Contributions To Physiology Research Articles

Abstract 509: Oxytocin Mediates Neuroendocrine Reprogramming of the Epicardium in Heart Regeneration

Cardiovascular disease (CVD) is the leading cause of mortality both in the United States and worldwide. CVD often results in the massive loss of contractile cardiac cells and tissue. Critical work in the last two decades demonstrates that lost cells can be partially replenished by the epicardium, the outermost mesothelial layer of the heart. Upon cardiac injury, mature epicardial cells activate and undergo epithelial-mesenchymal transition (EMT) to form epicardium-derived progenitor cells (EPDCs), which are a type of multipotent stem cell that can differentiate into several important cardiac lineages, including cardiomyocytes and vascular cells. This process alone is insufficient for significant regeneration, but its efficiency can be improved by priming with specific factors (e.g., thymosin beta-4). Our group has recently discovered evidence that oxytocin (OT), a hypothalamic neuroendocrine peptide, induces a pro-regenerative phenotype in vitro in human induced pluripotent stem cell (iPSC) derived epicardial cells. We hypothesize that upon cardiac injury, oxytocin is released into the bloodstream, causing activation of the epicardium and mobilization of EPDCs to elicit regeneration of damaged tissue and restoration of function. Here, we show that we can differentiate mature, high-quality epicardial cells from iPSCs and that Ki67 levels and cell counts increase after three days of OT exposure. In addition, the peptide alters gene expression levels of several epithelial, mesenchymal, and EMT markers, indicating a transition to a dedifferentiated gene profile characteristic of EPDCs. Finally, when OT is administered intravenously to mice, it accelerates healing from cardiac injury by inducing epicardial activation. Future studies will aim to further reveal the physiological contribution of OT to heart regeneration in vivo and determine its molecular mechanism of action. Our findings have the potential to uncover a novel mechanism of neuroendocrine reprogramming of the injured heart and yield significant translational advances in the treatment of CVD.

023 Investigation of Sensory Innervation in the Surgical Field of Mid-Urethral Sling and Loop Electrosurgical Excision Procedures in Periurethral and Cervical Tissues Using Immunohistochemistry

Female sexual dysfunction (FSD) has been reported following two procedures which impact hundreds of thousands of women each year: the mid-urethral sling (MUS) procedure to correct stress urinary incontinence, and the loop electrosurgical excision procedure (LEEP) to treat cervical dysplasia. The aspects of FSD affected following these procedures include lowered orgasm satisfaction, which impacts negatively on overall quality of life. The female periurethral tissue (FPT) and cervical tissue which are potentially being impacted by the MUS and LEEP procedures respectively, are known to contain glandular and vascular structures, as well as mixed nerve bundles. Preliminary studies have shown that both the FPT and cervical tissues may contain sensory innervation of these glandular and vascular structures, in addition to nerve bundles, which may have physiologic contribution to sexual function. The long-term goal of our research is to determine whether these procedures are negatively impacting tissues that can play a significant role in female sexual responses. The potential impact of decreased or altered sensations in a subpopulation of women undergoing MUS or LEEP procedures requires further investigation and a reassessment of current surgical practice.

Therapeutic application of extracellular vesicles for musculoskeletal repair & regeneration

ABSTRACT Traumatic musculoskeletal injuries are common in both the civilian and combat care settings. Significant barriers exist to repairing these injuries including fracture nonunion, muscle fibrosis, re-innervation, and compartment syndrome, as well as infection and inflammation. Recently, extracellular vesicles (EVs), including exosomes and microvesicles, have attracted attention in the field of musculoskeletal regeneration. These vesicles are released by different cell types and play a vital role in cell communication by delivering functional cargoes such as proteins and RNAs. Many of these cargo molecules can be utilized for repair purposes in skeletal disorders such as osteoporosis, osteogenesis imperfecta, sarcopenia, and fracture healing. There are, however, some challenges to overcome in order to advance the successful application of these vesicles in the therapeutic setting. These include large-scale production and isolation of exosomes, long-term storage, in vivo stability, and strategies for tissue-specific targeting and delivery. This paper reviews the general characteristics of exosomes along with their physiological roles and contribution to the pathogenesis of musculoskeletal diseases. We also highlight new findings on the use of synthetic exosomes to overcome the limitations of native exosomes in treating musculoskeletal injuries and disorders.

Extracellular vesicles and its advances in female reproduction

Intercellular communication is an essential mechanism for development and maintenance of multicellular organisms. Extracellular vesicles (EVs) were recently described as new players in the intercellular communication. EVs are double-membrane vesicles secreted by cells and are classified according to their biosynthesis, protein markers and morphology. These extracellular vesicles contain bioactive materials such as miRNA, mRNA, protein and lipids. These characteristics permit their involvement in different biological processes. Reproductive physiology is complex and involves constant communication between cells. Different laboratories have described the presence of EVs secreted by ovarian follicular cells, oviductal cells, in vitro produced embryos and by the endometrium, suggesting that EVs are involved in the development of gametes and embryos, in animals and humans. Therefore, is important to understand physiological mechanisms and contributions of EVs in female reproduction in order to develop new tools to improve in vivo reproductive events and assisted reproductive techniques (ARTs). This review will provide the current knowledge related to EVs in female reproductive tissues and their role in ARTs.

Tissue-specific disruption of Kbtbd2 uncovers adipocyte-intrinsic and -extrinsic features of the teeny lipodystrophy syndrome

Loss of KBTBD2 in all tissues causes the teeny phenotype, characterized by insulin resistance with late failure of insulin production, severe hyperglycemia/diabetes, lipodystrophy, hepatosteatosis, and growth retardation. KBTBD2 maintains insulin sensitivity in adipocytes by restricting the abundance of p85α. However, the possible physiological contribution or contributions of KBTBD2 have not yet been examined in other tissues. Here we show that mice with an adipocyte-specific knockout of Kbtbd2 accumulate p85α in white and brown adipose tissues, causing insulin resistance, moderate rather than severe hyperglycemia, sustained hyperinsulinemia without late failure of insulin production, and lipodystrophy leading to ectopic lipid accumulation in the liver. Adipocyte-extrinsic insulin resistance was observed in liver and muscle. None of these abnormalities were observed in liver- or muscle-specific Kbtbd2 knockout mice. Mice with Kbtbd2 knockout in adipocytes, liver, and muscle all showed normal growth, suggesting that KBTBD2 may be necessary to ensure IGF1 signaling in other tissues, notably bone. While much of the teeny phenotype results from loss of KBTBD2 in adipocytes, some features are adipocyte-extrinsic.

Metabolic utilization of propanediol by adherent-invasive E. coli regulates intestinal tissue immunity

Abstract Crohn’s Disease (CD) has been associated with alterations in the intestinal microbiota, but the microbial mechanisms that regulate host immunity are largely unknown. We have recently shown that Adherent-Invasive E. coli (AIEC), which are enriched in CD patients, are sufficient to induce intestinal Th17 cells. Although AIEC lack pathogenic factors including type III secretion systems, many CD-derived isolates express virulence-associated metabolic enzymes including propanediol dehydratase (PduC), which enables AIEC to use fucose-derived propanediol as an alternate carbon source. We found that pduC is enriched in the microbiome and among E. coli genomes in CD patients compared to healthy controls. To evaluate the physiologic contribution of propanediol utilization to AIEC Th17 induction, we generated a pduC-deficient mutant of a CD-derived, AIEC isolate. Deletion of pduC resulted in reduced, inflammatory Th17 cells and attenuated weight loss following T cell transfer colitis. Using genetic mouse models, we found that CX3CR1+ mononuclear phagocytes are required for AIEC-mediated Th17 induction and IL-10 is required to restrain pduC-dependent colitis. Using a catalytically-inactive mutant, we determined that PduC metabolic activity was required for this immune phenotype. Cell-free supernatants from WT AIEC (but not the isogenic, pduC-deficient clone) promoted ex vivo Th17 cell polarization and metabolomics analysis (LC-MS) of these supernatants defined PduC-dependent metabolites capable of promoting Th17 polarization. These studies reveal a link between AIEC metabolism and inflammatory Th17 cells with the potential to serve as a therapeutic target in the treatment of CD.

Multiple-Hit Hypothesis in Parkinson's Disease: LRRK2 and Inflammation.

The multiple hit hypothesis for Parkinson’s disease (PD) suggests that an interaction between multiple (genetic and/or environmental) risk factors is needed to trigger the pathology. Leucine-Rich Repeat Kinase 2 (LRRK2) is an interesting protein to study in this context and is the focus of this review. More than 15 years of intensive research have identified several cellular pathways in which LRRK2 is involved, yet its exact physiological role or contribution to PD is not completely understood. Pathogenic mutations in LRRK2 are the most common genetic cause of PD but most likely require additional triggers to develop PD, as suggested by the reduced penetrance of the LRRK2 G2019S mutation. LRRK2 expression is high in immune cells such as monocytes, neutrophils, or dendritic cells, compared to neurons or glial cells and evidence for a role of LRRK2 in the immune system is emerging. This has led to the hypothesis that an inflammatory trigger is needed for pathogenic LRRK2 mutations to induce a PD phenotype. In this review, we will discuss the link between LRRK2 and inflammation and how this could play an active role in PD etiology.

Resting-state “physiological networks”

Slow changes in systemic brain physiology can elicit large fluctuations in fMRI time series, which manifest as structured spatial patterns of temporal correlations between distant brain regions. Here, we investigated whether such “physiological networks”—sets of segregated brain regions that exhibit similar responses following slow changes in systemic physiology—resemble patterns associated with large-scale networks typically attributed to remotely synchronized neuronal activity. By analyzing a large group of subjects from the 3T Human Connectome Project (HCP) database, we demonstrate brain-wide and noticeably heterogenous dynamics tightly coupled to either respiratory variation or heart rate changes. We show, using synthesized data generated from physiological recordings across subjects, that these physiologically-coupled fluctuations alone can produce networks that strongly resemble previously reported resting-state networks, suggesting that, in some cases, the “physiological networks” seem to mimic the neuronal networks. Further, we show that such physiologically-relevant connectivity estimates appear to dominate the overall connectivity observations in multiple HCP subjects, and that this apparent “physiological connectivity” cannot be removed by the use of a single nuisance regressor for the entire brain (such as global signal regression) due to the clear regional heterogeneity of the physiologically-coupled responses. Our results challenge previous notions that physiological confounds are either localized to large veins or globally coherent across the cortex, therefore emphasizing the necessity to consider potential physiological contributions in fMRI-based functional connectivity studies. The rich spatiotemporal patterns carried by such “physiological” dynamics also suggest great potential for clinical biomarkers that are complementary to large-scale neuronal networks.

The unique expression profile of FAM19A1 in the mouse brain and its association with hyperactivity, long-term memory and fear acquisition

Neurodevelopment and mature brain function are spatiotemporally regulated by various cytokines and chemokines. The chemokine-like neuropeptide FAM19A1 is a member of family with sequence similarity 19 (FAM19), which is predominantly expressed in the brain. Its highly conserved amino acid sequence among vertebrates suggests that FAM19A1 may play important physiological roles in neurodevelopment and brain function. Here we used a LacZ reporter gene system to map the expression pattern of the FAM19A1 gene in the mouse brain. The FAM19A1 expression was observed in several brain regions starting during embryonic brain development. As the brain matured, the FAM19A1 expression was detected in the pyramidal cells of cortical layers 2/3 and 5 and in several limbic areas, including the hippocampus and the amygdala. FAM19A1-deficient mice were used to evaluate the physiological contribution of FAM19A1 to various brain functions. In behavior analysis, FAM19A1-deficient mice exhibited several abnormal behaviors, including hyperactive locomotor behavior, long-term memory deficits and fear acquisition failure. These findings provide insight into the potential contributions of FAM19A1 to neurodevelopment and mature brain function.

Editorial: Contributions of Behavior and Physiology to Conservation Biology

Editorial: Contributions of Behavior and Physiology to Conservation Biology

C2H2-Type Zinc Finger Proteins in Brain Development, Neurodevelopmental, and Other Neuropsychiatric Disorders: Systematic Literature-Based Analysis.

Neurodevelopmental disorders (NDDs) are multifaceted pathologic conditions manifested with intellectual disability, autistic features, psychiatric problems, motor dysfunction, and/or genetic/chromosomal abnormalities. They are associated with skewed neurogenesis and brain development, in part through dysfunction of the neural stem cells (NSCs) where abnormal transcriptional regulation on key genes play significant roles. Recent accumulated evidence highlights C2H2-type zinc finger proteins (C2H2-ZNFs), the largest transcription factor family in humans, as important targets for the pathologic processes associated with NDDs. In this review, we identified their significant accumulation (74 C2H2-ZNFs: ~10% of all human member proteins) in brain physiology and pathology. Specifically, we discuss their physiologic contribution to brain development, particularly focusing on their actions in NSCs. We then explain their pathologic implications in various forms of NDDs, such as morphological brain abnormalities, intellectual disabilities, and psychiatric disorders. We found an important tendency that poly-ZNFs and KRAB-ZNFs tend to be involved in the diseases that compromise gross brain structure and human-specific higher-order functions, respectively. This may be consistent with their characteristic appearance in the course of species evolution and corresponding contribution to these brain activities.

9 METABOLIC UTILIZATION OF PROPANEDIOL BY ADHERENT-INVASIVE E. COLI REGULATES INTESTINAL TISSUE IMMUNITY

Abstract While the molecular mechanisms by which the microbiome modulates mucosal immunity in Crohn’s disease (CD) are still largely unknown, recent data highlight the involvement of specific diet- and bacterial-derived metabolites in the regulation of intestinal immune cell activation and differentiation. We have recently shown that Adherent-Invasive E.coli (AIEC), which are enriched in CD patients, are sufficient to induce intestinal Th17 cells. Although AIEC lack pathogenic factors including type III secretion systems, many CD-derived isolates express virulence-associated metabolic enzymes including propanediol dehydratase (PduC), which enables AIEC to use fucose-derived propanediol as an alternate carbon source in the gut. We found that pduC is enriched in the microbiome and among E. coli genomes in CD patients compared to healthy controls. With fucosylated oligosaccharides on the surface of intestinal epithelial cells, we hypothesized that this propanediol utilization pathway provides AIEC a competitive advantage for epithelial cell adherence and intestinal immune cell activation. To evaluate the physiologic contribution of pduC to mucosal Th17 induction, we generated a pduC-deficient (ΔpduC) mutant of a CD-derived, AIEC isolate. Deletion of pduC resulted in reduced inflammatory Th17 cells and attenuated weight loss following T cell transfer colitis. Using genetic mouse models, we found that CX3CR1+ mononuclear phagocytes are required for this AIEC-mediated Th17 induction and IL-10 is required to restrain pduC-dependent dextran sodium sulfate (DSS)-induced colitis. Using a catalytically-inactive mutant, we determined that PduC metabolic activity was required for this immune phenotype. Cell-free supernatants from WT AIEC (but not the isogenic, pduC-deficient clone) promoted ex vivo Th17 cell polarization and metabolomics analysis (LC-MS) of these supernatants defined PduC-dependent metabolites capable of promoting Th17 polarization. These studies reveal a link between AIEC microbial metabolism and inflammatory Th17 cells with the potential to serve as a therapeutic target in the treatment of Crohn’s disease.

9 METABOLIC UTILIZATION OF PROPANEDIOL BY ADHERENT-INVASIVE E. COLI REGULATES INTESTINAL TISSUE IMMUNITY

While the molecular mechanisms by which the microbiome modulates mucosal immunity in Crohn’s disease (CD) are still largely unknown, recent data highlight the involvement of specific diet- and bacterial-derived metabolites in the regulation of intestinal immune cell activation and differentiation. We have recently shown that Adherent-Invasive E.coli (AIEC), which are enriched in CD patients, are sufficient to induce intestinal Th17 cells. Although AIEC lack pathogenic factors including type III secretion systems, many CD-derived isolates express virulence-associated metabolic enzymes including propanediol dehydratase (PduC), which enables AIEC to use fucose-derived propanediol as an alternate carbon source in the gut. We found that pduC is enriched in the microbiome and among E. coli genomes in CD patients compared to healthy controls. With fucosylated oligosaccharides on the surface of intestinal epithelial cells, we hypothesized that this propanediol utilization pathway provides AIEC a competitive advantage for epithelial cell adherence and intestinal immune cell activation. To evaluate the physiologic contribution of pduC to mucosal Th17 induction, we generated a pduC-deficient (ΔpduC) mutant of a CD-derived, AIEC isolate. Deletion of pduC resulted in reduced inflammatory Th17 cells and attenuated weight loss following T cell transfer colitis. Using genetic mouse models, we found that CX3CR1+ mononuclear phagocytes are required for this AIEC-mediated Th17 induction and IL-10 is required to restrain pduC-dependent dextran sodium sulfate (DSS)-induced colitis. Using a catalytically-inactive mutant, we determined that PduC metabolic activity was required for this immune phenotype. Cell-free supernatants from WT AIEC (but not the isogenic, pduC-deficient clone) promoted ex vivo Th17 cell polarization and metabolomics analysis (LC-MS) of these supernatants defined PduC-dependent metabolites capable of promoting Th17 polarization. These studies reveal a link between AIEC microbial metabolism and inflammatory Th17 cells with the potential to serve as a therapeutic target in the treatment of Crohn’s disease.

Renal sympathetic denervation for resistant hypertension: where do we stand after more than a decade.

Despite the current availability of safe and efficient drugs for treating hypertension, a substantial number of patients are drug-resistant hypertensives. Aiming this condition, a relatively new approach named catheter-based renal denervation was developed. We have now a clinically relevant time window to review the efficacy of renal denervation for treating this form of hypertension. This short review addresses the physiological contribution of renal sympathetic nerves for blood pressure control and discusses the pros and cons of renal denervation procedure for the treatment of resistant hypertension.

Predictors of Fear of Falling among Iranian Older Adults with Hip Fracture and Controls

ABSTRACT Objectives To investigate predictors of fear of falling (FOF) among older people with or without hip fracture. Methods The FOF was assessed by the Visual Analogue Scale (VAS-FOF), anxiety and depression by the Hospital Anxiety and Depression Scale (HADS). The modified Berg Balance Scale (mBBS) to evaluate functional balance was used. All people were asked to complete the dizziness Handicap Inventory (DHI) and the 36-item Short Form Health Survey (SF-36) for evaluating quality of life. Results Eighty-eight older adults (44 cases; 44 controls) took part in this study. The case group had received surgical intervention for femoral neck or trochanteric fracture resulting from a fall. The results showed significantly more intensity of FOF in hip fracture patients than controls (p < .001). The FOF was significantly correlated with anxiety, DHI, mBBS, and SF-36. The results of the multiple linear regression showed that four predictors explained about 44% of the variance of the FOF. It was found that mBBS and DHI significantly predicted FOF (p < .001 and < .001, respectively). Conclusions The hip fracture patients had a high degree of the fear of falling, low quality of life and low functional capacity. The mBBS and DHI were significant predictors of the FOF in older adults. Clinical implications It may be useful to employ an inter-disciplinary approach to addressing fear of falling to best understand physiological and psychological contributions.

Modulation of simultaneously collected hemodynamic and electrophysiological functional connectivity by ketamine and midazolam.

The pharmacological modulation of functional connectivity in the brain may underlie therapeutic efficacy for several neurological and psychiatric disorders. Functional magnetic resonance imaging (fMRI) provides a noninvasive method of assessing this modulation, however, the indirect nature of the blood‐oxygen level dependent signal restricts the discrimination of neural from physiological contributions. Here we followed two approaches to assess the validity of fMRI functional connectivity in developing drug biomarkers, using simultaneous electroencephalography (EEG)/fMRI in a placebo‐controlled, three‐way crossover design with ketamine and midazolam. First, we compared seven different preprocessing pipelines to determine their impact on the connectivity of common resting‐state networks. Independent components analysis (ICA)‐denoising resulted in stronger reductions in connectivity after ketamine, and weaker increases after midazolam, than pipelines employing physiological noise modelling or averaged signals from cerebrospinal fluid or white matter. This suggests that pipeline decisions should reflect a drug's unique noise structure, and if this is unknown then accepting possible signal loss when choosing extensive ICA denoising pipelines could engender more confidence in the remaining results. We then compared the temporal correlation structure of fMRI to that derived from two connectivity metrics of EEG, which provides a direct measure of neural activity. While electrophysiological estimates based on the power envelope were more closely aligned to BOLD signal connectivity than those based on phase consistency, no significant relationship between the change in electrophysiological and hemodynamic correlation structures was found, implying caution should be used when making cross‐modal comparisons of pharmacologically‐modulated functional connectivity.

Does Attention Modify Contributions to Heaviness Perception?

ABSTRACT Purpose: The current study investigated the effect of attention on heaviness perception and its physiological and kinematic contributions. Method: Participants lifted objects that varied in mass and volume while their muscle activity and movement were recorded. Participants were instructed to pay attention to their arm (internal) or the object (external). Results: While heaviness perception did not change as a function of attention, whether muscle activity and movement combined for perception differed across attention conditions. Specifically, muscle activity and movement combined to significantly predict heaviness perception in the external condition, but not the internal condition. Additionally, movement was more salient for perception in both conditions compared to previous research investigating the contribution of muscle activity and movement to heaviness perception. Conclusion: It is suggested that these results support the constrained action hypothesis, which suggests that adopting an external focus of attention benefits motor task performance and learning, and should be further explored in the context of a theory of haptic perception that suggests that the medium for haptic perception is the multifractal tensegrity structure of the body.

Helical fibrillar microstructure of tendon using serial block-face scanning electron microscopy and a mechanical model for interfibrillar load transfer.

Tendon's hierarchical structure allows for load transfer between its fibrillar elements at multiple length scales. Tendon microstructure is particularly important, because it includes the cells and their surrounding collagen fibrils, where mechanical interactions can have potentially important physiological and pathological contributions. However, the three-dimensional (3D) microstructure and the mechanisms of load transfer in that length scale are not known. It has been postulated that interfibrillar matrix shear or direct load transfer via the fusion/branching of small fibrils are responsible for load transfer, but the significance of these mechanisms is still unclear. Alternatively, the helical fibrils that occur at the microstructural scale in tendon may also mediate load transfer; however, these structures are not well studied due to the lack of a three-dimensional visualization of tendon microstructure. In this study, we used serial block-face scanning electron microscopy to investigate the 3D microstructure of fibrils in rat tail tendon. We found that tendon fibrils have a complex architecture with many helically wrapped fibrils. We studied the mechanical implications of these helical structures using finite-element modelling and found that frictional contact between helical fibrils can induce load transfer even in the absence of matrix bonding or fibril fusion/branching. This study is significant in that it provides a three-dimensional view of the tendon microstructure and suggests friction between helically wrapped fibrils as a mechanism for load transfer, which is an important aspect of tendon biomechanics.

RARG Gene Dysregulation in Acute Myeloid Leukemia.

Retinoic acid receptor γ (RARγ) belongs to the nuclear receptor superfamily and shares 90% homology with retinoic acid receptor α (RARα) and retinoic acid receptor β (RARβ). RARA rearrangements are well-known to be involved in acute promyelocytic leukemia (APL), but RARG rearrangements can also resemble this kind of leukemia. In this review we trace the role of RARγ, considering both its physiological and oncogenic contribution; from 2011 to date, nine cases of patients harboring RARG fusions have been reported. These patients showed typical APL features, including the clinical presentation, coagulation abnormalities and morphological features of bone marrow (BM), but are not responsive to APL standard therapy. We stress the urgent need for a better comprehension of the critical role of RARG dysregulation in the leukemogenesis process, since optimum therapy strategies have not yet been established.

Embryonic lineage tracing with Procr-CreER marks balanced hematopoietic stem cell fate during entire mouse lifespan

The functional heterogeneity of hematopoietic stem cells (HSCs) has been comprehensively investigated by single-cell transplantation assay. However, the heterogeneity regarding their physiological contribution remains an open question, especially for those with life-long hematopoietic fate of rigorous self-renewing and balanced differentiation capacities. In this study, we revealed that Procr expression was detected principally in phenotypical vascular endothelium co-expressing Dll4 and CD44 in the mid-gestation mouse embryos, and could enrich all the HSCs of the embryonic day 11.5 (E11.5) aorta-gonad-mesonephros (AGM) region. We then used a temporally restricted genetic tracing strategy to irreversibly label the Procr-expressing cells at E9.5. Interestingly, most labeled mature HSCs in multiple sites (such as AGM) around E11.5 were functionally categorized as lymphomyeloid-balanced HSCs assessed by direct transplantation. Furthermore, the labeled cells contributed to an average of 7.8% of immunophenotypically defined HSCs in E14.5 fetal liver (FL) and 6.9% of leukocytes in peripheral blood (PB) during one-year follow-up. Surprisingly, in aged mice of 24 months, the embryonically tagged cells displayed constant contribution to leukocytes with no bias to myeloid or lymphoid lineages. Altogether, we demonstrated, for the first time, the existence of a subtype of physiologically long-lived balanced HSCs as hypothesized, whose precise embryonic origin and molecular identity await further characterization.