Parsing patterns: Emerging roles of tissue self-organization in health and disease.

Patterned morphologies, such as segments, spirals, stripes, and spots, frequently emerge during embryogenesis through self-organized coordination between cells. Yet, complex patterns also emerge in adults, suggesting that the capacity for spontaneous self-organization is a ubiquitous property of biological tissues. We review current knowledge on the principles and mechanisms of self-organized patterning in embryonic tissues and explore how these principles and mechanisms apply to adult tissues that exhibit features of patterning. We discuss how and why spontaneous pattern generation is integral to homeostasis and healing of tissues, illustrating it with examples from regenerative biology. We examine how aberrant self-organization underlies diverse pathological states, including inflammatory skin disorders and tumors. Lastly, we posit that based on such blueprints, targeted engineering of pattern-driving molecular circuits can be leveraged for synthetic biology and the generation of organoids with intricate patterns.

Organ-level quorum sensing directs regeneration in hair stem cell populations.

Coordinated organ behavior is crucial for an effective response to environmental stimuli. By studying regeneration of hair follicles in response to patterned hair plucking, we demonstrate that organ-level quorum sensing allows coordinated responses to skin injury. Plucking hair at different densities leads to a regeneration of up to five times more neighboring, unplucked resting hairs, indicating activation of a collective decision-making process. Through data modeling, the range of the quorum signal was estimated to be on the order of 1 mm, greater than expected for a diffusible molecular cue. Molecular and genetic analysis uncovered a two-step mechanism, where release of CCL2 from injured hairs leads to recruitment of TNF-α-secreting macrophages, which accumulate and signal to both plucked and unplucked follicles. By coupling immune response with regeneration, this mechanism allows skin to respond predictively to distress, disregarding mild injury, while meeting stronger injury with full-scale cooperative activation of stem cells.

Emx2 underlies the development and evolution of marsupial gliding membranes.

Phenotypic variation among species is a product of evolutionary changes to developmental programs1,2. However, how these changes generate novel morphological traits remains largely unclear. Here we studied the genomic and developmental basis of the mammalian gliding membrane, or patagium-an adaptative trait that has repeatedly evolved in different lineages, including in closely related marsupial species. Through comparative genomic analysis of 15 marsupial genomes, both from gliding and non-gliding species, we find that the Emx2 locus experienced lineage-specific patterns of accelerated cis-regulatory evolution in gliding species. By combining epigenomics, transcriptomics and in-pouch marsupial transgenics, we show that Emx2 is a critical upstream regulator of patagium development. Moreover, we identify different cis-regulatory elements that may be responsible for driving increased Emx2 expression levels in gliding species. Lastly, using mouse functional experiments, we find evidence that Emx2 expression patterns in gliders may have been modified from a pre-existing program found in all mammals. Together, our results suggest that patagia repeatedly originated through a process of convergent genomic evolution, whereby regulation of Emx2 was altered by distinct cis-regulatory elements in independently evolved species. Thus, different regulatory elements targeting the same key developmental gene may constitute an effective strategy by which natural selection has harnessed regulatory evolution in marsupial genomes to generate phenotypic novelty.

Signalling by senescent melanocytes hyperactivates hair growth.

Niche signals maintain stem cells in a prolonged quiescence or transiently activate them for proper regeneration1. Altering balanced niche signalling can lead to regenerative disorders. Melanocytic skin nevi in human often display excessive hair growth, suggesting hair stem cell hyperactivity. Here, using genetic mouse models of nevi2,3, we show that dermal clusters of senescent melanocytes drive epithelial hair stem cells to exit quiescence and change their transcriptome and composition, potently enhancing hair renewal. Nevus melanocytes activate a distinct secretome, enriched for signalling factors. Osteopontin, the leading nevus signalling factor, is both necessary and sufficient to induce hair growth. Injection of osteopontin or its genetic overexpression is sufficient to induce robust hair growth in mice, whereas germline and conditional deletions of either osteopontin or CD44, its cognate receptor on epithelial hair cells, rescue enhanced hair growth induced by dermal nevus melanocytes. Osteopontin is overexpressed in human hairy nevi, and it stimulates new growth of human hair follicles. Although broad accumulation of senescent cells, such as upon ageing or genotoxic stress, is detrimental for the regenerative capacity of tissue4, we show that signalling by senescent cell clusters can potently enhance the activity of adjacent intact stem cells and stimulate tissue renewal. This finding identifies senescent cells and their secretome as an attractive therapeutic target in regenerative disorders.

Screening cell-cell communication in spatial transcriptomics via collective optimal transport.

Spatial transcriptomic technologies and spatially annotated single-cell RNA sequencing datasets provide unprecedented opportunities to dissect cell-cell communication (CCC). However, incorporation of the spatial information and complex biochemical processes required in the reconstruction of CCC remains a major challenge. Here, we present COMMOT (COMMunication analysis by Optimal Transport) to infer CCC in spatial transcriptomics, which accounts for the competition between different ligand and receptor species as well as spatial distances between cells. A collective optimal transport method is developed to handle complex molecular interactions and spatial constraints. Furthermore, we introduce downstream analysis tools to infer spatial signaling directionality and genes regulated by signaling using machine learning models. We apply COMMOT to simulation data and eight spatial datasets acquired with five different technologies to show its effectiveness and robustness in identifying spatial CCC in data with varying spatial resolutions and gene coverages. Finally, COMMOT identifies new CCCs during skin morphogenesis in a case study of human epidermal development.

Computational exploration of cellular communication in skin from emerging single-cell and spatial transcriptomic data.

Tissue development and homeostasis require coordinated cell-cell communication. Recent advances in single-cell sequencing technologies have emerged as a revolutionary method to reveal cellular heterogeneity with unprecedented resolution. This offers a great opportunity to explore cell-cell communication in tissues systematically and comprehensively, and to further identify signaling mechanisms driving cell fate decisions and shaping tissue phenotypes. Using gene expression information from single-cell transcriptomics, several computational tools have been developed for inferring cell-cell communication, greatly facilitating analysis and interpretation. However, in single-cell transcriptomics, spatial information of cells is inherently lost. Given that most cell signaling events occur within a limited distance in tissues, incorporating spatial information into cell-cell communication analysis is critical for understanding tissue organization and function. Spatial transcriptomics provides spatial location of cell subsets along with their gene expression, leading to new directions for leveraging spatial information to develop computational approaches for cell-cell communication inference and analysis. These computational approaches have been successfully applied to uncover previously unrecognized mechanisms of intercellular communication within various contexts and across organ systems, including the skin, a formidable model to study mechanisms of cell-cell communication due to the complex interactions between the different cell populations that comprise it. Here, we review emergent cell-cell communication inference tools using single-cell transcriptomics and spatial transcriptomics, and highlight the biological insights gained by applying these computational tools to exploring cellular communication in skin development, homeostasis, disease and aging, as well as discuss future potential research avenues.

Anion Recognition by Benzoxaborole.

The binding types (H-bonding or coordinate) and stability constants for complexes of 11 mono- and di-anions with benzoxaborole (1) were determined by 1H and 11B NMR titrations in DMSO or MeCN. Compared to phenylboronic acid (PBA), 1 is a stronger Lewis acid and a poorer H-bond donor with only one B-OH group, which is expected therefore to recognize anions mostly through the coordinate bonding. This is the case however only with F-, HPO42-, and PhPO32- anions, which are coordinately bonded to 1, and partially with SO42-, which forms only the H-bonded complex with PBA, but both H-bonded and coordinate complexes with 1. The majority of tested anions (AcO-, PhPO3H-, (PhO)2PO2-, Cl-, and Br-) form H-bonded complexes with both 1 and PBA, whereas H2PO4- changes the binding mode from coordinate for PBA to H-bonded for 1. The preferable binding type for each anion is confirmed by calculations of DFT-optimized structures of the anion complexes of 1. The preferable binding type can be rationalized considering the effects of the steric hindrance, more significant for the coordinate bonding, and of increased anion basicity, which is favorable for both binding types, but enhances the strength of coordinate bonding more significantly than the strength of H-bonding.

Diet-Induced Obesity Disrupts Histamine-Dependent Oleoylethanolamide Signaling in the Mouse Liver.

INTRODUCTION: Previous work suggests the existence of a paracrine signaling mechanism in which histamine released from visceral mast cells into the portal circulation contributes to fasting-induced ketogenesis by stimulating biosynthesis of the endogenous high-affinity PPAR-α agonist oleoylethanolamide (OEA). METHODS: Male C57Bl/6J mice were rendered obese by exposure to a high-fat diet (HFD; 60% fat). We measured histamine, OEA, and other fatty-acid ethanolamides by liquid-chromatography/mass spectrometry, gene transcription by RT-PCR, protein expression by ELISA, neutral lipid accumulation in the liver using Red Oil O and BODIPY staining, and collagen levels using picrosirius red staining. RESULTS: Long-term exposure to HFD suppressed both fasting-induced histamine release into portal blood and histamine-dependent OEA production in the liver. Additionally, subchronic OEA administration reduced lipid accumulation, inflammatory responses, and fibrosis in the liver of HFD-exposed mice. DISCUSSION: The results suggest that disruption of histamine-dependent OEA signaling in the liver might contribute to pathology in obesity-associated liver steatosis.

SDHAR-HOME: A Sensor Dataset for Human Activity Recognition at Home.

Nowadays, one of the most important objectives in health research is the improvement of the living conditions and well-being of the elderly, especially those who live alone. These people may experience undesired or dangerous situations in their daily life at home due to physical, sensorial or cognitive limitations, such as forgetting their medication or wrong eating habits. This work focuses on the development of a database in a home, through non-intrusive technology, where several users are residing by combining: a set of non-intrusive sensors which captures events that occur in the house, a positioning system through triangulation using beacons and a system for monitoring the user's state through activity wristbands. Two months of uninterrupted measurements were obtained on the daily habits of 2 people who live with a pet and receive sporadic visits, in which 18 different types of activities were labelled. In order to validate the data, a system for the real-time recognition of the activities carried out by these residents was developed using different current Deep Learning (DL) techniques based on neural networks, such as Recurrent Neural Networks (RNN), Long Short-Term Memory networks (LSTM) or Gated Recurrent Unit networks (GRU). A personalised prediction model was developed for each user, resulting in hit rates ranging from 88.29% to 90.91%. Finally, a data sharing algorithm has been developed to improve the generalisability of the model and to avoid overtraining the neural network.

A Course Design for Remote Teaching Advanced Topics in Neuroscience.

The COVID-19 pandemic pushed educators to engage in remote teaching out of necessity, but as our relationship with teaching technology grows, remote teaching has emerged as a suitable substitute for in-person education. In this manuscript, we detail a course design for remote teaching advanced topics in neuroscience at the undergraduate level. The course and its different features were designed to fulfill a set of learning goals that closely align with those put forth by the Faculty for Undergraduate Neuroscience (FUN) and the American Association for the Advancement of Science (AAAS). Furthermore, these learning goals can be applied to any advanced neuroscience class, regardless of the topic material. To achieve these goals, we created a curriculum with distinct design features. These features included a synchronous lecture-discussion system, asynchronous lesson content videos, guest principal investigators, and deemphasized grading. Instead of traditional examination, the students participated in assignments designed to give them extensive science communication experience. At the end of the course, we indirectly assessed student outcomes using an Instructor Course Evaluation survey distributed by the university. From this survey, we were able to conclude that students' perception of the final course outcome was highly satisfactory, with strong indications that the students believed we met our learning goals. Thus, the course design described herein represents a tool for others wishing to utilize it for remote teaching advanced topics in science.

Sexual segregation in the foraging behaviour of a slightly dimorphic seabird: Influence of the environment and fishery activity.

Sexual segregation in foraging strategies has been little studied in marine species with slight sexual size dimorphism (SSD), particularly regarding the role of environmental conditions and fishery activities. Sexual differences in fishery attendance are of particular concern because uneven mortality associated with bycatch may exacerbate impacts in wildlife populations. Using a seabird species with slight SSD, the Scopoli's shearwater Calonectris diomedea, we assessed sexual differences in foraging strategies and evaluated whether annual environmental conditions and fishery activity shaped such differences. We used a 4-year dataset combining bird GPS tracking, stable isotope analysis, the North Atlantic Oscillation index (NAO, as main proxy of the annual environmental conditions), and fishing vessel positioning data (Vessel Monitoring System, VMS) from the North Western Mediterranean, a region under intense fishery pressure. From 2012 to 2015, we tracked 635 foraging trips from 78 individuals. Females showed a greater foraging effort, a lower fishery attendance, a lower trophic level, and a narrower isotopic niche width than males. Moreover, in years with unfavourable environmental conditions, both sexes showed a lower fishery attendance and increased foraging effort compared to the year with most favourable conditions. Our results revealed that environmental conditions influence space use, feeding resources and fishery attendance differently in males and females, overall suggesting competitive exclusion of females by males from main foraging areas and feeding resources, particularly in unfavourable environmental conditions. We highlight the importance of evaluating sexual segregation under disparate environmental conditions, particularly in species with slight SSD, since segregation may pass otherwise unnoticed if only years with similar environmental conditions are considered. The higher fishery attendance of males likely explains the male-biased bycatch ratio for this species. Thus, inter-sexual differences in foraging strategies can lead to an unbalanced exposure to relevant threats and have implications for the conservation of long-lived species.

La segregación sexual en especies con dimorfismo sexual poco acusado ha sido escasamente estudiada, particularmente en relación al papel de las condiciones ambientales y las pesquerías en las estrategias de búsqueda de alimento. Diferencias entre sexos en la asociación con pesquerías son de especial interés, ya que el impacto de las capturas accidentales sobre la dinámica poblacional podría magnificarse. En este trabajo exploramos las diferencias entre sexos en las estrategias de búsqueda de alimento en la pardela cenicienta (Calonectris diomedea) en el noroeste del Mediterráneo, y evaluamos si cambios anuales en las condiciones ambientales y las pesquerías modulan dichas diferencias. Utilizamos cuatro años de datos, integrando el seguimiento GPS de las aves, el análisis de isótopos estables, el índice NAO, y el seguimiento remoto de barcos pesqueros que operan en la zona (datos VMS). Entre 2012 y 2015 obtuvimos 635 viajes de alimentación de 78 individuos. Encontramos diferencias en las estrategias de búsqueda de alimento entre sexos a pesar del dimorfismo sexual poco acusado de esta especie. En comparación con los machos, las hembras mostraron mayor esfuerzo (viajes más largos en tiempo y distancia), menor asociación con barcos de pesca, menor nivel trófico (es decir, valores de δ15 N en plasma que apuntan a un menor consumo de descartes) y un nicho isotópico más estrecho. Nuestros resultados revelaron que las condiciones ambientales influyen en las diferencias sexuales en las estrategias de búsqueda y uso de recursos de alimentación, así como en la interacción con pesquerías. En general, esto sugiere cierta exclusión competitiva de machos hacia hembras, particularmente en años desfavorables. Incluir años con condiciones ambientales dispares en el análisis puede ayudar a determinar la segregación sexual en especies con dimorfismo sexual poco acusado. Además, en especies longevas, las diferencias sexuales en las estrategias de búsqueda de alimento pueden conllevar diferente exposición a ciertas amenazas como las capturas accidentales en artes de pesca, lo que debe considerarse en el diseño de estrategias de conservación.

Sex-specific costs of reproduction on survival in a long-lived seabird.

Costs of reproduction on survival have captured the attention of researchers since life history theory was formulated. Adults of long-lived species may increase survival by reducing their breeding effort or even skipping reproduction. In this study, we aimed to evaluate the costs of current reproduction on survival and whether skipping reproduction increases adult survival in a long-lived seabird. We used capture-mark-recapture data (1450 encounters) from two populations of Bulwer's petrel (Bulweria bulwerii), breeding in the Azores and Canary Islands, North Atlantic Ocean. Using a multi-event model with two different breeding statuses (breeders versus non-breeders), we calculated probabilities of survival and of transitions between breeding statuses, evaluating potential differences between sexes. Females had lower survival probabilities than males, independent of their breeding status. When considering breeding status, breeding females had lower survival probabilities than non-breeding females, suggesting costs of reproduction on survival. Breeding males had higher survival probabilities than non-breeding males, suggesting that males do not incur costs of reproduction on survival and that only the highest quality males have access to breeding. The highest and the lowest probabilities of skipping reproduction were found in breeding males from the Azores and in breeding males from the Canary Islands, respectively. Intermediate values were observed in the females from both populations. This result is probably due to differences in the external factors affecting both populations, essentially predation pressure and competition. The existence of sex-specific costs of reproduction on survival in several populations of this long-lived species may have important implications for species population dynamics.

Daily Human Activity Recognition Using Non-Intrusive Sensors.

In recent years, Artificial Intelligence Technologies (AIT) have been developed to improve the quality of life of the elderly and their safety in the home. This work focuses on developing a system capable of recognising the most usual activities in the daily life of an elderly person in real-time to enable a specialist to monitor the habits of this person, such as taking medication or eating the correct meals of the day. To this end, a prediction model has been developed based on recurrent neural networks, specifically on bidirectional LSTM networks, to obtain in real-time the activity being carried out by the individuals in their homes, based on the information provided by a set of different sensors installed at each person's home. The prediction model developed in this paper provides a 95.42% accuracy rate, improving the results of similar models currently in use. In order to obtain a reliable model with a high accuracy rate, a series of processing and filtering processes have been carried out on the data, such as a method based on a sliding window or a stacking and re-ordering algorithm, that are subsequently used to train the neural network, obtained from the public database CASAS.

Physicians' brain drain - a gravity model of migration flows.

BACKGROUND: The past two decades have been marked by impressive growth in the migration of medical doctors. The medical profession is among the most mobile of highly skilled professions, particularly in Europe, and is also the sector that experiences the most serious labour shortages. However, surprisingly little is known about how medical doctors choose their destinations. In addition, the literature is scarce on the factors determining the sharp rise in the migration of doctors from Africa, Asia and Eastern and Southeastern Europe, and how the last economic crisis has shaped the migration flows of health professionals. METHODS: We use the new module on health worker migration provided by the Organisation for Economic Co-operation and Development (OECD) for 2000-2016 in order to examine the channels through which OECD countries attract foreign physicians from abroad. We estimate a gravity model using the Pseudo-Poisson Maximum Likelihood estimator. RESULTS: Our results reveal that a lower unemployment rate, good remuneration of physicians, an aging population, and a high level of medical technology at the destination are among the main drivers of physicians' brain drain. Furthermore, an analysis of the mobility of medical doctors from a number of regions worldwide shows that individuals react differently on a country-wise basis to various determinants present in the destination countries. Physicians from African countries are particularly attracted to destination countries offering higher wages, and to those where the density of medical doctors is relatively low. Concurrently, a higher demand for healthcare services and better medical technology in the receiving country drives the inflow of medical doctors from Central and Eastern Europe, while Asian doctors seem to preferentially migrate to countries with better school systems. CONCLUSIONS: This study contributes to a deeper understanding of the channels through which OECD countries attract foreign medical doctors from abroad. We find that, apart from dyadic factors, a lower unemployment rate, good remuneration of physicians, an aging population, and good medical infrastructure in the host country are among the main drivers of physicians' brain drain. Furthermore, we find that utility from migration to specific countries may be explained by the heterogeneity of origin countries.

Working hour mismatch, job quality, and mental well-being across the EU28: a multilevel approach.

OBJECTIVE: We aim to estimate the association between working hour mismatches and mental well-being. We also investigate the confounding and moderating role of job quality in this association. METHODS: We use cross-sectional data from the European Working Conditions Survey of 2015 in the analysis. The sample includes 9345 male and 10,998 female employees in 28 countries. We run a multilevel linear regression accounting for the clustering of countries with mental well-being assessed by the World Health Organization Index. We compute mismatches in working hours as the difference between desired and actual hours of work, categorized as underemployed, unconstrained, and overemployed. The main dependent variable is the combination of these mismatches for each of the following working schedules: ≤ 20; 21-34; 35-40; 41-47; and ≥ 48 h/week (h/w). RESULTS: The adverse association of short and long hours with well-being is mostly attributable to mismatches in working hours (except for men in the 41-47 h/w group). Once we adjust for job quality, overemployed men ≥ 48 h/w experience a reduction in mental well-being of - 5.2 (95 CI % - 7.04 to - 3.76) with respect to the unconstrained base category 35-40 h/w. Overemployed women experience a reduction in mental well-being ranging from - 4.94 (95 CI % - 6.54 to - 3.34) in the ≥ 48 h/w schedule to - 11.11 (95 CI % - 17.35 to - 4.87) in the ≤ 20 h/w schedule. We observe a confounding role of job quality across most working hour schedules, but the interaction effects are modest. CONCLUSION: Employee control over working hours is associated with mental well-being with differences by gender. Labour policies aimed at promoting flexibility on the employee side could be favoured to improve workers' mental well-being.

Temporary employment, work stress and mental health before and after the Spanish economic recession.

PURPOSE: This paper analyses the effects of temporary employment on work stress and mental health before (2006/2007) and during the economic recession (2011/2012), and examines whether the economic recession worsened these two health outcomes. METHODS: To control for selection bias, propensity scores (PS) are computed separately for salaried men and women using microdata from two cross-sectional health surveys in Spain, considering temporary (treatment group) versus permanent employment (control group). Next, we use difference-in-difference estimators stratifying by age, education level, and regional unemployment differences using PS as weights. RESULTS: Our results indicate that salaried worker with a temporary labour contract tends to have similar levels of high work stress and poorer mental health (only for men) than permanent ones for both periods. The economic recession does not appear to worsen both outcomes. However, when stratifying the sample, the economic recession is responsible for increasing stress among older temporary workers and male university graduates, without affecting women. Regarding mental health, we only find evidence of a negative impact of the economic recession on male temporary workers with university education. CONCLUSION: The economic recession has not affected poor mental health, but it has accentuated the adverse effects of work stress among some specific subgroups of male workers. These subgroups require specific preventive and support actions as the Spanish firms have not substantially changed their hiring practices after the recession.

Costs of breeding are rapidly buffered and do not affect migratory behavior in a long-lived bird species.

Life history theory states that individual fitness in one stage of life is conditioned by what occurred in previous stages. In migratory species, reproductive effort during breeding has often been found to influence body condition, molt schedule, self-provisioning and migration of individuals in subsequent seasons (i.e., carryover effects of breeding). However, there is a current uncertainty in understanding how long-distance migrants trade off among such energy-demanding activities (i.e., breeding, molting and migrating). To provide evidence to the field, we experimentally reduced the parental effort of a long-lived Procellariform, the Cory's shearwater (Calonectris borealis), by inducing failure at the incubation stage. Treatment and control birds were tracked during their subsequent migration by means of light-level and immersion loggers and sampled for six specific feathers (molted at different periods along the migratory cycle) upon the recovery of the loggers 1 yr later. Feathers were used to perform stable isotope analysis (SIA) and determine corticosterone levels (CORT). By these means, we evaluated the effect of breeding effort on migratory strategy, at-sea activity patterns, molt patterns, and levels of stress experienced by birds along the non-breeding period. We did not detect any difference between birds in the induced failure group and successful breeders in terms of spatio-temporal distribution: all birds shared common foraging areas throughout the study period and the timing of major phenological events did not differ. Failed birds significantly advanced their molt, as revealed by SIA and flying activity patterns. The stress levels of failed birds, inferred through CORT concentrations in feathers, were found to be consistently lower than in successful breeders, through the end of the breeding to the non-breeding period. Thus, we provide robust evidence that the costs of reproduction can be physiologically mediated from the breeding to the non-breeding period through molting schedules and CORT levels. However, we failed to detect clear effects on migratory behavior or subsequent breeding success, suggesting that costs of breeding in long-lived species may be rapidly buffered during the post-breeding period, as would be expected from life history theory.

Population genetic structure and long-distance dispersal of a recently expanding migratory bird.

Long-distance dispersal events and their derivable increases of genetic diversity have been highlighted as important ecological and evolutionary determinants that improve performances of range-expanding species. In the context of global environmental change, specific dispersal strategies have to be understood and foreseen if we like to prevent general biodiversity impoverishment or the spread of allochthonous diseases. We explored the genetic structure and potential population mixing on the recently range-expanding European bee-eater Merops apiaster. In addition, the species is suspected of harbouring and disseminating the most relevant disease for bees and apiculture, Nosema microsporidia. In agreement with complementary ringing recovery data and morphometric measurements, genetic results on two mitochondrial genes and 12 microsatellites showed a reasonably well-structured population partitioning along its breeding distribution. Microsatellite results indicated that not only did a few birds recently disperse long distance during their return migrations and change their natal breeding areas, but also that a group of allochthonous birds together founded a new colony. Although we did not provide evidence on the direct implication of birds in the widespread of Nosema parasites, our finding on the long-distance dispersal of bird flocks between remote breeding colonies adds concern about the role of European bee-eaters in the spread of such disease at a large, inter-continental scale.

Local circadian clock gates cell cycle progression of transient amplifying cells during regenerative hair cycling.

Regenerative cycling of hair follicles offers an unique opportunity to explore the role of circadian clock in physiological tissue regeneration. We focused on the role of circadian clock in actively proliferating transient amplifying cells, as opposed to quiescent stem cells. We identified two key sites of peripheral circadian clock activity specific to regenerating anagen hair follicles, namely epithelial matrix and mesenchymal dermal papilla. We showed that peripheral circadian clock in epithelial matrix cells generates prominent daily mitotic rhythm. As a consequence of this mitotic rhythmicity, hairs grow faster in the morning than in the evening. Because cells are the most susceptible to DNA damage during mitosis, this cycle leads to a remarkable time-of-day-dependent sensitivity of growing hair follicles to genotoxic stress. Same doses of γ-radiation caused dramatic hair loss in wild-type mice when administered in the morning, during mitotic peak, compared with the evening, when hair loss is minimal. This diurnal radioprotective effect becomes lost in circadian mutants, consistent with asynchronous mitoses in their hair follicles. Clock coordinates cell cycle progression with genotoxic stress responses by synchronizing Cdc2/Cyclin B-mediated G2/M checkpoint. Our results uncover diurnal mitotic gating as the essential protective mechanism in highly proliferative hair follicles and offer strategies for minimizing or maximizing cytotoxicity of radiation therapies.

Huntington's disease induced cardiac amyloidosis is reversed by modulating protein folding and oxidative stress pathways in the Drosophila heart.

Amyloid-like inclusions have been associated with Huntington's disease (HD), which is caused by expanded polyglutamine repeats in the Huntingtin protein. HD patients exhibit a high incidence of cardiovascular events, presumably as a result of accumulation of toxic amyloid-like inclusions. We have generated a Drosophila model of cardiac amyloidosis that exhibits accumulation of PolyQ aggregates and oxidative stress in myocardial cells, upon heart-specific expression of Huntingtin protein fragments (Htt-PolyQ) with disease-causing poly-glutamine repeats (PolyQ-46, PolyQ-72, and PolyQ-102). Cardiac expression of GFP-tagged Htt-PolyQs resulted in PolyQ length-dependent functional defects that included increased incidence of arrhythmias and extreme cardiac dilation, accompanied by a significant decrease in contractility. Structural and ultrastructural analysis of the myocardial cells revealed reduced myofibrillar content, myofibrillar disorganization, mitochondrial defects and the presence of PolyQ-GFP positive aggregates. Cardiac-specific expression of disease causing Poly-Q also shortens lifespan of flies dramatically. To further confirm the involvement of oxidative stress or protein unfolding and to understand the mechanism of PolyQ induced cardiomyopathy, we co-expressed expanded PolyQ-72 with the antioxidant superoxide dismutase (SOD) or the myosin chaperone UNC-45. Co-expression of SOD suppressed PolyQ-72 induced mitochondrial defects and partially suppressed aggregation as well as myofibrillar disorganization. However, co-expression of UNC-45 dramatically suppressed PolyQ-72 induced aggregation and partially suppressed myofibrillar disorganization. Moreover, co-expression of both UNC-45 and SOD more efficiently suppressed GFP-positive aggregates, myofibrillar disorganization and physiological cardiac defects induced by PolyQ-72 than did either treatment alone. Our results demonstrate that mutant-PolyQ induces aggregates, disrupts the sarcomeric organization of contractile proteins, leads to mitochondrial dysfunction and increases oxidative stress in cardiomyocytes leading to abnormal cardiac function. We conclude that modulation of both protein unfolding and oxidative stress pathways in the Drosophila heart model can ameliorate the detrimental PolyQ effects, thus providing unique insights into the genetic mechanisms underlying amyloid-induced cardiac failure in HD patients.