Hoxa-2 restricts the chondrogenic domain and inhibits bone formation during development of the branchial area

NSD2-mediated H3K36me2 exacerbates osteoporosis via activation of hoxa2 in bone marrow mesenchymal stem cells

BACKGROUND

Osteoporosis (OP) is a prevalent disease associated with age, and one of the primary pathologies is the defect of osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). This study aimed to elucidate whether Nuclear Receptor Binding SET Domain Protein 2 (NSD2) transcriptionally regulates osteogenic differentiation of BMSCs in osteoporosis.

METHODS

Identification of human BMSCs (hBMSCs) in vitro was measured by flow cytometry. Osteogenesis of hBMSCs in vitro was measured by Alizarin Red and Alkaline Phosphatase staining. The protein levels of H3K36me1/2/3, NSD2, and Hoxa2 were measured by western blotting. The mRNA levels of NSD2, Runx2, and BSP were measured by qPCR. The role of NSD2 in the osteogenic differentiation of BMSCs was further identified by silencing NSD2 via shRNA or overexpression of NSD2 via lentivirus transfection. The interactions of NSD2, H3K36me2 and Hoxa2 were identified via chromatin immunoprecipitation (ChIP). Luciferase reporting analysis was employed to confirm that NSD2 regulated the transcriptional activity of Hoxa2. Ovariectomized (OVX) was performed on mice to construct osteoporosis (OP) model. Subsequently, the bone mass was assessed by micro computed tomography (micro-CT) scan.

RESULTS

During the osteogenesis of OP-derived hBMSCs, the levels of NSD2 and H3K36me2 significantly increased in 14 days of osteogenic induction. Inhibition of NSD2 via shRNA increased the RUNX2 and BSP expression of hBMSCs, while overexpression of NSD2 decreased RUNX2 and BSP expression of hBMSCs. ChIP analysis indicated NSD2-mediated H3K36me2 reduced the osteogenic differentiation of hBMSCs by regulating the osteogenic inhibitor Hoxa2. Accordingly, inhibition of NSD2 in vivo via tail vein injection of LV-shNSD2 lentivirus greatly alleviated OVX-induced osteoporosis in mice.

CONCLUSION

We demonstrated that NSD2 inhibited the osteogenic differentiation in hBMSCs by transcriptionally downregulating Hoxa2 via H3K36me2 dimethylation. Inhibition of NSD2 effectively attenuated bone loss in murine osteoporosis and NSD2 is a promising target for clinical treatment of osteoporosis.

Hox-A2 protein expression in avian jaws cartilages and muscle primordia development

OBJECTIVE

To elucidate the branchial origin of the articular and the square (homology of the malleus and the incus of mammals), we used immunohistochemistry to analyse the expression of the Hox-A2 protein during cephalogenesis in chickens.

MATERIALS AND METHODS

Immunohistochemistry on paraffin sections of embryos from stage HH16 to HH40.

RESULTS

In addition to the columella (equivalent to the mammalian stapes), the joint between the articular and the quadrate bones, and the retro-articular process of the articular (homologous to the short process of the malleus) express Hox-A2, suggesting an intervention of the 2nd arch in their formation. However, we fortuitously observed very intense expression within the early muscle plate of the second arch, which then generalized to all cephalic muscles, and extended to the trunk's myotomes. In the cartilage, the presence of the protein disappeared at stage 35.

DISCUSSION AND CONCLUSION

The present results, while confirming the contribution of the second arch to the development of avian equivalents of the mammalian ear ossicles, strongly suggest that the Hox-A2 gene plays a role in muscle development, which remains to be elucidated by more sophisticated techniques.

Deficient GATA6-CXCR7 signaling leads to bicuspid aortic valve

The cardiac outflow tract (OFT) transiently links the ventricles to the aortic sac and forms the arterial valves. Abnormalities in these valves, such as bicuspid aortic valve (BAV), are common congenital anomalies. GATA6-inactivating variants cause cardiac OFT defects and BAV, but their mechanisms are unclear. We generated Gata6STOP/+ mice using CRISPR-Cas9, which show highly penetrant BAV (70%) and membranous ventricular septal defects (43%). These mice exhibited decreased proliferation and increased ISL1-positive progenitor cells in the OFT, indicating abnormal cardiovascular differentiation. Gata6 deletion with the Mef2cCre driver line recapitulated Gata6STOP/+ phenotypes, indicating a cell-autonomous role for Gata6 in the second heart field. Gata6STOP/+ mice showed reduced OFT length and caliber, associated with deficient cardiac neural crest cell contribution, which may cause valvulo-septal defects. RNA-sequencing analysis showed depletion in pathways related to cell proliferation and migration, highlighting Cxcr7 (also known as Ackr3) as a candidate gene. Reduced mesenchymal cell migration and invasion were observed in Gata6STOP/+ OFT tissue. CXCR7 agonists reduced mesenchymal cell migration and increased invasion in wild-type but not in Gata6STOP/+ explants, indicating the GATA6-dependent role of CXCR7 in OFT development and its potential link to BAV.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Effect of valproic acid on the formation and migration of cranial neural crest cells at the early developmental stages in rat embryos

Cranial neural crest cells (NCCs) are critical for craniofacial development. The administration of valproic acid (VPA) to pregnant females causes craniofacial malformations in offspring. However, the in vivo influence of VPA on mammalian cranial NCCs remains unclear. In this study, we aimed to elucidate the developmental stage-specific effect of VPA on cranial NCCs through the administration of a single dose of VPA to pregnant rat females immediately prior to the formation of the cranial neural crest (NC). We performed whole-mount immunohistochemistry or in situ hybridization to examine localization changes of gene transcripts associated with the epithelial-mesenchymal transition of the cranial NC (i.e., cranial NCC formation) and cranial NCC migration. The results showed that Hoxa2 mRNA was abnormally detected and Sox9 mRNA expression was decreased in the midbrain-rhombomere (R) 1/2 NC, which forms cranial NCCs that migrate to the frontonasal mass (FNM) and branchial arch (BA) 1, through VPA administration, thus reducing the formation of SNAI2-positive NCCs. Hoxa2-positive NCCs were detected normally in BA2 and abnormally in FNM and BA1, which are normally Hox-free, implying VPA-induced abnormal cranial NCC migration. In vitro verification experiments using the whole embryo culture system revealed that midbrain-R4 NCC migration was abnormal. These results indicate that VPA reduces the formation/delamination of the midbrain-R1/2 NCCs in a developmental stage-specific manner and subsequently causes the abnormal migration of R4 NCCs, which suggests that the abnormal formation and migration of cranial NCCs contribute to the inhibition of axonal elongation in the trigeminal nerve and a reduction in head size.

The Significance of Repressive Processes in Developmental Regulation

Encountering a developmental process confined to a limited time window or a restricted embryonic area, one may deem that the mechanism to activate the process occurs with such precision in temporal and spatial terms. However, in many instances, the activation mechanism is initiated in a broad time and space, but the mechanism is actuated only when repressive mechanisms are lifted. Thus, the operation of repressive processes is essential for precise developmental regulation. Repressive regulations occur at various levels. The following representative repressive regulations and their consequences at various levels will be discussed: intercellular signaling, epigenetic regulation, transcriptional regulation, and posttranscriptional regulation.

Chromatin accessibility and epigenetic deoxyribose nucleic acid (DNA) modifications in chronic kidney disease (CKD) osteoblasts: a study of bone and osteoblasts from pediatric patients with CKD

Maturation defects are intrinsic features of osteoblast lineage cells in CKD patients. These defects persist ex vivo, suggesting that CKD induces epigenetic changes in bone cells. To gain insights into which signaling pathways contribute to CKD-mediated, epigenetically driven, impairments in osteoblast maturation, we characterized RNA expression and DNA methylation patterns by RNA-Seq and MethylationEpic in primary osteoblasts from nine adolescent and young adult dialysis patients with end-stage kidney disease and three healthy references. ATAC-Seq was also performed on a subset of osteoblasts. Bone matrix protein expression was extracted from the iliac crest and evaluated by proteomics. Gene set enrichment analysis was used to establish signaling pathways consistently altered in chromatin accessibility, DNA methylation, and RNA expression patterns. Single genes were suppressed in primary osteoblasts using shRNA and mineralization characterized in vitro. The effect of nuclear factor of activated T cells (NFAT) signaling suppression was also assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) incorporation. We found that signaling pathways critical for osteoblast differentiation were strongly downregulated in CKD osteoblasts. Gene set enrichment analysis identified highly significant methylation changes, differential chromatin accessibility, and altered RNA expression in NFAT signaling targets. NFAT inhibition reduced osteoblast proliferation. Combined analysis of osteoblast RNA expression and whole bone matrix composition identified 13 potential ligand-receptor pairs. In summary, epigenetic changes in CKD osteoblasts associate with altered expression of multiple osteoblast genes and signaling pathways. An increase in NFAT signaling may play a role in impaired CKD osteoblast maturation. Epigenetic changes also associate with an altered bone matrix, which may contribute to bone fragility. Further studies are necessary to elucidate the pathways affected by these genetic alterations since elucidating these pathways will be vital to correcting the underlying biology of bone disease in the CKD population.

Cooperative Response to Endocardial Notch Reveals Interaction With Hippo Pathway

BACKGROUND

The endocardium is a crucial signaling center for cardiac valve development and maturation. Genetic analysis has identified several human endocardial genes whose inactivation leads to bicuspid aortic valve formation and calcific aortic valve disease, but knowledge is very limited about the role played in valve development and disease by noncoding endocardial regulatory regions and upstream factors.

METHODS

We manipulated Notch signaling in mouse embryonic endocardial cells by short-term and long-term coculture with OP9 stromal cells expressing Notch ligands and inhibition of Notch activity. We examined the transcriptional profile and chromatin accessibility landscape for each condition, integrated transcriptomic, transcription factor occupancy, chromatin accessibility, and proteomic datasets. We generated in vitro and in vivo models with CRISPR-Cas9-edited deletions of various noncoding regulatory elements and validated their regulatory potential.

RESULTS

We identified primary and secondary transcriptional responses to Notch ligands in the mouse embryonic endocardium, and a NOTCH-dependent transcriptional signature in valve development and disease. By defining the changes in the chromatin accessibility landscape and integrating with the landscape in developing mouse endocardium and adult human valves, we identify potential noncoding regulatory elements, validated selected candidates, propose interacting cofactors, and define the timeframe of their regulatory activity. Additionally, we found cooperative transcriptional repression with Hippo pathway by inhibiting nuclear Yap (Yes-associated protein) activity in the endocardium during cardiac valve development.

CONCLUSIONS

Sequential Notch-dependent transcriptional regulation in the embryonic endocardium involves multiple factors. Notch activates certain noncoding elements through these factors and simultaneously suppresses elements that could hinder cardiac valve development and homeostasis. Biorxviv: https://www.biorxiv.org/content/10.1101/2023.03.23.533882v1.full.

Nrg1 Regulates Cardiomyocyte Migration and Cell Cycle in Ventricular Development

BACKGROUND

Cardiac ventricles provide the contractile force of the beating heart throughout life. How the primitive endocardium-layered myocardial projections called trabeculae form and mature into the adult ventricles is of great interest for biology and regenerative medicine. Trabeculation is dependent on the signaling protein Nrg1 (neuregulin-1). However, the mechanism of action of Nrg1 and its role in ventricular wall maturation are poorly understood.

METHODS

We investigated the functions and downstream mechanisms of Nrg1 signaling during ventricular chamber development using confocal imaging, transcriptomics, and biochemical approaches in mice with cardiac-specific inactivation or overexpression of Nrg1.

RESULTS

Analysis of cardiac-specific Nrg1 mutant mice showed that the transcriptional program underlying cardiomyocyte-oriented cell division and trabeculae formation depends on endocardial Nrg1 to myocardial ErbB2 (erb-b2 receptor tyrosine kinase 2) signaling and phospho-Erk (phosphorylated extracellular signal-regulated kinase; pErk) activation. Early endothelial loss of Nrg1 and reduced pErk activation diminished cardiomyocyte Pard3 and Crumbs2 (Crumbs Cell Polarity Complex Component 2) protein and altered cytoskeletal gene expression and organization. These alterations are associated with abnormal gene expression related to mitotic spindle organization and a shift in cardiomyocyte division orientation. Nrg1 is crucial for trabecular growth and ventricular wall thickening by regulating an epithelial-to-mesenchymal transition-like process in cardiomyocytes involving migration, adhesion, cytoskeletal actin turnover, and timely progression through the cell cycle G2/M phase. Ectopic cardiac Nrg1 overexpression and high pErk signaling caused S-phase arrest, sustained high epithelial-to-mesenchymal transition-like gene expression, and prolonged trabeculation, blocking compact myocardium maturation. Myocardial trabecular patterning alterations resulting from above- or below-normal Nrg1-dependent pErk activation were concomitant with sarcomere actin cytoskeleton disorganization. The Nrg1 loss- and gain-of-function transcriptomes were enriched for Yap1 (yes-associated protein-1) gene signatures, identifying Yap1 as a potential downstream effector. Furthermore, biochemical and imaging data reveal that Nrg1 influences pErk activation and Yap1 nuclear-cytoplasmic distribution during trabeculation.

CONCLUSIONS

These data establish the Nrg1-ErbB2/ErbB4-Erk axis as a crucial regulator of cardiomyocyte cell cycle progression and migration during ventricular development.

Sox7-positive endothelial progenitors establish coronary arteries and govern ventricular compaction

The cardiac endothelium influences ventricular chamber development by coordinating trabeculation and compaction. However, the endothelial-specific molecular mechanisms mediating this coordination are not fully understood. Here, we identify the Sox7 transcription factor as a critical cue instructing cardiac endothelium identity during ventricular chamber development. Endothelial-specific loss of Sox7 function in mice results in cardiac ventricular defects similar to non-compaction cardiomyopathy, with a change in the proportions of trabecular and compact cardiomyocytes in the mutant hearts. This phenotype is paralleled by abnormal coronary artery formation. Loss of Sox7 function disrupts the transcriptional regulation of the Notch pathway and connexins 37 and 40, which govern coronary arterial specification. Upon Sox7 endothelial-specific deletion, single-nuclei transcriptomics analysis identifies the depletion of a subset of Sox9/Gpc3-positive endocardial progenitor cells and an increase in erythro-myeloid cell lineages. Fate mapping analysis reveals that a subset of Sox7-null endothelial cells transdifferentiate into hematopoietic but not cardiomyocyte lineages. Our findings determine that Sox7 maintains cardiac endothelial cell identity, which is crucial to the cellular cross-talk that drives ventricular compaction and coronary artery development.

Linking Vertebrate Gene Duplications to the New Head Hypothesis

Vertebrates have diverse morphologies and various anatomical novelties that set them apart from their closest invertebrate relatives. A conspicuous head housing a large brain, paired sense organs, and protected by a skeleton of cartilage and bone is unique to vertebrates and is a defining feature of this taxon. Gans and Northcutt (1980s) proposed that the evolution of this "new head" was dependent on two key developmental innovations: neural crest cells (NCCs) and ectodermal placodes. NCCs are migratory embryonic cells that form bone, cartilage, and neurons in the new head. Based on genome size, Ohno (1970s) proposed a separate hypothesis, stating that vertebrate genome content was quadrupled via two rounds (2R) of whole genome duplications (WGDs), and the surplus of genetic material potentiated vertebrate morphological diversification. While both hypotheses offer explanations for vertebrate success, it is unclear if, and how, the "new head" and "2R" hypotheses are linked. Here, we consider both hypotheses and evaluate the experimental evidence connecting the two. Overall, evidence suggests that while the origin of the NC GRN predates the vertebrate WGDs, these genomic events may have potentiated the evolution of distinct genetic subnetworks in different neural crest subpopulations. We describe the general composition of the NC GRN and posit that its increased developmental modularity facilitated the independent evolution of NC derivatives and the diversification of the vertebrate head skeleton. Lastly, we discuss experimental strategies needed to test whether gene duplications drove the diversification of neural crest derivatives and the "new head".

Novel Association of the NOTCH Pathway Regulator MIB1 Gene With the Development of Bicuspid Aortic Valve

Importance

Nonsyndromic bicuspid aortic valve (nsBAV) is the most common congenital heart valve malformation. BAV has a heritable component, yet only a few causative genes have been identified; understanding BAV genetics is a key point in developing personalized medicine.

Objective

To identify a new gene for nsBAV.

Design, Setting, and Participants

This was a comprehensive, multicenter, genetic association study based on candidate gene prioritization in a familial cohort followed by rare and common association studies in replication cohorts. Further validation was done using in vivo mice models. Study data were analyzed from October 2019 to October 2022. Three cohorts of patients with BAV were included in the study: (1) the discovery cohort was a large cohort of inherited cases from 29 pedigrees of French and Israeli origin; (2) the replication cohort 1 for rare variants included unrelated sporadic cases from various European ancestries; and (3) replication cohort 2 was a second validation cohort for common variants in unrelated sporadic cases from Europe and the US.

Main Outcomes and Measures

To identify a candidate gene for nsBAV through analysis of familial cases exome sequencing and gene prioritization tools. Replication cohort 1 was searched for rare and predicted deleterious variants and genetic association. Replication cohort 2 was used to investigate the association of common variants with BAV.

Results

A total of 938 patients with BAV were included in this study: 69 (7.4%) in the discovery cohort, 417 (44.5%) in replication cohort 1, and 452 (48.2%) in replication cohort 2. A novel human nsBAV gene, MINDBOMB1 homologue MIB1, was identified. MINDBOMB1 homologue (MIB1) is an E3-ubiquitin ligase essential for NOTCH-signal activation during heart development. In approximately 2% of nsBAV index cases from the discovery and replication 1 cohorts, rare MIB1 variants were detected, predicted to be damaging, and were significantly enriched compared with population-based controls (2% cases vs 0.9% controls; P = .03). In replication cohort 2, MIB1 risk haplotypes significantly associated with nsBAV were identified (permutation test, 1000 repeats; P = .02). Two genetically modified mice models carrying Mib1 variants identified in our cohort showed BAV on a NOTCH1-sensitized genetic background.

Conclusions and Relevance

This genetic association study identified the MIB1 gene as associated with nsBAV. This underscores the crucial role of the NOTCH pathway in the pathophysiology of BAV and its potential as a target for future diagnostic and therapeutic intervention.

Hox genes are crucial regulators of periosteal stem cell identity

Periosteal stem and progenitor cells (PSPCs) are major contributors to bone maintenance and repair. Deciphering the molecular mechanisms that regulate their function is crucial for the successful generation and application of future therapeutics. Here, we pinpoint Hox transcription factors as necessary and sufficient for periosteal stem cell function. Hox genes are transcriptionally enriched in periosteal stem cells and their overexpression in more committed progenitors drives reprogramming to a naïve, self-renewing stem cell-like state. Crucially, individual Hox family members are expressed in a location-specific manner and their stem cell-promoting activity is only observed when the Hox gene is matched to the anatomical origin of the PSPC, demonstrating a role for the embryonic Hox code in adult stem cells. Finally, we demonstrate that Hoxa10 overexpression partially restores the age-related decline in fracture repair. Together, our data highlight the importance of Hox genes as key regulators of PSPC identity in skeletal homeostasis and repair.

Skeletal dysplasia-causing TRPV4 mutations suppress the hypertrophic differentiation of human iPSC-derived chondrocytes

Mutations in the TRPV4 ion channel can lead to a range of skeletal dysplasias. However, the mechanisms by which TRPV4 mutations lead to distinct disease severity remain unknown. Here, we use CRISPR-Cas9-edited human-induced pluripotent stem cells (hiPSCs) harboring either the mild V620I or lethal T89I mutations to elucidate the differential effects on channel function and chondrogenic differentiation. We found that hiPSC-derived chondrocytes with the V620I mutation exhibited increased basal currents through TRPV4. However, both mutations showed more rapid calcium signaling with a reduced overall magnitude in response to TRPV4 agonist GSK1016790A compared to wildtype (WT). There were no differences in overall cartilaginous matrix production, but the V620I mutation resulted in reduced mechanical properties of cartilage matrix later in chondrogenesis. mRNA sequencing revealed that both mutations up-regulated several anterior HOX genes and down-regulated antioxidant genes CAT and GSTA1 throughout chondrogenesis. BMP4 treatment up-regulated several essential hypertrophic genes in WT chondrocytes; however, this hypertrophic maturation response was inhibited in mutant chondrocytes. These results indicate that the TRPV4 mutations alter BMP signaling in chondrocytes and prevent proper chondrocyte hypertrophy, as a potential mechanism for dysfunctional skeletal development. Our findings provide potential therapeutic targets for developing treatments for TRPV4-mediated skeletal dysplasias.

Changes in Hox Gene Chromatin Organization during Odontogenic Lineage Specification

Craniofacial tissues comprise highly evolved organs characterized by a relative lack of expression in the HOX family transcription factors. In the present study, we sought to define the epigenetic events that limit HOX gene expression from undifferentiated neural crest cells to semi-differentiated odontogenic progenitors and to explore the effects of elevated levels of HOX. The ChIP-chip data demonstrated high levels of repressive H3K27me3 marks on the HOX gene promoters in ES and cranial neural crest cells when compared to the H3K4me3 marks, while the K4/K27 ratio was less repressive in the odontogenic progenitors, dental follicle, dental pulp, periodontal ligament fibroblasts, alveolar bone osteoblasts, and cementoblasts. The gene expression of multiple HOX genes, especially those from the HOXA and HOXB clusters, was significantly elevated and many times higher in alveolar bone cells than in the dental follicle cells. In addition, the HOX levels in the skeletal osteoblasts were many times higher in the trunk osteoblasts compared to the alveolar bone osteoblasts, and the repressive mark H3K27me3 promoter occupancy was substantially and significantly elevated in the alveolar bone osteoblasts when compared to the trunk osteoblasts. To explore the effect of elevated HOX levels in craniofacial neural crest cells, HOX expression was induced by transfecting cells with the Cdx4 transcription factor, resulting in a significant decrease in the mineralization markers, RUNX2, OSX, and OCN upon HOX elevation. Promoting HOX gene expression in developing teeth using the small molecule EZH2 inhibitor GSK126 resulted in an increased number of patterning events, supernumerary cusp formation, and increased Hoxa4 and Hoxb6 gene expression when compared to the controls. Together, these studies illustrate the profound effects of epigenetic regulatory events at all stages of the differentiation of craniofacial peripheral tissues from the neural crest, including lineage specification, tissue differentiation, and patterning.

A Human Hereditary Cardiomyopathy Shares a Genetic Substrate With Bicuspid Aortic Valve

BACKGROUND

The complex genetics underlying human cardiac disease is evidenced by its heterogenous manifestation, multigenic basis, and sporadic occurrence. These features have hampered disease modeling and mechanistic understanding. Here, we show that 2 structural cardiac diseases, left ventricular noncompaction (LVNC) and bicuspid aortic valve, can be caused by a set of inherited heterozygous gene mutations affecting the NOTCH ligand regulator MIB1 (MINDBOMB1) and cosegregating genes.

METHODS

We used CRISPR-Cas9 gene editing to generate mice harboring a nonsense or a missense MIB1 mutation that are both found in LVNC families. We also generated mice separately carrying these MIB1 mutations plus 5 additional cosegregating variants in the ASXL3, APCDD1, TMX3, CEP192, and BCL7A genes identified in these LVNC families by whole exome sequencing. Histological, developmental, and functional analyses of these mouse models were carried out by echocardiography and cardiac magnetic resonance imaging, together with gene expression profiling by RNA sequencing of both selected engineered mouse models and human induced pluripotent stem cell-derived cardiomyocytes. Potential biochemical interactions were assayed in vitro by coimmunoprecipitation and Western blot.

RESULTS

Mice homozygous for the MIB1 nonsense mutation did not survive, and the mutation caused LVNC only in heteroallelic combination with a conditional allele inactivated in the myocardium. The heterozygous MIB1 missense allele leads to bicuspid aortic valve in a NOTCH-sensitized genetic background. These data suggest that development of LVNC is influenced by genetic modifiers present in affected families, whereas valve defects are highly sensitive to NOTCH haploinsufficiency. Whole exome sequencing of LVNC families revealed single-nucleotide gene variants of ASXL3, APCDD1, TMX3, CEP192, and BCL7A cosegregating with the MIB1 mutations and LVNC. In experiments with mice harboring the orthologous variants on the corresponding Mib1 backgrounds, triple heterozygous Mib1 Apcdd1 Asxl3 mice showed LVNC, whereas quadruple heterozygous Mib1 Cep192 Tmx3;Bcl7a mice developed bicuspid aortic valve and other valve-associated defects. Biochemical analysis suggested interactions between CEP192, BCL7A, and NOTCH. Gene expression profiling of mutant mouse hearts and human induced pluripotent stem cell-derived cardiomyocytes revealed increased cardiomyocyte proliferation and defective morphological and metabolic maturation.

CONCLUSIONS

These findings reveal a shared genetic substrate underlying LVNC and bicuspid aortic valve in which MIB1-NOTCH variants plays a crucial role in heterozygous combination with cosegregating genetic modifiers.

Meis2 controls skeletal formation in the hyoid region

A vertebrate skull is composed of many skeletal elements which display enormous diversity of shapes. Cranial bone formation embodies a multitude of processes, i.e., epithelial-mesenchymal induction, mesenchymal condensation, and endochondral or intramembranous ossification. Molecular pathways determining complex architecture and growth of the cranial skeleton during embryogenesis are poorly understood. Here, we present a model of the hyoid apparatus development in Wnt1-Cre2-induced Meis2 conditional knock-out (cKO) mice. Meis2 cKO embryos develop an aberrant hyoid apparatus—a complete skeletal chain from the base of the neurocranium to lesser horns of the hyoid, resembling extreme human pathologies of the hyoid-larynx region. We examined key stages of hyoid skeletogenesis to obtain a complex image of the hyoid apparatus formation. Lack of Meis2 resulted in ectopic loci of mesenchymal condensations, ectopic cartilage and bone formation, disinhibition of skeletogenesis, and elevated proliferation of cartilage precursors. We presume that all these mechanisms contribute to formation of the aberrant skeletal chain in the hyoid region. Moreover, Meis2 cKO embryos exhibit severely reduced expression of PBX1 and HAND2 in the hyoid region. Altogether, MEIS2 in conjunction with PBX1 and HAND2 affects mesenchymal condensation, specification and proliferation of cartilage precursors to ensure development of the anatomically correct hyoid apparatus.

Different Ectopic Hoxa2 Expression Levels in Mouse Cranial Neural Crest Cells Result in Distinct Craniofacial Anomalies and Homeotic Phenotypes

Providing appropriate positional identity and patterning information to distinct rostrocaudal subpopulations of cranial neural crest cells (CNCCs) is central to vertebrate craniofacial morphogenesis. Hox genes are not expressed in frontonasal and first pharyngeal arch (PA1) CNCCs, whereas a single Hox gene, Hoxa2, is necessary to provide patterning information to second pharyngeal arch (PA2) CNCCs. In frog, chick and mouse embryos, ectopic expression of Hoxa2 in Hox-negative CNCCs induced hypoplastic phenotypes of CNCC derivatives of variable severity, associated or not with homeotic transformation of a subset of PA1 structures into a PA2-like identity. Whether these different morphological outcomes are directly related to distinct Hoxa2 overexpression levels is unknown. To address this issue, we selectively induced Hoxa2 overexpression in mouse CNCCs, using a panel of mouse lines expressing different Hoxa2 ectopic expression levels, including a newly generated Hoxa2 knocked-in mouse line. While ectopic Hoxa2 expression at only 60% of its physiological levels was sufficient for pinna duplication, ectopic Hoxa2 expression at 100% of its normal level was required for complete homeotic repatterning of a subset of PA1 skeletal elements into a duplicated set of PA2-like elements. On the other hand, ectopic Hoxa2 overexpression at non-physiological levels (200% of normal levels) led to an almost complete loss of craniofacial skeletal structures. Moreover, ectopic Hoxa5 overexpression in CNCCs, while also resulting in severe craniofacial defects, did not induce homeotic changes of PA1-derived CNCCs, indicating Hoxa2 specificity in repatterning a subset of Hox-negative CNCCs. These results reconcile some discrepancies in previously published experiments and indicate that distinct subpopulations of CNCCs are differentially sensitive to ectopic levels of Hox expression.

Adhesion G protein-coupled receptor Gpr126/Adgrg6 is essential for placental development

Mutations in the G protein–coupled receptor GPR126/ADGRG6 cause human diseases, including defective peripheral nervous system (PNS) myelination. To study GPR126 function, we generated new genetic mice and zebrafish models. Murine Gpr126 is expressed in developing heart endocardium, and global Gpr126 inactivation is embryonically lethal, with mutants having thin-walled ventricles but unaffected heart patterning or maturation. Endocardial-specific Gpr126 deletion does not affect heart development or function, and transgenic endocardial GPR126 expression fails to rescue lethality in Gpr126-null mice. Zebrafish gpr126 mutants display unaffected heart development. Gpr126 is also expressed in placental trophoblast giant cells. Gpr126-null mice with a heterozygous placenta survive but exhibit GPR126-defective PNS phenotype. In contrast, Gpr126-null embryos with homozygous mutant placenta die but are rescued by placental GPR126 expression. Gpr126-deficient placentas display down-regulation of preeclampsia markers Mmp9, Cts7, and Cts8. We propose that the placenta-heart axis accounts for heart abnormalities secondary to placental defects in Gpr126 mutants.

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

Craniofacial and Long Bone Development in the Context of Distraction Osteogenesis

BACKGROUND

Bone retains regenerative potential into adulthood, and surgeons harness this plasticity during distraction osteogenesis. The underlying biology governing bone development, repair, and regeneration is divergent between the craniofacial and appendicular skeleton. Each type of bone formation is characterized by unique molecular signaling and cellular behavior. Recent discoveries have elucidated the cellular and genetic processes underlying skeletal development and regeneration, providing an opportunity to couple biological and clinical knowledge to improve patient care.

METHODS

A comprehensive literature review of basic and clinical literature regarding craniofacial and long bone development, regeneration, and distraction osteogenesis was performed.

RESULTS

The current understanding in craniofacial and long bone development and regeneration is discussed, and clinical considerations for the respective distraction osteogenesis procedures are presented.

CONCLUSIONS

Distraction osteogenesis is a powerful tool to regenerate bone and thus address a number of craniofacial and appendicular skeletal deficiencies. The molecular mechanisms underlying bone regeneration, however, remain elusive. Recent work has determined that embryologic morphogen gradients constitute important signals during regeneration. In addition, striking discoveries have illuminated the cellular processes underlying mandibular regeneration during distraction osteogenesis, showing that skeletal stem cells reactivate embryologic neural crest transcriptomic processes to carry out bone formation during regeneration. Furthermore, innovative adjuvant therapies to complement distraction osteogenesis use biological processes active in embryogenesis and regeneration. Additional research is needed to further characterize the underlying cellular mechanisms responsible for improved bone formation through adjuvant therapies and the role skeletal stem cells play during regeneration.

SATB2: A versatile transcriptional regulator of craniofacial and skeleton development, neurogenesis and tumorigenesis, and its applications in regenerative medicine

SATB2 (special AT-rich sequence-binding protein 2) is a member of the special AT-rich binding protein family. As a transcription regulator, SATB2 mainly integrates higher-order chromatin organization. SATB2 expression appears to be tissue- and stage-specific, and is governed by several cellular signaling molecules and mediators. Expressed in branchial arches and osteoblast-lineage cells, SATB2 plays a significant role in craniofacial pattern and skeleton development. In addition to regulating osteogenic differentiation, SATB2 also displays versatile functions in neural development and cancer progression. As an osteoinductive factor, SATB2 holds great promise in improving bone regeneration toward bone defect repair. In this review, we have summarized our current understanding of the physiological and pathological functions of SATB2 in craniofacial and skeleton development, neurogenesis, tumorigenesis and regenerative medicine.

Mechanisms of bone development and repair

Bone development occurs through a series of synchronous events that result in the formation of the body scaffold. The repair potential of bone and its surrounding microenvironment - including inflammatory, endothelial and Schwann cells - persists throughout adulthood, enabling restoration of tissue to its homeostatic functional state. The isolation of a single skeletal stem cell population through cell surface markers and the development of single-cell technologies are enabling precise elucidation of cellular activity and fate during bone repair by providing key insights into the mechanisms that maintain and regenerate bone during homeostasis and repair. Increased understanding of bone development, as well as normal and aberrant bone repair, has important therapeutic implications for the treatment of bone disease and ageing-related degeneration.

NOTCH Activation Promotes Valve Formation by Regulating the Endocardial Secretome

The endocardium is a specialized endothelium that lines the inner surface of the heart. Functional studies in mice and zebrafish have established that the endocardium is a source of instructive signals for the development of cardiac structures, including the heart valves and chambers. Here, we characterized the NOTCH-dependent endocardial secretome by manipulating NOTCH activity in mouse embryonic endocardial cells (MEEC) followed by mass spectrometry-based proteomics. We profiled different sets of soluble factors whose secretion not only responds to NOTCH activation but also shows differential ligand specificity, suggesting that ligand-specific inputs may regulate the expression of secreted proteins involved in different cardiac development processes. NOTCH signaling activation correlates with a transforming growth factor-β2 (TGFβ2)-rich secretome and the delivery of paracrine signals involved in focal adhesion and extracellular matrix (ECM) deposition and remodeling. In contrast, NOTCH inhibition is accompanied by the up-regulation of specific semaphorins that may modulate cell migration. The secretome protein expression data showed a good correlation with gene profiling of RNA expression in embryonic endocardial cells. Additional characterization by in situ hybridization in mouse embryos revealed expression of various NOTCH candidate effector genes (Tgfβ2, Loxl2, Ptx3, Timp3, Fbln2, and Dcn) in heart valve endocardium and/or mesenchyme. Validating these results, mice with conditional Dll4 or Jag1 loss-of-function mutations showed gene expression alterations similar to those observed at the protein level in vitro These results provide the first description of the NOTCH-dependent endocardial secretome and validate MEEC as a tool for assaying the endocardial secretome response to a variety of stimuli and the potential use of this system for drug screening.

The Forgotten Skeletogenic Condensations: A Comparison of Early Skeletal Development Amongst Vertebrates

The development of a skeletogenic condensation is perhaps the most critical yet considerably overlooked stage of skeletogenesis. Described in this comprehensive review are the mechanisms that facilitate skeletogenic condensation formation, growth, and maintenance to allow for overt differentiation into a skeletal element. This review discusses the current knowledge of gene regulation and characterization of skeletogenic condensations in the chicken, mouse, zebrafish, and other developmental models. We limited our scope to condensations that give rise to the bones and cartilages of the vertebrate skeleton, with a particular focus on craniofacial and limb bud regions. While many of the skeletogenic processes are similar among vertebrate lineages, differences are apparent in the site and timing of the initial epithelial⁻mesenchymal interactions as well as in whether the condensation has an osteogenic or chondrogenic fate, both within and among species. Further comparative studies are needed to clarify and broaden the existing knowledge of this intricate phenomenon.

Hox-A2 protein expression in mouse embryo middle ear ossicles

The origin of the mammalian middle ear ossicles from mandibular and hyoid pharyngeal arches remains controversial and discussed. Two adverse theories are proposed. The first claims that malleus and incus derive from the Meckel's cartilage of the mandibular arch, and stapes from Reichert's cartilage of the hyoid arch. The second postulates that handle of malleus and long process of the incus are derived from the second arch as well as the stapes. Contradictory analyses support alternatively each theory without any experimental evidence. In order to bring new data, we analyzed by immunohistochemistry the expression of Hox-A2 protein in ossicular anlagen in E11 to 13 mouse embryos. HOXA2 gene is known to be expressed in second arch cells and to be absent from mandibular arch derivatives. Surprisingly, Hox-A2 protein was present in all ossicular primordia, as well in Reichert's cartilage. Meckel's cartilage was free of staining. Unlabeled cells were also present in ossicular blastemata. These results suggest that ossicular condensations could arise from mixed cell populations originated in both mandibular and hyoid pharyngeal arches. However, we cannot exclude that diffuse Hox-A2 immunoreactivity could correspond to a secondary expression in craniofacial mesenchyme independently from the branchial origin of cells.

Control of cardiac jelly dynamics by NOTCH1 and NRG1 defines the building plan for trabeculation

In vertebrate hearts, the ventricular trabecular myocardium develops as a sponge-like network of cardiomyocytes that is critical for contraction and conduction, ventricular septation, papillary muscle formation and wall thickening through the process of compaction ¹ . Defective trabeculation leads to embryonic lethality^2-4 or non-compaction cardiomyopathy (NCC) ⁵ . There are divergent views on when and how trabeculation is initiated in different species. In zebrafish, trabecular cardiomyocytes extrude from compact myocardium ⁶ , whereas in chicks, chamber wall thickening occurs before overt trabeculation ⁷ . In mice, the onset of trabeculation has not been described, but is proposed to begin at embryonic day 9.0, when cardiomyocytes form radially oriented ribs ² . Endocardium-myocardium communication is essential for trabeculation, and numerous signalling pathways have been identified, including Notch^2,8 and Neuregulin (NRG) ⁴ . Late disruption of the Notch pathway causes NCC ⁵ . Whereas it has been shown that mutations in the extracellular matrix (ECM) genes Has2 and Vcan prevent the formation of trabeculae in mice^9,10 and the matrix metalloprotease ADAMTS1 promotes trabecular termination ³ , the pathways involved in ECM dynamics and the molecular regulation of trabeculation during its early phases remain unexplored. Here we present a model of trabeculation in mice that integrates dynamic endocardial and myocardial cell behaviours and ECM remodelling, and reveal new epistatic relationships between the involved signalling pathways. NOTCH1 signalling promotes ECM degradation during the formation of endocardial projections that are critical for individualization of trabecular units, whereas NRG1 promotes myocardial ECM synthesis, which is necessary for trabecular rearrangement and growth. These systems interconnect through NRG1 control of Vegfa, but act antagonistically to establish trabecular architecture. These insights enabled the prediction of persistent ECM and cardiomyocyte growth in a mouse NCC model, providing new insights into the pathophysiology of congenital heart disease.

Coupling the roles of Hox genes to regulatory networks patterning cranial neural crest

The neural crest is a transient population of cells that forms within the developing central nervous system and migrates away to generate a wide range of derivatives throughout the body during vertebrate embryogenesis. These cells are of evolutionary and clinical interest, constituting a key defining trait in the evolution of vertebrates and alterations in their development are implicated in a high proportion of birth defects and craniofacial abnormalities. In the hindbrain and the adjacent cranial neural crest cells (cNCCs), nested domains of Hox gene expression provide a combinatorial'Hox-code' for specifying regional properties in the developing head. Hox genes have been shown to play important roles at multiple stages in cNCC development, including specification, migration, and differentiation. However, relatively little is known about the underlying gene-regulatory mechanisms involved, both upstream and downstream of Hox genes. Furthermore, it is still an open question as to how the genes of the neural crest GRN are linked to Hox-dependent pathways. In this review, we describe Hox gene expression, function and regulation in cNCCs with a view to integrating these genes within the emerging gene regulatory network for cNCC development. We highlight early roles for Hox1 genes in cNCC specification, proposing that this may be achieved, in part, by regulation of the balance between pluripotency and differentiation in precursor cells within the neuro-epithelium. We then describe what is known about the regulation of Hox gene expression in cNCCs and discuss this from the perspective of early vertebrate evolution.

The Role of MicroRNAs in Arterial Stiffness and Arterial Calcification. An Update and Review of the Literature

Arterial stiffness is an independent risk factor for fatal and non-fatal cardiovascular events, such as systolic hypertension, coronary artery disease, stroke, and heart failure. Moreover it reflects arterial aging which in many cases does not coincide with chronological aging, a fact that is in large attributed to genetic factors. In addition to genetic factors, microRNAs (miRNAs) seem to largely affect arterial aging either by advancing or by regressing arterial stiffness. MiRNAs are small RNA molecules, ~22 nucleotides long that can negatively control their target gene expression posttranscriptionally. Pathways that affect main components of stiffness such as fibrosis and calcification seem to be influenced by up or downregulation of specific miRNAs. Identification of this aberrant production of miRNAs can help identify epigenetic changes that can be therapeutic targets for prevention and treatment of vascular diseases. The present review summarizes the specific role of the so far discovered miRNAs that are involved in pathways of arterial stiffness.

Hoxa2 Inhibits Bone Morphogenetic Protein Signaling during Osteogenic Differentiation of the Palatal Mesenchyme

Cleft palate is one of the most common congenital birth defects worldwide. The homeobox (Hox) family of genes are key regulators of embryogenesis, with Hoxa2 having a direct role in secondary palate development. Hoxa2^−/− mice exhibit cleft palate; however, the cellular and molecular mechanisms leading to cleft palate in Hoxa2^−/− mice is largely unknown. Addressing this issue, we found that Hoxa2 regulates spatial and temporal programs of osteogenic differentiation in the developing palate by inhibiting bone morphogenetic protein (BMP) signaling dependent osteoblast markers. Expression of osteoblast markers, including Runx2, Sp7, and AlpI were increased in Hoxa2^−/− palatal shelves at embryonic day (E) 13.5 and E15.5. Hoxa2^−/− mouse embryonic palatal mesenchyme (MEPM) cells exhibited increased bone matrix deposition and mineralization in vitro. Moreover, loss of Hoxa2 resulted in increased osteoprogenitor cell proliferation and osteogenic commitment during early stages of palate development at E13.5. Consistent with upregulation of osteoblast markers, Hoxa2^−/− palatal shelves displayed higher expression of canonical BMP signaling in vivo. Blocking BMP signaling in Hoxa2^−/− primary MEPM cells using dorsomorphin restored cell proliferation and osteogenic differentiation to wild-type levels. Collectively, these data demonstrate for the first time that Hoxa2 may regulate palate development by inhibiting osteogenic differentiation of palatal mesenchyme via modulating BMP signaling.

COUP-TFII is required for morphogenesis of the neural crest-derived tympanic ring

Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII) plays pivotal roles in cell growth, cell differentiation, and cell fate determination. Although genome-wide studies have identified COUP-TFII binding on gene sets mainly involved in neural crest cell (NCC) development and craniofacial morphogenesis, the direct functional connection between COUP-TFII and NCCs in vivo has not been well characterized. In this study, we show that COUP-TFII is expressed in the subpopulation of NCCs and its derivatives, and targeted ablation of COUP-TFII in mouse NCCs results in markedly shortened and bifurcated tympanic rings, which in turn disturb the caudal direction of external acoustic meatus invagination. However, formation of the manubrium of the malleus (MM) in Wnt1-Cre/+;COUP-TFII^flox/flox mice is not perturbed, suggesting that the rostral half of the tympanic ring is sufficient to support proper MM development. Interestingly, we found that loss of COUP-TFII up-regulates Sox9 in the tympanic ring primordium and affects the distribution of preosteoblasts before mesenchymal condensation. Together, our results demonstrate that COUP-TFII plays an essential role in regulating the patterning of the NCC-derived tympanic ring.

A tissue-specific, Gata6-driven transcriptional program instructs remodeling of the mature arterial tree

Connection of the heart to the systemic circulation is a critical developmental event that requires selective preservation of embryonic vessels (aortic arches). However, why some aortic arches regress while others are incorporated into the mature aortic tree remains unclear. By microdissection and deep sequencing in mouse, we find that neural crest (NC) only differentiates into vascular smooth muscle cells (SMCs) around those aortic arches destined for survival and reorganization, and identify the transcription factor Gata6 as a crucial regulator of this process. Gata6 is expressed in SMCs and its target genes activation control SMC differentiation. Furthermore, Gata6 is sufficient to promote SMCs differentiation in vivo, and drive preservation of aortic arches that ought to regress. These findings identify Gata6-directed differentiation of NC to SMCs as an essential mechanism that specifies the aortic tree, and provide a new framework for how mutations in GATA6 lead to congenital heart disorders in humans.

Hypertrophic differentiation of mesenchymal stem cells is suppressed by xanthotoxin via the p38‑MAPK/HDAC4 pathway

Chondrocyte hypertrophy is a physiological process in endochondral ossification. However, the hypertrophic-like alterations of chondrocytes at the articular surface may result in osteoarthritis (OA). In addition, the generation of fibrocartilage with a decreased biological function in tissue engineered cartilage, has been attributed to chondrocyte hypertrophy. Therefore, suppressing chondrocyte hypertrophy in OA and the associated regeneration of non-active cartilage is of primary concern. The present study examined the effects of xanthotoxin (XAT), which is classified as a furanocoumarin, on chondrocyte hypertrophic differentiation of mesenchymal stem cells. Following XAT treatment, the expression levels of genes associated with chondrocyte hypertrophy were detected via immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction. The results revealed that XAT inhibited the expression of various chondrocyte hypertrophic markers, including runt related transcription factor 2 (Runx2), matrix metalloproteinase 13 and collagen type X α1 chain. Further exploration indicated that XAT reduced the activation of p38-mitogen activated protein kinase and then increased the expression of histone deacetylase 4 to suppress Runx2. The findings indicated that XAT maintained the chondrocyte phenotype in regenerated cartilage and therefore may exhibit promise as a potential drug for the treatment of OA in the future.

Genetic diversity and signatures of selection in various goat breeds revealed by genome-wide SNP markers

Background

The detection of signatures of selection has the potential to elucidate the identities of genes and mutations associated with phenotypic traits important for livestock species. It is also very relevant to investigate the levels of genetic diversity of a population, as genetic diversity represents the raw material essential for breeding and has practical implications for implementation of genomic selection. A total of 1151 animals from nine goat populations selected for different breeding goals and genotyped with the Illumina Goat 50K single nucleotide polymorphisms (SNP) Beadchip were included in this investigation.

Results

The proportion of polymorphic SNPs ranged from 0.902 (Nubian) to 0.995 (Rangeland). The overall mean H_O and H_E was 0.374 ± 0.021 and 0.369 ± 0.023, respectively. The average pairwise genetic distance (D) ranged from 0.263 (Toggenburg) to 0.323 (Rangeland). The overall average for the inbreeding measures F_EH, F_VR, F_LEUT, F_ROH and F_PED was 0.129, −0.012, −0.010, 0.038 and 0.030, respectively. Several regions located on 19 chromosomes were potentially under selection in at least one of the goat breeds. The genomic population tree constructed using all SNPs differentiated breeds based on selection purpose, while genomic population tree built using only SNPs in the most significant region showed a great differentiation between LaMancha and the other breeds. We hypothesized that this region is related to ear morphogenesis. Furthermore, we identified genes potentially related to reproduction traits, adult body mass, efficiency of food conversion, abdominal fat deposition, conformation traits, liver fat metabolism, milk fatty acids, somatic cells score, milk protein, thermo-tolerance and ear morphogenesis.

Conclusions

In general, moderate to high levels of genetic variability were observed for all the breeds and a characterization of runs of homozygosity gave insights into the breeds’ development history. The information reported here will be useful for the implementation of genomic selection and other genomic studies in goats. We also identified various genome regions under positive selection using smoothed F_ST and hapFLK statistics and suggested genes, which are potentially under selection. These results can now provide a foundation to formulate biological hypotheses related to selection processes in goats.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3610-0) contains supplementary material, which is available to authorized users.

Low oxygen tension reveals distinct HOX codes in human cord blood-derived stromal cells associated with specific endochondral ossification capacities in vitro and in vivo

Effects of oxygen tension on the generation, expansion, proliferation and differentiation of stromal cell types is widely described in the literature. However, data on the internal heterogeneity of applied cell populations at different O₂ levels and possible impacts on differentiation potentials are controversial. Here, the expression of 39 human HOX genes was determined in neonatal cord blood stromal cells and linked to differentiation-associated signatures. In cord blood, unrestricted somatic stromal cells (USSCs), lacking HOX gene expression, and cord blood-derived multipotent stromal cells (CB-MSCs), expressing about 20 HOX genes, are distinguished by their specific HOX code. Interestingly, 74% of the clones generated at 21% O₂ were HOX-negative USSCs, whereas 73% of upcoming clones at 3% O₂ were HOX-positive CB-MSCs. In order to better categorize distinct cell lines generated at 3% O₂ , the expression of all 39 HOX genes within HOX clusters A, B, C and D were tested and new subtypes defined: cells negative in all four HOX clusters (USSCs); cells positive in all four clusters (CB-MSCs^ABCD ); and subpopulations missing a single cluster (CB-MSCs^ACD and CB-MSCs^BCD ). Comprehensive qPCR analyses of established chondro-osteomarkers revealed subtype-specific signatures verifiably associated with in vitro and in vivo differentiation capacity. The data presented here underline the necessity of better characterizing distinct cell populations at a clonal level, taking advantage of the inherent specific HOX code as a distinguishing feature between individual subtypes. Moreover, the correlation of subtype-specific molecular signatures with in vitro and in vivo bone formation is discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Sequential Notch activation regulates ventricular chamber development

Ventricular chambers are essential for the rhythmic contraction and relaxation occurring in every heartbeat throughout life. Congenital abnormalities in ventricular chamber formation cause severe human heart defects. How the early trabecular meshwork of myocardial fibres forms and subsequently develops into mature chambers is poorly understood. We show that Notch signalling first connects chamber endocardium and myocardium to sustain trabeculation, and later coordinates ventricular patterning and compaction with coronary vessel development to generate the mature chamber, through a temporal sequence of ligand signalling determined by the glycosyltransferase manic fringe (MFng). Early endocardial expression of MFng promotes Dll4-Notch1 signalling, which induces trabeculation in the developing ventricle. Ventricular maturation and compaction require MFng and Dll4 downregulation in the endocardium, which allows myocardial Jag1 and Jag2 signalling to Notch1 in this tissue. Perturbation of this signalling equilibrium severely disrupts heart chamber formation. Our results open a new research avenue into the pathogenesis of cardiomyopathies.

A new frontonasal dysplasia syndrome associated with deletion of the SIX2 gene

The frontonasal dysplasias are a group of craniofacial phenotypes characterized by hypertelorism, nasal clefting, frontal bossing, and abnormal hairline. These conditions are caused by recessive mutations in members of the aristaless gene family, resulting in abnormal cranial neural crest migration and differentiation. We report a family with a dominantly inherited craniofacial phenotype comprised of frontal bossing with high hairline, ptosis, hypertelorism, broad nasal tip, large anterior fontanelle, cranial base anomalies, and sagittal synostosis. Chromosomal microarray identified a heterozygous 108.3 kilobase deletion of chromosome 2p21 segregating with phenotype and limited to the sine oculis homeobox gene SIX2 and surrounding noncoding DNA. Similar to the human SIX2 deletion phenotype, one mouse model of frontonasal dysplasia, brachyrrhine, exhibits dominant inheritance and impaired cranial base chondrogenesis associated with reduced Six2 expression. We report the first human autosomal dominant frontonasal dysplasia syndrome associated with SIX2 deletion and with phenotypic similarities to murine models of Six2 Loss-of-function.

Mandible and Tongue Development

The tongue and mandible have common origins. They arise simultaneously from the mandibular arch and are coordinated in their development and growth, which is evident from several clinical conditions such as Pierre Robin sequence. Here, we review in detail the molecular networks controlling both mandible and tongue development. We also discuss their mechanical relationship and evolution as well as the potential for stem cell-based therapies for disorders affecting these organs.

Runx2/miR-3960/miR-2861 Positive Feedback Loop Is Responsible for Osteogenic Transdifferentiation of Vascular Smooth Muscle Cells

We previously reported that Runx2/miR-3960/miR-2861 regulatory feedback loop stimulates osteoblast differentiation. However, the effect of this feedback loop on the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) remains unclear. Our recent study showed that miR-2861 and miR-3960 expression increases significantly during β-glycerophosphate-induced osteogenic transdifferentiation of VSMCs. Overexpression of miR-2861 or miR-3960 in VSMCs enhances β-glycerophosphate-induced osteoblastogenesis, whereas inhibition of miR-2861 or miR-3960 expression attenuates it. MiR-2861 or miR-3960 promotes osteogenic transdifferentiation of VSMCs by targeting histone deacetylase 5 or Homeobox A2, respectively, resulting in increased runt-related transcription factor 2 (Runx2) protein production. Furthermore, overexpression of Runx2 induces miR-2861 and miR-3960 transcription, and knockdown of Runx2 attenuates β-glycerophosphate-induced miR-2861 and miR-3960 transcription in VSMCs. Thus, our data show that Runx2/miR-3960/miR-2861 positive feedback loop plays an important role in osteogenic transdifferentiation of VSMCs and contributes to vascular calcification.

Distinct effects of Hoxa2 overexpression in cranial neural crest populations reveal that the mammalian hyomandibular-ceratohyal boundary maps within the styloid process

Most gnathostomata craniofacial structures derive from pharyngeal arches (PAs), which are colonized by cranial neural crest cells (CNCCs). The anteroposterior and dorsoventral identities of CNCCs are defined by the combinatorial expression of Hox and Dlx genes. The mechanisms associating characteristic Hox/Dlx expression patterns with the topology and morphology of PAs derivatives are only partially known; a better knowledge of these processes might lead to new concepts on the origin of taxon-specific craniofacial morphologies and of certain craniofacial malformations. Here we show that ectopic expression of Hoxa2 in Hox-negative CNCCs results in distinct phenotypes in different CNCC subpopulations. Namely, while ectopic Hoxa2 expression is sufficient for the morphological and molecular transformation of the first PA (PA1) CNCC derivatives into the second PA (PA2)-like structures, this same genetic alteration does not provoke the transformation of derivatives of other CNCC subpopulations, but severely impairs their development. Ectopic Hoxa2 expression results in the transformation of the proximal Meckel's cartilage and of the malleus, two ventral PA1 CNCCs derivatives, into a supernumerary styloid process (SP), a PA2-derived mammalian-specific skeletal structure. These results, together with experiments to inactivate and ectopically activate the Edn1-Dlx5/6 pathway, indicate a dorsoventral PA2 (hyomandibular/ceratohyal) boundary passing through the middle of the SP. The present findings suggest context-dependent function of Hoxa2 in CNCC regional specification and morphogenesis, and provide novel insights into the evolution of taxa-specific patterning of PA-derived structures.

Hoxa2 selectively enhances Meis binding to change a branchial arch ground state

Hox transcription factors (TFs) are essential for vertebrate development, but how these evolutionary conserved proteins function in vivo remains unclear. Because Hox proteins have notoriously low binding specificity, they are believed to bind with cofactors, mainly homeodomain TFs Pbx and Meis, to select their specific targets. We mapped binding of Meis, Pbx, and Hoxa2 in the branchial arches, a series of segments in the developing vertebrate head. Meis occupancy is largely similar in Hox-positive and -negative arches. Hoxa2, which specifies second arch (IIBA) identity, recognizes a subset of Meis prebound sites that contain Hox motifs. Importantly, at these sites Meis binding is strongly increased. This enhanced Meis binding coincides with active enhancers, which are linked to genes highly expressed in the IIBA and regulated by Hoxa2. These findings show that Hoxa2 operates as a tissue-specific cofactor, enhancing Meis binding to specific sites that provide the IIBA with its anatomical identity.

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Meis provides a ground state that is common to all the branchial arches

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Hoxa2 recognizes Meis prebound sites in the second arch that contain Hox motifs

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Hoxa2 enhances Meis binding, which coincides with active enhancers, at these sites

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Hoxa2 modulates the ground-state binding of Meis to instruct second arch identity

Hoxb6 can interfere with somitogenesis in the posterior embryo through a mechanism independent of its rib-promoting activity

Formation of the vertebrate axial skeleton requires coordinated Hox gene activity. Hox group 6 genes are involved in the formation of the thoracic area due to their unique rib-promoting properties. We show here that the linker region (LR) connecting the homeodomain and the hexapeptide is essential for Hoxb6 rib-promoting activity. The LR-defective Hoxb6 protein was still able to bind a target enhancer together with Pax3 producing a dominant negative effect, indicating that the LR brings additional regulatory factors to target DNA elements. We also found an unexpected association between Hoxb6 and segmentation in the paraxial mesoderm. In particular, Hoxb6 can disturb somitogenesis and anterior-posterior somite patterning by deregulating Lfng expression. Interestingly, this interaction occurred differently in thoracic and more caudal embryonic areas, indicating functional differences in somitogenesis before and after the trunk to tail transition. Our results suggest the requirement of precisely regulated Hoxb6 expression for proper segmentation at tailbud stages.

Arid3b is essential for second heart field cell deployment and heart patterning

Arid3b, a member of the conserved ARID family of transcription factors, is essential for mouse embryonic development but its precise roles are poorly understood. Here, we show that Arid3b is expressed in the myocardium of the tubular heart and in second heart field progenitors. Arid3b-deficient embryos show cardiac abnormalities, including a notable shortening of the poles, absence of myocardial differentiation and altered patterning of the atrioventricular canal, which also lacks epithelial-to-mesenchymal transition. Proliferation and death of progenitors as well as early patterning of the heart appear normal. However, DiI labelling of second heart field progenitors revealed a defect in the addition of cells to the heart. RNA microarray analysis uncovered a set of differentially expressed genes in Arid3b-deficient tissues, including Bhlhb2, a regulator of cardiomyocyte differentiation, and Lims2, a gene involved in cell migration. Arid3b is thus required for heart development by regulating the motility and differentiation of heart progenitors. These findings identify Arid3b as a candidate gene involved in the aetiology of human congenital malformations.

Notch activation stimulates migration of breast cancer cells and promotes tumor growth

INTRODUCTION

Dysregulated NOTCH receptor activity has been implicated in breast cancer but the mechanisms by which NOTCH contributes to transformation are not yet clear, as it has context-dependent effects on the properties of transformed cells.

METHODS

We have used various in vitro and in vivo carcinogenic models to analyze the impact of Notch signaling in the onset and progression of breast tumors.

RESULTS

We found that ectopic expression of the Notch1 intracellular domain (N1ICD) in MCF-7 breast adenocarcinoma cell line caused reduction and delocalization of E-CADHERIN levels and increased migratory and invasive abilities. Notch inhibition in the invasive breast cancer cell line MDA-MB-231 resulted in increased E-CADHERIN expression and a parallel reduction in their invasive capacity. The growth of subcutaneous xenografts produced with MCF-7 cells was boosted after N1ICD induction, in a cell autonomous manner. In vivo Notch1 activation in the mammary gland using the MMTV-Cre driver caused the formation of papillary tumors that showed increased Hes1 and Hey1 expression and delocalized E-cadherin staining.

CONCLUSIONS

These results confirm NOTCH1 as a signal triggering epithelial-mesenchymal transition in epithelial cancer cells, which may have implications in tumor dissemination, metastasis and proliferation in vivo. The identification of specific factors interacting with NOTCH signaling could thus be relevant to fully understanding the role of NOTCH in breast neoplasia.

Microporous calcium phosphate ceramics driving osteogenesis through surface architecture

The presence of micropores in calcium phosphate (CaP) ceramics has shown its important role in initiating inductive bone formation in ectopic sites. To investigate how microporous CaP ceramics trigger osteoinduction, we optimized two biphasic CaP ceramics (i.e., BCP-R and BCP-S) to have the same chemical composition, equivalent surface area per volume, comparable protein adsorption, similar ion (i.e., calcium and phosphate) exchange and the same surface mineralization potential, but different surface architecture. In particular, BCP-R had a surface roughness (Ra) of 325.4 ± 58.9 nm while for BCP-S it was 231.6 ± 35.7 nm. Ceramic blocks with crossing or noncrossing channels of 250, 500, 1000, and 2000 µm were implanted in paraspinal muscle of dogs for 12 weeks. The percentage of bone volume in the channels was not affected by the type of pores (i.e., crossing vs. closed) or their size, but it was greatly influenced by the ceramic type (i.e., BCP-R vs. BCP-S). Significantly, more bone was formed in the channels of BCP-R than in those of BCP-S. Since the two CaP ceramics differed only in their surface architecture, the results hereby demonstrate that microporous CaP ceramics may induce ectopic osteogenesis through surface architecture.