Variants in the Kallikrein Gene Family and Hypermobile Ehlers-Danlos Syndrome.

Hypermobile Ehlers-Danlos syndrome (hEDS) is a common heritable connective tissue disorder that lacks a known genetic etiology. To identify genetic contributions to hEDS, whole exome sequencing was performed on families and a cohort of sporadic hEDS patients. A missense variant in Kallikrein-15 (KLK15 p. Gly226Asp ) , segregated with disease in two families and genetic burden analyses of 197 sporadic hEDS patients revealed enrichment of variants within the Kallikrein gene family. To validate pathogenicity, the variant identified in familial studies was used to generate knock-in mice. Consistent with our clinical cohort, Klk15 G224D/+ mice displayed structural and functional connective tissue defects within multiple organ systems. These findings support Kallikrein gene variants in the pathogenesis of hEDS and represent an important step towards earlier diagnosis and better clinical outcomes.

Evaluating the effects of single, multiple, and delayed systemic rapamycin injections to contextual fear reconsolidation: Implications for the neurobiology of memory and the treatment of PTSD-like re-experiencing.

The mechanistic target of rapamycin (mTOR) kinase is known to mediate the formation and persistence of aversive memories. Rapamycin, an mTOR inhibitor, administered around the time of reactivation blocks retrieval-induced mTOR activity and de novo protein synthesis in the brains of rodents, while correspondingly diminishing subsequent fear memory. The goal of the current experiments was to further explore rapamycin's effects on fear memory persistence. First, we examined whether mTOR blockade at different time-points after reactivation attenuates subsequent contextual fear memory. We show that rapamycin treatment 3 or 12 h post-reactivation disrupts memory persistence. Second, we examined whether consecutive days of reactivation paired with rapamycin had additive effects over a single pairing at disrupting a contextual fear memory. We show that additional reactivation-rapamycin pairings exacerbates the reconsolidation impairment. Finally, we examined if impaired reconsolidation of a contextual fear memory from rapamycin treatment had any after-effects on learning and recalling a new fear association. We show that rapamycin-impaired reconsolidation does not affect new learning or recall and protects against fear generalization. Our findings improve our understanding of mTOR- dependent fear memory processes, as well as provide insight into potentially novel treatment options for stress-related psychopathologies such as posttraumatic stress disorder.

Lift Every Voice: Engaging Black Adolescents in Social Justice Service-Learning to Promote Mental Health and Educational Equity.

This study reports on the feasibility and acceptability of a social justice infused service-learning (S-L) program to promote Black adolescent mental health and educational equity. We convened a community advisory board to help adapt and pilot test, via open trial mixed method design, an evidence-based service-learning program for Black middle school adolescents (n = 21) attending summer camp at a faith-based setting. We describe a S-L curriculum, with a focus on the achievement gap, and training for church staff and assess staff and youth reports of feasibility, acceptability, and promise to (a) improve/engage psychological engagement targets, and (b) improve academic motivation, and social-emotional and behavioral outcomes. Mixed method findings revealed high feasibility and acceptability of the S-L intervention as indicated by consistent attendance and enthusiastic engagement by staff and youth, high satisfaction, high completion rates of planned sessions, and emergent qualitative themes from staff interviews and adolescent focus groups highlighting that service-learning (1) facilitated skills (e.g., goal-setting, social-emotional and behavioral regulation, and problem-solving), (2) shaped perspectives and inspired openness, and (3) created a space for all to feel valued and included to address the inequities of education that directly impacted them. There was preliminary evidence for efficacy in that youth report of emotional symptoms, peer problems, and staff report of general internalizing symptoms decreased following the intervention, while youth report of prosocial behaviors increased. Implications suggest that S-L programming demonstrates promise to promote mental health outcomes, raise social awareness, and inspire critical consciousness and lift the voices of Black youth by providing tools for working toward systemic changes to reduce inequities in both education and mental health.

Diverse organic-mineral associations in Jezero crater, Mars.

The presence and distribution of preserved organic matter on the surface of Mars can provide key information about the Martian carbon cycle and the potential of the planet to host life throughout its history. Several types of organic molecules have been previously detected in Martian meteorites1 and at Gale crater, Mars2-4. Evaluating the diversity and detectability of organic matter elsewhere on Mars is important for understanding the extent and diversity of Martian surface processes and the potential availability of carbon sources1,5,6. Here we report the detection of Raman and fluorescence spectra consistent with several species of aromatic organic molecules in the Máaz and Séítah formations within the Crater Floor sequences of Jezero crater, Mars. We report specific fluorescence-mineral associations consistent with many classes of organic molecules occurring in different spatial patterns within these compositionally distinct formations, potentially indicating different fates of carbon across environments. Our findings suggest there may be a diversity of aromatic molecules prevalent on the Martian surface, and these materials persist despite exposure to surface conditions. These potential organic molecules are largely found within minerals linked to aqueous processes, indicating that these processes may have had a key role in organic synthesis, transport or preservation.

Big tau aggregation disrupts microtubule tyrosination and causes myocardial diastolic dysfunction: from discovery to therapy.

BACKGROUND: Amyloid plaques and neurofibrillary tangles, the molecular lesions that characterize Alzheimer's disease (AD) and other forms of dementia, are emerging as determinants of proteinopathies 'beyond the brain'. This study aims to establish tau's putative pathophysiological mechanistic roles and potential future therapeutic targeting of tau in heart failure (HF). METHODS AND RESULTS: A mouse model of tauopathy and human myocardial and brain tissue from patients with HF, AD, and controls was employed in this study. Tau protein expression was examined together with its distribution, and in vitro tau-related pathophysiological mechanisms were identified using a variety of biochemical, imaging, and functional approaches. A novel tau-targeting immunotherapy was tested to explore tau-targeted therapeutic potential in HF. Tau is expressed in normal and diseased human hearts, in contradistinction to the current oft-cited observation that tau is expressed specifically in the brain. Notably, the main cardiac isoform is high-molecular-weight (HMW) tau (also known as big tau), and hyperphosphorylated tau segregates in aggregates in HF and AD hearts. As previously described for amyloid-beta, the tauopathy phenotype in human myocardium is of diastolic dysfunction. Perturbation in the tubulin code, specifically a loss of tyrosinated microtubules, emerged as a potential mechanism of myocardial tauopathy. Monoclonal anti-tau antibody therapy improved myocardial function and clearance of toxic aggregates in mice, supporting tau as a potential target for novel HF immunotherapy. CONCLUSION: The study presents new mechanistic evidence and potential treatment for the brain-heart tauopathy axis in myocardial and brain degenerative diseases and ageing.

A review of microbial-environmental interactions recorded in Proterozoic carbonate-hosted chert.

The record of life during the Proterozoic is preserved by several different lithologies, but two in particular are linked both spatially and temporally: chert and carbonate. These lithologies capture a snapshot of dominantly peritidal environments during the Proterozoic. Early diagenetic chert preserves some of the most exceptional Proterozoic biosignatures in the form of microbial body fossils and mat textures. This fossiliferous and kerogenous chert formed in shallow marine environments, where chert nodules, layers, and lenses are often surrounded by and encased within carbonate deposits that themselves often contain kerogen and evidence of former microbial mats. Here, we review the record of biosignatures preserved in peritidal Proterozoic chert and chert-hosting carbonate and discuss this record in the context of experimental and environmental studies that have begun to shed light on the roles that microbes and organic compounds may have played in the formation of these deposits. Insights gained from these studies suggest temporal trends in microbial-environmental interactions and place new constraints on past environmental conditions, such as the concentration of silica in Proterozoic seawater, interactions among organic compounds and cations in seawater, and the influence of microbial physiology and biochemistry on selective preservation by silicification.

Aqueous alteration processes in Jezero crater, Mars-implications for organic geochemistry.

The Perseverance rover landed in Jezero crater, Mars, in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep-ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, which probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks and are preserved in minerals related to both aqueous environments.

Alteration history of Séítah formation rocks inferred by PIXL x-ray fluorescence, x-ray diffraction, and multispectral imaging on Mars.

Collocated crystal sizes and mineral identities are critical for interpreting textural relationships in rocks and testing geological hypotheses, but it has been previously impossible to unambiguously constrain these properties using in situ instruments on Mars rovers. Here, we demonstrate that diffracted and fluoresced x-rays detected by the PIXL instrument (an x-ray fluorescence microscope on the Perseverance rover) provide information about the presence or absence of coherent crystalline domains in various minerals. X-ray analysis and multispectral imaging of rocks from the Séítah formation on the floor of Jezero crater shows that they were emplaced as coarsely crystalline igneous phases. Olivine grains were then partially dissolved and filled by finely crystalline or amorphous secondary silicate, carbonate, sulfate, and chloride/oxychlorine minerals. These results support the hypothesis that Séítah formation rocks represent olivine cumulates altered by fluids far from chemical equilibrium at low water-rock ratios.

Cellular and Molecular Mechanisms of MEK1 Inhibitor-Induced Cardiotoxicity.

Background: Trametinib is a MEK1 (mitogen-activated extracellular signal-related kinase kinase 1) inhibitor used in the treatment of BRAF (rapid accelerated fibrosarcoma B-type)-mutated metastatic melanoma. Roughly 11% of patients develop cardiomyopathy following long-term trametinib exposure. Although described clinically, the molecular landscape of trametinib cardiotoxicity has not been characterized. Objectives: The aim of this study was to test the hypothesis that trametinib promotes widespread transcriptomic and cellular changes consistent with oxidative stress and impairs cardiac function. Methods: Mice were treated with trametinib (1 mg/kg/d). Echocardiography was performed pre- and post-treatment. Gross, histopathologic, and biochemical assessments were performed to probe for molecular and cellular changes. Human cardiac organoids were used as an in vitro measurement of cardiotoxicity and recovery. Results: Long-term administration of trametinib was associated with significant reductions in survival and left ventricular ejection fraction. Histologic analyses of the heart revealed myocardial vacuolization and calcification in 28% of animals. Bulk RNA sequencing identified 435 differentially expressed genes and 116 differential signaling pathways following trametinib treatment. Upstream gene analysis predicted interleukin-6 as a regulator of 17 relevant differentially expressed genes, suggestive of PI3K/AKT and JAK/STAT activation, which was subsequently validated. Trametinib hearts displayed elevated markers of oxidative stress, myofibrillar degeneration, an 11-fold down-regulation of the apelin receptor, and connexin-43 mislocalization. To confirm the direct cardiotoxic effects of trametinib, human cardiac organoids were treated for 6 days, followed by a 6-day media-only recovery. Trametinib-treated organoids exhibited reductions in diameter and contractility, followed by partial recovery with removal of treatment. Conclusions: These data describe pathologic changes observed in trametinib cardiotoxicity, supporting the exploration of drug holidays and alternative pharmacologic strategies for disease prevention.

In Situ Identification of Paleoarchean Biosignatures Using Colocated Perseverance Rover Analyses: Perspectives for In Situ Mars Science and Sample Return.

The NASA Mars 2020 Perseverance rover is currently exploring Jezero crater, a Noachian-Hesperian locality that once hosted a delta-lake system with high habitability and biosignature preservation potential. Perseverance conducts detailed appraisals of rock targets using a synergistic payload capable of geological characterization from kilometer to micron scales. The highest-resolution textural and chemical information will be provided by correlated WATSON (imaging), SHERLOC (deep-UV Raman and fluorescence spectroscopy), and PIXL (X-ray lithochemistry) analyses, enabling the distributions of organic and mineral phases within rock targets to be comprehensively established. Herein, we analyze Paleoarchean microbial mats from the ∼3.42 Ga Buck Reef Chert (Barberton greenstone belt, South Africa)-considered astrobiological analogues for a putative ancient martian biosphere-following a WATSON-SHERLOC-PIXL protocol identical to that conducted by Perseverance on Mars during all sampling activities. Correlating deep-UV Raman and fluorescence spectroscopic mapping with X-ray elemental mapping, we show that the Perseverance payload has the capability to detect thermally and texturally mature organic materials of biogenic origin and can highlight organic-mineral interrelationships and elemental colocation at fine spatial scales. We also show that the Perseverance protocol obtains very similar results to high-performance laboratory imaging, Raman spectroscopy, and µXRF instruments. This is encouraging for the prospect of detecting microscale organic-bearing textural biosignatures on Mars using the correlative micro-analytical approach enabled by WATSON, SHERLOC, and PIXL; indeed, laminated, organic-bearing samples such as those studied herein are considered plausible analogues of biosignatures from a potential Noachian-Hesperian biosphere. Were similar materials discovered at Jezero crater, they would offer opportunities to reconstruct aspects of the early martian carbon cycle and search for potential fossilized traces of life in ancient paleoenvironments. Such samples should be prioritized for caching and eventual return to Earth.

Application of Pharmacokinetic Prediction Platforms in the Design of Optimized Anti-Cancer Drugs.

Cancer is the second most common cause of death in the United States, accounting for 602,350 deaths in 2020. Cancer-related death rates have declined by 27% over the past two decades, partially due to the identification of novel anti-cancer drugs. Despite improvements in cancer treatment, newly approved oncology drugs are associated with increased toxicity risk. These toxicities may be mitigated by pharmacokinetic optimization and reductions in off-target interactions. As such, there is a need for early-stage implementation of pharmacokinetic (PK) prediction tools. Several PK prediction platforms exist, including pkCSM, SuperCypsPred, Pred-hERG, Similarity Ensemble Approach (SEA), and SwissADME. These tools can be used in screening hits, allowing for the selection of compounds were reduced toxicity and/or risk of attrition. In this short commentary, we used PK prediction tools in the optimization of mitogen activated extracellular signal-related kinase kinase 1 (MEK1) inhibitors. In doing so, we identified MEK1 inhibitors with retained activity and optimized predictive PK properties, devoid of hERG inhibition. These data support the use of publicly available PK prediction platforms in early-stage drug discovery to design safer drugs.

DCHS1, Lix1L, and the Septin Cytoskeleton: Molecular and Developmental Etiology of Mitral Valve Prolapse.

Mitral valve prolapse (MVP) is a common cardiac valve disease that often progresses to serious secondary complications requiring surgery. MVP manifests as extracellular matrix disorganization and biomechanically incompetent tissues in the adult setting. However, MVP has recently been shown to have a developmental basis, as multiple causal genes expressed during embryonic development have been identified. Disease phenotypes have been observed in mouse models with human MVP mutations as early as birth. This study focuses on the developmental function of DCHS1, one of the first genes to be shown as causal in multiple families with non-syndromic MVP. By using various biochemical techniques as well as mouse and cell culture models, we demonstrate a unique link between DCHS1-based cell adhesions and the septin-actin cytoskeleton through interactions with cytoplasmic protein Lix1-Like (LIX1L). This DCHS1-LIX1L-SEPT9 axis interacts with and promotes filamentous actin organization to direct cell-ECM alignment and valve tissue shape.

Metagenomic, (bio)chemical, and microscopic analyses reveal the potential for the cycling of sulfated EPS in Shark Bay pustular mats.

Cyanobacteria and extracellular polymeric substances (EPS) in peritidal pustular microbial mats have a two-billion-year-old fossil record. To understand the composition, production, degradation, and potential role of EPS in modern analogous communities, we sampled pustular mats from Shark Bay, Australia and analyzed their EPS matrix. Biochemical and microscopic analyses identified sulfated organic compounds as major components of mat EPS. Sulfur was more abundant in the unmineralized regions with cyanobacteria and less prevalent in areas that contained fewer cyanobacteria and more carbonate precipitates. Sequencing and assembly of the pustular mat sample resulted in 83 high-quality metagenome-assembled genomes (MAGs). Metagenomic analyses confirmed cyanobacteria as the primary sources of these sulfated polysaccharides. Genes encoding for sulfatases, glycosyl hydrolases, and other enzymes with predicted roles in the degradation of sulfated polysaccharides were detected in the MAGs of numerous clades including Bacteroidetes, Chloroflexi, Hydrogenedentes, Myxococcota, Verrucomicrobia, and Planctomycetes. Measurable sulfatase activity in pustular mats and fresh cyanobacterial EPS confirmed the role of sulfatases in the degradation of sulfated EPS. These findings suggest that the synthesis, modification, and degradation of sulfated polysaccharides influence microbial interactions, carbon cycling, and biomineralization processes within peritidal pustular microbial mats.

Mitral Valve Prolapse Induces Regionalized Myocardial Fibrosis.

Background Mitral valve prolapse (MVP) is one of the most common forms of cardiac valve disease and affects 2% to 3% of the population. Previous imaging reports have indicated that myocardial fibrosis is common in MVP and described its association with sudden cardiac death. These data combined with evidence for postrepair ventricular dysfunction in surgical patients with MVP support a link between fibrosis and MVP. Methods and Results We performed histopathologic analysis of left ventricular (LV) biopsies from peripapillary regions, inferobasal LV wall and apex on surgical patients with MVP, as well as in a mouse model of human MVP (Dzip1S14R/+). Tension-dependent molecular pathways were subsequently assessed using both computational modeling and cyclical stretch of primary human cardiac fibroblasts in vitro. Histopathology of LV biopsies revealed regionalized fibrosis in the peripapillary myocardium that correlated with increased macrophages and myofibroblasts. The MVP mouse model exhibited similar regional increases in collagen deposition that progress over time. As observed in the patient biopsies, increased macrophages and myofibroblasts were observed in fibrotic areas within the murine heart. Computational modeling revealed tension-dependent profibrotic cellular and molecular responses consistent with fibrosis locations related to valve-induced stress. These simulations also identified mechanosensing primary cilia as involved in profibrotic pathways, which was validated in vitro and in human biopsies. Finally, in vitro stretching of primary human cardiac fibroblasts showed that stretch directly activates profibrotic pathways and increases extracellular matrix protein production. Conclusions The presence of prominent regional LV fibrosis in patients and mice with MVP supports a relationship between MVP and progressive damaging effects on LV structure before overt alterations in cardiac function. The regionalized molecular and cellular changes suggest a reactive response of the papillary and inferobasal myocardium to increased chordal tension from a prolapsing valve. These studies raise the question whether surgical intervention on patients with MVP should occur earlier than indicated by current guidelines to prevent advanced LV fibrosis and potentially reduce residual risk of LV dysfunction and sudden cardiac death.

Kras mutation subtypes distinctly affect colorectal cancer cell sensitivity to FL118, a novel inhibitor of survivin, Mcl-1, XIAP, cIAP2 and MdmX.

Mutation-activated Kras in cancer cells is a well-known challenging treatment-resistant factor that plays a critical role in treatment resistance. Human colorectal cancer (CRC) has four major Kras mutations; KrasG12D (34.2%), KrasG12V (21%), KrasG13D (20%) and KrasG12C (8.4%). Here, we report that while FL118 (a novel inhibitor of survivin, Mcl-1, XIAP, cIAP2 and MdmX) exhibits high efficacy to kill CRC cells and eliminate CRC tumors, CRC cells/tumors with different Kras mutation subtypes in the defined p53/APC genetic statuses exhibit different sensitivity to FL118 treatment. Using CRC cell lines, SW620 (KrasG12V, mutant p53, mutant APC), DLD-1 (KrasG13D, wild type p53, mutant APC) and SNU-C2B (KrasG12D, mutant p53, wild type APC), we demonstrated that silencing of KrasG12V and KrasG12D using Kras-specific shRNA significantly increased CRC cell IC50, while silencing of KrasG13D decreased the CRC cell IC50. This finding suggests that both KrasG12V and KrasG12D are required for showing higher FL118 efficacy, while the presence of KrasG13D could somehow decrease FL118 efficacy under the defined p53/APC genetic status. Consistent with this notion, silencing of KrasG12V in SW620 cells decreased FL118-induced apoptosis, while silencing of KrasG13D in DLD-1 cells increased the FL118-induced apoptosis. Furthermore, forced expression of KrasG12V in SW620 cells increased FL118-induced apoptosis, while forced expression of KrasG13D in DLD-1 cells decreased FL118-induced apoptosis. Additionally, FL118 induced differential reactive oxygen species (ROS) production in SW620, DLD-1 and SNU-C2B cells. Our in vivo studies in animal models further confirmed that SW620 tumors are the most sensitive tumor to FL118 treatment; SNU-C2B tumors are the second most sensitive tumor to FL118 treatment; and the DLD-1 tumors are the least sensitive tumor. These findings would be useful for predicting FL118 sensitivity to patients' CRC tumors with the defined Kras mutation subtypes under the defined p53/APC genetic status.

A new model for silicification of cyanobacteria in Proterozoic tidal flats.

Microbial fossils preserved by early diagenetic chert provide a window into the Proterozoic biosphere, but seawater chemistry, microbial processes, and the interactions between microbes and the environment that contributed to this preservation are not well constrained. Here, we use fossilization experiments to explore the processes that preserve marine cyanobacterial biofilms by the precipitation of amorphous silica in a seawater medium that is analogous to Proterozoic seawater. These experiments demonstrate that the exceptional silicification of benthic marine cyanobacteria analogous to the oldest diagnostic cyanobacterial fossils requires interactions among extracellular polymeric substances (EPS), photosynthetically induced pH changes, magnesium cations (Mg2+ ), and >70 ppm silica.

PDGFRα: Expression and Function during Mitral Valve Morphogenesis.

Mitral valve prolapse (MVP) is a common form of valve disease and can lead to serious secondary complications. The recent identification of MVP causal mutations in primary cilia-related genes has prompted the investigation of cilia-mediated mechanisms of disease inception. Here, we investigate the role of platelet-derived growth factor receptor-alpha (PDGFRα), a receptor known to be present on the primary cilium, during valve development using genetically modified mice, biochemical assays, and high-resolution microscopy. While PDGFRα is expressed throughout the ciliated valve interstitium early in development, its expression becomes restricted on the valve endocardium by birth and through adulthood. Conditional ablation of Pdgfra with Nfatc1-enhancer Cre led to significantly enlarged and hypercellular anterior leaflets with disrupted endothelial adhesions, activated ERK1/2, and a dysregulated extracellular matrix. In vitro culture experiments confirmed a role in suppressing ERK1/2 activation while promoting AKT phosphorylation. These data suggest that PDGFRα functions to suppress mesenchymal transformation and disease phenotypes by stabilizing the valve endocardium through an AKT/ERK pathway.

DZIP1 regulates mammalian cardiac valve development through a Cby1-ß-catenin mechanism.

BACKGROUND: Mitral valve prolapse (MVP) is a common and progressive cardiovascular disease with developmental origins. How developmental errors contribute to disease pathogenesis are not well understood. RESULTS: A multimeric complex was identified that consists of the MVP gene Dzip1, Cby1, and ß-catenin. Co-expression during valve development revealed overlap at the basal body of the primary cilia. Biochemical studies revealed a DZIP1 peptide required for stabilization of the complex and suppression of ß-catenin activities. Decoy peptides generated against this interaction motif altered nuclear vs cytosolic levels of ß-catenin with effects on transcriptional activity. A mutation within this domain was identified in a family with inherited non-syndromic MVP. This novel mutation and our previously identified DZIP1S24R variant resulted in reduced DZIP1 and CBY1 stability and increased ß-catenin activities. The ß-catenin target gene, MMP2 was up-regulated in the Dzip1S14R/+ valves and correlated with loss of collagenous ECM matrix and myxomatous phenotype. CONCLUSION: Dzip1 functions to restrain ß-catenin signaling through a CBY1 linker during cardiac development. Loss of these interactions results in increased nuclear ß-catenin/Lef1 and excess MMP2 production, which correlates with developmental and postnatal changes in ECM and generation of a myxomatous phenotype.

Dynamic Expression Profiles of ß-Catenin during Murine Cardiac Valve Development.

ß-catenin has been widely studied in many animal and organ systems across evolution, and gain or loss of function has been linked to a number of human diseases. Yet fundamental knowledge regarding its protein expression and localization remains poorly described. Thus, we sought to define whether there was a temporal and cell-specific regulation of ß-catenin activities that correlate with distinct cardiac morphological events. Our findings indicate that activated nuclear ß-catenin is primarily evident early in gestation. As development proceeds, nuclear ß-catenin is down-regulated and becomes restricted to the membrane in a subset of cardiac progenitor cells. After birth, little ß-catenin is detected in the heart. The co-expression of ß-catenin with its main transcriptional co-factor, Lef1, revealed that Lef1 and ß-catenin expression domains do not extensively overlap in the cardiac valves. These data indicate mutually exclusive roles for Lef1 and ß-catenin in most cardiac cell types during development. Additionally, these data indicate diverse functions for ß-catenin within the nucleus and membrane depending on cell type and gestational timing. Cardiovascular studies should take into careful consideration both nuclear and membrane ß-catenin functions and their potential contributions to cardiac development and disease.

Desert hedgehog-primary cilia cross talk shapes mitral valve tissue by organizing smooth muscle actin.

Non-syndromic mitral valve prolapse (MVP) is the most common heart valve disease affecting 2.4% of the population. Recent studies have identified genetic defects in primary cilia as causative to MVP, although the mechanism of their action is currently unknown. Using a series of gene inactivation approaches, we define a paracrine mechanism by which endocardially-expressed Desert Hedgehog (DHH) activates primary cilia signaling on neighboring valve interstitial cells. High-resolution imaging and functional assays show that DHH de-represses smoothened at the primary cilia, resulting in kinase activation of RAC1 through the RAC1-GEF, TIAM1. Activation of this non-canonical hedgehog pathway stimulates α-smooth actin organization and ECM remodeling. Genetic or pharmacological perturbation of this pathway results in enlarged valves that progress to a myxomatous phenotype, similar to valves seen in MVP patients. These data identify a potential molecular origin for MVP as well as establish a paracrine DHH-primary cilium cross-talk mechanism that is likely applicable across developmental tissue types.