Fibronectin signals through integrin α5β1 to regulate cardiovascular development in a cell type-specific manner

Mesodermal fibronectin controls cell shape, polarity, and mechanotransduction in the second heart field during cardiac outflow tract development

Failure in the elongation of the cardiac outflow tract (OFT) results in congenital heart disease due to the misalignment of the great arteries with the left and right ventricles. The OFT lengthens via the accretion of progenitors from the second heart field (SHF). SHF cells are exquisitely regionalized and organized into an epithelial-like layer, forming the dorsal pericardial wall (DPW). Tissue tension, cell polarity, and proliferation within the DPW are important for the addition of SHF-derived cells to the heart and OFT elongation. However, the genes controlling these processes are not completely characterized. Using conditional mutagenesis in the mouse, we show that fibronectin (FN1) synthesized by the mesoderm coordinates multiple cellular behaviors in the anterior DPW. FN1 is enriched in the anterior DPW and plays a role in OFT elongation by maintaining a balance between pro- and anti-adhesive cell-extracellular matrix (ECM) interactions and controlling DPW cell shape, polarity, cohesion, proliferation, and mechanotransduction.

Polarity and migration of cranial and cardiac neural crest cells: underlying molecular mechanisms and disease implications

The Neural Crest cells are multipotent progenitor cells formed at the neural plate border that differentiate and give rise to a wide range of cell types and organs. Directional migration of NC cells and their correct positioning at target sites are essential during embryonic development, and defects in these processes results in congenital diseases. The NC migration begins with the epithelial-mesenchymal transition and extracellular matrix remodeling. The main cellular mechanisms that sustain this migration include contact inhibition of locomotion, co-attraction, chemotaxis and mechanical cues from the surrounding environment, all regulated by proteins that orchestrate cell polarity and motility. In this review we highlight the molecular mechanisms involved in neural crest cell migration and polarity, focusing on the role of small GTPases, Heterotrimeric G proteins and planar cell polarity complex. Here, we also discuss different congenital diseases caused by altered NC cell migration.

Thymus Ontogeny and Development

The thymus is a primary lymphoid organ composed of a three-dimensional (3D) epithelial network that provides a specialized microenvironment for the phenotypical and functional maturation of lymphoid progenitors. The specification of the pharyngeal endoderm to thymus fate occurs during the early stages of thymic organogenesis, independent of the expression of the transcription factor Foxn1. However, Foxn1 governs the later organogenesis of thymus together with the colonizing lymphoid cells. In the present chapter, we will review recent evidence on the topic covered in our original chapter (Muñoz and Zapata 2019). It described the early development of thymus and its resemblance to the development of endoderm-derived epithelial organs based on tubulogenesis and branching morphogenesis as well as the molecules known to be involved in these processes.

Development of bioengineered 3D patient derived breast cancer organoid model focusing dynamic fibroblast-stem cell reciprocity

Three-dimensional (3D) models, such as tumor spheroids and organoids, are increasingly developed by integrating tissue engineering, regenerative medicine, and personalized therapy strategies. These advanced 3Din-vitromodels are not merely endpoint-driven but also offer the flexibility to be customized or modulated according to specific disease parameters. Unlike traditional 2D monolayer cultures, which inadequately capture the complexities of solid tumors, 3D co-culture systems provide a more accurate representation of the tumor microenvironment. This includes critical interactions with mesenchymal stem/stromal cells (MSCs) and induced pluripotent stem cells (iPSCs), which significantly modulate cancer cell behavior and therapeutic responses. Most of the findings from the co-culture of Michigan Cancer Foundation-7 breast cancer cells and MSC showed the formation of monolayers. Although changes in the plasticity of MSCs and iPSCs caused by other cells and extracellular matrix (ECM) have been extensively researched, the effect of MSCs on cancer stem cell (CSC) aggressiveness is still controversial and contradictory among different research communities. Some researchers have argued that CSCs proliferate more, while others have proposed that cancer spread occurs through dormancy. This highlights the need for further investigation into how these interactions shape cancer aggressiveness. The objective of this review is to explore changes in cancer cell behavior within a 3D microenvironment enriched with MSCs, iPSCs, and ECM components. By describing various MSC and iPSC-derived 3D breast cancer models that replicate tumor biology, we aim to elucidate potential therapeutic targets for breast cancer. A particular focus of this review is the Transwell system, which facilitates understanding how MSCs and iPSCs affect critical processes such as migration, invasion, and angiogenesis. The gradient formed between the two chambers is based on diffusion, as seen in the human body. Once optimized, this Transwell model can serve as a high-throughput screening platform for evaluating various anticancer agents. In the future, primary cell-based and patient-derived 3D organoid models hold promise for advancing personalized medicine and accelerating drug development processes.

Mutations in fibronectin dysregulate chondrogenesis in skeletal dysplasia

Fibronectin (FN) is an extracellular matrix glycoprotein essential for the development and function of major vertebrate organ systems. Mutations in FN result in an autosomal dominant skeletal dysplasia termed corner fracture-type spondylometaphyseal dysplasia (SMDCF). The precise pathomechanisms through which mutant FN induces impaired skeletal development remain elusive. Here, we have generated patient-derived induced pluripotent stem cells as a cell culture model for SMDCF to investigate the consequences of FN mutations on mesenchymal stem cells (MSCs) and their differentiation into cartilage-producing chondrocytes. In line with our previous data, FN mutations disrupted protein secretion from MSCs, causing a notable increase in intracellular FN and a significant decrease in extracellular FN levels. Analyses of plasma samples from SMDCF patients also showed reduced FN in circulation. FN and endoplasmic reticulum (ER) protein folding chaperones (BIP, HSP47) accumulated in MSCs within ribosome-covered cytosolic vesicles that emerged from the ER. Massive amounts of these vesicles were not cleared from the cytosol, and a smaller subset showed the presence of lysosomal markers. The accumulation of intracellular FN and ER proteins elevated cellular stress markers and altered mitochondrial structure. Bulk RNA sequencing revealed a specific transcriptomic dysregulation of the patient-derived cells relative to controls. Analysis of MSC differentiation into chondrocytes showed impaired mesenchymal condensation, reduced chondrogenic markers, and compromised cell proliferation in mutant cells. Moreover, FN mutant cells exhibited significantly lower transforming growth factor beta-1 (TGFβ1) expression, crucial for mesenchymal condensation. Exogenous FN or TGFβ1 supplementation effectively improved the MSC condensation and promoted chondrogenesis in FN mutant cells. These findings demonstrate the cellular consequences of FN mutations in SMDCF and explain the molecular pathways involved in the associated altered chondrogenesis.

trans-Interacting Plasma Membrane Proteins and Binding Partner Identification

Plasma membrane proteins (PMPs) play critical roles in a myriad of physiological and disease conditions. A unique subset of PMPs functions through interacting with each other in trans at the interface between two contacting cells. These trans-interacting PMPs (tiPMPs) include adhesion molecules and ligands/receptors that facilitate cell-cell contact and direct communication between cells. Among the tiPMPs, a significant number have apparent extracellular binding domains but remain orphans with no known binding partners. Identification of their potential binding partners is therefore important for the understanding of processes such as organismal development and immune cell activation. While a number of methods have been developed for the identification of protein binding partners in general, very few are applicable to tiPMPs, which interact in a two-dimensional fashion with low intrinsic binding affinities. In this review, we present the significance of tiPMP interactions, the challenges of identifying binding partners for tiPMPs, and the landscape of method development. We describe current avidity-based screening approaches for identifying novel tiPMP binding partners and discuss their advantages and limitations. We conclude by highlighting the importance of developing novel methods of identifying new tiPMP interactions for deciphering the complex protein interactome and developing targeted therapeutics for diseases.

Buffering Mechanism in Aortic Arch Artery Formation and Congenital Heart Disease

BACKGROUND

The resiliency of embryonic development to genetic and environmental perturbations has been long appreciated; however, little is known about the mechanisms underlying the robustness of developmental processes. Aberrations resulting in neonatal lethality are exemplified by congenital heart disease arising from defective morphogenesis of pharyngeal arch arteries (PAAs) and their derivatives.

METHODS

Mouse genetics, lineage tracing, confocal microscopy, and quantitative image analyses were used to investigate mechanisms of PAA formation and repair.

RESULTS

The second heart field (SHF) gives rise to the PAA endothelium. Here, we show that the number of SHF-derived endothelial cells (ECs) is regulated by VEGFR2 (vascular endothelial growth factor receptor 2) and Tbx1. Remarkably, when the SHF-derived EC number is decreased, PAA development can be rescued by the compensatory endothelium. Blocking such compensatory response leads to embryonic demise. To determine the source of compensating ECs and mechanisms regulating their recruitment, we investigated 3-dimensional EC connectivity, EC fate, and gene expression. Our studies demonstrate that the expression of VEGFR2 by the SHF is required for the differentiation of SHF-derived cells into PAA ECs. The deletion of 1 VEGFR2 allele (VEGFR2SHF-HET) reduces SHF contribution to the PAA endothelium, while the deletion of both alleles (VEGFR2SHF-KO) abolishes it. The decrease in SHF-derived ECs in VEGFR2SHF-HET and VEGFR2SHF-KO embryos is complemented by the recruitment of ECs from the nearby veins. Compensatory ECs contribute to PAA derivatives, giving rise to the endothelium of the aortic arch and the ductus in VEGFR2SHF-KO mutants. Blocking the compensatory response in VEGFR2SHF-KO mutants results in embryonic lethality shortly after mid-gestation. The compensatory ECs are absent in Tbx1+/- embryos, a model for 22q11 deletion syndrome, leading to unpredictable arch artery morphogenesis and congenital heart disease. Tbx1 regulates the recruitment of the compensatory endothelium in an SHF-non-cell-autonomous manner.

CONCLUSIONS

Our studies uncover a novel buffering mechanism underlying the resiliency of PAA development and remodeling.

Identification of novel buffering mechanisms in aortic arch artery development and congenital heart disease

Rationale

The resiliency of embryonic development to genetic and environmental perturbations has been long appreciated; however, little is known about the mechanisms underlying the robustness of developmental processes. Aberrations resulting in neonatal lethality are exemplified by congenital heart disease (CHD) arising from defective morphogenesis of pharyngeal arch arteries (PAA) and their derivatives.

Objective

To uncover mechanisms underlying the robustness of PAA morphogenesis.

Methods and Results

The second heart field (SHF) gives rise to the PAA endothelium. Here, we show that the number of SHF-derived ECs is regulated by VEGFR2 and Tbx1 . Remarkably, when SHF-derived EC number is decreased, PAA development can be rescued by the compensatory endothelium. Blocking such compensatory response leads to embryonic demise. To determine the source of compensating ECs and mechanisms regulating their recruitment, we investigated three-dimensional EC connectivity, EC fate, and gene expression. Our studies demonstrate that the expression of VEGFR2 by the SHF is required for the differentiation of SHF-derived cells into PAA ECs. The deletion of one VEGFR2 allele (VEGFR2 SHF-HET ) reduces SHF contribution to the PAA endothelium, while the deletion of both alleles (VEGFR2 SHF-KO ) abolishes it. The decrease in SHF-derived ECs in VEGFR2 SHF-HET and VEGFR2 SHF-KO embryos is complemented by the recruitment of ECs from the nearby veins. Compensatory ECs contribute to PAA derivatives, giving rise to the endothelium of the aortic arch and the ductus in VEGFR2 SHF-KO mutants. Blocking the compensatory response in VEGFR2 SHF-KO mutants results in embryonic lethality shortly after mid-gestation. The compensatory ECs are absent in Tbx1 +/- embryos, a model for 22q11 deletion syndrome, leading to unpredictable arch artery morphogenesis and CHD. Tbx1 regulates the recruitment of the compensatory endothelium in an SHF-non-cell-autonomous manner.

Conclusions

Our studies uncover a novel buffering mechanism underlying the resiliency of PAA development and remodeling.

Nonstandard Abbreviations and Acronyms in Alphabetical Order

CHD - congenital heart disease; ECs - endothelial cells; IAA-B - interrupted aortic arch type B; PAA - pharyngeal arch arteries; RERSA - retro-esophageal right subclavian artery; SHF - second heart field; VEGFR2 - Vascular endothelial growth factor receptor 2.

Molecular Pathways and Animal Models of Semilunar Valve and Aortic Arch Anomalies

The great arteries of the vertebrate carry blood from the heart to the systemic circulation and are derived from the pharyngeal arch arteries. In higher vertebrates, the pharyngeal arch arteries are a symmetrical series of blood vessels that rapidly remodel during development to become the asymmetric aortic arch arteries carrying oxygenated blood from the left ventricle via the outflow tract. At the base of the aorta, as well as the pulmonary trunk, are the semilunar valves. These valves each have three leaflets and prevent the backflow of blood into the heart. During development, the process of aortic arch and valve formation may go wrong, resulting in cardiovascular defects, and these may, at least in part, be caused by genetic mutations. In this chapter, we will review models harboring genetic mutations that result in cardiovascular defects affecting the great arteries and the semilunar valves.

Fn1 Regulates the Third Pharyngeal Pouch Patterning and Morphogenesis

The parathyroid and thymus are derived from the common primordia, the third pharyngeal pouch. During their development, endodermal cells actively interact with surrounding mesenchymal cells, mainly derived from neural crest cells (NCCs). However, the mechanism by which NCCs regulate the development of the third pharyngeal pouch remains largely unknown. In this study, we showed that fibronectin 1 (Fn1), which is synthesized by NCCs, modulates the functions of NCCs in the third pharyngeal pouch patterning and in the morphogenesis of the thymus/parathyroid. Loss of Fn1 in NCCs leads to decreased Foxn1 expression in the presumptive thymus domain at E11.5. In the mutant, we detected upregulation of the Hedgehog signaling activity in the presumptive parathyroid domain and downregulation of Bmp4 in the presumptive thymus domain. Tbx1, a Hedgehog signaling target gene in endoderm development, was ectopically expanded to the presumptive mutant thymus domain at E11.5. Fgf10, an important gene regulating the proliferation of endoderm development, was downregulated in the mutant NCCs. At later organogenesis stages, derivatives of the third pharyngeal pouch endoderm of mutant embryos were abnormal, showing conditions such as hypoparathyroidism, hypoplastic thymus, and ectopic thymus and parathyroid. These data support that Fn1 plays an important role in NCCs by regulating the patterning of the third pharyngeal pouch and morphogenesis of the thymus/parathyroid.

Fibronectin and Integrin α5 play overlapping and independent roles in regulating the development of pharyngeal endoderm and cartilage

Craniofacial skeletal elements are derived from cranial neural crest cells (CNCCs), which migrate along discrete paths and populate distinct pharyngeal arches, structures that are separated by the neighboring endodermal pouches (EPs). Interactions between the CNCCs and the endoderm are critical for proper craniofacial development. In zebrafish, integrin α5 (Itga5) functions in the endoderm to regulate formation of specifically the first EP (EP1) and the development of the hyoid cartilage. Here we show that fibronectin (Fn), a major component of the extracellular matrix (ECM), is also required for these developmental processes, and that the penetrance of defects in mutants is temperature-dependent. fn1a^-/- embryos exhibited defects that are similar to, but much more severe than, those of itga5^-/- embryos, and a loss of integrin av (itgav) function enhanced both endoderm and cartilage defects in itga5^-/- embryos, suggesting that Itga5 and Itgav cooperate to transmit signals from Fn to regulate the development of endoderm and cartilage. Whereas the endodermal defects in itga5; itga5v^-/- double mutant embryos were comparable to those of fn1a^-/- mutants, the cartilage defects were much milder. Furthermore, Fn assembly was detected in migrating CNCCs, and the epithelial organization and differentiation of CNCC-derived arches were impaired in fn1a^-/- embryos, indicating that Fn1 exerts functions in arch development that are independent of Itga5 and Itgav. Additionally, reduction of itga5 function in fn1a^-/- embryos led to profound defects in body axis elongation, as well as in endoderm and cartilage formation, suggesting that other ECM proteins signal through Itga5 to regulate development of the endoderm and cartilage. Thus, our studies reveal that Fn1a and Itga5 have both overlapping and independent functions in regulating development of the pharyngeal endoderm and cartilage.

Identification of splice regulators of fibronectin-EIIIA and EIIIB by direct measurement of exon usage in a flow-cytometry based CRISPR screen

The extracellular matrix protein fibronectin (FN) is alternatively spliced in a variety of inflammatory conditions, resulting in increased inclusion of alternative exons EIIIA and EIIIB. Inclusion of these exons affects fibril formation, fibrosis, and inflammation. To define upstream regulators of alternative splicing in FN, we have developed an in vitro flow-cytometry based assay, using RNA-binding probes to determine alternative exon inclusion level in aortic endothelial cells. This approach allows us to detect exon inclusion in the primary transcripts themselves, rather than in surrogate splicing reporters. We validated this assay in cells with and without FN-EIIIA and -EIIIB expression. In a small-scale CRISPR KO screen of candidate regulatory splice factors, we successfully detected known regulators of EIIIA and EIIIB splicing, and detected several novel regulators. Finally, we show the potential in this approach to broadly interrogate upstream signaling pathways in aortic endothelial cells with a genome-wide CRISPR-KO screen, implicating the TNFalpha and RIG-I-like signaling pathways and genes involved in the regulation of fibrotic responses. Thus, we provide a novel means to screen the regulation of splicing of endogenous transcripts, and predict novel pathways in the regulation of FN-EIIIA inclusion.

Parallels between the extracellular matrix roles in developmental biology and cancer biology

Interaction of a tumor with its microenvironment is an emerging field of investigation, and the crosstalk between cancer cells and the extracellular matrix is of particular interest, since cancer patients with abundant and stiff extracellular matrices display a poorer prognosis. At the post-juvenile stage, the extracellular matrix plays predominantly a structural role by providing support to cells and tissues; however, during development, matrix proteins exert a plethora of diverse signals to guide the movement and determine the fate of pluripotent cells. Taking a closer look at the communication between the extracellular matrix and cells of a developing body may bring new insights into cancer biology and identify cancer weaknesses. This review discusses parallels between the extracellular matrix roles during development and tumor growth.

Cell-Extracellular Matrix Interactions Play Multiple Essential Roles in Aortic Arch Development

RATIONALE

Defects in the morphogenesis of the fourth pharyngeal arch arteries (PAAs) give rise to lethal birth defects. Understanding genes and mechanisms regulating PAA formation will provide important insights into the etiology and treatments for congenital heart disease.

OBJECTIVE

Cell-ECM (extracellular matrix) interactions play essential roles in the morphogenesis of PAAs and their derivatives, the aortic arch artery and its major branches; however, their specific functions are not well-understood. Previously, we demonstrated that integrin α5β1 and Fn1 (fibronectin) expressed in the Isl1 lineages regulate PAA formation. The objective of the current studies was to investigate cellular mechanisms by which integrin α5β1 and Fn1 regulate aortic arch artery morphogenesis.

METHODS AND RESULTS

Using temporal lineage tracing, whole-mount confocal imaging, and quantitative analysis of the second heart field (SHF) and endothelial cell (EC) dynamics, we show that the majority of PAA EC progenitors arise by E7.5 in the SHF and contribute to pharyngeal arch endothelium between E7.5 and E9.5. Consequently, SHF-derived ECs in the pharyngeal arches form a plexus of small blood vessels, which remodels into the PAAs by 35 somites. The remodeling of the vascular plexus is orchestrated by signals dependent on the pharyngeal ECM microenvironment, extrinsic to the endothelium. Conditional ablation of integrin α5β1 or Fn1 in the Isl1 lineages showed that signaling by the ECM regulates aortic arch artery morphogenesis at multiple steps: (1) accumulation of SHF-derived ECs in the pharyngeal arches, (2) remodeling of the EC plexus in the fourth arches into the PAAs, and (3) differentiation of neural crest-derived cells adjacent to the PAA endothelium into vascular smooth muscle cells.

CONCLUSIONS

PAA formation is a multistep process entailing dynamic contribution of SHF-derived ECs to pharyngeal arches, the remodeling of endothelial plexus into the PAAs, and the remodeling of the PAAs into the aortic arch artery and its major branches. Cell-ECM interactions regulated by integrin α5β1 and Fn1 play essential roles at each of these developmental stages.

Intrinsic Endocardial Defects Contribute to Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease characterized by abnormalities in the left ventricle, associated valves, and ascending aorta. Studies have shown intrinsic myocardial defects but do not sufficiently explain developmental defects in the endocardial-derived cardiac valve, septum, and vasculature. Here, we identify a developmentally impaired endocardial population in HLHS through single-cell RNA profiling of hiPSC-derived endocardium and human fetal heart tissue with an underdeveloped left ventricle. Intrinsic endocardial defects contribute to abnormal endothelial-to-mesenchymal transition, NOTCH signaling, and extracellular matrix organization, key factors in valve formation. Endocardial abnormalities cause reduced cardiomyocyte proliferation and maturation by disrupting fibronectin-integrin signaling, consistent with recently described de novo HLHS mutations associated with abnormal endocardial gene and fibronectin regulation. Together, these results reveal a critical role for endocardium in HLHS etiology and provide a rationale for considering endocardial function in regenerative strategies.

Adipose-derived mesenchymal stem cells promote the malignant phenotype of cervical cancer

Epidemiological studies indicate that obesity negatively affects the progression and treatment of cervical-uterine cancer. Recent evidence shows that a subpopulation of adipose-derived stem cells can alter cancer properties. In the present project, we described for the first time the impact of adipose-derived stem cells over the malignant behavior of cervical cancer cells. The transcriptome of cancer cells cultured in the presence of stem cells was analyzed using RNA-seq. Changes in gene expression were validated using digital-PCR. Bioinformatics tools were used to identify the main transduction pathways disrupted in cancer cells due to the presence of stem cells. In vitro and in vivo assays were conducted to validate cellular and molecular processes altered in cervical cancer cells owing to stem cells. Our results show that the expression of 95 RNAs was altered in cancer cells as a result of adipose-derived stem cells. Experimental assays indicate that stem cells provoke an increment in migration, invasion, angiogenesis, and tumorigenesis of cancer cells; however, no alterations were found in proliferation. Bioinformatics and experimental analyses demonstrated that the NF-kappa B signaling pathway is enriched in cancer cells due to the influence of adipose-derived stem cells. Interestingly, the tumor cells shift their epithelial to a mesenchymal morphology, which was reflected by the increased expression of specific mesenchymal markers. In addition, stem cells also promote a stemness phenotype in the cervical cancer cells. In conclusion, our results suggest that adipose-derived stem cells induce cervical cancer cells to acquire malignant features where NF-kappa B plays a key role.

Integrin α5 and Integrin α4 cooperate to promote endocardial differentiation and heart morphogenesis

Endocardium is critically important for proper function of the cardiovascular system. Not only does endocardium connect the heart to blood vasculature, it also plays an important role in heart morphogenesis, valve formation, and ventricular trabeculation. The extracellular protein Fibronectin (Fn1) promotes endocardial differentiation, but the signaling pathways downstream of Fn1 that regulate endocardial development are not understood. Here, we analyzed the role of the Fibronectin receptors Integrin alpha5 (Itga5) and Integrin alpha4 (Itga4) in zebrafish heart development. We show that itga5 mRNA is expressed in both endocardium and myocardium during early stages of heart development. Through analysis of both itga5 single mutants and itga4;itga5 double mutants, we show that loss of both itga5 and itga4 results in enhanced defects in endocardial differentiation and morphogenesis compared to loss of itga5 alone. Loss of both itga5 and itga4 results in cardia bifida and severe myocardial morphology defects. Finally, we find that loss of itga5 and itga4 results in abnormally narrow anterior endodermal sheet morphology. Together, our results support a model in which Itga5 and Itga4 cooperate to promote endocardial differentiation, medial migration of endocardial and myocardial cells, and morphogenesis of anterior endoderm.

Molecular mechanisms of coronary disease revealed using quantitative trait loci for TCF21 binding, chromatin accessibility, and chromosomal looping

BACKGROUND

To investigate the epigenetic and transcriptional mechanisms of coronary artery disease (CAD) risk, as well as the functional regulation of chromatin structure and function, we create a catalog of genetic variants associated with three stages of transcriptional cis-regulation in primary human coronary artery vascular smooth muscle cells (HCASMCs).

RESULTS

We use a pooling approach with HCASMC lines to map regulatory variants that mediate binding of the CAD-associated transcription factor TCF21 with ChIPseq studies (bQTLs), variants that regulate chromatin accessibility with ATACseq studies (caQTLs), and chromosomal looping with Hi-C methods (clQTLs). We examine the overlap of these QTLs and their relationship to smooth muscle-specific genes and transcription factors. Further, we use multiple analyses to show that these QTLs are highly associated with CAD GWAS loci and correlate to lead SNPs where they show allelic effects. By utilizing genome editing, we verify that identified functional variants can regulate both chromatin accessibility and chromosomal looping, providing new insights into functional mechanisms regulating chromatin state and chromosomal structure. Finally, we directly link the disease-associated TGFB1-SMAD3 pathway to the CAD-associated FN1 gene through a response QTL that modulates both chromatin accessibility and chromosomal looping.

CONCLUSIONS

Together, these studies represent the most thorough mapping of multiple QTL types in a highly disease-relevant primary cultured cell type and provide novel insights into their functional overlap and mechanisms that underlie these genomic features and their relationship to disease risk.

High expression of KITLG is a new hallmark activating the MAPK pathway in type A and AB thymoma

Background

KIT proto‐oncogene ligand (KITLG) is a pleiotropic factor which is found in diverse cancers and is involved in cell proliferation, differentiation, and survival. However, the value of KITLG in thymoma remains unclear.

Methods

A total of 121 thymoma samples from The Cancer Genome Atlas Thymoma (TCGA‐THYM) dataset were used to analyze KITLG related genome‐wide expression profiles, and microRNA profiles and methylation alterations and a GEO dataset‐GSE29695, including 37 samples was used as verification. For cell‐based studies, specific small interfering RNA targeting KITLG or a KITLG overexpression vector were used to clarify the changes of the MAPK pathway in an AB thymoma cell line Thy0517.

Results

Both datasets showed that high expression of KITLG was significantly associated with type A and AB thymoma. Through multiomic analysis of the TCGA‐THYM, it was found that with the high expression of KITLG, there were 220 upregulated and 72 downregulated genes at the mRNA level, 79 positive and 78 negative miRNAs, 28 hypermethylation and 163 hypomethylation regions. In the thymoma cell line Thy0517, it was found that the expression of GRB2 and the phosphorylation levels of BRAF, MEK1/2, and ERK1/2 in the MAPK pathway were positively correlated with the change in KITLG.

Conclusions

High expression of KITLG is a new hallmark of WHO type A and AB thymomas in which it might play a critical role through the activation of the MAPK signaling pathway. Additionally, it is hoped that KITLG will become a potential target for the diagnosis of type A and AB thymoma through further research in the future.

Key points

Significant findings of the study

KIT proto‐oncogene ligand (KITLG) is a new hallmark of type A and AB thymomas which induce a series of aberrant alteration of mRNA, miRNA and DNA methylation. The expression of KITLG is significantly higher in type A and AB than other subtypes of thymoma.

What this study adds

KITLG activated the MAPK signaling pathway to promote type A and AB thymoma which might be a potential diagnostic biomarker or target.

Effects of PUMILIO1 and PUMILIO2 knockdown on cardiomyogenic differentiation of human embryonic stem cells culture

Posttranscriptional regulation plays a fundamental role in the biology of embryonic stem cells (ESCs). Many studies have demonstrated that multiple mRNAs are coregulated by one or more RNA-binding proteins (RBPs) that orchestrate mRNA expression. A family of RBPs, which is known as the Pumilio-FBF (PUF) family, is highly conserved among different species and has been associated with the undifferentiated and differentiated states of different cell lines. In humans, two homologs of the PUF family have been found: Pumilio 1 (PUM1) and Pumilio 2 (PUM2). To understand the role of these proteins in human ESCs (hESCs), we first assessed the influence of the silencing of PUM1 and PUM2 on pluripotency genes and found that the knockdown of Pumilio genes significantly decreased the OCT4 and NANOG mRNA levels and reduced the amount of nuclear OCT4, which suggests that Pumilio proteins play a role in the maintenance of pluripotency in hESCs. Furthermore, we observed that PUM1-and-PUM2-silenced hESCs exhibited improved efficiency of in vitro cardiomyogenic differentiation. Through an in silico analysis, we identified mRNA targets of PUM1 and PUM2 that are expressed at the early stages of cardiomyogenesis, and further investigation will determine whether these target mRNAs are active and involved in the progression of cardiomyogenesis. Our findings contribute to the understanding of the role of Pumilio proteins in hESC maintenance and differentiation.

Improved viability and fertility of frozen-thawed dog sperm using adipose-derived mesenchymal stem cells

Cryopreservation procedures negatively affect the quality traits of sperm, causing certain changes at structural and molecular levels due to thermal, mechanical, osmotic, and oxidative damage. The objective of this study was to examine the potential of canine adipose-derived mesenchymal stem cells (Ad-MSCs) for providing protection to the dog sperm against cryo-damage. Canine Ad-MSCs were selected on the basis of the significantly higher gene expression for different proteins actively involved in the cell repair including annexin 1 (ANX1), histone H3 (H3) and high mobility group B (HMGB) protein compared to skin fibroblasts. Semen was collected from four healthy dogs by digital manipulation. The washed pooled ejaculates were diluted with buffer 2 (extender) supplemented without Ad-MSCs (Control), with 2.5 × 10⁶ Ad-MSCs/mL (Group 1) or with 5 × 10⁶ Ad-MSCs/mL (Group 2). Group 1 exhibited significantly higher post-thaw motility, live sperm, intact plasma membrane and normal acrosomes than the other groups. Additionally, Group 1 showed significantly higher expression levels of genes related to the repair of membranes (ANX1, dysferlin; DYSF, and fibronectin; FN1) and chromatin material (H3 and HMGB). Protein expression of ANX1, H 3, and FN1 was also statistically more in Group 1 than in Control. The results confirm that canine Ad-MSCs can effectively preserve the quality of frozen-thawed sperm by a reduction in cryoinjury. At an appropriate concentration, Ad-MSCs significantly improve the quality of post-thaw dog sperm.

The road best traveled: Neural crest migration upon the extracellular matrix

Neural crest cells have the extraordinary task of building much of the vertebrate body plan, including the craniofacial cartilage and skeleton, melanocytes, portions of the heart, and the peripheral nervous system. To execute these developmental programs, stationary premigratory neural crest cells first acquire the capacity to migrate through an extensive process known as the epithelial-to-mesenchymal transition. Once motile, neural crest cells must traverse a complex environment consisting of other cells and the protein-rich extracellular matrix in order to get to their final destinations. Herein, we will highlight some of the main molecular machinery that allow neural crest cells to first exit the neuroepithelium and then later successfully navigate this intricate in vivo milieu. Collectively, these extracellular and intracellular factors mediate the appropriate migration of neural crest cells and allow for the proper development of the vertebrate embryo.

Fibronectin has multifunctional roles in posterior capsular opacification (PCO)

Fibrotic posterior capsular opacification (PCO), one of the major complications of cataract surgery, occurs when lens epithelial cells (LCs) left behind post cataract surgery (PCS) undergo epithelial to mesenchymal transition, migrate into the optical axis and produce opaque scar tissue. LCs left behind PCS robustly produce fibronectin, although its roles in fibrotic PCO are not known. In order to determine the function of fibronectin in PCO pathogenesis, we created mice lacking the fibronectin gene (FN conditional knock out -FNcKO) from the lens. While animals from this line have normal lenses, upon lens fiber cell removal which models cataract surgery, FNcKO LCs exhibit a greatly attenuated fibrotic response from 3 days PCS onward as assessed by a reduction in surgery-induced cell proliferation, and fibrotic extracellular matrix (ECM) production and deposition. This is correlated with less upregulation of Transforming Growth Factor β (TGFβ) and integrin signaling in FNcKO LCs PCS concomitant with sustained Bone Morphogenetic Protein (BMP) signaling and elevation of the epithelial cell marker E cadherin. Although the initial fibrotic response of FNcKO LCs was qualitatively normal at 48 h PCS as measured by the upregulation of fibrotic marker protein αSMA, RNA sequencing revealed that the fibrotic response was already quantitatively attenuated at this time, as measured by the upregulation of mRNAs encoding molecules that control, and are controlled by, TGFβ signaling, including many known markers of fibrosis. Most notably, gremlin-1, a known regulator of TGFβ superfamily signaling, was upregulated sharply in WT LCs PCS, while this response was attenuated in FNcKO LCs. As exogenous administration of either active TGFβ1 or gremlin-1 to FNcKO lens capsular bags rescued the attenuated fibrotic response of fibronectin null LCs PCS including the loss of SMAD2/3 phosphorylation, this suggests that fibronectin plays multifunctional roles in fibrotic PCO development.

Secretome Analysis Performed During in vitro Cardiac Differentiation: Discovering the Cardiac Microenvironment

Human pluripotent stem cells are an important tool for the study of developmental processes, such as cardiomyogenic differentiation. Despite the advances made in this field, the molecular and cellular signals involved in the commitment of embryonic stem cells to the cardiac phenotype are still under investigation. Therefore, this study focuses on identifying the extracellular signals involved in in vitro cardiac differentiation of human embryonic stem cells. Using a three-dimensional cardiomyogenic differentiation protocol, the conditioned medium and the extracellular matrix (ECM) of embryoid body cultures were collected and characterized at four specific time points. Mass spectrometry (MS) and antibody array analysis of the secretome identified a number of secreted proteins related to signaling pathways, such as Wnt and TGFβ, as well as many ECM proteins. When comparing the proteins identified at selected time points, our data pointed out protein interactions and biological process related to cardiac differentiation. Interestingly, the great changes in secretome profile occurred during the cardiac progenitor specification. The secretome results were also compared with our previous RNAseq data, indicating that the secreted proteins undergo some level of gene regulation. During cardiac commitment it was observed an increase in complexity of the ECM, and some proteins as IGFBP7, FN1, HSPG2, as well as other members of the basal lamina could be highlighted. Thus, these findings contribute valuable information about essential microenvironmental signals working on cardiomyogenic differentiation that may be used in future strategies for cardiac differentiation, cardiomyocyte maturation, and in advances for future acellular therapies.

Improved Post-Thaw Quality of Canine Semen after Treatment with Exosomes from Conditioned Medium of Adipose-Derived Mesenchymal Stem Cells

Freezing decreases sperm quality, ultimately affecting fertilizing ability. The repair of freeze-damaged sperm is considered crucial for improving post-thaw viability and fertility. We investigated the effects of exosomes derived from canine adipose-derived mesenchymal stem cells on dog sperm structure and function during cryopreservation. The pooled ejaculate was diluted with buffer, without (Control), or with exosomal proteins (25, 50, or 100 µg/mL). Using fresh semen, the determined optimal exosomal protein concentration was 50 µg/mL (Group 2) which was used in further experiments. Post-thaw sperm treated with exosomes were superior to control (p < 0.05) in terms of motility (56.8 ± 0.3% vs. 47.2 ± 0.3%), live sperm percentage (55.9 ± 0.4% vs. 45.4 ± 0.4%), membrane integrity (55.6 ± 0.5% vs. 47.8 ± 0.3%), and acrosome integrity (60.4 ± 1.1% vs. 48.6 ± 0.4%). Moreover, expression of genes related to the repair of the plasma membrane (ANX 1, FN 1, and DYSF), and chromatin material (H3, and HMGB 1) was statistically higher in exosome-treated sperm than control, but the expression of the mitochondrial reactive oxygen species modulator 1 gene was significantly higher in control. Therefore, exosomal treatment may improve the quality of post-thaw dog semen through initiating damaged sperm repair and decreasing reactive oxygen species production.

Tbx1 regulates extracellular matrix-cell interactions in the second heart field

Tbx1, the major candidate gene for DiGeorge or 22q11.2 deletion syndrome, is required for efficient incorporation of cardiac progenitors of the second heart field (SHF) into the heart. However, the mechanisms by which TBX1 regulates this process are still unclear. Here, we have used two independent models, mouse embryos and cultured cells, to define the role of TBX1 in establishing morphological and dynamic characteristics of SHF in the mouse. We found that loss of TBX1 impairs extracellular matrix (ECM)-integrin-focal adhesion (FA) signaling in both models. Mosaic analysis in embryos suggested that this function is non-cell autonomous, and, in cultured cells, loss of TBX1 impairs cell migration and FAs. Additionally, we found that ECM-mediated integrin signaling is disrupted upon loss of TBX1. Finally, we show that interfering with the ECM-integrin-FA axis between E8.5 and E9.5 in mouse embryos, corresponding to the time window within which TBX1 is required in the SHF, causes outflow tract dysmorphogenesis. Our results demonstrate that TBX1 is required to maintain the integrity of ECM-cell interactions in the SHF and that this interaction is critical for cardiac outflow tract development. More broadly, our data identifies a novel TBX1 downstream pathway as an important player in SHF tissue architecture and cardiac morphogenesis.

Cardiac Extracellular Matrix Modification as a Therapeutic Approach

The cardiac extracellular matrix (cECM) is comprised of proteins and polysaccharides secreted by cardiac cell types, which provide structural and biochemical support to cardiovascular tissue. The roles of cECM proteins and the associated family of cell surface receptor, integrins, have been explored in vivo via the generation of knockout experimental animal models. However, the complexity of tissues makes it difficult to isolate the effects of individual cECM proteins on a particular cell process or disease state. The desire to further dissect the role of cECM has led to the development of a variety of in vitro model systems, which are now being used not only for basic studies but also for testing drug efficacy and toxicity and for generating therapeutic scaffolds. These systems began with 2D coatings of cECM derived from tissue and have developed to include recombinant ECM proteins, ECM fragments, and ECM mimics. Most recently 3D model systems have emerged, made possible by several developing technologies including, and most notably, 3D bioprinting. This chapter will attempt to track the evolution of our understanding of the relationship between cECM and cell behavior from in vivo model to in vitro control systems. We end the chapter with a summary of how basic studies such as these have informed the use of cECM as a direct therapy.

Genes involved in angiogenesis and circulatory system development are differentially expressed in porcine epithelial oviductal cells during long-term primary in vitro culture – a transcriptomic study

An oviduct is an essential organ for gamete transport, oocyte maturation, fertilization, spermatozoon capacitation and early embryo development. The epithelium plays an important role in oviduct functioning. The products of secretory cells provide an optimal environment and influence gamete activities and embryonic development. The oviduct physiology changes during the female cycle, thus, the ratio of the secreted molecules in the oviduct fluid differs between phases. In this study, a differential gene expression in porcine oviduct epithelial cells was examined during the long-term primary in vitro culture. The microarray expression analysis revealed 2552 genes, 1537 of which were upregulated and 995 were downregulated after 7 days of culture, with subsequent changes in expression during 30 day-long culture. The obtained genes were classified into 8 GO BP terms, connected with angiogenesis and circulatory system development, extracted by DAVID software. Among all genes, 10 most up-regulated and 10 most down-regulated genes were selected for further investigation. Interactions between genes were indicated by STRING software and REACTOME FIViz application to the Cytoscape 3.6.0 software. Most of the genes belonged to more than one ontology group. Although studied genes are mostly responsible for angiogenesis and circulatory system development, they can also be found to be expressed in processes connected with fertilization and early embryo development. The latter function is focused on more, considering the fact that these genes were expressed in epithelial cells of the fallopian tube which is largely responsible for reproductive processes.

Cardiac-specific developmental and epigenetic functions of Jarid2 during embryonic development

Epigenetic regulation is critical in normal cardiac development. We have demonstrated that the deletion of Jarid2 (Jumonji (Jmj) A/T-rich interaction domain 2) in mice results in cardiac malformations recapitulating human congenital cardiac disease and dysregulation of gene expression. However, the precise developmental and epigenetic functions of Jarid2 within the developing heart remain to be elucidated. Here, we determined the cardiac-specific functions of Jarid2 and the genetic networks regulated by Jarid2. Jarid2 was deleted using different cardiac-specific Cre mice. The deletion of Jarid2 by Nkx2.5-Cre mice (Jarid2^Nkx) caused cardiac malformations including ventricular septal defects, thin myocardium, hypertrabeculation, and neonatal lethality. Jarid2^Nkx mice exhibited elevated expression of neural genes, cardiac jelly, and other key factors including Isl1 and Bmp10 in the developing heart. By employing combinatorial genome-wide approaches and molecular analyses, we showed that Jarid2 in the myocardium regulates a subset of Jarid2 target gene expression and H3K27me3 enrichment during heart development. Specifically, Jarid2 was required for PRC2 occupancy and H3K27me3 at the Isl1 promoter locus, leading to the proper repression of Isl1 expression. In contrast, Jarid2 deletion in differentiated cardiomyocytes by cTnt-Cre mice caused no gross morphological defects or neonatal lethality. Thus, the early deletion of Jarid2 in cardiac progenitors, prior to the differentiation of cardiac progenitors into cardiomyocytes, results in morphogenetic defects manifested later in development. Our studies reveal that there is a critical window during early cardiac progenitor differentiation when Jarid2 is crucial to establish the epigenetic landscape at later stages of development.

Ripply3 is required for the maintenance of epithelial sheets in the morphogenesis of pharyngeal pouches

During tissue development, the morphogenesis of epithelial sheets is regulated by many factors, including mechanical force, although the underlying mechanisms remain largely unknown. In the pharyngeal region of the vertebrate embryo, endodermal epithelium is reiteratively folded outward to form pharyngeal pouches, making partitions between the pharyngeal arches. Ripply3, encoding a member of the Ripply family of adaptor proteins, is required for the pouch formation posterior to the 2nd pharyngeal pouch. In this study, we found that the expression of mouse Ripply3 was specifically activated in accordance with the bending of the endodermal epithelium during the pouch formation. In Ripply3-deficient embryos, a continuous monolayer of the endodermal epithelium was not maintained posterior to the 2nd pharyngeal pouch. Corresponding to the endodermal region of the deformed epithelium, the activated form of Integrin β1, which was localized at the basal side of the epithelial cells in the wild-type embryos, was not persistently observed in the mutants. On the other hand, cell proliferation and apoptotic cell death in the endoderm were not obviously affected by the Ripply3 deficiency. Significantly, Ripply3 expressed in cultured cells was found to be preferentially accumulated in the focal adhesions, which are Integrin-mediated adhesive contact sites transmitting mechanical force between the extracellular matrix and attached cells. Furthermore, Ripply3 promoted the maturation of focal adhesions in these cells. Thus, Ripply3 appears to have been activated to enhance the connection between the extracellular matrix and endodermal epithelial cells, as a mechanism to resist the mechanical stress generated during the bending of the epithelial sheets.

Decellularized Swine Dental Pulp as a Bioscaffold for Pulp Regeneration

Endodontic regeneration shows promise in treating dental pulp diseases; however, no suitable scaffolds exist for pulp regeneration. Acellular natural extracellular matrix (ECM) is a favorable scaffold for tissue regeneration since the anatomical structure and ECM of the natural tissues or organs are well-preserved. Xenogeneic ECM is superior to autologous or allogeneic ECM in tissue engineering for its unlimited resources. This study investigated the characteristics of decellularized dental pulp ECM from swine and evaluated whether it could mediate pulp regeneration. Dental pulps were acquired from the mandible anterior teeth of swine 12 months of age and decellularized with 10% sodium dodecyl sulfate (SDS) combined with Triton X-100. Pulp regeneration was conducted by seeding human dental pulp stem cells into decellularized pulp and transplanted subcutaneously into nude mice for 8 weeks. The decellularized pulp demonstrated preserved natural shape and structure without any cellular components. Histological analysis showed excellent ECM preservation and pulp-like tissue, and newly formed mineralized tissues were regenerated after being transplanted in vivo. In conclusion, decellularized swine dental pulp maintains ECM components favoring stem cell proliferation and differentiation, thus representing a suitable scaffold for improving clinical outcomes and functions of teeth with dental pulp diseases.

Bioinformatics analysis of gene expression profiles to identify causal genes in luminal B2 breast cancer

Patients with the luminal B subtype of breast cancer exhibit a poor prognosis, high metastatic risk and high incidence of chemotherapy resistance. Luminal B breast cancer is sub-classified into B1 and B2. The pathophysiological mechanism of luminal B2 breast cancer (LB2BC) progression has yet to be characterized. Therefore, the present study aimed to identify the genes involved in the pathogenesis of LB2BC. The data of 117 LB2BC expression profiles were downloaded from The Cancer Genome Atlas (TCGA) and differentially expressed genes (DEGs) were identified by comparison with non-tumor tissue expression profiles. Gene Ontology enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and protein-protein interaction (PPI) networks were used to obtain insight into the functions of DEGs. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis was performed to validate the expression level of DEGs in tissue samples. A total of 2,251 DEGs, including 759 upregulated and 1,492 downregulated genes, were identified between LB2BC and non-tumor tissues. The top 15 upregulated and downregulated genes were used to construct a PPI network: Epidermal growth factor receptor (EGFR), fibronectin-1 (FN1) and Polo-like kinase-1 had the highest connectivity degrees. KEGG analysis identified that DEGs were most significantly enriched in 'focal adhesion', 'pathways in cancer' and 'ECM-receptor interaction' pathways. The results of RT-qPCR demonstrated that EGFR was significantly downregulated in LB2BC, whereas FN1 was significantly upregulated, whereas neurotrophic receptor tyrosine kinase 2 (NTRK2) trended towards downregulation. In conclusion, the DEGs identified in the present study, including NTRK2, FN1 and EGFR, may serve pivotal roles in the tumorigenesis of LB2BC by affecting the 'focal adhesion', 'pathways in cancer' and 'ECM-receptor interaction' KEGG pathways.

Candidate genes on murine chromosome 8 are associated with susceptibility to Staphylococcus aureus infection in mice and are involved with Staphylococcus aureus septicemia in humans

We previously showed that chromosome 8 of A/J mice was associated with susceptibility to S. aureus infection. However, the specific genes responsible for this susceptibility are unknown. Chromosome substitution strain 8 (CSS8) mice, which have chromosome 8 from A/J but an otherwise C57BL/6J genome, were used to identify the genetic determinants of susceptibility to S. aureus on chromosome 8. Quantitative trait loci (QTL) mapping of S. aureus-infected N2 backcross mice (F1 [C8A] × C57BL/6J) identified a locus 83180780–88103009 (GRCm38/mm10) on A/J chromosome 8 that was linked to S. aureus susceptibility. All genes on the QTL (n~ 102) were further analyzed by three different strategies: 1) different expression in susceptible (A/J) and resistant (C57BL/6J) mice only in response to S. aureus, 2) consistently different expression in both uninfected and infected states between the two strains, and 3) damaging non-synonymous SNPs in either strain. Eleven candidate genes from the QTL region were significantly differently expressed in patients with S. aureus infection vs healthy human subjects. Four of these 11 genes also exhibited significantly different expression in S. aureus-challenged human neutrophils: Ier2, Crif1, Cd97 and Lyl1. CD97 ligand binding was evaluated within peritoneal neutrophils from A/J and C57BL/6J. CD97 from A/J had stronger CD55 but weaker integrin α5β1 ligand binding as compared with C57BL/6J. Because CD55/CD97 binding regulates immune cell activation and cytokine production, and integrin α5β1 is a membrane receptor for fibronectin, which is also bound by S. aureus, strain-specific differences could contribute to susceptibility to S. aureus. Down-regulation of Crif1 with siRNA was associated with increased host cell apoptosis among both naïve and S. aureus-infected bone marrow-derived macrophages. Specific genes in A/J chromosome 8, including Cd97 and Crif1, may play important roles in host defense against S. aureus.

Endothelium in the pharyngeal arches 3, 4 and 6 is derived from the second heart field

Oxygenated blood from the heart is directed into the systemic circulation through the aortic arch arteries (AAAs). The AAAs arise by remodeling of three symmetrical pairs of pharyngeal arch arteries (PAAs), which connect the heart with the paired dorsal aortae at mid-gestation. Aberrant PAA formation results in defects frequently observed in patients with lethal congenital heart disease. How the PAAs form in mammals is not understood. The work presented in this manuscript shows that the second heart field (SHF) is the major source of progenitors giving rise to the endothelium of the pharyngeal arches 3 - 6, while the endothelium in the pharyngeal arches 1 and 2 is derived from a different source. During the formation of the PAAs 3 - 6, endothelial progenitors in the SHF extend cellular processes toward the pharyngeal endoderm, migrate from the SHF and assemble into a uniform vascular plexus. This plexus then undergoes remodeling, whereby plexus endothelial cells coalesce into a large PAA in each pharyngeal arch. Taken together, our studies establish a platform for investigating cellular and molecular mechanisms regulating PAA formation and alterations that lead to disease.

Collaboration of fibronectin matrix with other extracellular signals in morphogenesis and differentiation

Tissue formation and cell differentiation depend on a properly assembled extracellular matrix (ECM). Fibronectin is a key constituent of the pericellular ECM, forming essential connections between cell surface integrin receptors and structural components of the ECM. Recent studies using vertebrate models, conditional gene knockouts, tissue explants, and cell culture systems have identified developmental processes that depend on fibronectin and its receptor α5β1 integrin. We describe requirements for fibronectin matrix in the cardiovascular system, somite and precartilage development, and epithelial-mesenchymal transition. Information about molecular mechanisms shows the importance of fibronectin and integrins during tissue morphogenesis and cell differentiation, as well as their cooperation with growth factors to mediate changes in cell behaviors.

Fibronectin assembly during early embryo development: A versatile communication system between cells and tissues

BACKGROUND

Fibronectin extracellular matrix is essential for embryogenesis. Its assembly is a cell-mediated process where secreted fibronectin dimers bind to integrin receptors on receiving cells, which actively assemble fibronectin into a fibrillar matrix. During development, paracrine communication between tissues is crucial for coordinating morphogenesis, typically being mediated by growth factors and their receptors. Recent reports of situations where fibronectin is produced by one tissue and assembled by another, with implications on tissue morphogenesis, suggest that fibronectin assembly may also be a paracrine communication event in certain contexts.

RESULTS

Here we addressed which tissues express fibronectin (Fn1) while also localizing assembled fibronectin matrix and determining the mRNA expression and/or protein distribution pattern of integrins α5 and αV, α chains of the major fibronectin assembly receptors, during early chick and mouse development. We found evidence supporting a paracrine system in fibronectin matrix assembly in several tissues, including immature mesenchymal tissues, components of central and peripheral nervous system and developing muscle.

CONCLUSIONS

Thus, similarly to growth factor signaling, fibronectin matrix assembly during early development can be both autocrine and paracrine. We therefore propose that it be considered a cell-cell communication event at the same level and significance as growth factor signaling during embryogenesis.

Walking the Line: A Fibronectin Fiber-Guided Assay to Probe Early Steps of (Lymph)angiogenesis

Angiogenesis and lymphangiogenesis are highly complex morphogenetic processes, central to many physiological and pathological conditions, including development, cancer metastasis, inflammation and wound healing. While it is described that extracellular matrix (ECM) fibers are involved in the spatiotemporal regulation of angiogenesis, current angiogenesis assays are not specifically designed to dissect and quantify the underlying molecular mechanisms of how the fibrillar nature of ECM regulates vessel sprouting. Even less is known about the role of the fibrillar ECM during the early stages of lymphangiogenesis. To address such questions, we introduced here an in vitro (lymph)angiogenesis assay, where we used microbeads coated with endothelial cells as simple sprouting sources and deposited them on single Fn fibers used as substrates to mimic fibrillar ECM. The fibers were deposited on a transparent substrate, suitable for live microscopic observation of the ensuing cell outgrowth events at the single cell level. Our proof-of-concept studies revealed that fibrillar Fn, compared to Fn-coated surfaces, provides far stronger sprouting and guidance cues to endothelial cells, independent of the tested mechanical strains of the Fn fibers. Additionally, we found that VEGF-A, but not VEGF-C, stimulates the collective outgrowth of lymphatic endothelial cells (LEC), while the collective outgrowth of blood vascular endothelial cells (HUVEC) was prominent even in the absence of these angiogenic factors. In addition to the findings presented here, the modularity of our assay allows for the use of different ECM or synthetic fibers as substrates, as well as of other cell types, thus expanding the range of applications in vascular biology and beyond.

Neural crest cell-autonomous roles of fibronectin in cardiovascular development

The chemical and mechanical properties of extracellular matrices (ECMs) modulate diverse aspects of cellular fates; however, how regional heterogeneity in ECM composition regulates developmental programs is not well understood. We discovered that fibronectin 1 (Fn1) is expressed in strikingly non-uniform patterns during mouse development, suggesting that regionalized synthesis of the ECM plays cell-specific regulatory roles during embryogenesis. To test this hypothesis, we ablated Fn1 in the neural crest (NC), a population of multi-potent progenitors expressing high levels of Fn1. We found that Fn1 synthesized by the NC mediated morphogenesis of the aortic arch artery and differentiation of NC cells into vascular smooth muscle cells (VSMCs) by regulating Notch signaling. We show that NC Fn1 signals in an NC cell-autonomous manner through integrin α5β1 expressed by the NC, leading to activation of Notch and differentiation of VSMCs. Our data demonstrate an essential role of the localized synthesis of Fn1 in cardiovascular development and spatial regulation of Notch signaling.