Rapid binding to protofilament edge sites facilitates tip tracking of EB1 at growing microtubule plus-ends

EB1 is a key cellular protein that delivers regulatory molecules throughout the cell via the tip-tracking of growing microtubule plus-ends. Thus, it is important to understand the mechanism for how EB1 efficiently tracks growing microtubule plus-ends. It is widely accepted that EB1 binds with higher affinity to GTP-tubulin subunits at the growing microtubule tip, relative to GDP-tubulin along the microtubule length. However, it is unclear whether this difference in affinity alone is sufficient to explain the tip-tracking of EB1 at growing microtubule tips. Previously, we found that EB1 binds to exposed microtubule protofilament-edge sites at a ~70 fold faster rate than to closed-lattice sites, due to diffusional steric hindrance to binding. Thus, we asked whether rapid protofilament-edge binding could contribute to efficient EB1 tip tracking. A computational simulation with differential EB1 on-rates based on closed-lattice or protofilament-edge binding, and with EB1 off-rates that were dependent on the tubulin hydrolysis state, robustly recapitulated experimental EB1 tip tracking. To test this model, we used cell-free biophysical assays, as well as live-cell imaging, in combination with a Designed Ankyrin Repeat Protein (DARPin) that binds exclusively to protofilament-edge sites, and whose binding site partially overlaps with the EB1 binding site. We found that DARPin blocked EB1 protofilament-edge binding, which led to a decrease in EB1 tip tracking on dynamic microtubules. We conclude that rapid EB1 binding to microtubule protofilament-edge sites contributes to robust EB1 tip tracking at the growing microtubule plus-end.

Contextualizing Cisgender Women's Histories of Intimate Partner Violence Victimization With Men and Women

Sexual minoritized women (SMW) are more likely than exclusively heterosexual women to experience intimate partner violence (IPV). We conducted in-depth interviews with a clinic-based sample of plurisexual SMW (n = 25) ages 18 to 34 about the gender of their perpetrators. Participants primarily experienced physical and sexual IPV in relationships with men and emotional abuse in relationships with women. IPV perpetrated by men often included weapons with women fearing for their lives. Offering patients information about IPV resources and supports that do not make assumptions about women's sexualities may create more opportunity for empathic and effective communication with SMW experiencing IPV.

"They are Assuming That We are Going to Accuse Them of Rape, and We are Assuming That They are Going to Rape us": A Developmental Perspective on Emerging Adults' Consent Conversations Post #MeToo

Prevalence of sexual assault remains high on American college campuses, and sexual consent education is lacking within school-based sexual health education programming. Much empirical research has aimed to reduce sexual violence through a deeper understanding of college students' perceptions of sexual consent. However, researchers have not yet examined the impact of broader social discourse, such as that initiated by the #MeToo movement, on emerging adults' conceptualizations of sexual consent. Gendered focus groups were conducted with 34 college students at a large midwestern university in spring of 2019. Qualitative analyses using a phenomenological framework revealed a developmental process of consent education shaped by socialized sexual scripts and public discourse of the #MeToo movement. Four distinct themes emerged: (1) Introductions to Consent in Childhood, (2) Lack of Sexual Consent Education in Adolescence, (3) The Nuanced College Context, and (4) Consent in the Era of #MeToo. Findings reveal that consent is introduced in childhood, outside the context of sexuality, but is generally not revisited within the context of sexual consent by parents or educators during adolescence, leaving media messaging and socialized sexual scripts to serve as guides for sexual consent. This lack of sexual consent education in adolescence then leaves emerging adults unprepared for nuanced sexual experiences in the college context and unable to critically engage with public discourse surrounding consent such as the #MeToo movement, which has caused both fearful and positive outcomes. Findings support the need for earlier and more comprehensive education about sexual consent in childhood and adolescence and the need for college sexual assault prevention programs to include further instruction on navigating ambiguous sexual consent experiences.

Reproductive coercion, intimate partner violence, and pregnancy risk among adolescent women with a history of foster care involvement

BACKGROUND

The current study is the first to explore the prevalence of reproductive coercion among adolescent women currently or previously involved in the U.S. foster care system. Reproductive coercion (RC), a form of intimate partner violence (IPV) involving exertion of power over a partner by controlling their reproductive health and decision making, is a significant public health concern. Existing research on RC has primarily been conducted in either healthcare settings or on college campuses. Foster youth are disproportionately impacted by both adolescent pregnancy and interpersonal violence. RC may contribute to this elevated risk.

METHODS

We conducted a cross-sectional survey in 2015 and 2016 of adolescent women (n=136), ages 16-24 years old, seeking services from youth-serving agencies affiliated with a child welfare system in Pennsylvania, United States. Participants completed measures assessing RC, experiences of physical and sexual violence, sexual behaviors, and pregnancy. We used multivariable logistic regression to assess associations between RC and study outcomes.

RESULTS

The sample was predominantly African American (67.4%) and largely identified as something other than heterosexual (46.6%). Nearly one-third of the sample (30.1%) reported a history of RC, with the most common being male partners telling them not to use birth control. High rates of IPV (62.1%), lifetime pregnancy (43.4%), and unwanted pregnancy (30.9%) were also reported. RC was associated with significantly higher odds of IPV (Adjusted Odds Ratio (AOR) = 4.22, 95% Confidence Interval (CI): 1.60, 11.13), multi-perpetrator rape (AOR 3.56, 95% CI: 1.04, 12.24), pregnancy (AOR = 5.39, 95% CI: 2.14, 13.60), and unintended pregnancy (AOR 5.39, 95% CI: 2.04, 14.25). Young women reporting RC also had elevated odds for using alcohol or drugs before sex (AOR = 4.34, 95% CI: 1.72, 10.97) and having sex with a male partner 5 years or more older (AOR = 7.32, 95% CI: 2.84, 18.87). No significant differences emerged between RC and sociodemographic characteristics.

IMPLICATIONS

These data suggest women involved in the U.S. foster care system, particularly women of color and/or LGBTQ+ identified who comprised the majority of participants in the current study, may be at an increased risk for experiencing RC and other forms of IPV associated with adolescent pregnancy. In addition to efforts to prevent IPV and sexual violence, assessment for RC, healthy relationships education, and access to sexual and reproductive health care may mitigate these risks and improve outcomes for these young women.

Sexual Assault, Alcohol Use, and Gender of Sexual Partners Among Cisgender Women Seeking Care at US College Health Centers, 2015-2018

Objectives. To assess differences by gender of sexual partner in the association between sexual assault and alcohol use among women seeking care in college health centers.Methods. This longitudinal study comprised 1578 women aged 18 to 24 years visiting 28 college health centers in Pennsylvania and West Virginia from 2015 to 2018. We used multilevel logistic regression and negative binomial regression, testing for interactions of gender of sexual partners, sexual assault, and prevalence and frequency of alcohol use and binge drinking.Results. Sexual assault was reported by 87.3% of women who had sex with women or with women and men (WSWM), 68.2% of women who had sex with men only (WSM), and 47.5% of women with no penetrative sexual partners. The relative associations between sexual assault and alcohol outcomes were smaller for WSWM (prevalence: odds ratios from 0.04 to 0.06; frequency: incidence rate ratios [IRRs] from 0.24 to 0.43) and larger for women who had no penetrative sexual partners (IRRs from 1.55 to 2.63), compared with WSM.Conclusions. Alcohol use patterns among women who have experienced sexual assault differ by gender of sexual partners.

Non-enzymatic Activity of the α-Tubulin Acetyltransferase αTAT Limits Synaptic Bouton Growth in Neurons

Neuronal axons terminate as synaptic boutons that form stable yet plastic connections with their targets. Synaptic bouton development relies on an underlying network of both long-lived and dynamic microtubules that provide structural stability for the boutons while also allowing for their growth and remodeling. However, a molecular-scale mechanism that explains how neurons appropriately balance these two microtubule populations remains a mystery. We hypothesized that α-tubulin acetyltransferase (αTAT), which both stabilizes long-lived microtubules against mechanical stress via acetylation and has been implicated in promoting microtubule dynamics, could play a role in this process. Using the Drosophila neuromuscular junction as a model, we found that non-enzymatic dαTAT activity limits the growth of synaptic boutons by affecting dynamic, but not stable, microtubules. Loss of dαTAT results in the formation of ectopic boutons. These ectopic boutons can be similarly suppressed by resupplying enzyme-inactive dαTAT or by treatment with a low concentration of the microtubule-targeting agent vinblastine, which acts to suppress microtubule dynamics. Biophysical reconstitution experiments revealed that non-enzymatic αTAT1 activity destabilizes dynamic microtubules but does not substantially impact the stability of long-lived microtubules. Further, during microtubule growth, non-enzymatic αTAT1 activity results in increasingly extended tip structures, consistent with an increased rate of acceleration of catastrophe frequency with microtubule age, perhaps via tip structure remodeling. Through these mechanisms, αTAT enriches for stable microtubules at the expense of dynamic ones. We propose that the specific suppression of dynamic microtubules by non-enzymatic αTAT activity regulates the remodeling of microtubule networks during synaptic bouton development.

Structural state recognition facilitates tip tracking of EB1 at growing microtubule ends

The microtubule binding protein EB1 specifically targets the growing ends of microtubules in cells, where EB1 facilitates the interactions of cellular proteins with microtubule plus-ends. Microtubule end targeting of EB1 has been attributed to high-affinity binding of EB1 to GTP-tubulin that is present at growing microtubule ends. However, our 3D single-molecule diffusion simulations predicted a ~ 6000% increase in EB1 arrivals to open, tapered microtubule tip structures relative to closed lattice conformations. Using quantitative fluorescence, single-molecule, and electron microscopy experiments, we found that the binding of EB1 onto opened, structurally disrupted microtubules was dramatically increased relative to closed, intact microtubules, regardless of hydrolysis state. Correspondingly, in cells, the blunting of growing microtubule plus-ends by Vinblastine was correlated with reduced EB1 targeting. Together, our results suggest that microtubule structural recognition, based on a fundamental diffusion-limited binding model, facilitates the tip tracking of EB1 at growing microtubule ends.

Manipulation and quantification of microtubule lattice integrity

Microtubules are structural polymers that participate in a wide range of cellular functions. The addition and loss of tubulin subunits allows the microtubule to grow and shorten, as well as to develop and repair defects and gaps in its cylindrical lattice. These lattice defects act to modulate the interactions of microtubules with molecular motors and other microtubule-associated proteins. Therefore, tools to control and measure microtubule lattice structure will be invaluable for developing a quantitative understanding of how the structural state of the microtubule lattice may regulate its interactions with other proteins. In this work, we manipulated the lattice integrity of in vitro microtubules to create pools of microtubules with common nucleotide states, but with variations in structural states. We then developed a series of novel semi-automated analysis tools for both fluorescence and electron microscopy experiments to quantify the type and severity of alterations in microtubule lattice integrity. These techniques will enable new investigations that explore the role of microtubule lattice structure in interactions with microtubule-associated proteins.

A novel role for SALL4 during scar-free wound healing in axolotl

The human response to serious cutaneous damage is limited to relatively primitive wound healing, whereby collagenous scar tissue fills the wound bed. Scars assure structural integrity at the expense of functional regeneration. In contrast, axolotls have the remarkable capacity to functionally regenerate full thickness wounds. Here, we identified a novel role for SALL4 in regulating collagen transcription after injury that is essential for perfect skin regeneration in axolotl. Furthermore, we identify miR-219 as a molecular regulator of Sall4 during wound healing. Taken together, our work highlights one molecular mechanism that allows for efficient cutaneous wound healing in the axolotl.

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.

Maximum O2 uptake, O2 debt and deficit, and muscle metabolites in Thoroughbred horses

This study determined maximal O2 uptake (VO2max), maximal O2 deficit, and O2 debt in the Thoroughbred racehorse exercising on an inclined treadmill. In eight horses the O2 uptake (VO2) vs. speed relationship was linear until 10 m/s and VO2max values ranged from 131 to 153 ml.kg-1.min-1. Six of these horses then exercised at 120% of their VO2max until exhaustion. VO2, CO2 production (VCO2), and plasma lactate (La) were measured before and during exercise and through 60 min of recovery. Muscle biopsies were collected before and at 0.25, 0.5, 1, 1.5, 2, 5, 10, 15, 20, 40, and 60 min after exercise. Muscle concentrations of adenosine 5'-triphosphate (ATP), phosphocreatine (PC), La, glucose 6-phosphate (G-6-P), and creatine were determined, and pH was measured. The O2 deficit was 128 +/- 32 (SD) ml/kg (64 +/- 13 liters). The O2 debt was 324 +/- 62 ml/kg (159 +/- 37 liters), approximately two to three times comparative values for human beings. Muscle [ATP] was unchanged, but [PC] was lower (P less than 0.01) than preexercise values at less than or equal to 10 min of recovery. [PC] and VO2 were negatively correlated during both the fast and slow phases of VO2 during recovery. Muscle [La] and [G-6-P] were elevated for 10 min postexercise. Mean muscle pH decreased from 7.05 (preexercise) to 6.75 at 1.5 min recovery, and the mean peak plasma La value was 34.5 mmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of inhibition of fructolysis in ram spermatozoa by chlorinated antifertility agents

When ejaculated ram spermatozoa were incubated with (S)-alpha-chlorohydrin (up to 0.25 mM) the oxidative metabolism of fructose to carbon dioxide was inhibited in a concentration-dependent manner. This appears to be due to inhibition of glyceraldehyde-3-phosphate dehydrogenase which leads to the accumulation of fructose-1,6-bisphosphate, dihydroxyacetone phosphate and, to a lesser extent, glyceraldehyde-3-phosphate. (R)-alpha-Chlorohydrin (10 mM) had no significant effect on the oxidative metabolism of fructose. The inhibition of the oxidative metabolism of fructose by (S)-alpha-chlorohydrin (0.1 mM) was not immediate but was detected after incubation for 15 min. By contrast, (R,S)-3-chlorolactaldehyde (5 mM) caused an immediate inhibition of this metabolic pathway. 1-Chloro-3-hydroxyacetone (0.5 mM) immediately decreased the oxidative metabolism of fructose which resulted in the accumulation of key fructolytic intermediates in a manner comparable to that produced by (S)-alpha-chlorohydrin. At a concentration of 20 mM, 6-chloro-6-deoxyglucose had no significant effect on the metabolic activity of ram spermatozoa. We suggest that the anti-fructolytic actions of (S)-alpha-chlorohydrin and 1-chloro-3-hydroxyacetone are mediated via a common metabolite, (S)-3-chlorolactaldehyde, and that the inactivity of 6-chloro-6-deoxyglucose is due to the inability of ram spermatozoa to metabolise this chlorinated sugar to (S)-3-chlorolactaldehyde.

The evolution of a human services network

The delivery of human services in most communities is complicated by competition between agencies for money, esteem, and clientele. There is a need for developing a strategy of interagency service coordination. Representatives of human service organizations in a suburban community worked together to establish a network of services emphasizing coordination and the utilization of multiple resources to meet identified program needs. The description of this project includes: (a) a discussion of the community and its special problems; (b) a specification of objectives for service coordination; (c) a presentation of the theoretical framework underlying the development of the network; (d) an analysis of the stages of development; and (e) a summary including evaluations, conclusions, and possible future directions.

Methods of suicide of English and Welsh immigrants in Australia

One of the better known facts about suicide rates is their remarkable stability in terms of the sex of the victim, the methods used and the age-specific rates in different societies over considerable periods of time. Suicide studies suggest that the frequency and methods of suicide are determined largely by the culture, social mores and a number of other factors— possibly demographic—which remain relatively stable over fairly long periods (Whitlock, 1971). Methods of suicide can vary from country to country (Dublin, 1963; Stengel, 1964). In Australia, there has been a remarkable consistency in the major methods of suicide throughout this century (Saint, 1965), although Hetzel (1971) has pointed out the marked rise in rates from self-poisoning in the last twenty years. Burvill (1970) has contrasted the methods of suicide in Western Australia with those reported in America and Britain, as has Whitlock (1971) among the various immigrant groups in Australia, although he warned that his results were based on comparatively small numbers of suicides in minority population groups. Overall age-standardized suicide rates among immigrants to Australia are substantially higher than those prevailing in their country of origin and among the Australian-born population (Whitlock, 1971; Burvill et al., 1972).