Mesenchymal Hox6 function is required for mouse pancreatic endocrine cell differentiation

Pancreatic organogenesis mapped through space and time

The spatial organization of cells within a tissue is dictated throughout dynamic developmental processes. We sought to understand whether cells geometrically coordinate with one another throughout development to achieve their organization. The pancreas is a complex cellular organ with a particular spatial organization. Signals from the mesenchyme, neurons, and endothelial cells instruct epithelial cell differentiation during pancreatic development. To understand the cellular diversity and spatial organization of the developing pancreatic niche, we mapped the spatial relationships between single cells over time. We found that four transcriptionally unique subtypes of mesenchyme in the developing pancreas spatially coordinate throughout development, with each subtype at fixed locations in space and time in relation to other cells, including beta cells, vasculature, and epithelial cells. Our work provides insight into the mechanisms of pancreatic development by showing that cells are organized in a space and time manner.

Machine Learning Uncovers Vascular Endothelial Cell Identity Genes by Expression Regulation Features in Single Cells

Deciphering cell identity genes is pivotal to understanding cell differentiation, development, and many diseases involving cell identity dysregulation. Here, we introduce SCIG, a machine-learning method to uncover cell identity genes in single cells. In alignment with recent reports that cell identity genes are regulated with unique epigenetic signatures, we found cell identity genes exhibit distinctive genetic sequence signatures, e.g., unique enrichment patterns of cis-regulatory elements. Using these genetic sequence signatures, along with gene expression information from single-cell RNA-seq data, enables SCIG to uncover the identity genes of a cell without a need for comparison to other cells. Cell identity gene score defined by SCIG surpassed expression value in network analysis to uncover master transcription factors regulating cell identity. Applying SCIG to the human endothelial cell atlas revealed that the tissue microenvironment is a critical supplement to master transcription factors for cell identity refinement. SCIG is publicly available at https://github.com/kaifuchenlab/SCIG , offering a valuable tool for advancing cell differentiation, development, and regenerative medicine research.

Characterization of a novel Hoxa5eGFP mouse line

BACKGROUND

Hox genes encode transcription factors that are important for establishing the body plan. Hoxa5 is a member of the mammalian Hox5 paralogous group that regulates the patterning and morphology of the cervical-thoracic region of the axial skeleton. Hoxa5 also plays crucial functions in lung morphogenesis.

RESULTS

We generated a Hoxa5eGFP reporter mouse line using CRISPR technology, allowing real-time visualization of Hoxa5 expression. Hoxa5eGFP recapitulates reported embryonic Hoxa5 mRNA expression patterns. Specifically, Hoxa5eGFP can be visualized in the developing mouse neural tube, somites, lung, diaphragm, foregut, and midgut, among other organs. In the stomach, posteriorly biased Hoxa5eGFP expression correlates with a drastic morphological reduction of the corpus in Hox5 paralogous mutants. Expression of Hoxa5eGFP in the lung continues in all lung fibroblast populations through postnatal and adult stages.

CONCLUSIONS

We identified cell types that express Hoxa5 in postnatal and adult mouse lungs, including various fibroblasts and vascular endothelial cells. This reporter line will be a powerful tool for studies of the function of Hoxa5 during mouse development, homeostasis, and disease processes.

Deep into the niche: Deciphering local endoderm-microenvironment interactions in development, homeostasis, and disease of pancreas and intestine

Unraveling molecular and functional heterogeneity of niche cells within the developing endoderm could resolve mechanisms of tissue formation and maturation. Here, we discuss current unknowns in molecular mechanisms underlying key developmental events in pancreatic islet and intestinal epithelial formation. Recent breakthroughs in single-cell and spatial transcriptomics, paralleled with functional studies in vitro, reveal that specialized mesenchymal subtypes drive the formation and maturation of pancreatic endocrine cells and islets via local interactions with epithelium, neurons, and microvessels. Analogous to this, distinct intestinal niche cells regulate both epithelial development and homeostasis throughout life. We propose how this knowledge can be used to progress research in the human context using pluripotent stem cell-derived multilineage organoids. Overall, understanding the interactions between the multitude of microenvironmental cells and how they drive tissue development and function could help us make more therapeutically relevant in vitro models.

Determinants and dynamics of pancreatic islet architecture

The islets of Langerhans are highly organized structures that have species-specific, three-dimensional tissue architecture. Islet architecture is critical for proper hormone secretion in response to nutritional stimuli. Islet architecture is disrupted in all types of diabetes mellitus and in cadaveric islets for transplantation during isolation, culture, and perfusion, limiting patient outcomes. Moreover, recapitulating native islet architecture remains a key challenge for in vitro generation of islets from stem cells. In this review, we discuss work that has led to the current understanding of determinants of pancreatic islet architecture, and how this architecture is maintained or disrupted during tissue remodeling in response to normal and pathological metabolic changes. We further discuss both empirical and modeling data that highlight the importance of islet architecture for islet function.

Paralogous Genes Involved in Embryonic Development: Lessons from the Eye and Other Tissues

During evolution, gene duplications lead to a naturally increased gene dosage. Duplicated genes can be further retained or eliminated over time by purifying selection pressure. The retention probability is increased by functional diversification and by the acquisition of novel functions. Interestingly, functionally diverged paralogous genes can maintain a certain level of functional redundancy and at least a partial ability to replace each other. In such cases, diversification probably occurred at the level of transcriptional regulation. Nevertheless, some duplicated genes can maintain functional redundancy after duplication and the ability to functionally compensate for the loss of each other. Many of them are involved in proper embryonic development. The development of particular tissues/organs and developmental processes can be more or less sensitive to the overall gene dosage. Alterations in the gene dosage or a decrease below a threshold level may have dramatic phenotypic consequences or even lead to embryonic lethality. The number of functional alleles of particular paralogous genes and their mutual cooperation and interactions influence the gene dosage, and therefore, these factors play a crucial role in development. This review will discuss individual interactions between paralogous genes and gene dosage sensitivity during development. The eye was used as a model system, but other tissues are also included.

Human pancreatic microenvironment promotes β-cell differentiation via non-canonical WNT5A/JNK and BMP signaling

In vitro derivation of pancreatic β-cells from human pluripotent stem cells holds promise as diabetes treatment. Despite recent progress, efforts to generate physiologically competent β-cells are still hindered by incomplete understanding of the microenvironment's role in β-cell development and maturation. Here, we analyze the human mesenchymal and endothelial primary cells from weeks 9-20 fetal pancreas and identify a time point-specific microenvironment that permits β-cell differentiation. Further, we uncover unique factors that guide in vitro development of endocrine progenitors, with WNT5A markedly improving human β-cell differentiation. WNT5A initially acts through the non-canonical (JNK/c-JUN) WNT signaling and cooperates with Gremlin1 to inhibit the BMP pathway during β-cell maturation. Interestingly, we also identify the endothelial-derived Endocan as a SST+ cell promoting factor. Overall, our study shows that the pancreatic microenvironment-derived factors can mimic in vivo conditions in an in vitro system to generate bona fide β-cells for translational applications.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

The Lung Elastin Matrix Undergoes Rapid Degradation Upon Adult Loss of Hox5 Function

Hox genes encode transcription factors that are critical for embryonic skeletal patterning and organogenesis. The Hoxa5, Hoxb5, and Hoxc5 paralogs are expressed in the lung mesenchyme and function redundantly during embryonic lung development. Conditional loss-of-function of these genes during postnatal stages leads to severe defects in alveologenesis, specifically in the generation of the elastin network, and animals display bronchopulmonary dysplasia (BPD) or BPD-like phenotype. Here we show the surprising results that mesenchyme-specific loss of Hox5 function at adult stages leads to rapid disruption of the mature elastin matrix, alveolar enlargement, and an emphysema-like phenotype. As the elastin matrix of the lung is considered highly stable, adult disruption of the matrix was not predicted. Just 2 weeks after deletion, adult Hox5 mutant animals show significant increases in alveolar space and changes in pulmonary function, including reduced elastance and increased compliance. Examination of the extracellular matrix (ECM) of adult Tbx4rtTA; TetOCre; Hox5a f a f bbcc lungs demonstrates a disruption of the elastin network although the underlying fibronectin, interstitial collagen and basement membrane appear unaffected. An influx of macrophages and increased matrix metalloproteinase 12 (MMP12) are observed in the distal lung 3 days after Hox5 deletion. In culture, fibroblasts from Hox5 mutant lungs exhibit reduced adhesion. These findings establish a novel role for Hox5 transcription factors as critical regulators of lung fibroblasts at adult homeostasis.

HomeoboxC6 promotes metastasis by orchestrating the DKK1/Wnt/β-catenin axis in right-sided colon cancer

Patients with right-sided colon cancer (RCC) generally have a poorer prognosis than those with left-sided colon cancer (LCC). We previously found that homeobox C6 (HOXC6) was the most significantly upregulated gene in RCC compared to LCC. However, it remains unclear whether HOXC6 plays a role in tumor proliferation and metastasis. Our study aimed to explore the potential oncogenic role and the detailed molecular mechanism of HOXC6 in RCC. In this study, HOXC6 was validated to be overexpressed in RCC and associated with poor prognosis. Furthermore, overexpression of HOXC6 promoted the migration and invasion of colon cancer cells through inducing EMT by activating the Wnt/β-catenin signaling pathway and inhibition of DKK1 secretion. Lastly, we preliminary explored the translational effect of HOXC6 and found that silencing of HOXC6 made HCT116 and HT29 cells more sensitive to irinotecan.

Effects of MLL5 and HOXA regulated by NRP1 on radioresistance in A549

Radiotherapy is widely used in the management of lung cancer, and physicians are aware that the effect of radiotherapy is dependent on radiosensitivity. Although a series of blockers and activators targeting molecules related to radioresistance have been developed as radiation sensitizers, compensatory mechanisms or drug resistance limits their clinical efficacy. The identification of a key molecule related to lung cancer cell radioresistance or an effective molecular target is a challenging but important problem in radiation oncology. A previous study found that neuropilin 1 (NRP1) is related to radioresistance in A549 cells and is associated with VEGF, PI3K-Akt, MAPK-ERK, P38, NF-κβ and TGF-β. Inhibition of NRP1 can increase the radiosensitivity of A549 cells. Therefore, NRP1 may be a molecular target for radiotherapy-sensitizing drugs in lung cancer. The present study investigated the key downstream genes of NRP1, verified their regulation and clarified their roles in regulating lung cancer radioresistance. NRP1 positively regulated the downstream homeobox genes (HOXs) HOXA6, HOXA9 and mixed lineage leukaemia 5 (MLL5) in addition to MLL5-regulated HOXA6 and HOXA9, but these genes did not regulate NRP1. MLL5, HOXA6 and HOXA9 levels were decreased in tumour tissues and positively correlated with NRP1. All of these genes were induced by ionizing radiation in vivo and in vitro. NRP1 expression was significantly lower in squamous cell carcinoma compared with that in adenocarcinoma, and lymph node metastasis occurred more often in patients with lung cancer with high MLL5 and NRP1 expression compared with patients with low MLL5 and NRP1 expression. Collectively, these data confirmed that NRP1 is associated with MLL5 and regulates radioresistance through HOXA6 and HOXA9.

Cellular Heterogeneity of Pancreatic Stellate Cells, Mesenchymal Stem Cells, and Cancer-Associated Fibroblasts in Pancreatic Cancer

Pancreatic cancer is projected to become the second deadliest cancer by 2030 in the United States, and the overall five-year survival rate stands still at around 9%. The stroma compartment can make up more than 90% of the pancreatic tumor mass, contributing to the hypoxic tumor microenvironment. The dense stroma with extracellular matrix proteins can be a physical and metabolic barrier reducing therapeutic efficacy. Cancer-associated fibroblasts are a source of extracellular matrix proteins. Therefore, targeting these cells, or extracellular matrix proteins, have been considered as therapeutic strategies. However, several studies show that deletion of cancer-associated fibroblasts may have tumor-promoting effects. Cancer-associated fibroblasts are derived from a variety of different cell types, such as pancreatic stellate cells and mesenchymal stem cells, and constitute a diverse cell population consisting of several functionally heterogeneous subtypes. Several subtypes of cancer-associated fibroblasts exhibit a tumor-restraining function. This review article summarizes recent findings regarding origin and functional heterogeneity of tumor-promoting as well as tumor-restraining cancer-associated fibroblasts. A better understanding of cancer-associated fibroblast heterogeneity could provide more specific and personalized therapies for pancreatic cancer patients in the future.

Pancreatic Fibroblast Heterogeneity: From Development to Cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by an extensive fibroinflammatory microenvironment that accumulates from the onset of disease progression. Cancer-associated fibroblasts (CAFs) are a prominent cellular component of the stroma, but their role during carcinogenesis remains controversial, with both tumor-supporting and tumor-restraining functions reported in different studies. One explanation for these contradictory findings is the heterogeneous nature of the fibroblast populations, and the different roles each subset might play in carcinogenesis. Here, we review the current literature on the origin and function of pancreatic fibroblasts, from the developing organ to the healthy adult pancreas, and throughout the initiation and progression of PDA. We also discuss clinical approaches to targeting fibroblasts in PDA.

A Specialized Niche in the Pancreatic Microenvironment Promotes Endocrine Differentiation

The interplay between pancreatic epithelium and the surrounding microenvironment is pivotal for pancreas formation and differentiation as well as adult organ homeostasis. The mesenchyme is the main component of the embryonic pancreatic microenvironment, yet its cellular identity is broadly defined, and whether it comprises functionally distinct cell subsets is not known. Using genetic lineage tracing, transcriptome, and functional studies, we identified mesenchymal populations with different roles during pancreatic development. Moreover, we showed that Pbx transcription factors act within the mouse pancreatic mesenchyme to define a pro-endocrine specialized niche. Pbx directs differentiation of endocrine progenitors into insulin- and glucagon-positive cells through non-cell-autonomous regulation of ECM-integrin interactions and soluble molecules. Next, we measured functional conservation between mouse and human pancreatic mesenchyme by testing identified mesenchymal factors in an iPSC-based differentiation model. Our findings provide insights into how lineage-specific crosstalk between epithelium and neighboring mesenchymal cells underpin the generation of different pancreatic cell types.

MiR-126 Regulates Properties of SOX9+ Liver Progenitor Cells during Liver Repair by Targeting Hoxb6

Liver progenitor cells (LPCs) have a remarkable contribution to the hepatocytes and ductal cells when normal hepatocyte proliferation is severely impaired. As a biomarker for LPCs, Sry-box 9 (Sox9) plays critical roles in liver homeostasis and repair in response to injury. However, the regulation mechanism of Sox9 in liver physiological and pathological state remains unknown. In this study, we found that miR-126 positively regulated the expression of Sox9, the proliferation and differentiation of SOX9+ LPCs by suppressing the translation of homeobox b6 (Hoxb6). As a transcription factor, HOXB6 directly binds to the promoter of Sox9 to inhibit Sox9 expression, resulting in the destruction of the properties of SOX9+ LPCs in CCl4-induced liver injury. These findings revealed the role of miR-126 in regulating SOX9+ LPCs fate by targeting Hoxb6 in liver injury repair. Our findings suggest the potential role of miR-126 as a nucleic acid therapy drug target for liver failure.

Differential Contribution of Pancreatic Fibroblast Subsets to the Pancreatic Cancer Stroma

BACKGROUND & AIMS

Although the healthy pancreas consists mostly of epithelial cells, pancreatic cancer and the precursor lesions known as pancreatic intraepithelial neoplasia, are characterized by an extensive accumulation of fibroinflammatory stroma that includes a substantial and heterogeneous fibroblast population. The cellular origin of fibroblasts within the stroma has not been determined. Here, we show that the Gli1 and Hoxb6 markers label distinct fibroblast populations in the healthy mouse pancreas. We then set out to determine whether these distinct fibroblast populations expanded during carcinogenesis.

METHODS

We developed genetically engineered models using a dual-recombinase approach that allowed us to induce pancreatic cancer formation through codon-optimized Flp recombinase-driven epithelial recombination of Kirsten rat sarcoma viral oncogene homolog while labeling Gli1+ or Hoxb6+ fibroblasts in an inducible manner. By using these models, we lineage-traced these 2 fibroblast populations during the process of carcinogenesis.

RESULTS

Although in the healthy pancreas Gli1+ fibroblasts and Hoxb6+ fibroblasts are present in similar numbers, they contribute differently to the stroma in carcinogenesis. Namely, Gli1+ fibroblasts expand dramatically, whereas Hoxb6+ cells do not.

CONCLUSIONS

Fibroblasts present in the healthy pancreas expand during carcinogenesis, but with a different prevalence for different subtypes. Here, we compared Gli1+ and Hoxb6+ fibroblasts and found only Gli1+ expanded to contribute to the stroma during pancreatic carcinogenesis.

HOXC6 in the prognosis of prostate cancer

Aims: Our study aimed to investigate the expression and prognostic role of homeobox C6 (HOXC6) in prostate cancer (PCa). Methods: Relative expression of HOXC6 at mRNA and protein levels in tissues and cell lines of PCa were measured using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis, respectively. Association between HOXC6 expression and clinical factors was analyzed by Chi-square test. HOXC6 effects on the proliferation, invasion and metastasis of PCa cells were severally examined through CCK-8 and transwell assays. Results: Relative expressions of HOXC6 at mRNA and protein levels were obviously higher in both PCa tissues and cells than in adjacent non-cancerous tissues and normal human prostate epithelial cells (p < .05). Chi-square test demonstrated that high expression of HOXC6 was significantly associated with PSA concentration, Gleason score and TNM stage (p < .05). The down-regulation of HOCX6 remarkably inhibited the proliferation, migration and invasion of PCa cells. Kaplan-Meier analysis showed that patients with high HOXC6 expression had shorter overall survival than those with low HOXC6 expression (log rank test, p < .001). Conclusion: Up-regulated HOXC6, in PCa patients, could not only participate in the progression of PCa but also function as an independent prognostic marker for the cancer.

Small molecules from natural products targeting the Wnt/β-catenin pathway as a therapeutic strategy

The Wnt/β-catenin signaling pathway is an evolutionarily conserved developmental signaling event that plays a critical role in regulating tissue development and maintaining homeostasis, the dysregulation of which contributes to various diseases. Natural products have been widely recognized as a treasure trove of novel drug discovery for millennia, and many clinical drugs are derived from natural small molecules. Mounting evidence has demonstrated that many natural small molecules could inhibit the Wnt/β-catenin pathway, while the efficacy of natural products remains to be determined. Therefore, this paper primarily reviews the targeting mechanism of natural small molecules for aberrant Wnt/β-catenin pathway that is intimately implicated in the pathogenesis of myriad diseases, such as cancers, renal diseases, neurodegenerative diseases and bone disorders. In addition, this review also highlights some natural products that have the potential to halt Wnt/β-catenin pathway, especially for porcupine, the receptors of Wnt ligands, β-catenin and β-catenin-dependent proteins. Additionally, a series of natural small molecules have shown good therapeutic effects against mutations of the Wnt/β-catenin pathway, which may dramatically facilitate the development of natural products in Wnt/β-catenin pathway intervention.

Wnt signaling: implications in endoderm development and pancreas organogenesis

The pancreas is derived from the foregut endoderm during embryonic development. After gastrulation and endoderm germ layer formation complex morphogenetic events coupled with cell differentiation programs pattern the gut tube and induce pancreas organogenesis. This results in formation of exocrine, ductal and hormone-producing endocrine cells. Among these, endocrine cells are responsible for blood glucose homeostasis and their malfunction leads to diabetes mellitus, which cannot be stopped or reversed by the current standard treatments. Thus, intense efforts to regenerate or replace the lost or dysfunctional insulin-producing β-cells are on the way. This depends on identifying the factors that coordinate pancreas organogenesis. Here, we highlight the contribution of canonical and non-canonical Wnt signaling branches in orchestrating endoderm formation, pancreatic morphogenesis as well as endocrine cell formation and function.

Generation of functional human pancreatic organoids by transplants of embryonic stem cell derivatives in a 3D-printed tissue trapper

Organoids can be regarded as a beneficial tool for discovery of new therapeutics for diabetes and/or maturation of pancreatic progenitors (PP) towards β cells. Here, we devised a strategy to enhance maturation of PP by assembly of three-dimensional (3D) pancreatic organoids (PO) containing human embryonic stem (ES) cell derivatives including ES-derived pancreatic duodenal homeobox 1 (PDX1) + early PP, mesenchymal stem cells, and endothelial cells at an optimized cell ratio, on Matrigel. The PO was placed in a 3D-printed tissue trapper and heterotopically implanted into the peritoneal cavity of immunodeficient mice where it remained for 90 days. Our results indicated that, in contrast to corresponding early PP transplants, 3D PO developed more vascularization as indicated by greater area and number of vessels, a higher number of insulin-positive cells and improvement of human C-peptide secretions. Based on our findings, PO-derived β cells could be considered a novel strategy to study human β-cell development, novel therapeutics, and regenerative medicine for diabetes.

Deciphering The Potential Role of Hox Genes in Pancreatic Cancer

The Hox gene family plays an important role in organogenesis and animal development. Currently, 39 Hox genes that are clustered in four chromosome regions have been identified in humans. Emerging evidence suggests that Hox genes are involved in the development of the pancreas. However, the expression of Hox genes in pancreatic tumor tissues has been investigated in only a few studies. In addition, whether specific Hox genes can promote or suppress cancer metastasis is not clear. In this article, we first review the recent progress in studies on the role of Hox genes in pancreatic cancer. By comparing the expression profiles of pancreatic cancer cells isolated from genetically engineered mice established in our laboratory with three different proliferative and metastatic abilities, we identified novel Hox genes that exhibited tumor-promoting activity in pancreatic cancer. Finally, a potential oncogenic mechanism of the Hox genes was hypothesized.

Modelling the endocrine pancreas in health and disease

Diabetes mellitus is a multifactorial disease affecting increasing numbers of patients worldwide. Progression to insulin-dependent diabetes mellitus is characterized by the loss or dysfunction of pancreatic β-cells, but the pathomechanisms underlying β-cell failure in type 1 diabetes mellitus and type 2 diabetes mellitus are still poorly defined. Regeneration of β-cell mass from residual islet cells or replacement by β-like cells derived from stem cells holds great promise to stop or reverse disease progression. However, the development of new treatment options is hampered by our limited understanding of human pancreas organogenesis due to the restricted access to primary tissues. Therefore, the challenge is to translate results obtained from preclinical model systems to humans, which requires comparative modelling of β-cell biology in health and disease. Here, we discuss diverse modelling systems across different species that provide spatial and temporal resolution of cellular and molecular mechanisms to understand the evolutionary conserved genotype-phenotype relationship and translate them to humans. In addition, we summarize the latest knowledge on organoids, stem cell differentiation platforms, primary micro-islets and pseudo-islets, bioengineering and microfluidic systems for studying human pancreas development and homeostasis ex vivo. These new modelling systems and platforms have opened novel avenues for exploring the developmental trajectory, physiology, biology and pathology of the human pancreas.

Hox5 genes direct elastin network formation during alveologenesis by regulating myofibroblast adhesion

Hox5 genes (Hoxa5, Hoxb5, Hoxc5) are exclusively expressed in the lung mesenchyme during embryogenesis, and the most severe phenotypes result from constitutive loss of function of all three genes. Because Hox5 triple null mutants exhibit perinatal lethality, the contribution of this paralogous group to postembryonic lung development is unknown. Intriguingly, expression of all three Hox5 genes peaks during the first 2 weeks after birth, reaching levels far exceeding those measured at embryonic stages, and surviving Hoxa5 single and Hox5 AabbCc compound mutants exhibit defects in the localization of alveolar myofibroblasts. To define the contribution of the entire Hox5 paralogous group to this process, we generated an Hoxa5 conditional allele to use with our existing null alleles for Hoxb5 and Hoxc5 Postnatally, mesenchymal deletion of Hoxa5 in an Hoxb5/Hoxc5 double-mutant background results in severe alveolar simplification. The elastin network required for alveolar formation is dramatically disrupted in Hox5 triple mutants, while the basal lamina, interstitial matrix, and fibronectin are normal. Alveolar myofibroblasts remain Pdgfrα+/SMA+ double positive and present in normal numbers, indicating that the irregular elastin network is not due to fibroblast differentiation defects. Rather, we observe that SMA+ myofibroblasts of Hox5 triple mutants are morphologically abnormal both in vivo and in vitro with highly reduced adherence to fibronectin. This loss of adhesion is a result of loss of the integrin heterodimer Itga5b1 in mutant fibroblasts. Collectively, these data show an important role for Hox5 genes in lung fibroblast adhesion necessary for proper elastin network formation during alveologenesis.

Loss of Hox5 function results in myofibroblast mislocalization and distal lung matrix defects during postnatal development

Alveologenesis is the final stage of lung development and is responsible for the formation of the principle gas exchange units called alveoli. The lung mesenchyme, in particular the alveolar myofibroblasts, are drivers of alveolar development, however, few key regulators that govern the proper distribution and behavior of these cells in the distal lung during alveologenesis have been identified. While Hox5 triple mutants (Hox5 aabbcc) exhibit neonatal lethality, four-allele, compound mutant mice (Hox5 AabbCc) are born in Mendelian ratios and are phenotypically normal at birth. However, they exhibit defects in alveologenesis characterized by a BPD-like phenotype by early postnatal stages that becomes more pronounced at adult stages. Invasive pulmonary functional analyses demonstrate significant increases in total lung volume and compliance and a decrease in elastance in Hox5 compound mutants. SMA+ myofibroblasts in the distal lung are distributed abnormally during peak stages of alveologenesis and aggregate, resulting in the formation of a disrupted elastin network. Examination of other key components of the distal lung ECM, as well as other epithelial cells and lipofibroblasts reveal no differences in distribution. Collectively, these data indicate that Hox5 genes play a critical role in alveolar development by governing the proper cellular behavior of myofibroblasts during alveologenesis.

Cellular and molecular mechanisms coordinating pancreas development

The pancreas is an endoderm-derived glandular organ that participates in the regulation of systemic glucose metabolism and food digestion through the function of its endocrine and exocrine compartments, respectively. While intensive research has explored the signaling pathways and transcriptional programs that govern pancreas development, much remains to be discovered regarding the cellular processes that orchestrate pancreas morphogenesis. Here, we discuss the developmental mechanisms and principles that are known to underlie pancreas development, from induction and lineage formation to morphogenesis and organogenesis. Elucidating such principles will help to identify novel candidate disease genes and unravel the pathogenesis of pancreas-related diseases, such as diabetes, pancreatitis and cancer.

Organotypic pancreatoids with native mesenchyme develop Insulin producing endocrine cells

Replacement of lost beta cells in patients with diabetes has the potential to alleviate them of their disease, yet current protocols to make beta cells are inadequate for therapy. In vitro screens can reveal the signals necessary for endocrine maturation to improve beta cell production, however the complexities of in vivo development that lead to beta cell formation are lost in two-dimensional systems. Here, we create three-dimensional organotypic pancreatic cultures, named pancreatoids, composed of embryonic day 10.5 murine epithelial progenitors and native mesenchyme. These progenitors assemble in scaffold-free, floating conditions and, with the inclusion of native mesenchyme, develop into pancreatoids expressing markers of different pancreatic lineages including endocrine-like cells. Treatment of pancreatoids with (-)-Indolactam-V or phorbol 12-myristate 13-acetate, two protein kinase C activators, leads to altered morphology which otherwise would be overlooked in two-dimensional systems. Protein kinase C activation also led to fewer Insulin+ cells, decreased Ins1 and Ins2 mRNA levels, and increased Pdx1 and Hes1 mRNA levels with a high number of DBA+ cells. Thus, organotypic pancreatoids provide a useful tool for developmental studies, and can further be used for disease modeling, small molecules and genetic screens, or applied to human pluripotent stem cell differentiation for beta-like cell formation.

Isolating and Analyzing Cells of the Pancreas Mesenchyme by Flow Cytometry

The pancreas is comprised of epithelial cells that are required for food digestion and blood glucose regulation. Cells of the pancreas microenvironment, including endothelial, neuronal, and mesenchymal cells were shown to regulate cell differentiation and proliferation in the embryonic pancreas. In the adult, the function and mass of insulin-producing cells were shown to depend on cells in their microenvironment, including pericyte, immune, endothelial, and neuronal cells. Lastly, changes in the pancreas microenvironment were shown to regulate pancreas tumorigenesis. However, the cues underlying these processes are not fully defined. Therefore, characterizing the different cell types that comprise the pancreas microenvironment and profiling their gene expression are crucial to delineate the tissue development and function under normal and diseased states. Here, we describe a method that allows for the isolation of mesenchymal cells from the pancreas of embryonic, neonatal, and adult mice. This method utilizes the enzymatic digestion of mouse pancreatic tissue and the subsequent fluorescence-activated cell sorting (FACS) or flow-cytometric analysis of labeled cells. Cells can be labeled by either immunostaining for surface markers or by the expression of fluorescent proteins. Cell isolation can facilitate the characterization of genes and proteins expressed in cells of the pancreas mesenchyme. This protocol was successful in isolating and culturing highly enriched mesenchymal cell populations from the embryonic, neonatal, and adult mouse pancreas.

Hox genes in the adult skeleton: Novel functions beyond embryonic development

Hox genes encode evolutionarily conserved transcription factors that control skeletal patterning in the developing embryo. They are expressed in regionally restricted domains and function to regulate the morphology of specific vertebral and long bone elements. Recent work has provided evidence that Hox genes continue to be regionally expressed in adult tissues. Fibroblasts cultured from adult tissues show broadly maintained Hox gene expression patterns. In the adult skeleton, Hox genes are expressed in progenitor-enriched populations of mesenchymal stem/stromal cells (MSCs), and genetic loss-of-function analyses have provided evidence that Hox genes function during the fracture healing process. This review will highlight our current understanding of Hox expression in the adult animal and its function in skeletal regeneration. Developmental Dynamics 246:310-317, 2017. © 2016 Wiley Periodicals, Inc.

The molecular and morphogenetic basis of pancreas organogenesis

The pancreas is an essential endoderm-derived organ that ensures nutrient metabolism via its endocrine and exocrine functions. Here we review the essential processes governing the embryonic and early postnatal development of the pancreas discussing both the mechanisms and molecules controlling progenitor specification, expansion and differentiation. We elaborate on how these processes are orchestrated in space and coordinated with morphogenesis. We draw mainly from experiments conducted in the mouse model but also from investigations in other model organisms, complementing a recent comprehensive review of human pancreas development (Jennings et al., 2015) [1]. The understanding of pancreas development in model organisms provides a framework to interpret how human mutations lead to neonatal diabetes and may contribute to other forms of diabetes and to guide the production of desired pancreatic cell types from pluripotent stem cells for therapeutic purposes.

Pancreatic Mesenchyme Regulates Islet Cellular Composition in a Patched/Hedgehog-Dependent Manner

Pancreas development requires restrained Hedgehog (Hh) signaling activation. While deregulated Hh signaling in the pancreatic mesenchyme has been long suggested to be detrimental for proper organogenesis, this association was not directly shown. Here, we analyzed the contribution of mesenchymal Hh signaling to pancreas development. To increase Hh signaling in the pancreatic mesenchyme of mouse embryos, we deleted Patched1 (Ptch1) in these cells. Our findings indicate that deregulated Hh signaling in mesenchymal cells was sufficient to impair pancreas development, affecting both endocrine and exocrine cells. Notably, transgenic embryos displayed disrupted islet cellular composition and morphology, with a reduced β-cell portion. Our results indicate that the cell-specific growth rates of α- and β-cell populations, found during normal development, require regulated mesenchymal Hh signaling. In addition, we detected hyperplasia of mesenchymal cells upon elevated Hh signaling, accompanied by them acquiring smooth-muscle like phenotype. By specifically manipulating mesenchymal cells, our findings provide direct evidence for the non-autonomous roles of the Hh pathway in pancreatic epithelium development. To conclude, we directly show that regulated mesenchymal Hh signaling is required for pancreas organogenesis and establishment of its proper cellular composition.

Hox6 genes modulate in vitro differentiation of mESCs to insulin-producing cells

The differentiation of glucose-responsive, insulin-producing cells from ESCs in vitro is promising as a cellular therapy for the treatment of diabetes, a devastating and common disease. Pancreatic β-cells are derived from the endoderm in vivo and therefore most current protocols attempt to generate a pure population of first endoderm, then pancreas epithelium, and finally insulin-producing cells. Despite this, differentiation protocols result in mixed populations of cells that are often poorly defined, but also contain mesoderm. Using an in vitro mESC-to-β cell differentiation protocol, we show that expression of region-specific Hox genes is induced. We also show that the loss of function of the Hox6 paralogous group, genes expressed only in the mesenchyme of the pancreas (not epithelium), affect the differentiation of insulin-producing cells in vitro. This work is consistent with the important role for these mesoderm-specific factors in vivo and highlights contribution of supporting mesenchymal cells in in vitro differentiation.

Hox genes and evolution

Hox proteins are a deeply conserved group of transcription factors originally defined for their critical roles in governing segmental identity along the antero-posterior (AP) axis in Drosophila. Over the last 30 years, numerous data generated in evolutionarily diverse taxa have clearly shown that changes in the expression patterns of these genes are closely associated with the regionalization of the AP axis, suggesting that Hox genes have played a critical role in the evolution of novel body plans within Bilateria. Despite this deep functional conservation and the importance of these genes in AP patterning, key questions remain regarding many aspects of Hox biology. In this commentary, we highlight recent reports that have provided novel insight into the origins of the mammalian Hox cluster, the role of Hox genes in the generation of a limbless body plan, and a novel putative mechanism in which Hox genes may encode specificity along the AP axis. Although the data discussed here offer a fresh perspective, it is clear that there is still much to learn about Hox biology and the roles it has played in the evolution of the Bilaterian body plan.