Differentiation requires continuous regulation

Stem cells and diabetes

Diabetes mellitus is a metabolic disorder affecting 2-5% of the population. Transplantation of isolated islets of Langerhans from donor pancreata could be a cure for diabetes; however, such an approach is limited by the scarcity of the transplantation material and the long-term side effects of immunosuppressive therapy. These problems may be overcome by using a renewable source of cells, such as islet cells derived from stem cells. Stem cells are defined as clonogenic cells capable of both self-renewal and multilineage differentiation. This mean that these cells can be expanded in vivo or in vitro and differentiated to produce the desired cell type. There exist several sources of stem cells that have been demonstrated to give rise to pluripotent cell lines: 1) embryonic stem cells; 2) embryonic germ cells; 3) embryonic carcinoma cells; and 4) adult stem cells. By using in vitro differentiation and selection protocols, embryonic stem cells can be guided into specific cell lineages and selected by applying genetic selection when a marker gene is expressed. Recently, differentiation and cell selection protocols have been used to generate embryonic stem cell-derived insulin-secreting cells that normalise blood glucose when transplanted into diabetic animals. Some recent reports suggest that functional plasticity of adult stem cells may be greater than expected. The use of adult stem cells will circumvent the ethical dilemma surrounding embryonic stem cells and will allow autotransplantation. These investigations have increased the expectations that cell therapy could be one of the solutions to diabetes.

From marrow to brain: expression of neuronal phenotypes in adult mice

After intravascular delivery of genetically marked adult mouse bone marrow into lethally irradiated normal adult hosts, donor-derived cells expressing neuronal proteins (neuronal phenotypes) developed in the central nervous system. Flow cytometry revealed a population of donor-derived cells in the brain with characteristics distinct from bone marrow. Confocal microscopy of individual cells showed that hundreds of marrow-derived cells in brain sections expressed gene products typical of neurons (NeuN, 200-kilodalton neurofilament, and class III beta-tubulin) and were able to activate the transcription factor cAMP response element-binding protein (CREB). The generation of neuronal phenotypes in the adult brain 1 to 6 months after an adult bone marrow transplant demonstrates a remarkable plasticity of adult tissues with potential clinical applications.

Cystic fibrosis revisited

Cystic fibrosis is a pleiotropic disease whose primary defect is thought to be abnormal chloride conductance. Despite intensive study, the role of the protein in the airway and the mechanism for its direct participation in the disease pathology remain unclear. This paper reviews CFTR's cell regulatory functions and data supporting the role of CFTR in secretory epithelial cell development. A hypothesis for CF pathophysiology based on secretory cell differentiation is proposed.

Diversification of haematopoietic stem cells to specific lineages

Diverse types of blood cell (lineages) are produced from rare haematopoietic stem cells that reside in the bone marrow. This process, known as haematopoiesis, provides a valuable model for examining how genetic programs are established and executed in vertebrates, and also how homeostasis of blood formation is altered in leukaemias. So, how does an apparently small group of critical lineage-restricted nuclear regulatory factors specify the diversity of haematopoietic cells? Recent findings not only indicate how this may be achieved but also show the extraordinary plasticity of tissue stem cells in vivo.

Ceramide mimics tumour necrosis factor-alpha in the induction of cell cycle arrest in endothelial cells. Induction of the tumour suppressor p53 with decrease in retinoblastoma/protein levels

Tumour necrosis factor (TNF)-alpha induces a transient increase in N-octanoylsphingosine (C8-ceramide) which has been postulated as an intracellular mediator in TNF-alpha signalling. We tested the ability of C8-ceramide to reproduce the TNF-alpha-mediated interference with endothelial cell proliferation and DNA synthesis. TNF-alpha (10 ng.mL-1) and C8-ceramide (20 microM) inhibited the incorporation of [3H]thymidine into DNA and led to an accumulation of cells in the G1 phase of the cell cycle. When the responses of the tumour suppressors p53 and RB were analysed, it was found that TNF-alpha and C8-ceramide induced increased expression of p53. Treatment with TNF-alpha or C8-ceramide lead to a significant decrease in total retinoblastoma protein (RB) content that correlated with high levels of p53. These results suggest that p53 and RB may complement each other in their contribution to cell cycle arrest. TNF-alpha prevented RB phosphorylation whereas C8-ceramide did not interfere with this process, suggesting that it follows a ceramide-independent pathway.

Reprogramming nuclei: insights from cloning, nuclear transfer and heterokaryons

Mammals and amphibians can be cloned following the transfer of embryonic nuclei into enucleated eggs or oocytes. As nuclear functions become more specialized in the differentiated cells of an adult, successful cloning using these nuclei as donors becomes more difficult. Differentiation involves the assembly of specialized forms of repressive chromatin including linker histones, Polycomb group proteins and methyl-CpG-binding proteins. These structures compartmentalize chromatin into functional domains and maintain the stability of the differentiated state through successive cell divisions. Efficient cloning requires the erasure of these structures. The erasure can be accomplished through use of molecular chaperones and enzymatic activities present in the oocyte, egg or zygote. We discuss the mechanisms involved in reprogramming nuclei after nuclear transfer and compare them with those that occur during remodeling of somatic nuclei after heterokaryon formation. Finally we discuss how one might alter the properties of adult nuclei to improve the efficiency of cloning.

The myoepithelial immunophenotype in 135 benign and malignant salivary gland tumors other than pleomorphic adenoma

BACKGROUND

We have previously studied the immunoreactivity of 3 novel smooth muscle-specific proteins, alpha-smooth muscle actin, smooth muscle myosin heavy chains, and calponin, to assess myoepithelial differentiation in pleomorphic adenomas.

OBJECTIVE

To further expand our knowledge of myoepithelial differentiation in other benign and malignant salivary gland tumors.

DESIGN

Formalin-fixed paraffin sections of 135 salivary gland tumors with associated normal glands were stained with monoclonal antibodies using the avidin-biotin complex immunoperoxidase method and enzymatic and microwave heat-induced epitope retrieval.

RESULTS

In adenoid cystic carcinomas and epithelial-myoepithelial carcinomas, all 3 markers exclusively highlighted the myoepithelial cell components and the epithelial cells were entirely negative. No immunostaining was detected in canalicular adenomas, oncocytomas, Warthin tumors, acinic cell carcinomas, mucoepidermoid carcinomas, squamous cell carcinomas, and polymorphous low-grade adenocarcinomas. Salivary duct carcinomas and adenocarcinomas, not otherwise specified had a distinctive pattern of uniform periductal staining of reactive myofibroblastic cells, and in salivary duct carcinomas some ducts retained a peripheral immunoreactive myoepithelial cell layer.

CONCLUSION

Immunoreactivity for these 3 smooth muscle-specific proteins confirms the known neoplastic myoepithelial component of adenoid cystic carcinomas and epithelial-myoepithelial carcinomas. The consistently positive staining pattern in adenoid cystic carcinomas may be diagnostically useful in discriminating histologically similar but consistently negative polymorphous low-grade adenocarcinomas. Periductal linear staining in adenocarcinoma, not otherwise specified and salivary duct carcinomas is distinctive and appears to represent a tight cuff of myofibroblasts associated with the infiltrating glands.

Hereditary stability and variation in evolution and development

Evolution and development are both lineage processes but are often conceptualized as occurring by different and mutually exclusive mechanisms. It is conventionally asserted that evolution occurs via the random generation of diversity and the subsequent survival of those that pass selection. On the other hand, development is too often presented as proceeding via the unfolding of a deterministic program encoded in the DNA sequence. In biology, universal generalizations are rare and dogmas are often wrong for particular cases. Deterministic mechanisms contribute some of the new DNA sequences that subsequently become substrates for natural selection. Conversely, stochastic and selective mechanisms are intrinsic to development, and also to maintenance of the immune, and possibly, nervous systems. Cancer appears to be another process that straddles distinctions between evolutionary and developmental modes of hereditary change and stabilization. DNA sequence changes are an essential feature of many cancers, but there are also aspects of the disease similar to developmental lineage gone awry. The literature suggests that the cellular changes that give rise to cancer occur by mechanisms commonly associated with both evolutionary and developmental lineage pathways.

Induction of apoptosis in rat hepatic stellate cells by disruption of integrin-mediated cell adhesion

Cell-matrix adhesion is recognized as a physiologic determinant of cell growth and survival. Integrin occupancy seems to be a primary role. We sought to investigate the signal transduction pathways for integrin effects on cell survival in hepatic stellate cells. Integrin function was antagonized by the soluble integrin recognition sequence pentapeptide Gly-Arg-Gly-Asp-Ser (GRGDS) in primary cultures of rat hepatic stellate cells. Integrin antagonism with GRGDS peptide induced apoptosis. To investigate signal transduction mechanisms for the effect of integrins on cell survival in hepatic stellate cells, the expression of p53, Bcl-2, and Bax was analyzed. Incubation with soluble GRGDS peptide resulted in increased expression of p53 and decreased the Bcl-2/Bax ratio. In conclusion, these findings indicate that the abrogation of cell adhesion with soluble GRGDS peptide plays a critical role in the induction of apoptosis of rat hepatic stellate cells.

Poly(ADP-ribose) polymerase binds with transcription enhancer factor 1 to MCAT1 elements to regulate muscle-specific transcription

Striated muscle-specific expression of the cardiac troponin T (cTNT) gene is mediated through two MCAT elements that act via binding of transcription enhancer factor 1 (TEF-1) to the MCAT core motifs and binding of an auxiliary protein to nucleotides flanking the 5' side of the core motif. Using DNA-protein and protein-protein binding experiments, we identified a 140-kDa polypeptide that bound both the muscle-specific flanking sequences of the most distal MCAT1 element and TEF-1. Screening of an expression library with the MCAT1 element yielded a cDNA encoding a truncated form of poly(ADP-ribose) polymerase (PARP). Endogenous PARP from embryonic tissue nuclear extracts migrated as a 140-kDa protein. Recombinant full-length PARP preferentially bound the wild-type MCAT1 element and was shown to physically interact with TEF-1. In addition, endogenous TEF-1 could be coimmunoprecipitated with PARP from extracts of primary skeletal muscle cells. Recombinant PARP was able to ADP-ribosylate TEF-1 in vitro. Inhibition of the enzymatic activity of PARP repressed expression of an MCAT1-dependent reporter in transiently transfected primary muscle cells. Together, these data implicate PARP as the auxiliary protein that binds with TEF-1 to the MCAT1 element to provide muscle-specific gene transcription.

Developmental biology of the vascular smooth muscle cell: building a multilayered vessel wall

The assembly of the vessel wall from its cellular and extracellular matrix components is a critical process in the development and maturation of the cardiovascular system. However, fundamental questions concerning the origin of vessel wall cells and the mechanisms that regulate their development and differentiation remain unanswered. The initial step of vessel wall morphogenesis is formation of a primary vascular network, comprised of nascent endothelial cell tubes, via the processes of vasculogenesis and angiogenesis. Subsequently, primordial vascular smooth muscle cells (VSMCs) are recruited to the endothelium to form a multilayered vessel wall. During the course of development and maturation, the VSMC plays diverse roles: it is a biosynthetic, proliferative, and contractile component of the vessel wall. Although the field of vascular development has blossomed in the past decade, the molecules and mechanisms that regulate this developmental pathway are not well defined. The focus of this review is on those facets of VSMC development important for transforming a nascent endothelial tube into a multilayered structure. We discuss the primordial VSMC with particular attention to its purported origins, the components of the extracellular milieu that contribute to its development, and the contribution of embryonic hemodynamics to vessel wall assembly.

Highly conserved RNA sequences that are sensors of environmental stress

The putative function of highly conserved regions (HCRs) within 3' untranslated regions (3'UTRs) as regulatory RNA sequences was efficiently and quantitatively assessed by using modular retroviral vectors. This strategy led to the identification of HCRs that alter gene expression in response to oxidative or mitogenic stress. Databases were screened for UTR sequences of >100 nucleotides that had retained 70% identity over more than 300 million years of evolution. The effects of 10 such HCRs on a standard reporter mRNA or protein were studied. To this end, we developed a modular retroviral vector that can allow for a direct comparison of the effects of different HCRs on gene expression independent of their gene-intrinsic 5'UTR, promoter, protein coding region, or poly(A) sequence. Five of the HCRs tested decreased mRNA steady-state levels 2- to 10-fold relative to controls, presumably by altering mRNA stability. One HCR increased translation, and one decreased translation. Elevated mitogen levels caused four HCRs to increase protein levels twofold. One HCR increased protein levels fourfold in response to hypoxia. Although nonconserved UTR sequences may also have a role, these results provide evidence that sequences that are highly conserved during evolution are good candidates for RNA motifs with posttranscriptional regulatory functions in gene expression.

Tetracycline-regulatable factors with distinct dimerization domains allow reversible growth inhibition by p16

Continuous regulation is required to maintain a given cell state or to allow it to change in response to the environment. Studies of the mechanisms underlying such regulation have often been hindered by the inability to control gene expression at will. Among the inducible systems available for regulating gene expression in eukaryotes, the tetracycline (tet) regulatable system has distinct advantages. It is highly specific, non-toxic and non-eukaryotic, and consequently does not have pleiotropic effects on host cell genes. Previously this system also had drawbacks, as it did not extinguish gene expression completely, precluding the study of toxic or growth-inhibitory gene products. We report here the development of a facile reversible tetracycline-inducible retroviral system (designated RetroTet-ART) in which activators and repressors together are expressed in cells. Gene expression can now be actively repressed in the absence of tet and induced in the presence of tet, as we have engineered distinct dimerization domains that allow co-expression of homodimeric tet-regulated transactivators and transrepressors in the same cells, without the formation of non-functional heterodimers. Using this system, we show that growth arrest by the cell cycle inhibitor p16 is reversible and dependent on its continuous expression.

Modification of development by the CFTR gene in utero

The in utero infection of rats at 16-17 days gestation with a recombinant adenovirus carrying the human cystic fibrosis transmembrane conductance regulator (cftr) gene resulted in altered lung development and morphology. These structural alterations prompted an evaluation of concurrent functional changes in the cftr-treated lung. CFTR protein could be detected in treated lungs for up to 30 days postinfection, although it was not detected in the intestines at this time. Increased levels of secreted glycoconjugates and lipids were found in lungs treated in utero with human cftr and large vacuoles containing glycoconjugates were detected within cells of the intestines. The scope and durability of these changes suggested that in utero cftr treatment influenced the activity of secretory cells in the developing lung. Altered secretory products in the lungs of cystic fibrosis patients are thought to be associated with increased susceptibility to Pseudomonas aeruginosa infection. We challenged 3-month-old rats (treated in utero with the human cftr gene) with a lethal, intratrachial dose of this bacteria. Rats treated with cftr exhibited enhanced resistance to Pseudomonas infection when compared to controls. These animals displayed little or no associated inflammatory response. No evidence of the adenovirus transgene was detectable at the time of P. aeruginosa inoculation, indicating that continuous ectopic expression of hcftr was not required for enhanced protection. These data demonstrate that in utero, cftr expression influenced the development and function of cells involved in the primary host defense against bacterial infection in the lung.

Identification of transcription factors expressed during ATRA-induced neutrophil differentiation of HL60 cells

A recent clinical therapeutic initiative has been the use of chemical agents which induce the leukaemic cells to overcome their block in differentiation. In order to understand this block the cascade of molecular events needs to be characterized. Haemopoietic differentiation is ultimately controlled at the level of gene transcription which is mediated by an array of transcription factors. Many transcription factors contain similar structural protein sequences, and we have used an RT-PCR-based approach to isolate sequences, from transcription factor gene families which share similar domains. Degenerate primers corresponding to the TFIIIA zinc-finger consensus amino acid sequences and to the POU-homeodomain and POU-specific domain were used to amplify genes on the basis that they contained similarities in structural motifs shared within these families of transcription factors. A serum-independent HL60 cell line was induced towards the neutrophil lineage by treatment with all-trans retinoic acid (ATRA) for 24 h. CD38+ cells committed towards this lineage were enriched and a population of these cells treated with dihydroxyvitamin D3 to induce neutrophil maturation. RNA extracted from uninduced, ATRA-induced CD38+ cells, and vitamin D3 treated maturing cell cultures were amplified using the degenerate primers. PCR fragments were cloned, sequenced, clustered into homologous groups, and the group sequences searched on the GenBank database. The Oct 1 transcription factor, and a very close homologue, KIAA0144, was identified using the POU family primers. The zinc-finger primers identified three zinc-finger genes. The pattern of gene expression was suggested from the number of clones in each group at neutrophil commitment and maturation. The differential expression of the genes in the zinc finger and POU families will lead to a better understanding of the cascade of gene expression which occurs following ATRA-induced differentiation.

Collagen gel overlay induces apoptosis of polarized cells in cultures: disoriented cell death

In this study, we attempted to investigate the response of polarized cells to inappropriate interaction with the extracellular matrix. Cell lines of epithelial [Madin-Darby canine kidney (MDCK) and LLC-PK1], endothelial [bovine aortic endothelial cells (BAEC)], and mesenchymal (ESK-4 and NIH/3T3) origins were employed. With collagen gel overlay, MDCK cells underwent membrane remodeling and gradually developed lumen formation within 24 h. Apoptosis could also be observed following cell remodeling. The ratio of apoptosis was enhanced from 12.1 +/- 2.4% within 24 h to 58.4 +/- 9.8% at day 3, and finally the monolayer was disintegrated. Collagen gel overlay-induced apoptosis was not a result of physical stress, since agarose gel overlay did not induce any morphological alterations. All epithelial and endothelial cells examined developed apoptosis in response to collagen overlay. In contrast, collagen overlay did not affect growth of fibroblasts at all, although their growth under agarose gel was slightly hindered due to physical stress. Collagen overlay-induced apoptosis seems to be a unique phenomenon for polarized cells and thus is defined as "disoriented cell death." Furthermore, anti-alpha2-integrin antibody could abolish collagen overlay-induced morphological changes and apoptosis in MDCK cells, indicating that signals through alpha2-integrin on the apical membrane are required for disoriented cell death. Finally, Bcl-2 overexpression prolonged survival of MDCK cells in response to collagen overlay, but these cells eventually developed apoptosis due to downregulation of Bcl-2 protein. These findings indicate that inappropriate cell-matrix interaction results in apoptosis, which may account for cell death mechanisms during developmental processes or under pathological conditions.

Immunohistochemical study of proliferating mesenchymal spindle cells in heterogenous soft tissue lesions

Proliferation of mesenchymal spindle cells is a main event in a variety of lesions with similar morphological features but widely divergent biological behaviour. In order to identify criteria for precise histological diagnosis, 60 human soft tissue lesions, divided into 40 cases of fibroblastic cell proliferation, 10 smooth muscle cell tumours and 10 nerve sheath cell tumours, were examined for the immunohistochemical profile of the main lesional cell in addition to other histological features. The three groups could be differentiated by determining the lineage of the constituent spindle cell on the pattern of expression of vimentin, alpha-smooth muscle actin (ASMA) and macrophage antigen CD68 (MA-CD68). Smooth muscle cells expressed ASMA and vimentin but not MA-CD68, while nerve sheath cells were negative for ASMA but positive for vimentin and MA-CD68. The fibroblastic cell lesions as a group were easily differentiated on the basis of positive reactivity for all three markers but individual lesions could only be distinguished by additional assessment of histological features. Because of consistent co-expression of ASMA, vimentin and MA-CD68 in the spindle mesenchymal cell present in all varieties of lesions in this heterogeneous group, we suggest that this proliferating "fibroblastic" cell is phenotypically a fibromyohistiocyte.

Disruption of genes regulated during hematopoietic differentiation of mouse embryonic stem cells

A retroviral gene trap vector (U3Tkneo) that selects for integrations in or near expressed 5' exons has been used to identify genes that are repressed during hematopoietic differentiation of mouse totipotent embryonic stem cells. The vector contains coding sequences for an HSV-thymidine kinase/neomycin phosphotransferase fusion protein in the U3 region of a Moloney murine leukemia virus LTR and allows selection for (G418) and against (Ganciclovir; GC) U3 gene expression. A total of 208 neomycin-resistant clones were isolated following infection with U3tkneo and screened for integrations into regulated genes by using a two-step, semisolid culture system that supports hematopoietic differentiation. Two clones contained U3Tkneo integrations in genes that were repressed selectively in hematopoietic cells. Analysis of upstream proviral flanking sequences indicated that both integrations occurred into unknown genes. One up-stream sequence identified a cellular transcript that was expressed differentially in the kidneys and liver of adult mice. When this fusion gene was passaged to the germ line, homozygous offspring with nearly null mutations were obtained. However, mutant mice were normal, suggesting that potential loss of function phenotypes are subtle and may be restricted to the kidneys and the liver.

Molecular pathophysiology of cystic fibrosis based on the rescued knockout mouse model

Cystic fibrosis transmembrane conductance regulator (cftr) gene mutations are thought to result in cystic fibrosis due to an absence of the protein's chloride channel. Recently, the lethal intestinal blockage in the cftr knockout mouse was reversed by a single in utero dose of a recombinant adenovirus containing the human cftr gene. The rescue of these animals did not require continuous expression of the gene and the cAMP-dependent chloride channel was not permanently restored. These data suggested that cftr was required for normal development of the intestine but not for normal function of the adult organ. Phenotypic changes in the intestines and lungs of in utero cftr-treated knockout and heterozygous mice revealed that altered development was induced. The intestines of the untreated knockout mice were shown to be deficient in both intracellular calcium and UTP receptors. Both of these deficiencies were partially corrected in the rescued knockout mice, whereas treatment of heterozygous animals disrupted the normal pattern of these markers. Examination of the lungs of knockout cftr (-/-) mice with lectins showed an increase in secreted glycoconjugates containing alpha(2,6)-sialic acid and fucose as compared with control heterozygotes. The in utero-treated knockouts showed an increase in this material as well, but it was contained in intracellular vesicles. Electron microscopy of these tissues confirmed the developmental alteration of secretory cell differentiation in the lungs. These data show that cftr is required in both the lung and intestines for normal differentiation of a secretory cell population and that in its absence these cells fail to develop properly.

Type VI collagen increases cell survival and prevents anti-beta 1 integrin-mediated apoptosis

Cell-matrix interactions are important in the development of the avian cornea. Type VI collagen is present within the periocular mesenchyme prior to the migration of cells into the corneal stroma and is abundant in the mature stroma. Whether the interaction of cells with type VI collagen is essential for cellular survival in the cornea is not known. In the present study, we examined the interaction of corneal cells with type VI collagen in vitro to determine if it can increase cell proliferation and decrease apoptosis. In vivo analysis demonstrated that apoptosis occurs in the periocular region during early stages of avian corneal development, but in fully mature corneas apoptosis only occurs in the corneal epithelium and not in the stroma. In vitro analysis examined the importance of beta 1 integrin interactions with type VI collagen in mature corneal fibroblasts and the precursor cells. Using an anti-beta 1 integrin blocking antibody, CSAT, integrin/matrix interactions were disrupted. Results indicated that viability of both corneal fibroblasts and periocular mesenchyme cells was greater on type VI collagen than on type I collagen or BSA-blocked glass. In addition, less apoptosis was observed for both cell types on type VI collagen when beta 1 integrin--matrix interactions were disrupted. These data indicated that these cells require intact beta 1 interactions with type I collagen and with BSA-coated glass controls to remain viable. Thus, type VI collagen may play a role in the rescue of corneal cells from anti-beta 1 integrin-induced apoptosis by increasing cell survival, probably via a non-beta 1 integrin-dependent mechanism.

PDGF, TGF-beta, and heterotypic cell-cell interactions mediate endothelial cell-induced recruitment of 10T1/2 cells and their differentiation to a smooth muscle fate

We aimed to determine if and how endothelial cells (EC) recruit precursors of smooth muscle cells and pericytes and induce their differentiation during vessel formation. Multipotent embryonic 10T1/2 cells were used as presumptive mural cell precursors. In an under-agarose coculture, EC induced migration of 10T1/2 cells via platelet-derived growth factor BB. 10T1/2 cells in coculture with EC changed from polygonal to spindle-shaped, reminiscent of smooth muscle cells in culture. Immunohistochemical and Western blot analyses were used to examine the expression of smooth muscle (SM)-specific markers in 10T1/2 cells cultured in the absence and presence of EC. SM-myosin, SM22alpha, and calponin proteins were undetectable in 10T1/2 cells cultured alone; however, expression of all three SM-specific proteins was significantly induced in 10T1/2 cells cocultured with EC. Treatment of 10T1/2 cells with TGF-beta induced phenotypic changes and changes in SM markers similar to those seen in the cocultures. Neutralization of TGF-beta in the cocultures blocked expression of the SM markers and the shape change. To assess the ability of 10T1/2 cells to contribute to the developing vessel wall in vivo, prelabeled 10T1/2 cells were grown in a collagen matrix and implanted subcutaneously into mice. The fluorescently marked cells became incorporated into the medial layer of developing vessels where they expressed SM markers. These in vitro and in vivo observations shed light on the cell-cell interactions that occur during vessel development, as well as in pathologies in which developmental processes are recapitulated.

Developmental and hormonal regulation of keratinocyte growth factor expression and action in the ovarian follicle

The developing ovarian follicle is one of the most rapidly proliferating normal tissues in vivo. Mesenchymal-epithelial cell interactions between theca cells and granulosa cells are essential for this follicular expansion. Ovarian hormones (i.e. estrogen and LH) may promote follicular development by regulating the local production of mesenchymal inducer proteins that mediate theca cell-granulosa cell interactions. Recently, theca cells were shown to produce keratinocyte growth factor (KGF) that can act in a paracrine manner to stimulate granulosa cell growth. In this study, the developmental and hormonal regulation of KGF was examined during follicular development in the bovine ovary. Expression of KGF in theca cells and the KGF receptor (KGFR, or splice variant of the fibroblast growth factor family receptor family, FGFR-2) in granulosa cells was examined using RT-PCR. Both KGF and KGFR were detected throughout follicular development in small (<5 mm), medium (5-10 mm), and large (>10 mm) follicles. Quantitative RT-PCR assays were used to determine steady-state levels of KGF and KGFR messenger RNAs. Developmental regulation of KGF and KGFR was analyzed in freshly isolated theca cells and granulosa cells from small, medium, and large follicles. Observations demonstrated that expression of KGF (in theca cells) and KGFR (in granulosa cells) was highest in large follicles. These results suggest that KGF actions are important for the rapid proliferation of granulosa cells in large follicles. Estrogen and LH are the primary endocrine hormones that regulate theca cell function in vivo. Therefore, hormonal regulation of KGF was analyzed by treating serum-free theca cell cultures with estrogen and human CG (hCG, an LH agonist). Results showed that both estrogen and hCG stimulated KGF gene expression in theca cells. These results suggest that estrogen and LH may promote follicular growth (i.e. granulosa cell proliferation), in part, by stimulating the local production of KGF. Effects of KGF on granulosa cell differentiated functions were examined. Treatment with KGF reduced basal levels and FSH-stimulated levels of aromatase activity in bovine and rat granulosa cells. In addition, KGF inhibited the ability of hCG to stimulate progesterone production by granulosa cells. The inhibition of granulosa cell steroid production by KGF was likely the indirect effect of promoting cellular proliferation. Therefore, KGF directly stimulates granulosa cell proliferation and indirectly inhibits granulosa cell differentiated functions. Combined results suggest that theca cell production of KGF may be important for ovarian folliculogenesis. This is the first report of the regulation of KGF expression in the ovary. The developmental and hormonal regulation of KGF and KGFR during folliculogenesis provides evidence that KGF may be important for hormone-induced granulosa cell proliferation. As a result, KGF may be essential for establishing the microenvironment required for oocyte maturation in the ovary.

Gravity and developmental plasticity

Living organisms, especially plants, show some plasticity in their overall development, usually as a response to the external environment. Plasticity may apply not only to the external form of organisms but also to their physiology as well as to the detailed structure of their genome. A further example of plasticity may be developmental instability, where anomalous development seems to appear spontaneously, probably as a result of some transient environmental perturbation. Whether the absence of gravity would have sufficient impact on any living process to evoke a specific course of plastic development is unknown, though it is possible that in certain circumstances special forms, or 'agravimorphs', could be produced. Through such new forms, it should be possible to identify processes required for development in which 1 x g gravity is a necessary participant.

Direct actions of kit-ligand on theca cell growth and differentiation during follicle development

The direct actions of kit-ligand/stem cell factor (KL) in developing ovarian follicles were investigated. Previous studies have shown that granulosa cells express KL that can support oocyte development. The current study demonstrates that KL can also act directly on theca cells to promote cellular growth and differentiation. Through RT-PCR analysis it was shown that bovine granulosa cells express KL, and theca cells express the receptor c-kit. Bovine theca interna cells were isolated and cultured in serum-free conditions to study KL actions. KL stimulated theca cell growth in a dose-dependent manner as measured by [3H]thymidine incorporation into DNA when cells were cultured under subconfluent conditions. KL had no effect on theca cell androstenedione or progesterone production under these growth-permissive conditions. In contrast, KL stimulated theca cell androstenedione production but had no effect on progesterone production when theca cells were cultured under confluent (non-growth-permissive) conditions. Estradiol (10(-7) M) and human CG (100 ng/ml) were used as controls and regulated theca cell steroid production at any cell density. These results demonstrate that KL can directly stimulate theca cell growth and steroid production during follicular development. The observation that KL stimulated androstenedione production but not progesterone production suggests that KL promotes a follicular phase differentiated state in theca cells. The potential regulation of KL and c-kit expression during follicular development was studied using a specific quantitative RT-PCR procedure. Total RNA from granulosa cells (for KL) and theca cells (for c-kit) was examined from small (<5 mm), medium (5-10 mm), and large (>10 mm) size follicles. Steady state levels of KL messenger RNA were highest in granulosa cells from large size follicles and lowest in small and medium size follicles. No differences were observed in the steady state levels of c-kit messenger RNA in theca cells from small, medium, or large size follicles. The observation that KL expression is highest in large size follicles suggests that KL may be important for increased growth and steroid production in large and dominant follicles. Observations demonstrate that KL can dramatically alter theca cell function and support the hypothesis that local granulosa-theca cell interactions play an important role in regulating cellular function within ovarian follicles. This study identifies KL as the first granulosa cell-derived growth factor that can directly stimulate theca cell growth and androstenedione production in the absence of gonadotropins.

Differentiation, dedifferentiation, and apoptosis of smooth muscle cells during the development of the human ductus arteriosus

Differentiation of vascular smooth muscle cells (SMCs) is characterized by several molecular transitions. As differentiation proceeds, proteins of the cytoskeletal and contractile apparatus, such as alpha-smooth muscle actin, smooth muscle myosin, calponin, and heavy caldesmon, and the expression of the membrane-related protein smooth muscle phosphoglucomutase-related protein increase, whereas the expression of other proteins, such as fibronectin splice variants with extradomains A (EDA) and B (EDB), decreases. In this study, we investigated the differentiation of the SMCs of the ductus arteriosus during the development of intimal thickening. Ascending and descending aortas of the same age were used for comparison because these vessels lack intimal thickening. In the fetal ductus arteriosus, a relatively early differentiation of the contractile apparatus was observed compared with the ascending and descending aortas. EDA and EDB expression was already low, being similar in the ductus and descending aorta and even lower in the ascending aorta. In the neonatal ductus, SMCs of the media and outer intima were well differentiated and comparable with SMCs of the ascending aorta. Dedifferentiated SMCs, with a low expression of cytoskeletal and contractile proteins and a high expression of EDA and EDB, were found in regions in the inner intima that show features of progression of intimal thickening and in areas of cytolytic necrosis in the media. With a technique using in situ end labeling of DNA fragments, we found extensive apoptosis in the area of cytolytic necrosis and to a lesser extent in these areas of the inner intima. In conclusion, SMCs of the fetal ductus arteriosus have an advanced differentiation of the contractile apparatus compared with the adjacent aorta. Reexpression of fetal characteristics is seen in a number of cells in inner intima and media of the neonatal ductus arteriosus. The finding of apoptosis in these areas suggests that dedifferentiation and apoptosis are associated processes that may play a role in vascular remodeling.

Induction of apoptosis in human neuroblastoma cells by abrogation of integrin-mediated cell adhesion

The survival, proliferation and differentiation of neuroblastoma (NB) cells are largely dependent on adhesion to extracellular matrix (ECM) proteins. Integrin occupancy seems to play a primary role. To elucidate the role of integrin heterodimers during neuronal cell death, we have analysed the changes in integrin expression in 2 human NB cell lines which represent different stages of neuronal maturation. Retinoic acid (RA) had different effects on the 2 NB cell lines: on LAN-5 cells it acted as a differentiation-promoting agent, while it had an anti-proliferative effect on GI-LI-N cells, driving them to apoptosis. Indeed, this occurrence was evidenced by the visualization of a "DNA ladder" on gel electrophoresis, by propidium iodide staining, and by DNA flow cytofluorimetric analysis. RA treatment rapidly and drastically decreased integrin expression and cell adhesion on GI-LI-N cells. These findings were also obtained by treating both NB cell lines with the apoptotic agent fenretinide. Furthermore, treatment of NB cells with anti-sense oligonucleotides to beta 1 integrin chain specifically induced chromatin condensation and nucleosomal DNA laddering. Moreover, blocking cell-matrix interactions by means of perturbing antibody against beta 1 subunit resulted in the induction of typical features of apoptotic cells. In conclusion, these findings indicate that abrogation of cell adhesion through down-modulation of integrin receptors plays a crucial role in the induction of neuroblastoma programmed cell death.

Osteoblastic proliferation in bone biopsies from patients with end-stage chronic renal failure

Osteoblasts have traditionally been considered to be terminally differentiated cells and therefore unable to divide. Data in recent years, however, indicate that cellular differentiation does not usually preclude preservation of proliferative ability and that most differentiated cells are able to divide under adequate stimuli. The aim of this study was to assess whether cubic osteoblasts undergo proliferation during the formation phase of the remodeling cycle under a stimulus that increased bone turnover. For that purpose, the osteoblastic proliferation index (OPI) was analyzed by DNA image cytometry in transiliac bone biopsies from 33 patients with chronic renal failure (23 men, 10 women; mean age 50.4 +/- 15.1 years) who have been classified into low (n = 13), normal (n = 15), and high (n = 15) bone turnover according to activation frequency (Ac.f). OPI was significantly higher (p < 0.002) in the high bone turnover group (13.90 +/- 4.72%) compared with the low (2.38 +/- 4.13%) and normal turnover groups (2.84 +/- 4.04%). There was a positive correlation between OPI and the following histomorphometric parameters: bone formation rate, surface referent (r = 0.76, p = 0.00001), activation frequency (r = 0.73, p = 0.00001), mineral apposition rate (r = 0.73, p = 0.00001), bone formation rate, volume referent (r = 0.71, p = 0.00001), and mineralizing surface (r = 0.62, p = 0.0001). This study shows that a rise in bone turnover is associated with a marked increase of bone-forming cell proliferation in patients with end-stage chronic renal failure. From this finding, it may be concluded that cubic osteoblasts do not behave as "terminally differentiated" cells in vivo, because a high proportion of them are still able to divide.

Regulation of differentiation/maturation in vascular smooth muscle cells by hormones and growth factors

Smooth muscle cells (SMC) within atherosclerotic lesions show marked alterations in their differentiated properties as compared to normal medial SMC. This process of de-differentiation of SMC has been referred to as "phenotypic modulation", and is characterized by increased growth responsiveness, altered lipid metabolism, increased matrix production, and loss of contractile proteins, all of which can contribute to the development and/or progression of atherosclerotic disease. As such there has been much interest in understanding mechanisms and factors that control the differentiation of the vascular SMC. This paper reviews the effects of growth factors, growth inhibitors, and other extrinsic factors on differentiation/maturation of SMC, with a particular emphasis on consideration of factors that may contribute to abnormal control of SMC differentiation in vascular disease. In addition, we will briefly summarize what is currently known regarding molecular mechanisms that control the coordinate expression of genes encoding for SMC-selective/specific proteins that are required for the differentiated function of the vascular SMC.

Integrin-dependent activation of the p70 ribosomal S6 kinase signaling pathway

Interaction of the cell surface integrin receptors with extracellular matrix proteins results in the activation of intracellular signaling pathways, including activation of the p42/p44 mitogen-activated protein kinases. The protein tyrosine kinase focal adhesion kinase, or FAK, is linked to integrin signaling and interacts with several molecules involved in signal transduction. Here we report that exposure of fibroblast cells to extracellular matrix proteins activates the p70/p85 ribosomal S6 kinase (S6K) pathway in a ligand dependent manner. Treatment of cells with inhibitors of phosphatidylinositol 3-kinase, or FRAP (FKBP 12/rapamycin-associated protein) blocks integrin-mediated activation of S6K. In contrast to the integrin-directed activation of the mitogen-activated protein kinases, cytochalasin D treatment does not inhibit S6K activation. Treatment with the protein tyrosine kinase inhibitors herbimycin A and genistein completely blocks S6K activation, indicating a requirement for tyrosine kinase activity. Overexpression of the COOH-terminal noncatalytic domain of FAK, FRNK (FAK-related non-kinase) in chick embryo cells results in a significant reduction in the integrin-mediated activation of S6K and a concomitant reduction in FAK tyrosine phosphorylation. These results indicate at least a partial requirement for FAK in the S6K activation pathway.

Type I collagen-deficient Mov-13 mice do not retain SPARC in the extracellular matrix: implications for fibroblast function

The Mov-13 strain of mice was created by the insertion of the murine Moloney leukemia virus into the first intron of the alpha 1 (I) collagen gene. Consequently, Mov-13 embryos do not transcribe alpha 1 (I) collagen mRNA and lack type I collagen protein in the extracellular matrix (ECM). Homozygotes die within 12-14 days of embryonic development, in part from the rupture of large blood vessels, and also exhibit deficiencies in hematopoesis and assembly of the ECM (Lohler et al. [1984] Cell 38:597-607). Several matricellular proteins, proteoglycans, and growth factors bind to type I collagen, e.g., fibronectin, secreted protein acidic and rich in cysteine (SPARC), decorin, and transforming growth factor-beta. Here we investigate the expression and function of SPARC in the absence of type I collagen. We show that fibroblasts isolated from Mov-13 homozygous, heterozygous, and wild-type embryos transcribed and translated SPARC mRNA in vitro. However, accumulation of extracellular SPARC was severely affected in the tissues of Mov-13 homozygotes, whereas extracellular deposition of the secreted glycoproteins fibronectin and type III collagen was not altered. Since SPARC has been shown to be a regulator of cell shape, the functional consequences of the absence of extracellular SPARC were evaluated in collagen gel contraction assays. Fibroblasts isolated from homozygous Mov-13 mice did not contract native type I collagen gels as efficiently as fibroblasts from heterozygous littermates; however, addition of exogenous SPARC enhanced the contraction of collagen by homozygous Mov-13 fibroblasts. The stimulatory effect of SPARC was blocked by antibodies specific for the amino terminus of the protein. These results provide evidence that type I collagen is one of the major extracellular proteins that binds SPARC in vivo. Furthermore, the capacity of fibroblasts to contract ECM in vitro is enhanced by extracellular SPARC. We therefore propose that the remodeling of ECM by cells in vivo is regulated in part by a specific interaction between SPARC and type I collagen.

Merosin and laminin in myogenesis; specific requirement for merosin in myotube stability and survival

Laminin (laminin-1; alpha 1-beta 1-gamma 1) is known to promote myoblast proliferation, fusion, and myotube formation. Merosin (laminin-2 and -4; alpha 2-beta 1/beta 2-gamma 1) is the predominant laminin variant in skeletal muscle basement membranes; genetic defects affecting its structure or expression are the causes of some types of congenital muscular dystrophy. However, the precise nature of the functions of merosin in muscle remain unknown. We have developed an in vitro system that exploits human RD and mouse C2C12 myoblastic cell lines and their clonal variants to study the roles of merosin and laminin in myogenesis. In the parental cells, which fuse efficiently to multinucleated myotubes, merosin expression is upregulated as a function of differentiation while laminin expression is downregulated. Cells from fusion-deficient clones do not express either protein, but laminin or merosin added to the culture medium induced their fusion. Clonal variants which fuse, but form unstable myotubes, express laminin but not merosin. Exogenous merosin converted these myotubes to a stable phenotype, while laminin had no effect. Myotube instability was corrected most efficiently by transfection of the merosin-deficient cells with the merosin alpha 2 chain cDNA. Finally, merosin appears to promote myotube stability by preventing apoptosis. Hence, these studies identify novel biological functions for merosin in myoblast fusion and muscle cell survival; furthermore, these explain some of the pathogenic events observed in congenital muscular dystrophy caused by merosin deficiency and provide in vitro models to further investigate the molecular mechanisms of this disease.

Charting a new course through the chaos of KS (Kaposi's sarcoma)

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Effects of extracellular matrix and Bruch's membrane on retinal outer segment phagocytosis by cultured human retinal pigment epithelium

The goal of this study was to determine the effect of extracellular matrix components on the phagocytic function of the retinal pigment epithelial (RPE) cell. Cultured human fetal RPE cells were established in culture and plated on three commercially-prepared substrates: collagen IV, fibronectin and laminin and on three native matrices: bovine corneal endothelial cell matrix (BCEM) denuded bovine Bruch's membrane and denuded human Bruch's membrane. Cultured cells were allowed to become confluent and maintained for an additional two weeks before uptake of fluorescent bovine retinal outer segments (ROS) was measured by flow cytometry. Morphology by phase contrast microscopy and melanization was also determined as measures of differentiation. The results showed that morphology, melanization and ROS uptake by cells on collagen IV, laminin and fibronectin were not different from control cells plated on tissue culture plastic. However, ROS uptake by cells plated on BCEM was significantly less than that of cells cultured on plastic and melanization was greater. ROS uptake by cells plated on both types of Bruch's membrane was also significantly less than control cells. Treatment of cells plated on tissue culture plastic with 44 mM NaHCO3, which increased melanization, also reduced ROS uptake. We conclude that native matrices seem to contain components that significantly depress ROS uptake in culture. The inhibition is not mimicked by collagen, laminin or fibronectin coated wells. The ECM may play a significant role in controlling phagocytosis of ROS either by determining morphology, increasing differentiation or by directly influencing intracellular metabolism, and thus serve as another level of control for this RPE function which may not occur in cells plated on tissue culture plastic. These results may also have implications for the effects of aging or disease in which there are changes in the ECM.

Uncoordinated, transient mosaic patterns of intestinal hydrolase expression in differentiating human enterocytes

The heterogenous expression of brush border membrane hydrolases by the human enterocyte-like Caco-2 cell line during morphological and functional differentiation in vitro was investigated at the cellular level. Indirect immunofluorescence revealed that the heterogeneous ("mosaic") expression of sucrase-isomaltase, lactase, aminopeptidase N, and alkaline phosphatase was, in fact, transient in nature. The labeling indexes for each hydrolase gradually increased during culture at postconfluence in order to reach a maximum (> or = 90%) after 30 days, concomitant with an upregulation of their respective protein expression levels. In contrast, dipeptidylpeptidase IV labeling remained relatively constant. Backscattered electron imaging analysis in midstage (12 days postconfluence) monolayers demonstrated a lack of correlation between brush border membrane development and expression of each enzyme studied. Moreover, double immunostaining revealed that none of the other four hydrolases correlated directly with sucrase-isomaltase expression. Finally, immunodetection for the proliferation-associated antigen KI-67 revealed a transient mosaic pattern of proliferation which was inversely related to Caco-2 cell differentiation. These data indicate that enterocytic differentiation-related (as well as proliferation-related) gene expression in Caco-2 cells is regulated but uncoordinated at the cellular level, suggesting that an overall control mechanism is lacking.

Differential regulation of cytochrome P450 3A1 and P450 3A2 in rat liver following dexamethasone treatment

Induction of P450 3A1 and P450 3A2 was studied in adult rat liver following treatment with a single high dose of dexamethasone (DEX). The increase of both P450 3A1 and 3A2 occurred at the level of mRNA as well as protein. P450 3A isozymes thus induced were catalytically active. No constitutive expression of P450 3A1 mRNA or protein was observed in males or females. Constitutive expression of P450 3A2 mRNA and protein was observed in males but not in females. Additionally, in females, P450 3A2 was almost nondetectable compared to that in males, at any dose of DEX. A time course study following DEX treatment showed that P450 3A1 mRNA and protein were detectable in both sexes at 12 hours, increased until 48 hours, and then declined. The decline was more rapid in males. P450 3A2 mRNA and protein increased as early as 3 hours, increased further up to 48 hours, and slowly declined thereafter. A dose-response study indicated that P450 3A1 mRNA and protein progressively increased in both sexes from a dose of 30 mg/kg. In contrast, P450 3A2 mRNA and protein in males did not increase up to a dose of 30 mg/kg but increased at higher doses. Total P450 content and P450 3A catalytic activity were also found to increase with time and dose.

TGF-betas upregulate NCAM and L1 expression in cultured Schwann cells, suppress cyclic AMP-induced expression of O4 and galactocerebroside, and are widely expressed in cells of the Schwann cell lineage in vivo

We have examined both how the molecular phenotype of Schwann cells in vitro is regulated by transforming growth factor beta (TGF-beta), using immunohistochemistry and immunoblotting, and the distribution of TGF-beta 2 and 3 in embryonic and mature nerves and ganglia, using immunohistochemistry and in situ hybridisation. We find that TGF-beta 2 and -3 upregulate expression of the neural cell adhesion molecules NCAM and L1. In TGF-beta-treated cultures, in addition to the 140 and 120 kD isoforms known to be present in Schwann cells, small amounts of the 180 kD isoform can be detected. TGF-beta s also block cAMP-induced expression of the lipid antigens galactocerebroside (GalC) and O4, in addition to blocking expression of protein zero (P0), the major peripheral myelin glycoprotein, as previously shown. Using antibodies specific to TGF-beta 2 and -3, respectively, we confirm the presence of these proteins in myelin-forming Schwann cells and show also that TGF-beta 2 and -3 are clearly expressed by peripheral glia that are not involved in myelination. This includes Schwann cell precursors, embryonic Schwann cells, non-myelin-forming Schwann cells and satellite cells from adult nerves and ganglia, and neonatal Schwann cells in purified cultures without neurones. In situ hybridisation with a digoxygenin-labelled riboprobe reveals a strong TGF-beta 3 mRNA signal in Schwann cells, satellite cells, and some neurones. Schwann cells in culture also secrete TGF-beta in a latent form, whereas purified cultures of dorsal root ganglion neurones from 1-day-old rats secrete active TGF beta during the first 48 h in culture.

Insulin-like growth factor-I promotes cell proliferation in the absence of modulation of collagen phenotypes and utilizes IRS-1, not PLC-gamma 1, in corneal endothelial cells

Corneal endothelial cells are differentiated cells and are thus incapable of physiologic regeneration. In a search for a growth factor that would promote optimal proliferation of corneal endothelial cells in the absence of other modulating activities, the effect of insulin-like growth factor-I (IGF-I) on rabbit corneal endothelial cells was studied. In addition, cellular effector molecules responsible for the signal pathway for IGF-I were studied. IGF-I at 50 ng/ml stimulated corneal endothelial cell proliferation after at least 8 h of treatment. IGF-I did not change cell shape of corneal endothelial cells: the cells treated with IGF-I at 50 ng/ml maintained polygonal morphology regardless of the duration of exposure. IGF-I did not alter collagen phenotypes either qualitatively or quantitatively: the treated cells continued to synthesize types IV and VIII collagen, as did the control cells. The steady-state levels of alpha 2(I) collagen RNA and alpha 2(IV) RNA were not altered by IGF-I treatment. Immunohistochemical analysis showed that IGF-I is present in corneal endothelium in vivo, while the underlying Descemet's membrane demonstrated no staining. Corneal endothelial cells also produce IGF binding protein-2 (IGFBP-2), which appears to bind IGF-I that has been introduced exogenously in the medium. Further investigation as to how the signals of IGF-I were transmitted for the biological activities demonstrated that the expression of insulin receptor substrate-1 (IRS-1) is up-regulated by IGF-I treatment, while PLC-gamma 1 expression is not altered by this growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

A retinoic acid-induced clonal cell line derived from multipotential P19 embryonal carcinoma cells expresses smooth muscle characteristics

Despite intense interest in understanding the differentiation of vascular smooth muscle, very little is known about the cellular and molecular mechanisms that control differentiation of this cell type. Progress in this field has been hampered by the lack of an inducible in vitro system for study of the early steps of smooth muscle differentiation. In this study, we describe a model system in which multipotential mouse P19 embryonal carcinoma cells (P19s) can be induced to express multiple characteristics of differentiated smooth muscle. Treatment of P19s with retinoic acid was associated with profound changes in cell morphology and with the appearance at high frequency of smooth muscle alpha-actin-positive cells that were absent or present at extremely low frequency in parental P19s. A clonal line derived from retinoic acid-treated P19s (9E11G) stably expressed multiple characteristics of differentiated smooth muscle, including smooth muscle-specific isoforms of alpha-actin and myosin heavy chain, as well as functional responses to the contractile agonists phenylephrine, angiotensin II, ATP, bradykinin, histamine, platelet-derived growth factor (PDGF)-AA, and PDGF-BB. Additionally, 9E11G cells expressed transcripts for MHox, a muscle homeobox gene expressed in smooth, cardiac, and skeletal muscles, but not the skeletal muscle-specific regulatory factors, MyoD and myogenin. Results demonstrate that retinoic acid treatment of multipotential P19 cells is associated with formation of cell lines that stably express multiple properties of differentiated smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherosclerotic calcification: relation to developmental osteogenesis

Calcium deposits of atherosclerotic plaque consist of hydroxyapatite and may appear identical to fully formed lamellar bone, including trabeculae, lacunae, and areas resembling marrow. Possible mechanisms for bone formation in artery walls are developmental retention of pluripotent cells or osteoblastic immigration coupled with loss of molecular regulatory control that unmasks an embryonic osteogenic program. In situ hybridization of calcified human atherosclerotic lesions shows expression of bone morphogenetic protein type 2, a potent osteogenic differentiation factor. Medial cells of bovine aorta cultured (Dulbecco's modified Eagle's medium plus 15% fetal calf serum) for > 2 weeks form nodules similar to those formed by cultured osteoblasts, including the elaboration of hydroxyapatite.

Extinction of autonomous growth potential in embryonic: adult vascular smooth muscle cell heterokaryons

Vascular smooth muscle cells (SMC) isolated from embyronic and early fetal (e13-e18) rat aortas exhibit an "embryonic growth phenotype" in culture (Cook, C. L., M. C. M. Weiser, P. E. Schwartz, C. L. Jones, and R. A. Majack. 1994. Circ. Res. 74:189-196). Cells in this growth phenotype exhibit autonomous, serum-independent replication, in contrast to SMC in the "adult" growth phenotype, whose proliferation in culture is dependent on exogenous mitogens. To determine which of these two phenotypes is genetically dominant, heterokaryons were constructed between adult and embryonic (day e17) rat aortic SMC. The fused cells were maintained in serum-free medium for 3 d, then were labeled with bromodeoxyuridine (BrdU) for an additional 24 h. Under these conditions, parental e17 SMC exhibited a high rate of self-driven DNA synthesis (73-85% BrdU-positive cells), while parental adult SMC showed minimal replication (13-21% BrdU-positive cells). Homokaryons of parental cells exhibited parental growth phenotypes and showed the expected mitogenic response when stimulated with serum. Heterokaryons between e17 and adult SMC exhibited a nonautonomous growth phenotype; the "adult" growth phenotype was calculated to be dominant in > 89% of all true heterokaryons. The data suggest that adult SMC express molecules capable of genetically extinguishing or otherwise inhibiting the autonomous replication of embryonic SMC.

The origin of the myofibroblasts in breast cancer. Recapitulation of tumor environment in culture unravels diversity and implicates converted fibroblasts and recruited smooth muscle cells

The origin of myofibroblasts in stromal reaction has been a subject of controversy. To address this question definitively, we developed techniques for purification and characterization of major stromal cell types. We defined a panel of markers that could, in combination, unequivocally distinguish these cell types by immunocytochemistry, iso-electric focusing, immunoblotting, and two-dimensional gel electrophoresis. We then devised an assay to recapitulate in culture, within two weeks of incubation, critical aspects of the microenvironment in vivo including the typical tissue histology and stromal reaction. When confronted with tumor cells in this assay, fibroblasts readily converted into a graded pattern of myogenic differentiation, strongest in the immediate vicinity of tumor cells. Vascular smooth muscle cells (VSMC), in contrast, did not change appreciably and remained coordinately smooth muscle differentiated. Midcapillary pericytes showed only a slight propensity for myogenic differentiation. Analysis of ten primary tumors implicated converted fibroblasts (10/10), vascular smooth muscle cells (4/10), and pericytes (1/10) in the stromal reaction. Tumor cells were shown to specifically denude the venules both in culture and in vivo, explaining the VSMC phenotype in the stroma. The establishment of this assay and clarification of the origin of these cells pave the way for further analysis of the mechanisms of conversion, and of the consequence of such heterogeneity for diagnosis and treatment.

E1a induces the expression of epithelial characteristics

Cells closely resembling epithelia constitute the first specific cell type in a mammalian embryo. Many other cell types emerge via epithelial-mesenchymal differentiation. The transcription factors and signal transduction pathways involved in this differentiation are being elucidated. I have previously reported (Frisch, 1991) that adenovirus E1a is a tumor suppressor gene in certain human cell lines. In the present report, I demonstrate that E1a expression caused diverse human tumor cells (rhabdomyosarcoma, fibrosarcoma, melanoma, osteosarcoma) and fibroblasts to assume at least two of the following epithelial characteristics: (a) epithelioid morphology; (b) epithelial-type intercellular adhesion proteins localized to newly formed junctional complexes; (c) keratin-containing intermediate filaments; and (d) down-regulation of non-epithelial genes. E1a thus appeared to partially convert diverse human tumor cells into an epithelial phenotype. This provides a new system for molecular analysis of epithelial-mesenchymal interconversions. This effect may also contribute to E1a's tumor suppression activity, possibly through sensitization to anoikis (Frisch, S.M., and H. Francis, 1994. J. Cell Biol. 124:619-626).

Restricted expression of a new paired-class homeobox gene in normal and regenerating adult goldfish retina

We describe the cloning and expression pattern of a new paired-class homeobox gene, Vsx-1, in the continuously growing retina of the goldfish. Vsx-1 belongs to a subset of paired-class homeobox genes that lack a second DNA binding domain, the paired-domain, and is closely related to the C. elegans ceh-10 gene. In the adult goldfish, Vsx-1 expression is restricted to the neural retina. In the central, mature retina, Vsx-1 mRNA is synthesized in a subset of differentiated cells in the inner nuclear layer in a pattern suggestive of bipolar cells. In immature retina, adjacent to the retinal margin, Vsx-1 is expressed in a relatively broader subset of newly postmitotic cells but is downregulated in some of these cells to form the mature expression pattern. Following retinal injury, during the early phase of regeneration, Vsx-1 mRNA synthesis appears to be upregulated in cells in the inner nuclear layer and is expressed de novo in cells outside this layer. By virtue of its identity as a transcriptional regulatory gene and its patterns of expression, we speculate that Vsx-1 may stabilize the differentiated state of a subset of cells in the inner nuclear layer and may be involved in cellular differentiation during retinal development and regeneration.