Collagen type VI in neural crest development: distribution in situ and interaction with cells in vitro

Recommendations for intervertebral disc notochordal cell investigation: From isolation to characterization

Background

Lineage-tracing experiments have established that the central region of the mature intervertebral disc, the nucleus pulposus (NP), develops from the embryonic structure called "the notochord". However, changes in the cells derived from the notochord which form the NP (i.e., notochordal cells [NCs]), in terms of their phenotype and functional identity from early developmental stages to skeletal maturation are less understood. These key issues require further investigation to better comprehend the role of NCs in homeostasis and degeneration as well as their potential for regeneration. Progress in utilizing NCs is currently hampered due to poor consistency and lack of consensus methodology for in vitro NC extraction, manipulation, and characterization.

Methods

Here, an international group has come together to provide key recommendations and methodologies for NC isolation within key species, numeration, in vitro manipulation and culture, and characterization.

Results

Recommeded protocols are provided for isolation and culture of NCs. Experimental testing provided recommended methodology for numeration of NCs. The issues of cryopreservation are demonstrated, and a pannel of immunohistochemical markers are provided to inform NC characterization.

Conclusions

Together we hope this article provides a road map for in vitro studies of NCs to support advances in research into NC physiology and their potential in regenerative therapies.

Dynamic integration of enteric neural stem cells in ex vivo organotypic colon cultures

Enteric neural stem cells (ENSC) have been identified as a possible treatment for enteric neuropathies. After in vivo transplantation, ENSC and their derivatives have been shown to engraft within colonic tissue, migrate and populate endogenous ganglia, and functionally integrate with the enteric nervous system. However, the mechanisms underlying the integration of donor ENSC, in recipient tissues, remain unclear. Therefore, we aimed to examine ENSC integration using an adapted ex vivo organotypic culture system. Donor ENSC were obtained from Wnt1^cre/+;R26R^YFP/YFP mice allowing specific labelling, selection and fate-mapping of cells. YFP⁺ neurospheres were transplanted to C57BL6/J (6–8-week-old) colonic tissue and maintained in organotypic culture for up to 21 days. We analysed and quantified donor cell integration within recipient tissues at 7, 14 and 21 days, along with assessing the structural and molecular consequences of ENSC integration. We found that organotypically cultured tissues were well preserved up to 21-days in ex vivo culture, which allowed for assessment of donor cell integration after transplantation. Donor ENSC-derived cells integrated across the colonic wall in a dynamic fashion, across a three-week period. Following transplantation, donor cells displayed two integrative patterns; longitudinal migration and medial invasion which allowed donor cells to populate colonic tissue. Moreover, significant remodelling of the intestinal ECM and musculature occurred upon transplantation, to facilitate donor cell integration within endogenous enteric ganglia. These results provide critical evidence on the timescale and mechanisms, which regulate donor ENSC integration, within recipient gut tissue, which are important considerations in the future clinical translation of stem cell therapies for enteric disease.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

A genome-wide assessment of the ancestral neural crest gene regulatory network

The neural crest (NC) is an embryonic cell population that contributes to key vertebrate-specific features including the craniofacial skeleton and peripheral nervous system. Here we examine the transcriptional and epigenomic profiles of NC cells in the sea lamprey, in order to gain insight into the ancestral state of the NC gene regulatory network (GRN). Transcriptome analyses identify clusters of co-regulated genes during NC specification and migration that show high conservation across vertebrates but also identify transcription factors (TFs) and cell-adhesion molecules not previously implicated in NC migration. ATAC-seq analysis uncovers an ensemble of cis-regulatory elements, including enhancers of Tfap2B, SoxE1 and Hox-α2 validated in the embryo. Cross-species deployment of lamprey elements identifies the deep conservation of lamprey SoxE1 enhancer activity, mediating homologous expression in jawed vertebrates. Our data provide insight into the core GRN elements conserved to the base of the vertebrates and expose others that are unique to lampreys.

The clinical significance of collagen family gene expression in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a subtype of esophageal cancer with high incidence and mortality. Due to the poor 5-year survival rates of patients with ESCC, exploring novel diagnostic markers for early ESCC is emergent. Collagen, the abundant constituent of extracellular matrix, plays a critical role in tumor growth and epithelial-mesenchymal transition. However, the clinical significance of collagen genes in ESCC has been rarely studied. In this work, we systematically analyzed the gene expression of whole collagen family in ESCC, aiming to search for ideal biomarkers.

METHODS

Clinical data and gene expression profiles of ESCC patients were collected from The Cancer Genome Atlas and the gene expression omnibus databases. Bioinformatics methods, including differential expression analysis, survival analysis, gene sets enrichment analysis (GSEA) and co-expression network analysis, were performed to investigate the correlation between the expression patterns of 44 collagen family genes and the development of ESCC.

RESULTS

A total of 22 genes of collagen family were identified as differentially expressed genes in both the two datasets. Among them, COL1A1, COL10A1 and COL11A1 were particularly up-regulated in ESCC tissues compared to normal controls, while COL4A4, COL6A5 and COL14A1 were notably down-regulated. Besides, patients with low COL6A5 expression or high COL18A1 expression showed poor survival. In addition, a 7-gene prediction model was established based on collagen gene expression to predict patient survival, which had better predictive accuracy than the tumor-node-metastasis staging based model. Finally, GSEA results suggested that collagen genes might be tightly associated with PI3K/Akt/mTOR pathway, p53 pathway, apoptosis, cell cycle, etc.

CONCLUSION

Several collagen genes could be potential diagnostic and prognostic biomarkers for ESCC. Moreover, a novel 7-gene prediction model is probably useful for predicting survival outcomes of ESCC patients. These findings may facilitate early detection of ESCC and help improves prognosis of the patients.

Collagen VI in healthy and diseased nervous system

Collagen VI is a major extracellular matrix protein exerting a number of functions in different tissues, spanning from biomechanical to regulatory signals in the cell survival processes, and playing key roles in maintaining the stemness or determining the differentiation of several types of cells. In the last couple of years, emerging findings on collagen VI have led to increased interest in its role in the nervous system. The role of this protein in the peripheral nervous system was intensely studied and characterized in detail. Collagen VI acts as a regulator of Schwann cell differentiation and is required for preserving peripheral nerve myelination, function and structure, as well as for orchestrating nerve regeneration after injury. Although the role and distribution of collagen VI in the peripheral nervous system is now well established, the role of this distinctive extracellular matrix component in the central nervous system, along with its links to human neurological and neurodegenerative disorders, remains an open field of investigation. In this Review, we summarize and discuss a number of recent findings related to collagen VI in the central and peripheral nervous systems. We further link these findings to different aspects of the protein that are relevant to human diseases in these compartments in order to provide a comprehensive overview of the roles of this key matrix component in the nervous system.

Commonality amid diversity: Multi-study proteomic identification of conserved disease mechanisms in spinal muscular atrophy

The neuromuscular disease spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality, resulting from low levels of full-length survival motor neuron (SMN) protein. Despite having a good understanding of the underlying genetics of SMA, the molecular pathways downstream of SMN that regulate disease pathogenesis remain unclear. The identification of molecular perturbations downstream of SMN is required in order to fully understand the fundamental biological role(s) for SMN in cells and tissues of the body, as well as to develop a range of therapeutic targets for developing novel treatments for SMA. Recent developments in proteomic screening technologies have facilitated proteome-wide investigations of a range of SMA models and tissues, generating novel insights into disease mechanisms by highlighting conserved changes in a range of molecular pathways. Comparative analysis of distinct proteomic datasets reveals conserved changes in pathways converging on GAP43, GAPDH, NCAM, UBA1, LMNA, ANXA2 and COL6A3. Proteomic studies therefore represent a leading tool with which to dissect the molecular mechanisms of disease pathogenesis in SMA, serving to identify potentially attractive targets for the development of novel therapies.

A collagen VI-dependent pathogenic mechanism for Hirschsprung's disease

Hirschsprung's disease (HSCR) is a severe congenital anomaly of the enteric nervous system (ENS) characterized by functional intestinal obstruction due to a lack of intrinsic innervation in the distal bowel. Distal innervation deficiency results from incomplete colonization of the bowel by enteric neural crest cells (eNCCs), the ENS precursors. Here, we report the generation of a mouse model for HSCR--named Holstein--that contains an untargeted transgenic insertion upstream of the collagen-6α4 (Col6a4) gene. This insertion induces eNCC-specific upregulation of Col6a4 expression that increases total collagen VI protein levels in the extracellular matrix (ECM) surrounding both the developing and the postnatal ENS. Increased collagen VI levels during development mainly result in slower migration of eNCCs. This appears to be due to the fact that collagen VI is a poor substratum for supporting eNCC migration and can even interfere with the migration-promoting effects of fibronectin. Importantly, for a majority of patients in a HSCR cohort, the myenteric ganglia from the ganglionated region are also specifically surrounded by abundant collagen VI microfibrils, an outcome accentuated by Down syndrome. Collectively, our data thus unveil a clinically relevant pathogenic mechanism for HSCR that involves cell-autonomous changes in ECM composition surrounding eNCCs. Moreover, as COL6A1 and COL6A2 are on human Chr.21q, this mechanism is highly relevant to the predisposition of patients with Down syndrome to HSCR.

Two novel COLVI long chains in zebrafish that are essential for muscle development

Collagen VI (COLVI), a protein ubiquitously expressed in connective tissues, is crucial for structural integrity, cellular adhesion, migration and survival. Six different genes are recognized in mammalians, encoding six COLVI-chains that assemble as two 'short' (α1, α2) and one 'long' chain (theoretically any one of α3-6). In humans, defects in the most widely expressed heterotrimer (α123), due to mutations in the COL6A1-3 genes, cause a heterogeneous group of neuromuscular disorders, collectively termed COLVI-related muscle disorders. Little is known about the function(s) of the recently described α4-6 chains and no mutations have been detected yet. In this study, we characterized two novel COLVI long chains in zebrafish that are most homologous to the mammalian α4 chain; therefore, we named the corresponding genes col6a4a and col6a4b. These orthologues represent ancestors of the mammalian Col6a4-6 genes. By in situ hybridization and RT-qPCR, we unveiled a distinctive expression kinetics for col6a4b, compared with the other col6a genes. Using morpholino antisense oligonucleotides targeting col6a4a, col6a4b and col6a2, we modelled partial and complete COLVI deficiency, respectively. All morphant embryos presented altered muscle structure and impaired motility. While apoptosis was not drastically increased, autophagy induction was defective in all morphants. Furthermore, motoneuron axon growth was abnormal in these morphants. Importantly, some phenotypical differences emerged between col6a4a and col6a4b morphants, suggesting only partial functional redundancy. Overall, our results further confirm the importance of COLVI in zebrafish muscle development and may provide important clues for potential human phenotypes associated with deficiency of the recently described COLVI-chains.

Overexpression of collagen VI α3 in gastric cancer

Collagen VI is significant in the progression of numerous types of cancer. Type VI collagen consists of three α-chains and collagen VI α3 (COL6A3) encodes the α3 chain. The overexpression of COL6A3 has been demonstrated to correlate with high-grade ovarian cancer and contributes to cisplatin resistance; however, its role in human gastric cancer (GC) remains unclear. Using microarray meta-analysis, COL6A3 was observed to be frequently overexpressed in the GC tissues, furthermore, this overexpression was identified in five GC cell lines. A microarray-based co-expression network analysis was conducted and identified a total of 62 genes that were co-expressed with COL6A3, with the majority of the genes being involved in cancer-related processes, such as cell differentiation, migration and adhesion. Network analysis of these 62 genes demonstrated that fibronectin 1, a well-characterized oncogene, was located at the center of the COL6A3 co-expression network. Therefore, COL6A3 may act as an oncogene in human GC and the antagonism of COL6A3 may be an effective therapeutic treatment for GC.

The collagen VI-related myopathies: muscle meets its matrix

The collagen VI-related myopathy known as Ullrich congenital muscular dystrophy is an early-onset disease that combines substantial muscle weakness with striking joint laxity and progressive contractures. Patients might learn to walk in early childhood; however, this ability is subsequently lost, concomitant with the development of frequent nocturnal respiratory failure. Patients with intermediate phenotypes of collagen VI-related myopathy display a lesser degree of weakness and a longer period of ambulation than do individuals with Ullrich congenital muscular dystrophy, and the spectrum of disease finally encompasses mild Bethlem myopathy, in which ambulation persists into adulthood. Dominant and recessive autosomal mutations in the three major collagen VI genes-COL6A1, COL6A2, and COL6A3-can underlie this entire clinical spectrum, and result in deficient or dysfunctional microfibrillar collagen VI in the extracellular matrix of muscle and other connective tissues, such as skin and tendons. The potential effects on muscle include progressive dystrophic changes, fibrosis and evidence for increased apoptosis, which potentially open avenues for pharmacological intervention. Optimized respiratory management, including noninvasive nocturnal ventilation together with careful orthopedic management, are the current mainstays of treatment and have already led to a considerable improvement in life expectancy for children with Ullrich congenital muscular dystrophy.

The collagen VI-related myopathies Ullrich congenital muscular dystrophy and Bethlem myopathy

Mutations in the genes COL6A1, COL6A2, and COL6A3, coding for three α chains of collagen type VI, underlie a spectrum of myopathies, ranging from the severe congenital muscular dystrophy-type Ullrich (UCMD) to the milder Bethlem myopathy (BM), with disease manifestations of intermediate severity in between. UCMD is characterized by early-onset weakness, associated with pronounced distal joint hyperlaxity and the early onset or early progression of more proximal contractures. In the most severe cases ambulation is not achieved, or it may be achieved only for a limited period of time. BM may be of early or later onset, but is milder in its manifestations, typically allowing for ambulation well into adulthood, whereas typical joint contractures are frequently prominent. A genetic spectrum is emerging, with BM being caused mostly by dominantly acting mutations, although rarely recessive inheritance of BM is also possible, whereas both dominantly as well as recessively acting mutations underlie UCMD.

Fluorescence-based assays for in vitro analysis of cell adhesion and migration

Cell adhesion and cell migration are two primary cellular phenomena for which in vitro approaches may be exploited to effectively dissect the individual events and underlying molecular mechanisms. The use of assays dedicated to the analysis of cell adhesion and migration in vitro also afford an efficient way of conducting larger basic and applied research screenings on the factors affecting these processes and are potentially exploitable in the context of routine diagnostic, prognostic, and predictive tests in the biological and medical fields. Therefore, there is a longstanding continuum in the interest in devising more rationale such assays and major contributions in this direction have been provided by the advent of procedures based on fluorescence cell tagging, the design of instruments capable of detecting fluorescent signals with high sensitivity, and informatic tools allowing sophisticated elaboration of data generated through these instruments. In this report, we describe three representative fluorescence-based model assays for the qualitative and quantitative assessment of cell adhesion and cell locomotion in static and dynamic conditions. The assays are easily performed, accurate and reproducible, and can be automated for high-to-medium throughput screenings of cell behavior in vitro. Performance of the assays involves the use of certain dedicated disposable accessories, which are commercially available, and a few instruments that, due to their versatility, can be regarded as constituents of a more generic laboratory setup.

Abnormalities in neural crest cell migration in laminin alpha5 mutant mice

Although numerous in vitro experiments suggest that extracellular matrix molecules like laminin can influence neural crest migration, little is known about their function in the embryo. Here, we show that laminin alpha5, a gene up-regulated during neural crest induction, is localized in regions of newly formed cranial and trunk neural folds and adjacent neural crest migratory pathways in a manner largely conserved between chick and mouse. In laminin alpha5 mutant mice, neural crest migratory streams appear expanded in width compared to wild type. Conversely, neural folds exposed to laminin alpha5 in vitro show a reduction by half in the number of migratory neural crest cells. During gangliogenesis, laminin alpha5 mutants exhibit defects in condensing cranial sensory and trunk sympathetic ganglia. However, ganglia apparently recover at later stages. These data suggest that the laminin alpha5 subunit functions as a cue that restricts neural crest cells, focusing their migratory pathways and condensation into ganglia. Thus, it is required for proper migration and timely differentiation of some neural crest populations.

MLL-mediated transcriptional gene regulation investigated by gene expression profiling

The human mixed lineage leukemia (MLL) gene is involved in about 50 different chromosomal translocations, associated with the disease phenotype of acute leukemia. However, the normal function of MLL is less understood. Homozygous knockouts of murine Mll were embryonal lethal, while heterozygous disruption led to aberrant hox gene expression associated with skeletal malformations, growth retardation, and impaired hematopoiesis. To understand MLL functions on the molecular level, gene expression profiling experiments were performed with a pair of murine cell lines (MLL(+/+) and MLL(-/-)). Microarray hybridization experiments revealed 197 potential target genes that are differentially expressed, providing new and important clues about MLL functions.

Mechanisms of transcriptional activation of the col6a1 gene during Schwann cell differentiation

A transgenic mouse line expressing the lacZ reporter under the control of a regulatory region of the col6a1 gene has been used to investigate differentiation of Schwann cells. The data suggest that: (1) activation of col6a1 gene transcription in the peripheral nervous system is part of the differentiation program of Schwann cells from neural crest cells stimulated by neuregulins; (2) once the Schwann cell precursors have acquired the competence of transcribing the col6a1 gene, transcriptional regulation becomes independent from neuregulins and is modulated by different mechanisms, including cell cycle; (3) activation of transgene expression after birth in sciatic nerves corresponds to the time of withdrawal of immature Schwann cells from the cell cycle and the beginning of their differentiation into myelinating Schwann cells.

A novel model to study the dorsolateral migration of melanoblasts

Melanocytes derived from pluripotent neural crest cells migrate initially in the dorsolateral pathway between the ectoderm and dermomyotome. To understand the role of specific proteins involved in this cell migration, we looked for a cellular model that mimics the in vivo behavior of melanoblasts, and that allows functional studies of their migration. We report here that wild-type embryonic stem (ES) cells are able to follow the ventral and dorsolateral neural crest pathways after being grafted into chicken embryos. By contrast, a mutant ES cell line deficient for beta1 integrin subunits, proteins involved in cell-extracellular interactions, had a severely impaired migratory behavior. Interestingly, ES cells deficient for Kit, the tyrosine kinase receptor for the stem cell factor (SCF), behaved similarly to wild-type ES cells. Thus, grafting mouse ES cells into chicken embryos provides a new cellular system that allows both in vitro and in vivo studies of the molecular mechanisms controlling dorsolateral migration.

Amyloid precursor-like protein 2 promotes cell migration toward fibronectin and collagen IV

Previous studies have established that in response to wounding, the expression of amyloid precursor-like protein 2 (APLP2) in the basal cells of migrating corneal epithelium is greatly up-regulated. To further our understanding of the functional significance of APLP2 in wound healing, we have measured the migratory response of transfected Chinese hamster ovary (CHO) cells expressing APLP2 isoforms to a variety of extracellular matrix components including laminin, collagen types I, IV, and VII, fibronectin, and heparan sulfate proteoglycans (HSPGs). CHO cells overexpressing either of two APLP2 variants, differing in chondroitin sulfate (CS) attachment, exhibit a marked increase in chemotaxis toward type IV collagen and fibronectin but not to laminin, collagen types I and VII, and HSPGs. Cells overexpressing APLP2-751 (CS-modified) exhibited a greater migratory response to fibronectin and type IV collagen than their non-CS-attached counterparts (APLP2-763), suggesting that CS modification enhanced APLP2 effects on cell migration. Moreover, in the presence of chondroitin sulfate, transfectants overexpressing APLP2-751 failed to exhibit this enhanced migration toward fibronectin. The APLP2-ECM interactions were also explored by solid phase adhesion assays. While overexpression of APLP2 isoforms moderately enhanced CHO adhesion to laminin, collagen types I and VII, and HSPGs lines, especially those overexpressing APLP2-751, exhibited greatly increased adhesion to type IV collagen and fibronectin. These observations suggest that APLP2 contributes to re-epithelialization during wound healing by supporting epithelial cell adhesion to fibronectin and collagen IV, thus influencing their capacity to migrate over the wound bed. Furthermore, APLP2 interactions with fibronectin and collagen IV appear to be potentiated by the addition of a CS chain to the core proteins.

Identification of domains responsible for von Willebrand factor type VI collagen interaction mediating platelet adhesion under high flow

We have identified type VI collagen (Col VI) as a primary subendothelial extracellular matrix component responsible for von Willebrand factor (vWF)-dependent platelet adhesion and aggregation under high tensile strength. Intact tetrameric Col VI was the form of the collagen found to be capable of promoting vWF-mediated platelet adhesion/aggregation under this shear condition, whereas removal of the predominant portion of the terminal globules by pepsin treatment abrogated its activity. The inability of the pepsin-digested Col VI to support any platelet interaction at high flow was because of the failure of the A3(vWF) domain to bind to this form of collagen, suggesting a stringent requirement of a tridimensional conformation or of intactness of its macromolecular structure. In contrast, the A1(vWF) domain bound to both intact and pepsin-digested Col VI tetramers but, in accordance with the cooperating function of the two vWF domains, failed to support platelet adhesion/aggregation under high shear onto Col VI by itself. The putative A1(vWF) binding site resided within the A7(VI) module (residues 413-613) of the globular amino-terminal portion of the alpha3(VI) chain. Soluble recombinant A7(VI) polypeptide strongly perturbed the vWF-mediated platelet adhesion to Col VI under high shear rates, without affecting the binding of the vWF platelet receptor glycoprotein Ibalpha to its cognate ligand A1(vWF). The findings provide evidence for a concerted action of the A1(vWF) and A3(vWF) domains in inducing platelet arrest on Col VI. This is accomplished via an interaction of the A1(vWF) domain with a site contained in the alpha3 chain A7(VI) domain and via a conformation-dependent interaction of the A3(vWF) domain with the intact tetrameric collagen. The data further emphasize that Col VI microfilaments linking the subendothelial basement membrane to the interstitial collagenous network may play a pivotal role in the hemostatic process triggered upon damage of the blood vessel wall.

Expression of type VI collagen in the developing mouse heart

During development, the embryonic atrioventricular (AV) endocardial cushions undergo a morphogenic process to form mature valve leaflets and the membranous septa in the heart. Several extracellular matrix (ECM) proteins are expressed in the developing AV endocardial cushions, but it remains to be established if any specific ECM proteins are necessary for normal cushion morphogenesis. Abnormal development of the cardiac AV valves is a frequent cause of congenital heart defects, particularly in infants with trisomy 21 (Down syndrome). The genes encoding the alpha1 and alpha2 chains of type VI collagen are located on human chromosome 21 within the region thought to be critical for congenital heart defects in trisomy 21 infants. This suggests that the type VI collagen alpha1(VI) and alpha2(VI) chains may be important in normal AV valve morphogenesis. As a first step in understanding the role of type VI collagen in valve development, the authors examined the normal spatial and temporal expression patterns of mRNA and protein for type VI collagen in the embryonic mouse heart. Ribonuclease protection assay analysis demonstrates cardiac expression of the type VI collagen for alpha1(VI), alpha2(VI), and alpha3(VI) transcripts beginning at embryonic days 11-11.5 of mouse development. In situ hybridization studies demonstrate a coordinated pattern of cardiac expression within the AV valves for each type VI collagen chain from embryonic day 11.5 through the neonatal period. Immunohistochemical studies confirm a concentrated type VI collagen localization pattern in the endocardial cushions from the earliest stages of valve development through the neonatal period. These data indicate that type VI collagen is expressed in the developing AV canal in a pattern consistent with cushion tissue mesenchymal cell migration and proliferation, and suggest that type VI collagen plays a role in the morphogenesis of the developing cardiac AV endocardial cushions into the valve leaflets and membranous septa of the heart.

Role of the extracellular matrix in neural crest cell migration

Development of the neural crest involves a remarkable feat of coordinated cell migration in which cells detach from the neural tube, take varying routes of migration through the embryonic tissues and then differentiate at the end of their journey to participate in the formation of a number of organ systems. In general, neural crest cells appear to migrate without the guidance of long-range physical or chemical cues, but rather they respond to heterogeneity in the extracellular matrix that forms their migration substrate. Molecules such as fibronectin and laminin act as permissive substrate components, encouraging neural crest cell attachment and spreading, whereas chondroitin sulphate proteoglycans are nonpermissive for migration. A balance between permissive and nonpermissive substrate components seems to be necessary to ensure successful migration, as indicated by a number of studies in mouse mutant systems where nonpermissive molecules are over-expressed, leading to inhibition of neural crest migration. The neural crest expresses cell surface receptors that permit interaction with the extracellular matrix and may also modify the matrix by secretion of proteases. Thus the principles that govern the complex migration of neural crest cells are beginning to emerge.

A central segment of the NG2 proteoglycan is critical for the ability of glioma cells to bind and migrate toward type VI collagen

Previous studies have established that the NG2 proteoglycan binds directly to type VI collagen. To further our understanding of the biochemical and functional significance of this interaction we have used NG2 cDNA to construct a series of NG2 mutants with deletions spaced throughout the entire length of the 260-kDa NG2 core protein. Following transfection of these mutant cDNAs into B28 glioma cells, we determined the ability of mutant NG2 molecules to anchor type VI collagen on the cell surface. Eight of 11 transfectant populations were able to anchor type VI collagen. The three NG2 variants incapable of anchoring type VI collagen have deletions clustered within the central one-third of the NG2 ectodomain. These deletions identify a 469-amino-acid domain of NG2 responsible for binding of type VI collagen. Functional consequences of the NG2-type VI collagen interaction were explored by testing the relative ability of NG2-transfected and untransfected glioma cells to migrate toward type VI collagen. NG2-expressing cells exhibited a greater migratory response toward type VI collagen than their NG2-negative counterparts. This enhanced migration could be specifically inhibited with NG2 antibodies. Furthermore, glioma cells expressing NG2 in which the collagen-binding domain was deleted failed to exhibit this enhanced migration, whereas NG2 mutants in which non-collagen-binding regions were deleted continued to exhibit increased chemotaxis toward the type VI collagen. These comparisons confirm the importance of the central collagen-binding domain in mediating functionally important interactions between NG2 and type VI collagen.

Microfibrillar elements of the dermal matrix

Connective tissue microfibrils are key structural elements of the dermal matrix which play major roles in establishing and maintaining the structural and mechanical integrity of this complex tissue. Type VI collagen microfibrils form extensive microfibrillar networks which intercalate between the major collagen fibrils and are juxtaposed to cellular basement membranes, blood vessels and other interstitial structures. Fibrillin microfibrils define the continuous elastic network of skin, and are present in dermis as microfibril bundles devoid of measureable elastin extending from the dermal-epithelial junction and as components of the thick elastic fibres present in the deep reticular dermis. Electron microscopic analyses have revealed both classes of microfibrils to have complex ultrastructures. The ability to isolate intact native microfibrils from skin has enabled a combination of high resolution and biochemical techniques to be applied to elucidate their structure:function relationships. These approaches have generated new information about their molecular organisation and physiological interactions in health and disease.

Effects of extracellular matrix molecules on subepidermal neural crest cell migration in wild type and white mutant (dd) axolotl embryos

Migration of neural crest (NC) derived pigment cells is restricted in the white mutant (dd) axolotl embryo (Ambystoma mexicanum). Transplantations between mutant and wild type embryos show that the extracellular matrix (ECM) of the white mutant is unable to support the migration of prospective pigment cells in wild type embryos (Löfberg et al., 1989, Dev. Biol. 131:168-181). In the present study, we test the effects of various purified ECM molecules on NC cell migration in the subepidermal migratory pathway of wild type (D/-) and white mutant (dd) axolotl embryos. We adsorbed the ECM molecules onto membrane microcarriers, which were then implanted under the epidermis. Fibronectin (FN), tenascin (TN), collagens I and VI, and a chick aggrecan stimulated migration in both types of embryos. Laminin-nidogen, rat chondrosarcoma aggrecan, and shark aggrecan stimulated migration in dd embryos but did not affect migration in D/- embryos. Collagen III, fibromodulin and bovine aggrecan had no effect on migration in either type of embryo. NC cells did not migrate on control microcarriers, which lacked ECM molecules. Some cells observed contacting, and presumably migrating on, coated microcarriers could be identified as pigment cells by their ultrastructure. Enzymatic digestion in vivo with chondroitinase ABC had no effect on NC cell migration. The neutral or stimulatory effect of the aggrecans is surprising; when tested in vitro they inhibited NC cell migration. The effect of three-dimensionality and other molecules present either in the embryonic ECM or in solution may overcome the inhibitory effect of aggrecans.

Expression of type VI collagen during glioblastoma cell invasion in brain tissue cultures

Human glioblastoma cells, U-87 MG, were utilized in two separate rat brain tissue culture systems. In both cases, the glioblastoma cells deeply penetrated and formed tumor masses inside the brain tissues. Immunofluorescence technique, utilizing anti-type VI collagen antibodies demonstrated strong immunoreactivity of type VI collagen in the tumor masses, invading cells, and cell groups. We suggest that type VI collagen may be involved in tumor cells infiltration and invasion of healthy rat brain tissues. Furthermore, the brain tissue culture method may provide a rapid in vitro model with which cellular and extracellular determinants of invasiveness may be studied.

Biosynthesis of type VI collagen by glioblastoma cells and possible function in cell invasion of three-dimensional matrices

The biosynthesis of type VI collagen was studied in human glioblastoma cell line, U-87 MG. The effects of ascorbic acid on type VI collagen synthesis and secretion were investigated. After ascorbic acid treatment, type VI collagen in cell layers increased from 4.48% in control to 6.63% in the ascorbic acid treated cultures, an increase of 48%. The effect of ascorbic acid on type VI collagen synthesized by glioblastoma cells was lower than that reported for osteosarcoma cells (Engvall et al., 1986). The reason for these differences is still under investigation. The function of type VI collagen in glioblastoma cells is still unknown. We utilized the collagen gel system to elucidate the possible roles of type VI collagen in glioblastoma cells in vitro. Glioblastoma cells in collagen gels showed a stellate shape with long, branched processes in all directions. The strong positive reactivity of type VI collagen detected on cell bodies and cell processes by anti-type VI collagen antibody indicated that this specific collagen was associated with cell surfaces and processes, without releasing or diffusing into the gels. Type VI collagen was directly involved in the cell process extension. When living cells were treated with anti-type VI collagen antibody, a variation of cell morphology was observed. Instead of a stellate shape with processes, cells formed clusters without or with very short processes. These data suggest that type VI collagen, synthesized and secreted by glioblastoma cells, may play a role in tumor cell adhesion and spreading, and enhance cell process extension, penetration, and invasion into collagen gels.