of anxiety and functional impairment. Analyses of covariance were conducted, examining changes in anxiety and impairment between treatment groups, controlling for admission levels. No significant differences in posttreatment anxiety or impairment were observed between conditions. This study illustrates that intensive, group-based treatment for pediatric anxiety and OCD using VCBT is associated with comparable reductions in anxiety and impairment. It marks a crucial step toward providing broader access to quality care for youth in need.

Feasibility and Acceptance of Direct-to-Home Tele-neuropsychology Services during the COVID-19 Pandemic.

OBJECTIVE: Neuropsychological assessment via video conferencing has been proposed during the COVID-19 pandemic. Existing literature has demonstrated feasibility and acceptance of neuropsychological measures administered by videoconference, although few studies have examined feasibility and patient acceptance of TNP visits directly to patients' homes (DTH-TNP). METHODS: We modified a previously published patient satisfaction survey for DTH-TNP and developed a clinician feasibility survey to examine experiences during DTH-TNP. RESULTS: Seventy-two patients (age range: preschool-geriatric) evaluated by DTH-TNP for cognitive problems at an academic medical center responded to voluntary surveys between April 20, 2020, and August 19, 2020, and 100% indicated satisfaction. Fifty-nine percent of patients reported limitations (e.g., technological concern) during the appointment. 134 clinician surveys were collected and indicated that clinicians achieved the goal of their appointment in 90% of encounters. CONCLUSIONS: These qualitative data suggest that patients and clinicians found DTH-TNP to be satisfactory during the COVID-19 pandemic, while also recognizing limitations of the practice. These results are limited in that voluntary surveys are subject to bias. They support the growing body of literature suggesting that DTH-TNP provides a valuable service, though additional research to establish reliability and validity is needed.

Differences/Disorders of Sex Development: Medical Conditions at the Intersection of Sex and Gender.

Defined as congenital conditions in which development of chromosomal, gonadal, or anatomic sex is atypical, differences or disorders of sex development (DSDs) comprise many discrete diagnoses ranging from those associated with few phenotypic differences between affected and unaffected individuals to those where questions arise regarding gender of rearing, gonadal tumor risk, genital surgery, and fertility. Controversies exist in numerous areas including how DSDs are conceptualized, how to refer to the set of conditions and those affected by them, and aspects of clinical management that extend from social media to legislative bodies, courts of law, medicine, clinical practice, and scholarly research in psychology and sociology. In addition to these aspects, this review covers biological and social influences on psychosocial development and adjustment, the psychosocial and psychosexual adaptation of people born with DSDs, and roles for clinical psychologists in the clinical management of DSDs.

Mechanism of microtubule lumen entry for the α-tubulin acetyltransferase enzyme αTAT1.

Microtubules are structural polymers inside of cells that are subject to posttranslational modifications. These posttranslational modifications create functionally distinct subsets of microtubule networks in the cell, and acetylation is the only modification that takes place in the hollow lumen of the microtubule. Although it is known that the α-tubulin acetyltransferase (αTAT1) is the primary enzyme responsible for microtubule acetylation, the mechanism for how αTAT1 enters the microtubule lumen to access its acetylation sites is not well understood. By performing biochemical assays, fluorescence and electron microscopy experiments, and computational simulations, we found that αTAT1 enters the microtubule lumen through the microtubule ends, and through bends or breaks in the lattice. Thus, microtubule structure is an important determinant in the acetylation process. In addition, once αTAT1 enters the microtubule lumen, the mobility of αTAT1 within the lumen is controlled by the affinity of αTAT1 for its acetylation sites, due to the rapid rebinding of αTAT1 onto highly concentrated α-tubulin acetylation sites. These results have important implications for how acetylation could gradually accumulate on stable subsets of microtubules inside of the cell.

Gender destinies: assigning gender in Disorders of Sex Development-Intersex clinics.

Based on audio recordings of consultations in three U.S. paediatric multidisciplinary Disorders of Sex Development-Intersex clinics, we examine the process of gender assignment of children with "atypical" genitalia. Rather than fully determined by the presence of biological sex traits, the gender assignment discussion hinges on how clinician and parent collaboratively imagine different aspects of what constitutes being a gendered person. They orient towards the potential for sexual intimacy, fertility, gender dysphoria, stigma, and gonadal cancer risk. While these futures remain inherently uncertain, clinicians and parents plan to mobilise gender socialisation and medical interventions to render their choice of gender a self-fulfilling prophecy. Gender destinies capture that the child always had a specific, innate gender awaiting discovery, and presumes a project for medical and social monitoring, intervention, correction, and optimisation.

Is there a role for GPs in teaching neurology to medical students? A qualitative evaluation.

INTRODUCTION: The purpose of this study was to evaluate whether GPs can support medical students in learning basic neurology in the context of a traditional hospital neurology attachment. METHOD: This was a qualitative evaluation using routinely collected data from stakeholders, consisting of qualitative data in the form of student evaluation questionnaires, course documentation and correspondence from faculty staff. RESULTS: The addition of GP teaching to the programme increased availability of patients with neurological problems accessible to students and provided a safe, supportive environment for students to learn their fundamental clinical skills. Students gained valuable insights into the impact of neurological disease from the perspective of patients, their families and carers. GP teaching of neurology was well regarded by students. Some GP tutors felt they lacked adequate experience to teach more technical aspects of neurology, and some students shared this concern. Concepts of professional boundaries between generalists and specialists were not observed, but GP teaching was perceived to be 'other' or outside normal medical school activity. CONCLUSIONS: General practitioners can successfully facilitate students' access to patients with neurological disease and employ their generalist to enhance neurological learning. Some GPs were initially uncomfortable with teaching skills such as detailed neurological physical examination.

Suppression of microtubule assembly kinetics by the mitotic protein TPX2.

TPX2 is a widely conserved microtubule-associated protein that is required for mitotic spindle formation and function. Previous studies have demonstrated that TPX2 is required for the nucleation of microtubules around chromosomes; however, the molecular mechanism by which TPX2 promotes microtubule nucleation remains a mystery. In this study, we found that TPX2 acts to suppress tubulin subunit off-rates during microtubule assembly and disassembly, thus allowing for the support of unprecedentedly slow rates of plus-end microtubule growth, and also leading to a dramatically reduced microtubule shortening rate. These changes in microtubule dynamics can be explained in computational simulations by a moderate increase in tubulin-tubulin bond strength upon TPX2 association with the microtubule lattice, which in turn acts to reduce the departure rate of tubulin subunits from the microtubule ends. Thus, the direct suppression of tubulin subunit off-rates by TPX2 during microtubule growth and shortening could provide a molecular mechanism to explain the nucleation of new microtubules in the presence of TPX2.

Coordination of autophagosome-lysosome fusion and transport by a Klp98A-Rab14 complex in Drosophila.

Degradation of cellular material by autophagy is essential for cell survival and homeostasis, and requires intracellular transport of autophagosomes to encounter acidic lysosomes through unknown mechanisms. Here, we identify the PX-domain-containing kinesin Klp98A as a new regulator of autophagosome formation, transport and maturation in Drosophila. Depletion of Klp98A caused abnormal clustering of autophagosomes and lysosomes at the cell center and reduced the formation of starvation-induced autophagic vesicles. Reciprocally, overexpression of Klp98A redistributed autophagic vesicles towards the cell periphery. These effects were accompanied by reduced autophagosome-lysosome fusion and autophagic degradation. In contrast, depletion of the conventional kinesin heavy chain caused a similar mislocalization of autophagosomes without perturbing their fusion with lysosomes, indicating that vesicle fusion and localization are separable and independent events. Klp98A-mediated fusion required the endolysosomal GTPase Rab14, which interacted and colocalized with Klp98A, and required Klp98A for normal localization. Thus, Klp98A coordinates the movement and fusion of autophagic vesicles by regulating their positioning and interaction with the endolysosomal compartment.

Psychosocial Aspects of Short Stature and rhGH Treatment: Implicit Trends over 60+ Years.

Between 1958 and today, advances in research and the clinical management of short stature with GH have occurred. Initially, limited supply of pituitary-derived hGH led to strict criteria for diagnosing GH deficiency and tightly controlled treatment protocols. With the advent of biosynthetic GH, the supply has increased, the number of indications for treatment has grown, and the focus of intervention changed from hormone replacement to treatment of short stature. Improved psychosocial adaptation is an underlying, albeit largely unspoken and inadequately researched, target of treatment. Complicating the ability to make a definitive statement on the effects of rhGH on psychosocial adaptation is the rigor of the psychological outcomes literature. A high risk of bias present in the majority of rhGH treatment studies on psychological outcomes substantially weakens confidence in their results. Studies that convincingly demonstrate, through rigorous research design and methodology, that the benefits of rhGH exceed the risks and burdens are needed.

Interdisciplinary care in disorders/differences of sex development (DSD): The psychosocial component of the DSD-Translational research network.

Scientific discovery and clinical management strategies for Disorders/Differences of Sex Development (DSD) have advanced in recent years. The 2006 Consensus Statement on Management of Intersex Disorders stated that a mental health component to care is integral to promote positive adaptation, yet the parameters of this element have not been described. The objective of this paper is threefold: to describe the psychosocial screening protocol adopted by the clinical centers of the DSD-Translational Research Network; to summarize psychosocial data collected at 1 of the 10 network sites; and to suggest how systematic behavioral health screenings can be employed to tailor care in DSD that results in better health and quality of life outcomes. Steps taken in developing the largely "noncategorical" screening protocol are described. These preliminary findings suggest that DSD, as one category of pediatric chronic conditions, is not associated with marked disturbances of psychosocial adaptation, either for the family or the child; however, screening frequently uncovered "risk factors" for individual families or patients that can potentially be addressed in the context of ongoing clinical care. Administration of the DSD-TRN psychosocial screening protocol was demonstrated to be feasible in the context of interdisciplinary team care and was acceptable to families on a longitudinal basis. The ultimate value of systematic screening will be demonstrated through a tailoring of psychosocial, medical and surgical services, based on this information that enhances the quality of patient and family-centered care and subsequent outcomes.