Early restriction of peripheral and proximal cell lineages during formation of the lung

Smad4 deficiency ameliorates the progressive corneal stroma thinning caused by the loss of Tbr1

PURPOSE

To understand how Tbr1 and Smad4 play a pivotal role in controlling ECM synthesis versus degradation for maintaining corneal stromal homeostasis and otherwise leading to corneal ectasia.

METHODS

Keratocyte-specific and inducible knockout (iKO) of Tbr1, Smad4, or Tbr1/Smad4 double KO (iDKO) mice were generated. OCT was used to assess corneal thickness in vivo. Masson's trichrome and collagen hybridizing peptide stainings were performed to examine collagen expression. Immunostaining with an anti-cathepsin B antibody was used to assess ECM degradation. Cathepsin B inhibitor, CA-074Me, eyedrop was conducted to test its effect on treating stromal thinning in Tbr1 iKO mice.

RESULTS

Tbr1 iKO and Smad4 iKO displayed corneal thinning, but Tbr1 iKO revealed a progressive and more severe pathology than Smad4 iKO. Tbr1 iKO cornea lost most of its stroma and thus a dome shape. Collagen ECM is evenly distributed in Smad4 iKO as well as control littermates but was lost mainly in the anterior stroma of the Tbr1 iKO. Interestingly, Tbr1/Smad4 iDKO ameliorated Tbr1 iKO phenotype. The basal level of Cathepsin b (Ctsb) could be detected in the control stroma but was significantly increased in the Tbr1 iKO stromal cells and this effect was canceled in Tbr1/Smad4 iDKO. CA-074Me eyedrops administration significantly inhibited progressive corneal thinning caused by the Tbr1 iKO.

CONCLUSION

Our data from Tbr1/Smad4 iDKO argued that Smad4 played a pivotal role in controlling Tbr1-dependent ECM synthesis and Tbr1-independent ECM degradation to maintain corneal stromal integrity and homeostasis.

Identifying specific functional roles for senescence across cell types

Cellular senescence plays critical roles in aging, regeneration, and disease; yet, the ability to discern its contributions across various cell types to these biological processes remains limited. In this study, we generated an in vivo genetic toolbox consisting of three p16Ink4a-related intersectional genetic systems, enabling pulse-chase tracing (Sn-pTracer), Cre-based tracing and ablation (Sn-cTracer), and gene manipulation combined with tracing (Sn-gTracer) of defined p16Ink4a+ cell types. Using liver injury and repair as an example, we found that macrophages and endothelial cells (ECs) represent distinct senescent cell populations with different fates and functions during liver fibrosis and repair. Notably, clearance of p16Ink4a+ macrophages significantly mitigates hepatocellular damage, whereas eliminating p16Ink4a+ ECs aggravates liver injury. Additionally, targeted reprogramming of p16Ink4a+ ECs through Kdr overexpression markedly reduces liver fibrosis. This study illuminates the functional diversity of p16Ink4a+ cells and offers insights for developing cell-type-specific senolytic therapies in the future.

Rediscovering the Rete Ovarii: a secreting auxiliary structure to the ovary

The rete ovarii (RO) is an appendage of the ovary that has been given little attention. Although the RO appears in drawings of the ovary in early versions of Grays Anatomy, it disappeared from recent textbooks, and is often dismissed as a functionless vestige in the adult ovary. Using PAX8 immunostaining and confocal microscopy, we characterized the fetal development of the RO in the context of the ovary. The RO consists of three distinct regions that persist in adult life, the intraovarian rete (IOR), the extraovarian rete (EOR), and the connecting rete (CR). While the cells of the IOR appear to form solid cords within the ovary, the EOR rapidly develops into a convoluted tubular epithelium ending in a distal dilated tip. Cells of the EOR are ciliated and exhibit cellular trafficking capabilities. The CR, connecting the EOR to the IOR, gradually acquires tubular epithelial characteristics by birth. Using microinjections into the distal dilated tip of the EOR, we found that luminal contents flow towards the ovary. Mass spectrometry revealed that the EOR lumen contains secreted proteins potentially important for ovarian function. We show that the cells of the EOR are closely associated with vasculature and macrophages, and are contacted by neuronal projections, consistent with a role as a sensory appendage of the ovary. The direct proximity of the RO to the ovary and its integration with the extraovarian landscape suggest that it plays an important role in ovary development and homeostasis.

Wnt7b overexpression in osteoblasts stimulates bone formation and reduces obesity in mice on a high-fat diet

Previous studies have shown that Wnt7b potently stimulates bone formation by promoting osteoblast differentiation and activity. As high-fat feeding leads to obesity and systemic metabolic dysregulation, here we investigate the potential benefit of Wnt7b overexpression in osteoblasts on both bone and whole-body metabolism in mice fed with a high-fat diet (HFD). Wnt7b overexpression elicited massive overgrowth of trabecular and cortical bone but seemed to ameliorate body fat accumulation in mice with prolonged HFD feeding. In addition, Wnt7b overexpression modestly improved glucose tolerance in male mice on HFD. Collectively, the results indicate that targeted overexpression of Wnt7b in osteoblasts not only stimulates bone formation but also improves certain aspects of global metabolism in overnourished mice.

β-Catenin gain of function mutant in mouse periocular neural crest-derived mesenchymal cells impairs embryonic eyelid morphogenesis and leads to blepharophimosis syndrome in mice

PURPOSE

The aberrant canonical Wnt-β-catenin signaling can cause devastating outcomes of tissue morphogenesis and tumor formation. In this study, we examined the impact of overexpression of constitutive active β-catenin in mouse periocular neural crest-derived mesenchymal cells during embryonic eyelid morphogenesis.

METHODS

We expressed a stabilized β-catenin in which the exon 3 of the Ctnnb1 gene was deleted in periocular neural crest (PONC)-derived eyelid stromal cells (Ctnnb1Δex3-PONC). Histopathological examinations were performed to examine the eyelid morphogenetic alterations in Ctnnb1Δex3-PONC mice. Immunohistochemical investigations for cell proliferation, apoptosis, and differentiation were also assessed.

RESULTS

We discovered that nuclear accumulation of β-catenin resulted in a reduction of nuclear Ki-67 and phospho-Erk1/2 expression levels and elevation of apoptosis in PONC cells during embryonic eyelid closure morphogenesis. Interestingly, however, the eyelid epithelial migration was not affected, which resulted in only eyelid epidermal closure but lacked underneath dermal formation at embryonic (E) day 16.5. The sequelae of Ctnnb1Δex3-PONC revealed the malformation of the eyelid margin and Meibomian gland and deficiency of Muller's smooth muscle fibers formation. Consequently, Ctnnb1Δex3-PONC mice manifested blepharophimosis syndrome at P21.

CONCLUSION

Our data suggested that aberrant expression of β-catenin gain of function in PONC interrupts the interplay between epithelium and stroma for the morphogenesis of eyelid closure during embryonic development.

Mesenchymal Vangl1 and Vangl2 facilitate airway elongation and widening independently of the planar cell polarity complex

Adult mammalian lungs exhibit a fractal pattern, as each successive generation of airways is a fraction of the size of the parental branch. Achieving this structure likely requires precise control of airway length and diameter, as the embryonic airways initially lack the fractal scaling observed in the adult. In monolayers and tubes, directional growth can be regulated by the planar cell polarity (PCP) complex. Here, we characterized the roles of PCP complex components in airway initiation, elongation and widening during branching morphogenesis of the lung. Using tissue-specific knockout mice, we surprisingly found that branching morphogenesis proceeds independently of PCP complex function in the lung epithelium. Instead, we found a previously unreported Celsr1-independent role for the PCP complex components Vangl1 and Vangl2 in the pulmonary mesenchyme, where they are required for branch initiation, elongation and widening. Our data thus reveal an explicit function for Vangl1 and Vangl2 that is independent of the core PCP complex, suggesting a functional diversification of PCP complex components in vertebrate development. These data also reveal an essential role for the embryonic mesenchyme in generating the fractal structure of airways in the mature lung.

Cxcr4 regulates a pool of adipocyte progenitors and contributes to adiposity in a sex-dependent manner

Sex steroids modulate the distribution of mammalian white adipose tissues. Moreover, WAT remodeling requires adipocyte progenitor cells. Nevertheless, the sex-dependent mechanisms regulating adipocyte progenitors remain undetermined. Here, we uncover Cxcr4 acting in a sexually dimorphic manner to affect a pool of proliferating cells leading to restriction of female fat mass. We find that deletion of Cxcr4 in Pparγ-expressing cells results in female, not male, lipodystrophy, which cannot be restored by high-fat diet consumption. Additionally, Cxcr4 deletion is associated with a loss of a pool of proliferating adipocyte progenitors. Cxcr4 loss is accompanied by the upregulation of estrogen receptor alpha in adipose-derived PPARγ-labelled cells related to estradiol hypersensitivity and stalled adipogenesis. Estrogen removal or administration of antiestrogens restores WAT accumulation and dynamics of adipose-derived cells in Cxcr4-deficient mice. These findings implicate Cxcr4 as a female adipogenic rheostat, which may inform strategies to target female adiposity.

Cerebellar output neurons impair non-motor behaviors by altering development of extracerebellar connectivity

The capacity of the brain to compensate for insults during development depends on the type of cell loss, whereas the consequences of genetic mutations in the same neurons are difficult to predict. We reveal powerful compensation from outside the cerebellum when the excitatory cerebellar output neurons are ablated embryonically and demonstrate that the minimum requirement for these neurons is for motor coordination and not learning and social behaviors. In contrast, loss of the homeobox transcription factors Engrailed1/2 (EN1/2) in the cerebellar excitatory lineage leads to additional deficits in adult learning and spatial working memory, despite half of the excitatory output neurons being intact. Diffusion MRI indicates increased thalamo-cortico-striatal connectivity in En1/2 mutants, showing that the remaining excitatory neurons lacking En1/2 exert adverse effects on extracerebellar circuits regulating motor learning and select non-motor behaviors. Thus, an absence of cerebellar output neurons is less disruptive than having cerebellar genetic mutations.

HDAC1/2 and HDAC3 play distinct roles in controlling adult Meibomian gland homeostasis

PURPOSE

To investigate the roles of HDAC1/2 and HDAC3 in adult Meibomian gland (MG) homeostasis.

METHODS

HDAC1/2 or HDAC3 were inducibly deleted in MG epithelial cells of adult mice. The morphology of MG was examined. Proliferation, apoptosis, and expression of MG acinus and duct marker genes, meibocyte differentiation genes, and HDAC target genes, were analyzed via immunofluorescence, TUNEL assay, and RNA in situ hybridization.

RESULTS

Co-deletion of HDAC1/2 in MG epithelium caused gradual loss of acini and formation of cyst-like structures in the central duct. These phenotypes required homozygous deletion of both HDAC1 and HDAC2, indicating that they function redundantly in the adult MG. Short-term deletion of HDAC1/2 in MG epithelium had little effect on meibocyte maturation but caused decreased proliferation of acinar basal cells, excessive DNA damage, ectopic apoptosis, and increased p53 acetylation and p16 expression in the MG. By contrast, HDAC3 deletion in MG epithelium caused dilation of central duct, atrophy of acini, defective meibocyte maturation, increased acinar basal cell proliferation, and ectopic apoptosis and DNA damage. Levels of p53 acetylation and p21 expression were elevated in HDAC3-deficient MGs, while the expression of the differentiation regulator PPARγ and the differentiation markers PLIN2 and FASN was downregulated.

CONCLUSIONS

HDAC1 and HDAC2 function redundantly in adult Meibomian gland epithelial progenitor cells and are essential for their proliferation and survival, but not for acinar differentiation, while HDAC3 is required to limit acinar progenitor cell proliferation and permit differentiation. HDAC1/2 and HDAC3 have partially overlapping roles in maintaining survival of MG cells.

FGF signaling modulates mechanotransduction/WNT signaling in progenitors during tooth root development

Stem/progenitor cells differentiate into different cell lineages during organ development and morphogenesis. Signaling pathway networks and mechanotransduction are important factors to guide the lineage commitment of stem/progenitor cells during craniofacial tissue morphogenesis. Here, we used tooth root development as a model to explore the roles of FGF signaling and mechanotransduction as well as their interaction in regulating the progenitor cell fate decision. We show that Fgfr1 is expressed in the mesenchymal progenitor cells and their progeny during tooth root development. Loss of Fgfr1 in Gli1+ progenitors leads to hyperproliferation and differentiation, which causes narrowed periodontal ligament (PDL) space with abnormal cementum/bone formation leading to ankylosis. We further show that aberrant activation of WNT signaling and mechanosensitive channel Piezo2 occurs after loss of FGF signaling in Gli1-CreER;Fgfr1fl/fl mice. Overexpression of Piezo2 leads to increased osteoblastic differentiation and decreased Piezo2 leads to downregulation of WNT signaling. Mechanistically, an FGF/PIEZO2/WNT signaling cascade plays a crucial role in modulating the fate of progenitors during root morphogenesis. Downregulation of WNT signaling rescues tooth ankylosis in Fgfr1 mutant mice. Collectively, our findings uncover the mechanism by which FGF signaling regulates the fate decisions of stem/progenitor cells, and the interactions among signaling pathways and mechanotransduction during tooth root development, providing insights for future tooth root regeneration.

The molecular and cellular choreography of early mammalian lung development

Mammalian lung development starts from a specific cluster of endodermal cells situated within the ventral foregut region. With the orchestrating of delicate choreography of transcription factors, signaling pathways, and cell-cell communications, the endodermal diverticulum extends into the surrounding mesenchyme, and builds the cellular and structural basis of the complex respiratory system. This review provides a comprehensive overview of the current molecular insights of mammalian lung development, with a particular focus on the early stage of lung cell fate differentiation and spatial patterning. Furthermore, we explore the implications of several congenital respiratory diseases and the relevance to early organogenesis. Finally, we summarize the unprecedented knowledge concerning lung cell compositions, regulatory networks as well as the promising prospect for gaining an unbiased understanding of lung development and lung malformations through state-of-the-art single-cell omics.

LARP7 overexpression alleviates aortic senescence and atherosclerosis

Atherosclerosis, characterized by the accumulation of lipid plaques on the inner walls of arteries, is the leading cause of heart attack, stroke and severe ischemic injuries. Senescent cells have been found to accumulate within atherosclerotic lesions and contribute to the progression of atherosclerosis. In our previous study, we discovered that suppressing Larp7 accelerates senescence by inhibiting Sirt1 activity, resulting in increased atherosclerosis in high-fat diet (HFD) fed and ApoE deficient (ApoEKO) mice. However, there has been no direct evidence demonstrating Larp7 per se could attenuate atherosclerosis. To this end, we generated a tetO-controlled and Cre-activated Larp7 gain-of-function mouse. Through RT-PCR and western blotting, we confirmed Larp7 overexpression in the aortas of HFD-fed ApoEKO; Larp7tetO mice. Larp7 overexpression led to increased Sirt1 activity and decreased cellular senescence signals mediated by p53/p65 in the aortas. Additionally, Larp7 overexpression reduced the presence of p16-positive senescent cells in the aortic lesions. Furthermore, Larp7 overexpression resulted in a decrease in pro-inflammatory macrophages and SASP factors. Consequently, Larp7 overexpression led to a reduction in the area of atherosclerotic lesions in HFD-fed ApoEKO; Larp7tetO mice. In summary, our study provides evidence that Larp7 overexpression holds promise as an approach to inhibit cellular senescence and prevent atherosclerosis.

Stabilization of Epithelial β-Catenin Compromises Mammary Cell Fate Acquisition and Branching Morphogenesis

The Wnt/β-catenin pathway plays a critical role in cell fate specification, morphogenesis, and stem cell activation across diverse tissues, including the skin. In mammals, the embryonic surface epithelium gives rise to the epidermis as well as the associated appendages including hair follicles and mammary glands, both of which depend on epithelial Wnt/β-catenin activity for initiation of their development. Later on, Wnts are thought to enhance mammary gland growth and branching, whereas in hair follicles, they are essential for hair shaft formation. In this study, we report a strong downregulation of epithelial Wnt/β-catenin activity as the mammary bud progresses to branching. We show that forced activation of epithelial β-catenin severely compromises embryonic mammary gland branching. However, the phenotype of conditional Lef1-deficient embryos implies that a low level of Wnt/β-catenin activity is necessary for mammary cell survival. Transcriptomic profiling suggests that sustained high β-catenin activity leads to maintenance of mammary bud gene signature at the expense of outgrowth/branching gene signature. In addition, it leads to upregulation of epidermal differentiation genes. Strikingly, we find a partial switch to hair follicle fate early on upon stabilization of β-catenin, suggesting that the level of epithelial Wnt/β-catenin signaling activity may contribute to the choice between skin appendage identities.

Kidney collecting duct cell type composition is regulated by Notch signaling via modulation of mTORC1

The plasticity and diversity of cell types with specialized functions likely defines the capacity of multicellular organisms to adapt to physiologic stressors. The kidney collecting ducts contribute to water, electrolyte, and pH homeostasis and are composed of mature intermingled epithelial cell types that are susceptible to transdifferentiate. The conversion of kidney collecting duct principal cells to intercalated cells is actively inhibited by Notch signaling to ensure urine concentrating capability. Here we identify Hes1, a target of Notch signaling, allows for maintenance of functionally distinct epithelial cell types within the same microenvironment by regulating mechanistic target of rapamycin complex 1 (mTORC1) activity. Hes1 directly represses the expression of insulin receptor substrate 1 ( Irs1 ), an upstream component of mTOR pathway and suppresses mTORC1 activity in principal cells. Genetic inactivation of tuberous sclerosis complex 2 ( Tsc2 ) to increase mTORC1 activity in mature principal cells is sufficient to promote acquisition of intercalated cell properties, while inhibition of mTORC1 in adult kidney epithelia suppresses intercalated cell properties. Considering that mTORC1 integrates environmental cues, the linkage of functionally distinct epithelial cell types to mTORC1 activity levels likely allows for cell plasticity to be regulated by physiologic and metabolic signals and the ability to sense/transduce these signals.

Modulating inflammation with interleukin 37 treatment ameliorates murine Autosomal Dominant Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a leading cause of kidney failure and is associated with substantial morbidity and mortality. Interstitial inflammation is attributed to the action of infiltrating macrophages and is a feature thought to aggravate disease progression. Here, we investigated the therapeutic potential of the anti-inflammatory IL37b cytokine as a treatment for ADPKD using genetic mouse models, demonstrating that transgenic expression of human IL37b reduced collecting duct cyst burden in both early and adult-onset ADPKD rodent models. Moreover, injection of recombinant human IL37b could also reduce cyst burden in early onset ADPKD mice, an observation not associated with increased macrophage number at early stages of cyst formation. Interestingly, transgenic IL37b expression also did not alter macrophage numbers in advanced disease. Whole kidney RNA-seq highlighted an IL37b-mediated upregulation of the interferon signaling pathway and single-cell RNA-seq established that these changes originate at least partly from kidney resident macrophages. We further found that blocking type I interferon signaling in mice expressing IL37b resulted in increased cyst number, confirming this as an important pathway by which IL37b exerts its beneficial effects. Thus, our studies show that IL37b promotes interferon signaling in kidney resident macrophages which suppresses cyst initiation, identifying this protein as a potential therapy for ADPKD.

Streamlined identification of clinically and functionally relevant genetic regulators of lower-tract urogenital development

Congenital anomalies of the lower genitourinary (LGU) tract are frequently comorbid due to genetically linked developmental pathways, and are among the most common yet most socially stigmatized congenital phenotypes. Genes involved in sexual differentiation are prime candidates for developmental anomalies of multiple LGU organs, but insufficient prospective screening tools have prevented the rapid identification of causative genes. Androgen signaling is among the most influential modulators of LGU development. The present study uses SpDamID technology in vivo to generate a comprehensive map of the pathways actively regulated by the androgen receptor (AR) in the genitalia in the presence of the p300 coactivator, identifying wingless/integrated (WNT) signaling as a highly enriched AR-regulated pathway in the genitalia. Transcription factor (TF) hits were then assayed for sexually dimorphic expression at two critical time points and also cross-referenced to a database of clinically relevant copy number variations to identify 252 TFs exhibiting copy variation in patients with LGU phenotypes. A subset of 54 TFs was identified for which LGU phenotypes are statistically overrepresented as a proportion of total observed phenotypes. The 252 TF hitlist was then subjected to a functional screen to identify hits whose silencing affects genital mesenchymal growth rates. Overlap of these datasets results in a refined list of 133 TFs of both functional and clinical relevance to LGU development, 31 of which are top priority candidates, including the well-documented renal progenitor regulator, Sall1. Loss of Sall1 was examined in vivo and confirmed to be a powerful regulator of LGU development.

Platelet-derived growth factor receptor beta is required for embryonic specification and confinement of the adult white adipose lineage

White adipose tissue (WAT) development and adult homeostasis rely on distinct adipocyte progenitor cells (APCs). While adult APCs are defined early during embryogenesis and generate adipocytes after WAT organogenesis, the mechanisms underlying adult adipose lineage determination and preservation remain undefined. Here, we uncover a critical role for platelet-derived growth factor receptor beta (Pdgfrβ) in identifying the adult APC lineage. Without Pdgfrβ, APCs lose their adipogenic competency to incite fibrotic tissue replacement and inflammation. Through lineage tracing analysis, we reveal that the adult APC lineage is lost and develops into macrophages when Pdgfrβ is deleted embryonically. Moreover, to maintain the APC lineage, Pdgfrβ activation stimulates p38/MAPK phosphorylation to promote APC proliferation and maintains the APC state by phosphorylating peroxisome proliferator activated receptor gamma (Pparγ) at serine 112. Together, our findings identify a role for Pdgfrβ acting as a rheostat for adult adipose lineage confinement to prevent unintended lineage switches.

Sensory nerve regulates progenitor cells via FGF-SHH axis in tooth root morphogenesis

Nerves play important roles in organ development and tissue homeostasis. Stem/progenitor cells differentiate into different cell lineages responsible for building the craniofacial organs. The mechanism by which nerves regulate stem/progenitor cell behavior in organ morphogenesis has not yet been comprehensively explored. Here, we use tooth root development in mouse as a model to investigate how sensory nerves regulate organogenesis. We show that sensory nerve fibers are enriched in the dental papilla at the initiation of tooth root development. Through single cell RNA-sequencing analysis of the trigeminal ganglion and developing molar, we reveal several signaling pathways that connect the sensory nerve with the developing molar, of which FGF signaling appears to be one of the important regulators. Fgfr2 is expressed in the progenitor cells during tooth root development. Loss of FGF signaling leads to shortened roots with compromised proliferation and differentiation of progenitor cells. Furthermore, Hh signaling is impaired in Gli1-CreER;Fgfr2fl/fl mice. Modulation of Hh signaling rescues the tooth root defects in these mice. Collectively, our findings elucidate the nerve-progenitor crosstalk and reveal the molecular mechanism of the FGF-SHH signaling cascade during tooth root morphogenesis.

Sweat gland development requires an eccrine dermal niche and couples two epidermal programs

Eccrine sweat glands are indispensable for human thermoregulation and, similar to other mammalian skin appendages, form from multipotent epidermal progenitors. Limited understanding of how epidermal progenitors specialize to form these vital organs has precluded therapeutic efforts toward their regeneration. Herein, we applied single-nucleus transcriptomics to compare the expression content of wild-type, eccrine-forming mouse skin to that of mice harboring a skin-specific disruption of Engrailed 1 (En1), a transcription factor that promotes eccrine gland formation in humans and mice. We identify two concurrent but disproportionate epidermal transcriptomes in the early eccrine anlagen: one that is shared with hair follicles and one that is En1 dependent and eccrine specific. We demonstrate that eccrine development requires the induction of a dermal niche proximal to each developing gland in humans and mice. Our study defines the signatures of eccrine identity and uncovers the eccrine dermal niche, setting the stage for targeted regeneration and comprehensive skin repair.

The leptin receptor has no role in delta-cell control of beta-cell function in the mouse

Introduction

Leptin inhibits insulin secretion from isolated islets from multiple species, but the cell type that mediates this process remains elusive. Several mouse models have been used to explore this question. Ablation of the leptin receptor (Lepr) throughout the pancreatic epithelium results in altered glucose homeostasis and ex vivo insulin secretion and Ca2+ dynamics. However, Lepr removal from neither alpha nor beta cells mimics this result. Moreover, scRNAseq data has revealed an enrichment of LEPR in human islet delta cells.

Methods

We confirmed LEPR upregulation in human delta cells by performing RNAseq on fixed, sorted beta and delta cells. We then used a mouse model to test whether delta cells mediate the diminished glucose-stimulated insulin secretion in response to leptin.

Results

Ablation of Lepr within mouse delta cells did not change glucose homeostasis or insulin secretion, whether mice were fed a chow or high-fat diet. We further show, using a publicly available scRNAseq dataset, that islet cells expressing Lepr lie within endothelial cell clusters.

Conclusions

In mice, leptin does not influence beta-cell function through delta cells.

Conditional deletion of CD25 in the corneal epithelium reveals sex differences in barrier disruption

PURPOSE

IL-2 promotes activation, clonal expansion, and deletion of T cells. IL-2 signals through its heterotrimeric receptor (IL-2R) consisting of the CD25, CD122 and CD132 chains. CD25 knockout (KO) mice develop Sjögren Syndrome-like disease. This study investigates whether corneal CD25/IL-2 signaling is critical for ocular health.

METHODS

Eyes from C57BL/6 mice were collected and prepared for immunostaining or in-situ hybridization. Bulk RNA sequencing was performed on the corneal epithelium from wild-type and CD25KO mice. We generated a conditional corneal-specific deletion of CD25 in the corneal epithelium (CD25Δ/ΔCEpi). Corneal barrier function was evaluated based on the uptake of a fluorescent dye. Mice were subjected to unilateral corneal debridement, followed by epithelial closure over time.

RESULTS

In C57BL/6 mice, CD25 mRNA was expressed in ocular tissues. Protein expression of CD25, CD122, and CD132 was confirmed in the corneal epithelium. Delayed corneal re-epithelization was seen in female but not male CD25KO mice. There were 771 differentially expressed genes in the corneal epithelium of CD25KO compared to wild-type mice. While barrier function is disrupted in CD25Δ/ΔCEpi mice, re-epithelialization rates are not delayed.

CONCLUSIONS

All three chains of the IL-2R are expressed in the corneal epithelium. Our results indicate for the first time, deleting CD25 systemically in all tissues in the mouse and deleting CD25 locally in just the corneal epithelium compromises corneal epithelial barrier function, leading to dry eye disease in female mice. Future studies are needed to delineate the pathways used by IL-2 signaling to influence cornea homeostasis.

Abnormal Fetal Lung of Hoxa1-/- Piglets Is Rescued by Maternal Feeding with All-Trans Retinoic Acid

Neonatal Hoxa1-/- piglets were characterized by dyspnea owing to the Hoxa1 mutation, and maternal administration with ATRA alleviated the dyspnea of neonatal Hoxa1-/- piglets. The purpose of this experiment was to explore how maternal ATRA administration rescued the abnormal fetal lungs of Hoxa1-/- piglets. Samples of the lungs were collected from neonatal Hoxa1-/- and non-Hoxa1-/- piglets delivered by sows in the control group, and from neonatal Hoxa1-/- piglets born by sows administered with ATRA at 4 mg/kg body weight on dpc 12, 13, or 14, respectively. These were used for the analysis of ELISA, histological morphology, immunofluorescence staining, immunohistochemistry staining, and quantitative real-time PCR. The results indicate that the Hoxa1 mutation had adverse impacts on the development of the alveoli and pulmonary microvessels of Hoxa1-/- piglets. Maternal administration with ATRA at 4 mg/kg body weight on dpc 14 rescued the abnormal lung development of Hoxa1-/- piglets by increasing the IFN-γ concentration (p < 0.05), airspace area (p < 0.01) and pulmonary microvessel density (p < 0.01); increasing the expression of VEGFD (p < 0.01), PDGFD (p < 0.01), KDR (p < 0.01), ID1 (p < 0.01), and NEDD4 (p < 0.01); and decreasing the septal wall thickness (p < 0.01) and the expression of SFTPC (p < 0.01) and FOXO3 (p < 0.01). Maternal administration with ATRA plays a vital role in rescuing the abnormal development of lung of Hoxa1-/- fetal piglets.

Cell type and stage specific transcriptional, chromatin and cell-cell communication landscapes in the mammary gland

The mammary gland (MG) is composed of three main epithelial lineages, the basal cells (BC), the estrogen receptor (ER) positive luminal cells (ER+ LC), and the ER negative LC (ER- LC). Defining the cell identity of each lineage and how it is modulated throughout the different stages of life is important to understand how these cells function and communicate throughout life. Here, we used transgenic mice specifically labelling ER+ LC combined to cell surface markers to isolate with high purity the 3 distinct cell lineages of the mammary gland and defined their expression profiles and chromatin landscapes by performing bulk RNAseq and ATACseq of these isolated populations in puberty, adulthood and mid-pregnancy. Our analysis identified conserved genes, ligands and transcription factor (TF) associated with a specific lineage throughout life as well as genes, ligands and TFs specific for a particular stage of the MG. In summary, our study identified genes and TF network associated with the identity, function and cell-cell communication of the different epithelial lineages of the MG at different stages of life.

Dichotomous ovarian cancer-initiating potential of Pax8+ cells revealed by a mouse genetic mosaic model

Different cellular compartments within a tissue present distinct cancer-initiating capacities. Current approaches to dissect such heterogeneity require cell-type-specific genetic tools based on a well-understood lineage hierarchy, which are lacking for many tissues. Here, we circumvented this hurdle and revealed the dichotomous capacity of fallopian tube Pax8+ cells in initiating ovarian cancer, utilizing a mouse genetic system that stochastically generates rare GFP-labeled mutant cells. Through clonal analysis and spatial profiling, we determined that only clones founded by rare, stem/progenitor-like Pax8+ cells can expand on acquiring oncogenic mutations whereas vast majority of clones stall immediately. Furthermore, expanded mutant clones undergo further attrition: many turn quiescent shortly after the initial expansion, whereas others sustain proliferation and manifest a bias toward Pax8+ fate, underlying early pathogenesis. Our study showcases the power of genetic mosaic system-based clonal analysis for revealing cellular heterogeneity of cancer-initiating capacity in tissues with limited prior knowledge of lineage hierarchy.

Osteoblast-intrinsic defect in glucose metabolism impairs bone formation in type II diabetic male mice

Skeletal fragility is associated with type 2 diabetes mellitus (T2D), but the underlying mechanism is not well understood. Here, in a mouse model for youth-onset T2D, we show that both trabecular and cortical bone mass is reduced due to diminished osteoblast activity. Stable isotope tracing in vivo with 13C-glucose demonstrates that both glycolysis and glucose fueling of the TCA cycle are impaired in diabetic bones. Similarly, Seahorse assays show suppression of both glycolysis and oxidative phosphorylation by diabetes in bone marrow mesenchymal cells as a whole, whereas single-cell RNA sequencing reveals distinct modes of metabolic dysregulation among the subpopulations. Metformin not only promotes glycolysis and osteoblast differentiation in vitro, but also improves bone mass in diabetic mice. Finally, osteoblast-specific overexpression of either Hif1a, a general inducer of glycolysis, or Pfkfb3 which stimulates a specific step in glycolysis, averts bone loss in T2D mice. The study identifies osteoblast-intrinsic defects in glucose metabolism as an underlying cause of diabetic osteopenia, which may be targeted therapeutically.

ARF suppression by MYC but not MYCN confers increased malignancy of aggressive pediatric brain tumors

Medulloblastoma, the most common malignant pediatric brain tumor, often harbors MYC amplifications. Compared to high-grade gliomas, MYC-amplified medulloblastomas often show increased photoreceptor activity and arise in the presence of a functional ARF/p53 suppressor pathway. Here, we generate an immunocompetent transgenic mouse model with regulatable MYC that develop clonal tumors that molecularly resemble photoreceptor-positive Group 3 medulloblastoma. Compared to MYCN-expressing brain tumors driven from the same promoter, pronounced ARF silencing is present in our MYC-expressing model and in human medulloblastoma. While partial Arf suppression causes increased malignancy in MYCN-expressing tumors, complete Arf depletion promotes photoreceptor-negative high-grade glioma formation. Computational models and clinical data further identify drugs targeting MYC-driven tumors with a suppressed but functional ARF pathway. We show that the HSP90 inhibitor, Onalespib, significantly targets MYC-driven but not MYCN-driven tumors in an ARF-dependent manner. The treatment increases cell death in synergy with cisplatin and demonstrates potential for targeting MYC-driven medulloblastoma.

Sensory nerve niche regulates mesenchymal stem cell homeostasis via FGF/mTOR/autophagy axis

Mesenchymal stem cells (MSCs) reside in microenvironments, referred to as niches, which provide structural support and molecular signals. Sensory nerves are niche components in the homeostasis of tissues such as skin, bone marrow and hematopoietic system. However, how the sensory nerve affects the behavior of MSCs remains largely unknown. Here we show that the sensory nerve is vital for mesenchymal tissue homeostasis and maintenance of MSCs in the continuously growing adult mouse incisor. Loss of sensory innervation leads to mesenchymal disorder and a decrease in MSCs. Mechanistically, FGF1 from the sensory nerve directly acts on MSCs by binding to FGFR1 and activates the mTOR/autophagy axis to sustain MSCs. Modulation of mTOR/autophagy restores the MSCs and rescues the mesenchymal tissue disorder of Fgfr1 mutant mice. Collectively, our study provides insights into the role of sensory nerves in the regulation of MSC homeostasis and the mechanism governing it.

Osteoblast-intrinsic defect in glucose metabolism impairs bone formation in type II diabetic mice

Skeletal fragility is associated with type 2 diabetes mellitus (T2D), but the underlying mechanism is not well understood. Here, in a mouse model for youth-onset T2D, we show that both trabecular and cortical bone mass are reduced due to diminished osteoblast activity. Stable isotope tracing in vivo with 13 C-glucose demonstrates that both glycolysis and glucose fueling of the TCA cycle are impaired in diabetic bones. Similarly, Seahorse assays show suppression of both glycolysis and oxidative phosphorylation by diabetes in bone marrow mesenchymal cells as a whole, whereas single-cell RNA sequencing reveals distinct modes of metabolic dysregulation among the subpopulations. Metformin not only promotes glycolysis and osteoblast differentiation in vitro, but also improves bone mass in diabetic mice. Finally, targeted overexpression of Hif1a or Pfkfb3 in osteoblasts of T2D mice averts bone loss. The study identifies osteoblast-intrinsic defects in glucose metabolism as an underlying cause of diabetic osteopenia, which may be targeted therapeutically.

FOXM1 acts sexually dimorphically to regulate functional β-cell mass

The transcription factor FOXM1 regulates β-cell proliferation and insulin secretion. Our previous work demonstrates that expressing an activated form of FOXM1 (FOXM1*) in β cells increases β-cell proliferation and mass in aged male mice. Additionally, FOXM1* enhances β-cell function even in young mice, in which no β-cell mass elevation occurs. Here, we demonstrate that FOXM1 acts in a sexually dimorphic manner in the β cell. Expression of FOXM1* in female mouse β cells does not affect β-cell proliferation or glucose tolerance. Transduction of male but not female human islets with FOXM1* enhances insulin secretion in response to elevated glucose. Estrogen contributes to diabetes susceptibility differences between males and females, and the estrogen receptor (ER)α is the primary mediator of β-cell estrogen signaling. We show that FOXM1* can rescue impaired glucose tolerance in female mice with a pancreas-wide ERα deletion. Further, FOXM1 and ERα binding sites overlap with each other and with other β-cell-enriched transcription factors, including ISL1, PAX6, MAF, and GATA. These data indicate that FOMX1 and ERα cooperate to regulate β-cell function and suggest a general mechanism contributing to the lower incidence of diabetes observed in women.

The tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase 1 regulates polycystic kidney disease progression

Autosomal dominant polycystic kidney disease (ADPKD), the most common monogenic nephropathy, is characterized by phenotypic variability that exceeds genic effects. Dysregulated metabolism and immune cell function are key disease modifiers. The tryptophan metabolites, kynurenines, produced through indoleamine 2,3-dioxygenase 1 (IDO1), are known immunomodulators. Here, we study the role of tryptophan metabolism in PKD using an orthologous disease model (C57BL/6J Pkd1RC/RC). We found elevated kynurenine and IDO1 levels in Pkd1RC/RC kidneys versus wild type. Further, IDO1 levels were increased in ADPKD cell lines. Genetic Ido1 loss in Pkd1RC/RC animals resulted in reduced PKD severity, as measured by cystic index and percentage kidney weight normalized to body weight. Consistent with an immunomodulatory role of kynurenines, Pkd1RC/RC;Ido1-/- mice presented with significant changes in the cystic immune microenvironment (CME) versus controls. Kidney macrophage numbers decreased and CD8+ T cell numbers increased, both known PKD modulators. Also, pharmacological IDO1 inhibition in Pkd1RC/RC mice and kidney-specific Pkd2-knockout mice with rapidly progressive PKD resulted in less severe PKD versus controls, with changes in the CME similar to those in the genetic model. Our data suggest that tryptophan metabolism is dysregulated in ADPKD and that its inhibition results in changes to the CME and slows disease progression, making IDO1 a therapeutic target for ADPKD.

Generation of Pmel-dependent conditional and inducible Cre-driver mouse line for melanocytic-targeted gene manipulation

Conditional and inducible gene targeting using Cre/loxP-mediated recombination is a powerful reverse genetics approach used to study spatiotemporal gene functions in specified cell types. To enable temporal gene manipulation in the melanocyte lineage, we established a novel inducible Cre-driver mouse line by targeting an all-in-one tetracycline/doxycycline (Dox)-inducible Cre expression cassette into the Pmel locus (Pmel^{P2A-TetON3G-TRE3G-iCre} ), a gene locus preferentially expressed in pigment cells. By crossing these Cre-driver mice with a strong Cre-reporter mouse line, Gt(ROSA)26Sor^{tm9(CAG-tdTomato)Hze} , we show the effectiveness of the Pmel^{P2A-TetON3G-TRE3G-iCre} mouse line in facilitating Dox-inducible Cre/loxP recombination in a wide variety of pigment cell lineages including hair follicle melanocytes and their stem cells. Furthermore, to demonstrate proof of concept, we ablated Notch signaling postnatally in the Pmel^{P2A-TetON3G-TRE3G-iCre} mice. In agreement with the previously reported phenotype, induced ablation of Notch signaling in the melanocyte lineage resulted in premature hair graying, demonstrating the utility of the Pmel^{P2A-TetON3G-TRE3G-iCre} allele. Therefore, the Pmel^{P2A-TetON3G-TRE3G-iCre} mouse line is suitable for assessing gene functions in melanocytes using an in vivo inducible reverse genetics approach. Furthermore, we unexpectedly identified previously unrecognized PMEL-expressing cells in non-pigmentary organs in the mice, suggesting unanticipated functions of PMEL other than melanosome formation.

Development of an in-vitro high-throughput screening system to identify modulators of genitalia development

Sexually dimorphic outgrowth and differentiation of the embryonic genital tubercles (GTs) give rise to the penis in males and the clitoris in females. Defects in androgen production or in response to androgen signaling can lead to various congenital penile anomalies in both mice and humans. Due to lack of a high-throughput screening system, identification of crucial regulators of GT sexual differentiation has been slow. To overcome this research barrier, we isolated embryonic GT mesenchymal (GTme) cells to model genitalia growth and differentiation in vitro. Using either a mechanical or fluorescence-activated cell sorting-assisted purification method, GTme cells were isolated and assayed for their proliferation using a microscopy and image analysis system, on a single cell level over time. Male and female GTme cells inherently exhibit different cellular dynamics, consistent with their in-vivo behaviors. This system allows for the rapid quantitative analyses of numerous drug treatments, and enables the discovery of potential genetic modulators of GT morphogenesis on a large scale. Using this system, we completed a 438-compound library screen and identified 82 kinase inhibitor hits. In mice, in-utero exposure to one such candidate kinase inhibitor, Cediranib, resulted in embryos with severe genitalia defects, especially in males. Gene silencing by RNAi was optimized in this system, laying the foundation for future larger-scale genetic screenings. These findings demonstrate the power of this novel high-throughput system to rapidly and successfully identify modulators of genitalia growth and differentiation, expanding the toolbox for the study of functional genomics and environmental factors.

Dysregulated Polycomb Repressive Complex 2 contributes to chronic obstructive pulmonary disease by rewiring stem cell fate

Aberrant lung cell differentiation is a hallmark of many lung diseases including chronic obstructive pulmonary disease (COPD). The EZH2-containing Polycomb Repressive Complex 2 (PRC2) regulates embryonic lung stem cell fate, but its role in adult lung is obscure. Histological analysis of patient tissues revealed that loss of PRC2 activity was correlated with aberrant bronchiolar cell differentiation in COPD lung. Histological and single-cell RNA-sequencing analyses showed that loss of EZH2 in mouse lung organoids led to lowered self-renewal capability, increased squamous morphological development, and marked shifts in progenitor cell populations. Evaluation of in vivo models revealed that heterozygosity of Ezh2 in mice with ovalbumin-induced lung inflammation led to epithelial cell differentiation patterns similar to those in COPD lung. We also identified cystathionine-β-synthase as a possible upstream factor for PRC2 destabilization. Our findings suggest that PRC2 is integral to facilitating proper lung stem cell differentiation in humans and mice.

Monitoring of cell-cell communication and contact history in mammals

Monitoring of cell-cell communication in multicellular organisms is fundamental to understanding diverse biological processes such as embryogenesis and tumorigenesis. To track cell-cell contacts in vivo, we developed an intercellular genetic technology to monitor cell-cell contact and to trace cell contact histories by permanently marking contacts between cells. In mice, we engineered an artificial Notch ligand into one cell (the sender cell) and an artificial receptor into another cell (the receiver cell). Contact between the sender and receiver cells triggered a synthetic Notch signaling that activated downstream transcriptional programs in the receiver cell, thereby transiently or permanently labeling it. In vivo cell-cell contact was observed during development, tissue homeostasis, and tumor growth. This technology may be useful for studying dynamic in vivo cell-cell contacts and cell fate plasticity.

Structural or functional defects of PTEN in urothelial cells lacking P53 drive basal/squamous-subtype muscle-invasive bladder cancer

Muscle-invasive bladder cancer (MIBC) exhibits strong inter- and intra-tumor heterogeneity that affects biological behaviors, therapeutic responses, and prognoses. Mutations that activate RTK-RAS-PI3K and inactivate P19-P53-P21 coexist in 60-70% of MIBC. By time-controlled ablation of Tp53 and Pten, singly or combined, in adult mouse urothelium, we found that Tp53 loss alone produced no abnormality. While Pten loss elicited hyperplasia, it synergized with Tp53 loss to trigger 100% penetrant MIBC that exhibited basal/squamous features that resembled its human counterpart. Furthermore, PTEN was inactivated in human MIBC cell lines and specimens primarily by hyperphosphorylation of the C-terminus. Mutated or tailless PTEN incapable of C-terminal phosphorylation demonstrated increased inhibition of proliferation and invasion than full-length PTEN in cultured MIBC cells. In xenograft and transgenic mice, tailless PTEN, but not full-length PTEN, prevented further growth in established tumors. Collectively, deficiencies of both PTEN and P53 drive basal/squamous subtype MIBC. PTEN is inactivated by C-terminal hyperphosphorylation, and this modification may serve as a biomarker for subtyping MIBC and predicting tumor progression. Tailless PTEN is a potential molecular therapeutic for tumors, such as bladder cancer (BC), that can be readily accessed.

Development of a Lung Vacancy Mouse Model through CRISPR/Cas9-Mediated Deletion of Thyroid Transcription Factor 1 Exon 2

A developmental niche vacancy in host embryos is necessary for stem cell complementation-based organ regeneration (SCOG). Thyroid transcription factor 1 (TTF-1) is a tissue-specific transcription factor that regulates the embryonic development and differentiation of the thyroid and, more importantly, lungs; thus, it has been considered as a master gene to knockout in order to develop a lung vacancy host. TTF-1 knockout mice were originally produced by inserting a stop codon in Exon 3 of the gene (E3stop) through embryonic stem cell-based homologous recombination. The main problems of utilizing E3stop host embryos for lung SCOG are that these animals all have a tracheoesophageal fistula (TEF), which cannot be corrected by donor stem cells, and most of them have monolateral sac-like lungs. To improve the mouse model towards achieving SCOG-based lung generation, in this project, we used the CRISPR/Cas9 tool to remove Exon 2 of the gene by zygote microinjection and successfully produced TTF-1 knockout (E2del) mice. Similar to E3stop, E2del mice are birth-lethal due to retarded lung development with sac-like lungs and only a rudimentary bronchial tree, increased basal cells but without alveolar type II cells and blood vessels, and abnormal thyroid development. Unlike E3stop, 57% of the E2del embryos presented type I tracheal agenesis (TA, a kind of human congenital malformation) with a shortened trachea and clear separations of the trachea and esophagus, while the remaining 43% had TEF. Furthermore, all the E2del mice had bilateral sac-like lungs. Both TA and bilateral sac-like lungs are preferred in SCOG. Our work presents a new strategy for producing SCOG host embryos that may be useful for lung regeneration.

Sex differences in resilience to ferroptosis underlie sexual dimorphism in kidney injury and repair

In both humans and mice, repair of acute kidney injury is worse in males than in females. Here, we provide evidence that this sexual dimorphism results from sex differences in ferroptosis, an iron-dependent, lipid-peroxidation-driven regulated cell death. Using genetic and single-cell transcriptomic approaches in mice, we report that female sex confers striking protection against ferroptosis, which was experimentally induced in proximal tubular (PT) cells by deleting glutathione peroxidase 4 (Gpx4). Single-cell transcriptomic analyses further identify the NFE2-related factor 2 (NRF2) antioxidant protective pathway as a female resilience mechanism against ferroptosis. Genetic inhibition and pharmacological activation studies show that NRF2 controls PT cell fate and plasticity by regulating ferroptosis. Importantly, pharmacological NRF2 activation protects male PT cells from ferroptosis and improves cellular plasticity as in females. Our data highlight NRF2 as a potential therapeutic target to prevent failed renal repair after acute kidney injury in both sexes by modulating cellular plasticity.

The mitochondrial calcium uniporter of pulmonary type 2 cells determines severity of acute lung injury

Acute Lung Injury (ALI) due to inhaled pathogens causes high mortality. Underlying mechanisms are inadequately understood. Here, by optical imaging of live mouse lungs we show that a key mechanism is the viability of cytosolic Ca²⁺ buffering by the mitochondrial Ca²⁺ uniporter (MCU) in the lung’s surfactant-secreting, alveolar type 2 cells (AT2). The buffering increased mitochondrial Ca²⁺ and induced surfactant secretion in wild-type mice, but not in mice with AT2-specific MCU knockout. In the knockout mice, ALI due to intranasal LPS instillation caused severe pulmonary edema and mortality, which were mitigated by surfactant replenishment prior to LPS instillation, indicating surfactant’s protective effect against alveolar edema. In wild-type mice, intranasal LPS, or Pseudomonas aeruginosa decreased AT2 MCU. Loss of MCU abrogated buffering. The resulting mortality was reduced by spontaneous recovery of MCU expression, or by MCU replenishment. Enhancement of AT2 mitochondrial buffering, hence endogenous surfactant secretion, through MCU replenishment might be a therapy against ALI.

Acute lung injury caused by inhalation of pathogens leads to mortality, but the mechanisms are unclear. Here, the authors show in mice that that loss of the mitochondrial calcium uniporter (MCU) of alveolar type 2 cells (AT2) impaired mitochondrial Ca²⁺ buffering and surfactant secretion, and increased mortality, in response to LPS instillation, suggesting the MCU as a potential therapeutic target in ALI.

Maternal Adipocyte Connexin43 Gap Junctions Affect Breastmilk Lactose Levels and Neonate Growth in Mice

Simple Summary

Breastfeeding offers many health benefits for both mothers and infants. However, overnutrition and a steady increase in obesity in the U.S. has made it harder for many mothers to produce and express breastmilk. Moreover, the quality of breastmilk from obese mothers is frequently compromised in that it contains fewer nutrients and more inflammatory components. In this study, we used mice to model this phenomenon. We found that short-term high-fat feeding at the start of breeding reduces litter size and pups’ body weight. It also impairs adipocyte remodeling during lactation. Connexin43 is the primary building block for gap junctions in the adipose tissue. It is postulated to play an essential role in adipose tissue remodeling to accommodate mammary gland development and breastmilk production. Using genetically engineered mice without Connexin43 in their adipocytes, we demonstrated that the deletion of adipocyte Connexin43 affects the disappearance of adipocytes during lactation and affects milk composition, which is postulated to impair the pups’ growth. Altogether, this study suggests that increasing or enhancing adipocyte Connexin43 gap junctions may help obese mothers produce better breastmilk to support their neonates.

Abstract

Breastfeeding offers a broad spectrum of health benefits for infants. However, overnutrition and a steady increase in maternal obesity in the U.S. have made it harder for many mothers to produce and express breastmilk, and the quality of milk from obese mothers is also frequently compromised. Adipocytes, the primary cell type in the non-lactating breast, display a drastic morphological and functional change during lactation in mice. Lipid-filled adipocytes undergo lipolysis, and lipid droplets disappear to provide fatty acids and energy for breastmilk production. Once the animal stops lactation, these lipid-depleted adipocytes return as lipid-laden cells. This dynamic remodeling of the tissue is likely the result of active intercellular communications. Connexin43 (Cx43) is the most abundant connexin in the mammary adipose tissue that makes up the gap junctions for direct intercellular communications. Its expression is increased during lactation and reduced in obese mammary adipose tissue, which is resistant to lactation-induced remodeling. However, whether Cx43 is required for adipocyte remodeling and breastmilk production to support neonates’ growth has not been established. In this study, we used doxycycline-inducible adipocyte-specific Cx43-deleted mice and demonstrated that adipocyte Cx43 played a vital role in determining the carbohydrate levels in breastmilk, which may subsequently affect neonates’ growth.

Tetracycline response element driven Cre causes ectopic recombinase activity independent of transactivator element

OBJECTIVE

Tamoxifen is widely used for inducible Cre-LoxP systems but has several undesirable side effects for researchers investigating metabolism or energy balance, including weight loss, lipoatrophy, and drug incorporation into lipid stores. For this reason, we sought to determine whether a doxycycline-inducible system would be more advantageous for adipocyte-specific Cre mouse models, but serendipitously discovered widespread ectopic tetracycline response element Cre (TRE-Cre) recombinase activity.

METHODS

Adipocyte-specific tamoxifen- and doxycycline-inducible Cre mice were crossed to fluorescent Cre reporter mice and visualized by confocal microscopy to assess efficiency and background activity. TRE-Cre mice were crossed to stop-floxed diphtheria toxin mice to selectively ablate cells with background Cre activity.

RESULTS

Tamoxifen- and doxycycline-inducible systems performed similarly in adipose tissues, but ectopic Cre recombination was evident in numerous other cell types of the latter, most notably neurons. The source of ectopic Cre activity was isolated to the TRE-Cre transgene, driven by the pTet (tetO7) tetracycline-inducible promoter. Ablation of cells with ectopic recombination in mice led to stunted growth, diminished survival, and reduced brain mass.

CONCLUSIONS

These results indicate that tamoxifen- and doxycycline-inducible adipocyte-specific Cre mouse models are similarly efficient, but the TRE-Cre component of the latter is inherently leaky. TRE-Cre background activity is especially pronounced in the brain and peripheral nerve fibers, and selective ablation of these cells impairs mouse development and survival. Caution should be taken when pairing TRE-Cre with floxed alleles that have defined roles in neural function, and additional controls should be included when using this model system.

Deciphering the origins and fates of steroidogenic lineages in the mouse testis

Leydig cells (LCs) are the major androgen-producing cells in the testis. They arise from steroidogenic progenitors (SPs), whose origins, maintenance, and differentiation dynamics remain largely unknown. Single-cell transcriptomics reveal that the mouse steroidogenic lineage is specified as early as embryonic day 12.5 (E12.5) and has a dual mesonephric and coelomic origin. SPs specifically express the Wnt5a gene and evolve rapidly. At E12.5 and E13.5, they give rise first to an intermediate population of pre-LCs, and finally to fetal LCs. At E16.5, SPs possess the characteristics of the dormant progenitors at the origin of adult LCs and are also transcriptionally closely related to peritubular myoid cells (PMCs). In agreement with our in silico analysis, in vivo lineage tracing indicates that Wnt5a-expressing cells are bona fide progenitors of PMCs as well as fetal and adult LCs, contributing to most of the LCs present in the fetal and adult testis.

HDAC1/2 Control Proliferation and Survival in Adult Epidermis and Pre‒Basal Cell Carcinoma through p16 and p53

HDAC inhibitors show therapeutic promise for skin malignancies; however, the roles of specific HDACs in adult epidermal homeostasis and in disease are poorly understood. We find that homozygous epidermal codeletion of Hdac1 and Hdac2 in adult mouse epidermis causes reduced basal cell proliferation, apoptosis, inappropriate differentiation, and eventual loss of Hdac1/2-null keratinocytes. Hdac1/2-deficient epidermis displays elevated acetylated p53 and increased expression of the senescence gene p16. Loss of p53 partially restores basal proliferation, whereas p16 deletion promotes long-term survival of Hdac1/2-null keratinocytes. In activated GLI2-driven pre-basal cell carcinoma, Hdac1/2 deletion dramatically reduces proliferation and increases apoptosis, and knockout of either p53 or p16 partially rescues both proliferation and basal cell viability. Topical application of the HDAC inhibitor romidepsin to the normal epidermis or to GLI2ΔN-driven lesions produces similar defects to those caused by genetic Hdac1/2 deletion, and these are partially rescued by loss of p16. These data reveal essential roles for HDAC1/2 in maintaining proliferation and survival of adult epidermal and basal cell carcinoma progenitors and suggest that the efficacy of therapeutic HDAC1/2 inhibition will depend in part on the mutational status of p53 and p16.

The Role of Autophagy in Lamellar Body Formation and Surfactant Production in Type 2 Alveolar Epithelial Cells

The lamellar body (LB), a concentric structure loaded with surfactant proteins and phospholipids, is an organelle specific to type 2 alveolar epithelial cells (AT2). However, the origin of LBs has not been fully elucidated. We have previously reported that autophagy regulates Weibel-Palade bodies (WPBs) formation, and here we demonstrated that autophagy is involved in LB maturation, another lysosome-related organelle. We found that during development, LBs were transformed from autophagic vacuoles containing cytoplasmic contents such as glycogen. Fusion between LBs and autophagosomes was observed in wild-type neonate mice. Moreover, the markers of autophagic activity, microtubule-associated protein 1 light chain 3B (LC3B), largely co-localized on the limiting membrane of the LB. Both autophagy-related gene 7 (Atg7) global knockout and conditional Atg7 knockdown in AT2 cells in mice led to defects in LB maturation and surfactant protein B production. Additionally, changes in autophagic activity altered LB formation and surfactant protein B production. Taken together, these results suggest that autophagy plays a critical role in the regulation of LB formation during development and the maintenance of LB homeostasis during adulthood.

Impact of Motile Ciliopathies on Human Development and Clinical Consequences in the Newborn

Motile cilia are hairlike organelles that project outward from a tissue-restricted subset of cells to direct fluid flow. During human development motile cilia guide determination of the left-right axis in the embryo, and in the fetal and neonatal periods they have essential roles in airway clearance in the respiratory tract and regulating cerebral spinal fluid flow in the brain. Dysregulation of motile cilia is best understood through the lens of the genetic disorder primary ciliary dyskinesia (PCD). PCD encompasses all genetic motile ciliopathies resulting from over 60 known genetic mutations and has a unique but often underrecognized neonatal presentation. Neonatal respiratory distress is now known to occur in the majority of patients with PCD, laterality defects are common, and very rarely brain ventricle enlargement occurs. The developmental function of motile cilia and the effect and pathophysiology of motile ciliopathies are incompletely understood in humans. In this review, we will examine the current understanding of the role of motile cilia in human development and clinical considerations when assessing the newborn for suspected motile ciliopathies.

The Tetracycline-Controlled Transactivator (Tet-On/Off) System in β-Cells Reduces Insulin Expression and Secretion in Mice

Controllable genetic manipulation is an indispensable tool in research, greatly advancing our understanding of cell biology and physiology. However in β-cells, transgene silencing, low inducibility, ectopic expression, and off-targets effects are persistent challenges. In this study, we investigated whether an inducible Tetracycline (Tet)-Off system with β-cell-specific mouse insulin promoter (MIP)-itTA-driven expression of tetracycline operon (TetO)-CreJaw/J could circumvent previous issues of specificity and efficacy. Following assessment of tissue-specific gene recombination, β-cell architecture, in vitro and in vivo glucose-stimulated insulin secretion, and whole-body glucose homeostasis, we discovered that expression of any tetracycline-controlled transactivator (e.g., improved itTA, reverse rtTA, or tTA) in β-cells significantly reduced Insulin gene expression and decreased insulin content. This translated into lower pancreatic insulin levels and reduced insulin secretion in mice carrying any tTA transgene, independent of Cre recombinase expression or doxycycline exposure. Our study echoes ongoing challenges faced by fundamental researchers working with β-cells and highlights the need for consistent and comprehensive controls when using the tetracycline-controlled transactivator systems (Tet-On or Tet-Off) for genome editing.

YAP regulates alveolar epithelial cell differentiation and AGER via NFIB/KLF5/NKX2-1

Ventilation is dependent upon pulmonary alveoli lined by two major epithelial cell types, alveolar type-1 (AT1) and 2 (AT2) cells. AT1 cells mediate gas exchange while AT2 cells synthesize and secrete pulmonary surfactants and serve as progenitor cells which repair the alveoli. We developed transgenic mice in which YAP was activated or deleted to determine its roles in alveolar epithelial cell differentiation. Postnatal YAP activation increased epithelial cell proliferation, increased AT1 cell numbers, and caused indeterminate differentiation of subsets of alveolar cells expressing atypical genes normally restricted to airway epithelial cells. YAP deletion increased expression of genes associated with mature AT2 cells. YAP activation enhanced DNA accessibility in promoters of transcription factors and motif enrichment analysis predicted target genes associated with alveolar cell differentiation. YAP participated with KLF5, NFIB, and NKX2-1 to regulate AGER. YAP plays a central role in a transcriptional network that regulates alveolar epithelial differentiation.

Deficiency of eIF4B Increases Mouse Mortality and Impairs Antiviral Immunity

Eukaryotic translation initiation factor 4B (eIF4B) plays an important role in mRNA translation initiation, cell survival and proliferation in vitro. However, its function in vivo is poorly understood. Here, we identified that eIF4B knockout (KO) in mice led to embryonic lethality, and the embryos displayed severe liver damage. Conditional KO (CKO) of eIF4B in adulthood profoundly increased the mortality of mice, characterized by severe pathological changes in several organs and reduced number of peripheral blood lymphocytes. Strikingly, eIF4B CKO mice were highly susceptible to viral infection with severe pulmonary inflammation. Selective deletion of eIF4B in lung epithelium also markedly promoted replication of influenza A virus (IAV) in the lung of infected animals. Furthermore, we observed that eIF4B deficiency significantly enhanced the expression of several important inflammation-associated factors and chemokines, including serum amyloid A1 (Saa1), Marco, Cxcr1, Ccl6, Ccl8, Ccl20, Cxcl2, Cxcl17 that are implicated in recruitment and activation of neutrophiles and macrophages. Moreover, the eIF4B-deficient mice exhibited impaired natural killer (NK) cell-mediated cytotoxicity during the IAV infection. Collectively, the results reveal that eIF4B is essential for mouse survival and host antiviral responses, and establish previously uncharacterized roles for eIF4B in regulating normal animal development and antiviral immunity in vivo.

Cell tracing reveals the transdifferentiation fate of mouse lung epithelial cells during pulmonary fibrosis in vivo

Idiopathic pulmonary fibrosis (IPF) is a progressive and devastating interstitial lung disease. The origin of myofibroblasts is still to be elucidated and the existence of epithelial-mesenchymal transition (EMT) in IPF remains controversial. Hence, it is important to clarify the origin of fibroblasts by improving modeling and labeling methods and analyzing the differentiation pathway of alveolar epithelial cells (AEC) in pulmonary fibrosis with cell tracking technology. In the present study, adult transgenic mice with SPC-rtTA^+/-/tetO₇-CMV-Cre^+/-/mTmG^+/- were induced with doxycycline for 15 days. The gene knockout phenomenon occurred in type II AECs in the lung and the reporter gene cell membrane-localized enhanced green fluorescence protein (mEGFP) was expressed in the cell membrane. The expression of Cre recombinase and SPC was analyzed using immunohistochemical (IHC) staining to detect the labeling efficiency. A repetitive intraperitoneal bleomycin-induced pulmonary fibrosis model was established, and the mice were sacrificed on day 28. The co-localization of mEGFP and mesenchymal markers α-smooth muscle actin (α-SMA) and S100 calcium binding protein A4 (S100A4) were detected by multiple IHC staining. The results revealed that Cre was expressed in the airway and AECs in the lung tissue of adult transgenic mice with SPC-rtTA^+/-/tetO₇-CMV-Cre^+/-/mTmG^+/- induced by doxycycline; the labeling efficiency in the peripheral lung tissue was 63.27±7.51%. mEGFP was expressed on the membrane of type II AECs and their differentiated form of type I AECs. Expression of mEGFP was mainly observed in the fibrotic region in bleomycin-induced pulmonary fibrosis; 1.94±0.08% of α-SMA-positive cells were mEGFP-positive and 9.68±2.06% of S100A4-positive cells were mEGFP-positive in bleomycin-induced pulmonary fibrosis. In conclusion, the present results suggested that while EMT contributes to the pathogenesis of pulmonary fibrosis, it is not the major causative factor of this condition.

Quantitative lineage analysis identifies a hepato-pancreato-biliary progenitor niche

Studies based on single cells have revealed vast cellular heterogeneity in stem cell and progenitor compartments, suggesting continuous differentiation trajectories with intermixing of cells at various states of lineage commitment and notable degrees of plasticity during organogenesis^1-5. The hepato-pancreato-biliary organ system relies on a small endoderm progenitor compartment that gives rise to a variety of different adult tissues, including the liver, pancreas, gall bladder and extra-hepatic bile ducts^6,7. Experimental manipulation of various developmental signals in the mouse embryo has underscored important cellular plasticity in this embryonic territory⁶. This is reflected in the existence of human genetic syndromes as well as congenital malformations featuring multi-organ phenotypes in liver, pancreas and gall bladder⁶. Nevertheless, the precise lineage hierarchy and succession of events leading to the segregation of an endoderm progenitor compartment into hepatic, biliary and pancreatic structures have not yet been established. Here we combine computational modelling approaches with genetic lineage tracing to accurately reconstruct the hepato-pancreato-biliary lineage tree. We show that a multipotent progenitor subpopulation persists in the pancreato-biliary organ rudiment, contributing cells not only to the pancreas and gall bladder but also to the liver. Moreover, using single-cell RNA sequencing and functional experiments we define a specialized niche that supports this subpopulation in a multipotent state for an extended time during development. Together these findings indicate sustained plasticity underlying hepato-pancreato-biliary development that might also explain the rapid expansion of the liver while attenuating pancreato-biliary growth.