MMP-2 expression during early avian cardiac and neural crest morphogenesis

Cardiac Neural Crest

Cardiac neural crest (CNC) cells are pluripotent cells derived from the dorsal neural tube that migrate and contribute to the remodeling of pharyngeal arch arteries and septation of the cardiac outflow tract (OFT). Numerous molecular cascades regulate the induction, specification, delamination, and migration of the CNC. Extensive analyses of the CNC ranging from chick ablation models to molecular biology studies have explored the mechanisms of heart development and disease, particularly involving the OFT and aortic arch (AA) system. Recent studies focus more on reciprocal signaling between the CNC and cells originated from the second heart field (SHF), which are essential for the development of the OFT myocardium, providing new insights into the molecular mechanisms underlying congenital heart diseases (CHDs) and some human syndromes.

Dynamic transcriptome profiling toward understanding the development of the human embryonic heart during different Carnegie stages

Transcriptional regulation participates in heart development. However, the transcriptomes of human embryonic hearts during Carnegie stage (CS)10-CS16 have not been elucidated. Here, we found marked changes in the morphology and transcriptome of the human embryonic heart from CS10 to CS11. At CS12-CS14, the embryonic heart undergoes hypoxia-to-aerobic transformation. At CS14-CS16, transcriptome functions were related to energy metabolism, regulation of cholesterol, and processes related to inorganic substances. Moreover, the transcriptomes of cardiac progenitor cells derived from human embryonic stem cells (hESCs) most overlapped with those of human embryonic hearts at CS10. Cardiomyocytes derived from hESCs considerably overlapped with embryonic hearts at CS14-CS16. Overall, these results provide a new perspective into the characteristics of human embryonic heart development.

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.

Conserved role of matrix metalloproteases 2 and 9 in promoting the migration of neural crest cells in avian and mammalian embryos

Neural crest cells (NCCs) are a unique embryonic cell population that initially reside at the dorsal neural tube but later migrate in the embryo and differentiate into multiple types of derivatives. To acquire motility, NCCs undergo epithelial-to-mesenchymal transition and invade the surrounding extracellular matrix (ECM). Matrix metalloproteases (MMPs) are a large family of proteases which regulate migration of various embryonic and adult cells via ECM remodeling. The gelatinase's subgroup of MMPs is the most studied one due to its key role in metastasis. As it is composed of only two proteases, MMP2 and MMP9, it is important to understand whether each is indispensable or redundant in its biological function. Here we explored the role of the gelatinases in executing NCC migration, by determining whether MMP2 and/or MMP9 regulate migration across species in singular, combined, or redundant manners. Chick and mouse embryos were utilized to compare expression and activity of both MMPs using genetic and pharmacological approaches in multiple in vivo and ex vivo assays. Both MMPs were found to be expressed and active in mouse and chick NCCs. Inhibition of each MMP was sufficient to prevent NCC migration in both species. Yet, NCC migration was maintained in MMP2^-/- or MMP9^-/- mouse mutants due to compensation between the gelatinases, but reciprocal pharmacological inhibition in each mutant prevented NCC migration. This study reveals for the first time that both gelatinases are expressed in avian and mammalian NCCs, and demonstrates their fundamental and conserved role in promoting embryonic cell migration.

The origin and evolution of vertebrate neural crest cells

The neural crest is a vertebrate-specific migratory stem cell population that generates a remarkably diverse set of cell types and structures. Because many of the morphological, physiological and behavioural novelties of vertebrates are derived from neural crest cells, it is thought that the origin of this cell population was an important milestone in early vertebrate history. An outstanding question in the field of vertebrate evolutionary-developmental biology (evo-devo) is how this cell type evolved in ancestral vertebrates. In this review, we briefly summarize neural crest developmental genetics in vertebrates, focusing in particular on the gene regulatory interactions instructing their early formation within and migration from the dorsal neural tube. We then discuss how studies searching for homologues of neural crest cells in invertebrate chordates led to the discovery of neural crest-like cells in tunicates and the potential implications this has for tracing the pre-vertebrate origins of the neural crest population. Finally, we synthesize this information to propose a model to explain the origin of neural crest cells. We suggest that at least some of the regulatory components of early stages of neural crest development long pre-date vertebrate origins, perhaps dating back to the last common bilaterian ancestor. These components, originally directing neuroectodermal patterning and cell migration, served as a gene regulatory 'scaffold' upon which neural crest-like cells with limited migration and potency evolved in the last common ancestor of tunicates and vertebrates. Finally, the acquisition of regulatory programmes controlling multipotency and long-range, directed migration led to the transition from neural crest-like cells in invertebrate chordates to multipotent migratory neural crest in the first vertebrates.

MMP14 Regulates Cranial Neural Crest Epithelial-to-Mesenchymal Transition and Migration

BACKGROUND

Neural crest is a vertebrate specific cell population. Induced at lateral borders of the neural plate, neural crest cells (NCCs) subsequently undergo epithelial-to-mesenchymal transition (EMT) to detach from the neuroepithelium before migrating into various locations in the embryo. Despite the wealth of knowledge of transcription factors involved in this process, little is known about the effectors that directly regulate neural crest EMT and migration.

RESULTS

Here, we examined the activity of matrix metalloproteinase MMP14 in NCCs and found that MMP14 is expressed in both premigratory and migrating NCCs. Overexpression of MMP14 led to premature migration of NCCs, while down-regulation of MMP14 resulted in reduced neural crest migration. Transplantation experiment further showed that MMP14 is required in NCCs, whereas MMP2, which can be activated by MMP14, is required in the surrounding mesenchyme. in vitro explant culture showed that MMP14 is required for neural crest EMT but not for spreading. This is possibly mediated by the changes in cadherin levels, as decreasing MMP14 level led to increased cadherin expression and increasing MMP14 level led to reduced cadherin expression.

CONCLUSIONS

The results demonstrate that MMP14 is critical for neural crest EMT and migration, partially through regulating the levels of cadherins. Developmental Dynamics 247:1083-1092, 2018. © 2018 Wiley Periodicals, Inc.

Cadherin-6B proteolytic N-terminal fragments promote chick cranial neural crest cell delamination by regulating extracellular matrix degradation

During epithelial-to-mesenchymal transitions (EMTs), chick cranial neural crest cells simultaneously delaminate from the basement membrane and segregate from the epithelia, in part, via multiple protease-mediated mechanisms. Proteolytic processing of Cadherin-6B (Cad6B) in premigratory cranial neural crest cells by metalloproteinases not only disassembles cadherin-based junctions but also generates shed Cad6B ectodomains or N-terminal fragments (NTFs) that may possess additional roles. Here we report that Cad6B NTFs promote delamination by enhancing local extracellular proteolytic activity around neural crest cells undergoing EMT en masse. During EMT, Cad6B NTFs of varying molecular weights are observed, indicating that Cad6B may be cleaved at different sites by A Disintegrin and Metalloproteinases (ADAMs) 10 and 19 as well as by other matrix metalloproteinases (MMPs). To investigate Cad6B NTF function, we first generated NTF constructs that express recombinant NTFs with similar relative mobilities to those NTFs shed in vivo. Overexpression of either long or short Cad6B NTFs in premigratory neural crest cells reduces laminin and fibronectin levels within the basement membrane, which then facilitates precocious neural crest cell delamination. Zymography assays performed with supernatants of neural crest cell explants overexpressing Cad6B long NTFs demonstrate increased MMP2 activity versus controls, suggesting that Cad6B NTFs promote delamination through a mechanism involving MMP2. Interestingly, this increase in MMP2 does not involve up-regulation of MMP2 or its regulators at the transcriptional level but instead may be attributed to a physical interaction between shed Cad6B NTFs and MMP2. Taken together, these results highlight a new function for Cad6B NTFs and provide insight into how cadherins regulate cellular delamination during normal developmental EMTs as well as aberrant EMTs that underlie human disease.

Cut loose and run: The complex role of ADAM proteases during neural crest cell development

ADAM metalloproteases have been shown to play critical roles during development. In this review, we will describe functional evidence that implicates ADAM proteins during the genesis, migration and differentiation of neural crest cells. We will restrict our analysis to the transmembrane ADAMs as other reviews have addressed the role of extracellular metalloproteases (Christian et al. [2013] Critical Reviews in Biochemistry and Molecular Biology 48:544-560). This review will describe advances that have been obtained mainly through the use of two vertebrate model systems, the frog, and avian embryos. The role of the principal substrates of ADAMs, the cadherins, has been extensively described in other reviews, most recently in (Cousin [1997] Mechanisms of Development 148:79-88; Taneyhill and Schiffmacher [2017] Genesis, 55). The function of ADAMs in the migration of other cell types, including the immune system, wound healing and cancer has been described previously in (Dreymueller et al. [2017] Mediators of Inflammation 2017: 9621724). Our goal is to illustrate both the importance of ADAMs in controlling neural crest behavior and how neural crest cells have helped us understand the molecular interactions, substrates, and functions of ADAM proteins in vivo.

Neural crest delamination and migration: Looking forward to the next 150 years

Neural crest (NC) cells were described for the first time in 1868 by Wilhelm His. Since then, this amazing population of migratory stem cells has been intensively studied. It took a century to fully unravel their incredible abilities to contribute to nearly every organ of the body. Yet, our understanding of the cell and molecular mechanisms controlling their migration is far from complete. In this review, we summarize the current knowledge on epithelial-mesenchymal transition and collective behavior of NC cells and propose further stops at which the NC train might be calling in the near future.

Leaders in collective migration: are front cells really endowed with a particular set of skills?

Collective cell migration is the coordinated movement emerging from the interaction of at least two cells. In multicellular organisms, collective cell migration is ubiquitous. During development, embryonic cells often travel in numbers, whereas in adults, epithelial cells close wounds collectively. There is often a division of labour and two categories of cells have been proposed: leaders and followers. These two terms imply that followers are subordinated to leaders whose proposed broad range of actions significantly biases the direction of the group of cells towards a specific target. These two terms are also tied to topology. Leaders are at the front while followers are located behind them. Here, we review recent work on some of the main experimental models for collective cell migration, concluding that leader-follower terminology may not be the most appropriate. It appears that not all collectively migrating groups are driven by cells located at the front. Moreover, the qualities that define leaders (pathfinding, traction forces and matrix remodelling) are not specific to front cells. These observations indicate that the terms leaders and followers are not suited to every case. We think that it would be more accurate to dissociate the function of a cell from its position in the group. The position of cells can be precisely defined with respect to the direction of movement by purely topological terms such as "front" or "rear" cells. In addition, we propose the more ample and strictly functional definition of "steering cells" which are able to determine the directionality of movement for the entire group. In this context, a leader cell represents only a specific case in which a steering cell is positioned at the front of the group.

Should I stay or should I go? Cadherin function and regulation in the neural crest

Our increasing comprehension of neural crest cell development has reciprocally advanced our understanding of cadherin expression, regulation, and function. As a transient population of multipotent stem cells that significantly contribute to the vertebrate body plan, neural crest cells undergo a variety of transformative processes and exhibit many cellular behaviors, including epithelial-to-mesenchymal transition (EMT), motility, collective cell migration, and differentiation. Multiple studies have elucidated regulatory and mechanistic details of specific cadherins during neural crest cell development in a highly contextual manner. Collectively, these results reveal that gradual changes within neural crest cells are accompanied by often times subtle, yet important, alterations in cadherin expression and function. The primary focus of this review is to coalesce recent data on cadherins in neural crest cells, from their specification to their emergence as motile cells soon after EMT, and to highlight the complexities of cadherin expression beyond our current perceptions, including the hypothesis that the neural crest EMT is a transition involving a predominantly singular cadherin switch. Further advancements in genetic approaches and molecular techniques will provide greater opportunities to integrate data from various model systems in order to distinguish unique or overlapping functions of cadherins expressed at any point throughout the ontogeny of the neural crest.

Matrix Metalloproteinases are required for membrane motility and lumenogenesis during Drosophila heart development

Matrix Metalloproteinases (Mmps) degrade glycoproteins and proteoglycans of the extracellular matrix (ECM) or cell surface and are crucial for morphogenesis. Mmps and their inhibitors are expressed during early stages of cardiac development in vertebrates and expression is altered in multiple congenital cardiomyopathies such as cardia bifida. Drosophila genome encodes two copies of Mmps, Mmp1 and Mmp2 whereas in humans up to 25 Mmps have been identified with overlapping functions. We investigated the role of Mmps during embryonic heart development in Drosophila, a process which is morphogenetically similar to early heart tube formation in vertebrates. We demonstrate that the two Mmps in Drosophila have distinct and overlapping roles in cell motility, cell adhesion and cardiac lumenogenesis. We determined that Mmp1 and Mmp2 promote Leading Edge membrane dynamics of cardioblasts during collective migration. Mmp2 is essential for cardiac lumen formation, and mutants generate a cardia bifida phenotype. Mmp1 is required for luminal expansion. Mmp1 and Mmp2 both localise to the basal domains of cardiac cells, however, occupy non-overlapping domains apically. Mmp1 and Mmp2 regulate the proteoglycan composition and size of the apical and basal ECM, yet only Mmp2 is required to restrict ECM assembly to the lumen. Mmp1 negatively regulates the size of the adhesive Cadherin cell surface domain, whereas in a complementary fashion, Mmp2 negatively regulates the size of the Integrin-ECM domain and thereby prescribes the domain to establish and restrict Slit morphogen signalling. Inhibition of Mmp activity through ectopic expression of Tissue Inhibitor of Metalloproteinase in the ectoderm blocks lumen formation. Therefore, Mmp expression and function identifies ECM differentiation and remodelling as a key element for cell polarisation and organogenesis.

Matrix metalloproteinases in coronary artery disease

Matrix metalloproteinases (MMP) are a family of zinc-containing endoproteinases that degrade extracellular matrix (ECM) components. MMP have important roles in the development, physiology and pathology of cardiovascular system. Metalloproteases also play key roles in adverse cardiovascular remodeling, atherosclerotic plaque formation and plaque instability, vascular smooth muscle cell (SMC) migration and restenosis that lead to coronary artery disease (CAD), and progressive heart failure. The study of MMP in developing animal model cardiovascular systems has been helpful in deciphering numerous pathologic conditions in humans. Increased peripheral blood MMP-2 and MMP-9 in acute coronary syndrome (ACS) may be useful as noninvasive tests for detection of plaque vulnerability. MMP function can be modulated by certain pharmacological drugs that can be exploited for treatment of ACS. CAD is a polygenic disease and hundreds of genes contribute toward its predisposition. A large number of sequence variations in MMP genes have been identified. Case-control association studies have highlighted their potential association with CAD and its clinical manifestations. Although results thus far are inconsistent, meta-analysis has demonstrated that MMP-3 Glu45Lys and MMP-9 1562C/T gene polymorphisms were associated with CAD risk.

Extracellular metalloproteinases in neural crest development and craniofacial morphogenesis

The neural crest (NC) is a population of migratory stem/progenitor cells that is found in early vertebrate embryos. NC cells are induced during gastrulation, and later migrate to multiple destinations and contribute to many types of cells and tissues, such as craniofacial structures, cardiac tissues, pigment cells and the peripheral nervous system. Recently, accumulating evidence suggests that many extracellular metalloproteinases, including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAMs with thrombospondin motifs (ADAMTSs), play important roles in various stages of NC development. Interference with metalloproteinase functions often causes defects in craniofacial structures, as well as in other cells and tissues that are contributed by NC cells, in humans and other vertebrates. In this review, we summarize the current state of the field concerning the roles of these three families of metalloproteinases in NC development and related tissue morphogenesis, with a special emphasis on craniofacial morphogenesis.

Circulating matrix metalloproteinase-2 and -9 enzyme activities in the children with ventricular septal defect

Ventricular septal defect (VSD) is the most common form of congenital heart diseases. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases involved in causal cardiac tissue remodeling. We studied the changes of circulating MMP-2 and MMP-9 activities in the patients with VSD severity and closure. There were 96 children with perimembranous VSD enrolled in this study. We assigned the patients into three groups according to the ratio of VSD diameter/diameter of aortic root (Ao). They were classified as below: Trivial (VSD/Ao ratio ≤ 0.2), Small (0.2 < VSD/Ao ≤ 0.3) and Median (0.3 < VSD/Ao) group. Plasma MMP-2 and MMP-9 activities were assayed by gelatin zymography. There was a significant higher MMP-2 activity in the VSD (Trivial, Small and Median) groups compared with that in Control group. The plasma MMP-9 activity showed a similar trend as the findings in MMP-2 activity. After one year follow-up, a significant difference in the MMP-9 activity was found between VSD spontaneous closure and non-closure groups. In conclusion, a positive trend between the severity of VSD and activities of MMP-2 and MMP-9 was found. Our data imply that MMP-2 and MMP-9 activities may play a role in the pathogenesis of VSD.

Riding the crest of the wave: parallels between the neural crest and cancer in epithelial-to-mesenchymal transition and migration

The neural crest (NC) is first induced as an epithelial population of cells at the neural plate border requiring complex signaling between bone morphogenetic protein, Wnt, and fibroblast growth factors to differentiate the neural and NC fate from the epidermis. Remarkably, following induction, these cells undergo an epithelial-to-mesenchymal transition (EMT), delaminate from the neural tube, and migrate through various tissue types and microenvironments before reaching their final destination where they undergo terminal differentiation. This process is mirrored in cancer metastasis, where a primary tumor will undergo an EMT before migrating and invading other cell populations to create a secondary tumor site. In recent years, as our understanding of NC EMT and migration has deepened, important new insights into tumorigenesis and metastasis have also been achieved. These discoveries have been driven by the observation that many cancers misregulate developmental genes to reacquire proliferative and migratory states. In this review, we examine how the NC provides an excellent model for studying EMT and migration. These data are discussed from the perspective of the gene regulatory networks that control both NC and cancer cell EMT and migration. Deciphering these processes in a comparative manner will expand our knowledge of the underlying etiology and pathogenesis of cancer and promote the development of novel targeted therapeutic strategies for cancer patients. © 2013 Wiley Periodicals, Inc.

MT2-MMP expression during early avian morphogenesis

Membrane-type 2 matrix metalloproteinase (MT2-MMP; also called MMP15) is a membrane-bound protease that degrades extracellular matrix and activates proMMPs such as proMMP-2. MMP-2 expression in avian embryos is well documented, but it is not clear how proMMP-2 is activated during avian embryogenesis. Herein, we report that MT2-MMP mRNA is expressed in several tissues including the neural folds and epidermal ectoderm, intermediate mesoderm, pharyngeal arches, limb buds, and dermis. Several, but not all, of these tissues are known to express MMP-2. These observations suggest MT2-MMP may play a role during embryonic development not only through its own proteolytic activity but also by activating proMMP-2.

Expression and function of cell adhesion molecules during neural crest migration

Neural crest cells are highly migratory cells that give rise to many derivatives including peripheral ganglia, craniofacial structures and melanocytes. Neural crest cells migrate along defined pathways to their target sites, interacting with each other and their environment as they migrate. Cell adhesion molecules are critical during this process. In this review we discuss the expression and function of cell adhesion molecules during the process of neural crest migration, in particular cadherins, integrins, members of the immunoglobulin superfamily of cell adhesion molecules, and the proteolytic enzymes that cleave these cell adhesion molecules. The expression and function of these cell adhesion molecules and proteases are compared across neural crest emigrating from different axial levels, and across different species of vertebrates.

Can mesenchymal cells undergo collective cell migration? The case of the neural crest

Cell migration is critical for proper development of the embryo and is also used by many cell types to perform their physiological function. For instance, cell migration is essential for immune cells to monitor the body and for epithelial cells to heal a wound whereas, in cancer cells, acquisition of migratory capabilities is a critical step towards malignancy. Migratory cells are often categorized into two groups: mesenchymal cells, produced by an epithelium-to-mesenchyme transition, that undergo solitary migration and epithelial-like cells which migrate collectively. However, on some occasions, mesenchymal cells may travel in large, dense groups and exhibit key features of collectively migrating cells such as coordination and cooperation. Here, using data published on Neural Crest cells, a highly invasive mesenchymal cell population that extensively migrate throughout the embryo, we explore the idea that other mesenchymal cells, including cancer cells, might be able to undergo collective cell migration under certain conditions and discuss how they could do so.

Epithelial to mesenchymal transition: new and old insights from the classical neural crest model

The epithelial-to-mesenchymal transition (EMT) is an important event converting compact and ordered epithelial cells into migratory mesenchymal cells. Given the molecular and cellular similarities between pathological and developmental EMTs, studying this event during neural crest development offers and excellent in vivo model for understanding the mechanisms underlying this process. Here, we review new and old insight into neural crest EMT in search of commonalities with cancer progression that might aid in the design of specific therapeutic prevention.

Neural crest delamination and migration: from epithelium-to-mesenchyme transition to collective cell migration

After induction and specification in the ectoderm, at the border of the neural plate, the neural crest (NC) population leaves its original territory through a delamination process. Soon afterwards, the NC cells migrate throughout the embryo and colonize a myriad of tissues and organs where they settle and differentiate. The delamination involves a partial or complete epithelium-to-mesenchyme transition (EMT) regulated by a complex network of transcription factors including several proto-oncogenes. Studying the relationship between these genes at the time of emigration, and their individual or collective impact on cell behavior, provides valuable information about their role in EMT in other contexts such as cancer metastasis. During migration, NC cells are exposed to large number of positive and negative regulators that control where they go by generating permissive and restricted areas and by modulating their motility and directionality. In addition, as most NC cells migrate collectively, cell-cell interactions play a crucial role in polarizing the cells and interpreting external cues. Cell cooperation eventually generates an overall polarity to the population, leading to directional collective cell migration. This review will summarize our current knowledge on delamination, EMT and migration of NC cells using key examples from chicken, Xenopus, zebrafish and mouse embryos. Given the similarities between neural crest migration and cancer invasion, these cells may represent a useful model for understanding the mechanisms of metastasis.

Diversity in the molecular and cellular strategies of epithelium-to-mesenchyme transitions: Insights from the neural crest

Although epithelial to mesenchymal transitions (EMT) are often viewed as a unique event, they are characterized by a great diversity of cellular processes resulting in strikingly different outcomes. They may be complete or partial, massive or progressive, and lead to the complete disruption of the epithelium or leave it intact. Although the molecular and cellular mechanisms of EMT are being elucidated owing chiefly from studies on transformed epithelial cell lines cultured in vitro or from cancer cells, the basis of the diversity of EMT processes remains poorly understood. Clues can be collected from EMT occuring during embryonic development and which affect equally tissues of ectodermal, endodermal or mesodermal origins. Here, based on our current knowledge of the diversity of processes underlying EMT of neural crest cells in the vertebrate embryo, we propose that the time course and extent of EMT do not depend merely on the identity of the EMT transcriptional regulators and their cellular effectors but rather on the combination of molecular players recruited and on the possible coordination of EMT with other cellular processes.

Matrix metalloproteinase-induced epithelial-mesenchymal transition in breast cancer

Matrix metalloproteinases (MMPs) degrade and modify the extracellular matrix (ECM) as well as cell-ECM and cell-cell contacts, facilitating detachment of epithelial cells from the surrounding tissue. MMPs play key functions in embryonic development and mammary gland branching morphogenesis, but they are also upregulated in breast cancer, where they stimulate tumorigenesis, cancer cell invasion and metastasis. MMPs have been investigated as potential targets for cancer therapy, but clinical trials using broad-spectrum MMP inhibitors yielded disappointing results, due in part to lack of specificity toward individual MMPs and specific stages of tumor development. Epithelial-mesenchymal transition (EMT) is a developmental process in which epithelial cells take on the characteristics of invasive mesenchymal cells, and activation of EMT has been implicated in tumor progression. Recent findings have implicated MMPs as promoters and mediators of developmental and pathogenic EMT processes in the breast. In this review, we will summarize recent studies showing how MMPs activate EMT in mammary gland development and in breast cancer, and how MMPs mediate breast cancer cell motility, invasion, and EMT-driven breast cancer progression. We also suggest approaches to inhibit these MMP-mediated malignant processes for therapeutic benefit.

A chemical genomic approach identifies matrix metalloproteinases as playing an essential and specific role in Xenopus melanophore migration

To dissect the function of matrix metalloproteinases (MMPs) involved in cellular migration in vivo, we undertook both a forward chemical genomic screen and a functional approach to discover modulators of melanophore (pigment cell) migration in Xenopus laevis. We identified the 8-quinolinol derivative NSC 84093 as affecting melanophore migration in the developing embryo and have shown it to act as a MMP inhibitor. Potential targets of NSC 84093 investigated include MMP-14 and MMP-2. MMP-14 is expressed in migrating neural crest cells from which melanophores are derived. MMP-2 is expressed at the relevant time of development and in a pattern that suggests it contributes to melanophore migration. Morpholino-mediated knockdown of both MMPs demonstrates they play a key role in melanophore migration and partially phenocopy the effect of NSC 84093.

A gene regulatory network orchestrates neural crest formation

The neural crest is a multipotent, migratory cell population that is unique to vertebrate embryos and gives rise to many derivatives, ranging from the peripheral nervous system to the craniofacial skeleton and pigment cells. A multimodule gene regulatory network mediates the complex process of neural crest formation, which involves the early induction and maintenance of the precursor pool, emigration of the neural crest progenitors from the neural tube via an epithelial to mesenchymal transition, migration of progenitor cells along distinct pathways and overt differentiation into diverse cell types. Here, we review our current understanding of these processes and discuss the molecular players that are involved in the neural crest gene regulatory network.

Molecular analysis of neural crest migration

The neural crest (NC) cells have been called the 'explorers of the embryos' because they migrate all over the embryo where they differentiate into a variety of diverse kinds of cells. In this work, we analyse the role of different molecules controlling the migration of NC cells. First, we describe the strong similarity between the process of NC migration and metastasis in tumour cells. The epithelial-mesenchymal transition process that both kinds of cells undergo is controlled by the same molecular machinery, including cadherins, connexins, Snail and Twist genes and matrix metalloproteases. Second, we analysed the molecular signals that control the patterned migration of the cephalic and trunk NC cells. Most of the factors described so far, such as Eph/ephrins, semaphorins/neuropilins and Slit/Robo, are negative signals that prohibit the migration of NC cells into target areas of the embryo. Finally, we analyse how the direction of migration is controlled by regulation of cell polarity and how the planar cell polarity or non-canonical Wnt signalling is involved in this process.

Altered expression of mitochondrial and extracellular matrix genes in the heart of human fetuses with chromosome 21 trisomy

BACKGROUND

The Down syndrome phenotype has been attributed to overexpression of chromosome 21 (Hsa21) genes. However, the expression profile of Hsa21 genes in trisomic human subjects as well as their effects on genes located on different chromosomes are largely unknown. Using oligonucleotide microarrays we compared the gene expression profiles of hearts of human fetuses with and without Hsa21 trisomy.

RESULTS

Approximately half of the 15,000 genes examined (87 of the 168 genes on Hsa21) were expressed in the heart at 18-22 weeks of gestation. Hsa21 gene expression was globally upregulated 1.5 fold in trisomic samples. However, not all genes were equally dysregulated and 25 genes were not upregulated at all. Genes located on other chromosomes were also significantly dysregulated. Functional class scoring and gene set enrichment analyses of 473 genes, differentially expressed between trisomic and non-trisomic hearts, revealed downregulation of genes encoding mitochondrial enzymes and upregulation of genes encoding extracellular matrix proteins. There were no significant differences between trisomic fetuses with and without heart defects.

CONCLUSION

We conclude that dosage-dependent upregulation of Hsa21 genes causes dysregulation of the genes responsible for mitochondrial function and for the extracellular matrix organization in the fetal heart of trisomic subjects. These alterations might be harbingers of the heart defects associated with Hsa21 trisomy, which could be based on elusive mechanisms involving genetic variability, environmental factors and/or stochastic events.

Versican proteolysis mediates myocardial regression during outflow tract development

An important phase of cardiac outflow tract (OFT) formation is the remodeling of the distal region of the common outlet in which the myocardial sleeve is replaced by with smooth muscle. Here we demonstrate that expression of the proteoglycan versican is reduced before the loss of myocardium from the distal cardiac outlet concomitant with an increase in production of the N-terminal cleavage fragment of versican. To test whether versican proteolysis plays a role in OFT remodeling, we determined the effects of adenoviral-mediated expression of a versican isoform devoid of known matrix metalloproteinase cleavage sites (V3) and an N-terminal fragment of versican (G1). V3 expression promoted an increase in thickness of the proximal OFT myocardial layer independent of proliferation. In contrast, the G1 domain caused thinning and interruptions of the OFT myocardium. These in vivo findings were consistent with findings using cultured primary cardiomyocytes showing that the V3 promoted myocardial cell-cell association while the G1 domain caused a loss of myocardial cell-cell association. Taken together, we conclude that intact versican and G1-containing versican cleavage products have opposing effects on myocardial cells and that versican proteolysis may facilitate the loss of distal myocardium during OFT remodeling.

Proteolytic cleavage of versican during cardiac cushion morphogenesis

The proteoglycan versican is essential to the formation of endocardial cushion mesenchyme by epithelial-mesenchymal transformation (EMT). A potentially important factor in the regulation of versican activity during cushion EMT is proteolysis by ADAMTS metalloproteinases. Using antibodies to the DPEAAE neoepitope created by ADAMTS proteolysis of versican, we detected the amino terminal 70-kDa versican cleavage fragment in cardiac cushions. Initially (i.e., 9.5 days post coitum [dpc]), the fragment is associated with endocardial cells undergoing EMT and with newly derived mesenchymal cells. ADAMTS-1 and its cofactor fibulin-1 were also associated with these cells. As cushions become increasingly populated with mesenchymal cells (10.5-12.5 dpc), the fragment remains asymmetrically distributed compared with the pattern of total versican. Highest levels of the fragment are present in regions immediately subjacent to the endocardium characterized as having densely packed, rounded cells, lacking cellular protrusions. With further development (i.e., 12.5-14.5 dpc), the pattern of fragment distribution within cushions broadens to include the ECM surrounding loosely packed mesenchymal cells in the cushion core. Together, the findings reveal that versican proteolysis leading to the production of the 70-kDa fragment is integral to the formation and differentiation of endocardial cushion mesenchyme.

Cardiac myxoma cells exhibit embryonic endocardial stem cell features

The origin of myxoma, the most frequent tumour of the heart, remains uncertain. Previous phenotypic characterizations have shown heterogeneous results and the most recent hypothesis suggests that cardiac myxoma originates from a primitive pluripotential cardiogenic cell. We investigated the expression of actin isoforms in 30 left atrial myxomas by immunohistochemistry and in eight consecutive tumours by RT-PCR. alpha-Smooth muscle actin (alpha-SMA) protein and/or transcripts were detected in all cases, whereas alpha-cardiac actin was observed in few cases and alpha-skeletal actin was always absent. Besides classical features, vessel-like structures were characterized by cells expressing CD34 and, less frequently, alpha-SMA. Confocal microscopy showed focal co-expression of CD34 and alpha-SMA in myxoma cells, suggesting a gradual loss of stem endothelial markers and the acquisition of myocytic antigens. In order to confirm this hypothesis, early cardiac differentiation markers were also investigated. RT-PCR documented the presence of transcripts for Sox9 (100%), Notch1 (87.5%), NFATc1 (37.5%), Smad6, metalloproteinases 1 and 2 alone or in variable combinations and the absence of ErbB3 and WT1. Myxoma cells maintained phenotypic heterogeneity in vitro, including the expression of alpha-SMA and the presence of stress fibres. These findings document in cardiac myxoma cells phenotypic markers of the embryonic endothelial-to-mesenchymal transformation that precedes terminal differentiation of endocardial cushions, supporting the hypothesis that cardiac myxoma cells may derive from adult developmental remnants.

Cardiac morphogenesis: matrix metalloproteinase coordination of cellular mechanisms underlying heart tube formation and directionality of looping

During heart organogenesis, the spatiotemporal organization of the extracellular matrix (ECM) undergoes significant remodeling. Because matrix metalloproteinases (MMPs) are known to be key regulators of cell-matrix interactions, we analyzed the role(s) of MMPs, and specifically MMP-2, in early heart development. Both MMP-2 neutralizing antibody and the broad-spectrum MMP inhibitor Ilomastat in a temporal manner, when applied between chick embryonic stages 5 (primitive streak stage) to stage 12 ( approximately 16-somites), produced severe heart tube defects. Exposure to the MMP inhibitor at stage 5 produced various degrees of cardia bifida. At the seven-somite stage, MMP-2/Ilomastat inhibition caused a shift in normal left-right patterning of cell proliferation within the dorsal mesocardium and mesoderm of the anterior heart field that correlated with a change in looping direction. MMP inhibition at the 10- to 12-somite stage resulted in an arrest of heart tube bending by inhibiting the breakdown of the dorsal mesocardial ECM. The experimental observations suggest that MMP activity regulates the coordination of early heart organogenesis by affecting ventral closure of the heart and gut tubes, asymmetric cell proliferation in the dorsal mesocardium to drive looping direction, and ECM degradation within the dorsal mesocardium allowing looping to proceed toward completion.

Disruption of actin cytoskeleton and anchorage-dependent cell spreading induces apoptotic death of mouse neural crest cells cultured in vitro

In vertebrate embryos, neural crest cells emigrate out of the neural tube and contribute to the formation of a variety of neural and nonneural tissues. Some neural crest cells undergo apoptotic death during migration, but its biological significance and the underlying mechanism are not well understood. We carried out an in vitro study to examine how the morphology and survival of cranial neural crest (CNC) cells of the mouse embryo are affected when their actin cytoskeleton or anchorage-dependent cell spreading is perturbed. Disruption of actin fiber organization by cytochalasin D (1 microg/ml) and inhibition of cell attachment by matrix metalloproteinase-2 (MMP-2; 2.0 units/ml) were followed by morphologic changes and apoptotic death of cultured CNC cells. When the actin cytoskeleton was disrupted by cytochalasin D, the morphologic changes of cultured CNC cells preceded DNA fragmentation. These results indicate that the maintenance of cytoskeleton and anchorage-dependent cell spreading are required for survival of CNC cells. The spatially and temporally regulated expression of proteinases may be essential for the differentiation and migration of neural crest cells.

Tissue inhibitor of metalloproteinase-2 (TIMP-2) expression during cardiac neural crest cell migration and its role in proMMP-2 activation

Matrix metalloproteinases (MMPs) are important mediators of neural crest (NC) cell migration. Here, we examine the distribution of tissue inhibitor of metalloproteinase (TIMP) -2 and TIMP-3 and test whether manipulating TIMP levels alters chicken cardiac NC cell migration. TIMP-2 mRNA is expressed at stage 11 in the neural epithelium and only in migrating cardiac NC cells. TIMP-3 mRNA is expressed only in the notochord at stage 8 and later in the outflow tract myocardium. Exogenous TIMP-2 increases NC motility in vitro at low concentrations but has no effect when concentrations are increased. In vitro, NC cells express membrane type-1 matrix metalloproteinase (MT1-MMP) and TIMP-2 and they secrete and activate proMMP-2. Antisense TIMP-2 oligonucleotides block proMMP-2 activation, decrease NC cell migration from explants, and perturb NC morphogenesis in ovo. Because TIMP-2 is required for activation of proMMP-2 by MT1-MMP, this finding suggests TIMP-2 expression by cardiac NC cells initiates proMMP-2 activation important for their migration.

Matrix metalloproteinase genes in Xenopus development

Matrix metalloproteinases (MMPs) are a large family of proteins in vertebrates, consisting of over 24 genes in humans, only a few of which have been identified in Xenopus. Three genes coding for MMPs in Xenopus have been identified and their expression studied during development. The membrane-bound XMMP-14 and -15 (XMT1-MMP and XMT2-MMP) both showed restricted expression patterns, the former principally localising to cranial neural crest tissues and the latter to the epidermis of the embryo. XMMP-7 codes for an MMP that lacks the hemopexin-like domain. It is expressed exclusively in macrophages or other myeloid cell types from early in development.

Expression of metalloproteinases and inhibitors in the differentiation of P19CL6 cells into cardiac myocytes

P19CL6 are a clonal derivative of P19 embryonal carcinoma cells, a euploid, multipotent mouse cell line, that differentiate efficiently into cardiac myocytes, with spontaneous beating evident within 10 days, following DMSO treatment. Using real-time quantitative RT-PCR we have profiled the expression of the complete matrix metalloproteinase and tissue inhibitor of metalloproteinase gene families during P19CL6 differentiation to cardiac myocytes. The genes subdivide into eight groups based upon their expression profile. Their expression was both qualitatively and quantitatively highly homologous to that seen during mouse heart development.

MMP-2 plays an essential role in producing epithelial-mesenchymal transformations in the avian embryo

To investigate the roles that matrix-degrading proteases may have in development of the chicken embryo, we documented the expression pattern of matrix metalloprotease-2 (MMP-2, 72-kDa type IV collagenase or gelatinase A) and perturbed its function in vitro and in vivo. MMP-2 is expressed as neural crest cells detach from the neural epithelium during an epithelial-mesenchymal transformation (EMT) but is rapidly extinguished as they disperse. It is also expressed in the sclerotome and in the dermis at the time that the EMT is initiated, and also as these cells migrate, and is down-regulated once motility has ceased. These patterns suggest that MMP-2 plays a role in cell motility during the EMT and during later morphogenesis. Inhibitors of MMPs, including BB-94 and TIMP-2 (tissue inhibitor of metalloprotease-2), prevent the EMT that generates neural crest cells, both in tissue culture and in vivo, but do not affect migration of the cells that have already detached from the neural tube. Similarly, knockdown of MMP-2 expression in the dorsal neural tube using antisense morpholino oligos perturbs the EMT, but also does not affect migration of neural crest cells after they have detached from the neural tube. On the other hand, when somites in culture are treated with TIMP-2, some mesenchymal cells are produced, suggesting that they undergo the EMT, but show greatly reduced migration through the collagen gel. MMP-2 is also expressed in mesenchyme where tissue remodeling is in progress, such as in the developing feather germs, in the head mesenchyme, in the lateral plate mesoderm, and in the limb dermis, especially in the regions where tendons are developing. Comparisons of these expression patterns in multiple embryonic tissues suggest a probable role for MMP-2 in the migration phase of the EMT, in addition to mesenchyme dispersion and tissue remodeling. Developmental Dynamics 229:42-53, 2004.

PNA-positive glycoconjugates are negatively correlated with the access of neural crest cells to the gut in chicken embryos

Neural crest cells give rise to many derivatives, including the neurons and glia of the peripheral nervous system, adrenomedulary cells, and melanocytes, and migrate through precise pathways that differ according to their axial level and/or state of specification. The migratory routes taken by neural crest cells are reported to be regulated by extracellular matrix molecules. We examined the possible influence of glycoconjugates on the establishment of barriers to neural crest access to ventral regions leading to the gut, by labeling stage-16-28 white Leghorn (WL) and Silky (SK) embryos with peanut agglutinin (PNA) at vagal, thoracic, and sacral levels. We observed a transitory expression of glycoconjugates that correlate with a barrier to the entrance of neural crest cells into the gut at the thoracic level, which is not present at vagal and sacral levels. In later stages, neural crest cells of melanocytic lineage were observed entering the gut in embryos of the SK chicken, a mutant with an altered pattern of pigmentation. The ventral regions occupied by melanoblasts in SK embryos were free of PNA labeling, while in WL embryos, in which PNA-positive molecules are strongly expressed, melanoblasts were restricted to peripheral regions. We suggest that PNA-binding glycoconjugates are good molecular marker for barriers that control the access of neural crest cells to the gut.

ADAM 10: an active metalloprotease expressed during avian epithelial morphogenesis

The ADAMs are a family of proteins containing multiple functional domains. We have cloned the avian orthologue of ADAM 10 and demonstrate that it has metalloprotease activity. Chick ADAM 10 is expressed in the developing dermatome and myotome of the somite, epidermis, gut endoderm, the epithelial tissues of the kidney, liver, and heart, and in neural crest cells. The expression patterns and protein distribution of ADAM 10 suggest it may play a significant role in the morphogenesis of several epithelial tissues. When a dominant-negative metalloprotease-mutant form of ADAM 10 is expressed in the ectoderm or ADAM 10 expression is knocked down with morpholinos, morphogenesis and tissue specification are altered.

Early events in valvulogenesis: a signaling perspective

The proper formation and function of the vertebrate heart requires a multitude of specific cell and tissue interactions. These interactions drive the early specification and assembly of components of the cardiovascular system that lead to a functioning system before the attainment of the definitive cardiac and vascular structures seen in the adult. Many of these adult structures are hypothesized to require both proper molecular and physical cues to form correctly. Unlike any other organ system in the embryo, the cardiovascular system requires concurrent function and formation for the embryo to survive. An example of this complex interaction between molecular and physical cues is the formation of the valves of the heart. Both molecular cues that regulate cell transformation, migration, and extracellular matrix deposition, and physical cues emanating from the beating heart, as well as hemodynamic forces, are required for valvulogenesis. This review will focus on molecules and emerging pathways that guide early events in valvulogenesis.

Homocysteine inhibits cardiac neural crest cell formation and morphogenesis in vivo

Elevated homocysteine increases the risk of neurocristopathies. Here, we determined whether elevating homocysteine altered the proliferation or number of chick neural crest cells that form between the midotic and third somite in vivo. Homocysteine increased the number of neural tube cells but decreased neural crest cell number. However, the sum total of cells was not different from controls. In controls, the 5-bromo-2'-deoxyuridine-labeling index was higher in newly formed neural crest cells than in their progenitors, paralleling reports showing these progenitors must pass the restriction point before undergoing epithelial-mesenchymal transition. Homocysteine decreased the labeling index of newly formed neural crest cells, suggesting that it inhibited cell cycle progression of neural crest progenitors or the S-phase entry of newly formed neural crest cells. Homocysteine also inhibited neural crest dispersal and decreased the distance they migrated from the neural tube. These results show neural crest morphogenesis is directly altered by elevated homocysteine in vivo. Developmental Dynamics 229:63-73, 2004.

Synthetic matrix metalloproteinase inhibitor decreases early cardiac neural crest migration in chicken embryos

During early embryonic development, cardiac neural crest (NC) cells emerge from the forming neural tube, migrate beneath the ectoderm, enter the pharyngeal arches, and subsequently participate in the septation of the heart. Like tumor cells, NC cells penetrate through basement membranes and invade extracellular matrix during their emigration and migration and, therefore, are liable to use similar invasive mechanisms. Matrix metalloproteinases (MMPs) are a family of zinc proteolytic enzymes known to be important in cell migration and invasion of normal and metastatic cells. In an earlier study, we found that the spatial and temporal distribution pattern of MMP-2 positively correlates with cardiac NC migration, suggesting MMP enzymatic activity may be important in mediating cardiac cell NC migration. To test this hypothesis, a synthetic MMP inhibitor, KB8301, was used to block MMP enzymatic activity during in vitro and in vivo cardiac NC cell migration in chick embryos. Injection of KB8301 into the cell-free space adjacent to the neural tube at the level of the second somite before the NC cells emigrated caused major morphologic anomalies in embryos and disrupted cardiac NC morphogenesis. Unilateral injection of KB8301 at lower concentrations, significantly decreased cardiac NC migration on the injected side compared with the noninjected side and compared with that of the injected controls. This decrease correlated with a decrease in MMP activity in the embryos and was not attributable to differences in embryo size or rate of embryonic development after injection. KB8301 also significantly decreased the rate of NC cell motility and distance NC cells migrated from explanted neural tubes and increased cell area and perimeter. These data suggest that MMP enzymatic activity is an important mediator of early cardiac NC migration and that perturbation of endogenous MMP activity may lead to NC-related congenital defects.

Expression of tissue inhibitor of metalloproteinases (TIMPs) during early cardiac development

Matrix metalloproteinases (MMPs) mediate cell migration and tissue remodeling and are important in cardiac development. We examined the expression patterns of two MMP inhibitors, tissue inhibitor of metalloproteinase (TIMP)-2 and TIMP-3, during critical stages of cardiac development. Both TIMP-2 and TIMP-3 mRNA were expressed in the endocardium prior to and during early cushion cell formation. TIMP-2 was continually expressed within the outflow tract (OT) and atrioventricular (AV) cushion cells at all stages examined, whereas TIMP-3 mRNA was undetectable in the AV cushion cells soon after their formation. Subsequently, TIMP-3 mRNA disappeared in cushion cells of the distal OT and this loss progressed toward the ventricle until eventually all of the OT cushion cells lacked detectable TIMP-3 transcripts. TIMP-3, but not TIMP-2, was also expressed within remodeling myocardium. Immunocytochemistry confirmed these findings. These observations suggest that TIMP-2 and TIMP-3 have important but unique roles in early cardiac development.

Myocardial remodelling and matrix metalloproteinases in heart failure: turmoil within the interstitium

The progression of left ventricular (LV) dysfunction is often accompanied by changes in LV geometry and myocardial architecture that can be defined as LV myocardial remodelling. An important event in LV myocardial remodelling is alterations in the extracellular matrix (ECM). A family of zinc-dependent proteases implicated in facilitating myocardial tissue remodelling by degrading components of the ECM are the matrix metalloproteinases (MMPs). The temporal expression of MMPs and the local tissue inhibitors of MMPs (TIMPs) appear to be differentially regulated in several cardiovascular disease states such as myocardial infarction, LV hypertrophy, and dilated cardiomyopathy. Both pharmacological and genetic modulation of myocardial MMP expression has been demonstrated to alter the course of LV myocardial remodelling and LV dysfunction. The induction of MMPs within the myocardium during the heart failure process probably results in liberation of bioactive molecules, proteolytic degradation of ECM structural proteins, and alterations in cell-cell contact and adhesion. Modifying MMP expression and activation may reduce this turmoil within the myocardial interstitium and, in turn, prove to be a useful therapeutic paradigm for heart failure treatment.