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Biomedical subjects

M Solursh

Publications and source records attributed to M Solursh.

At least 109 records · Page 6Linked to original sources
PubMed1985

Dynamic activity of the filopodia of sea urchin embryonic cells and their role in directed migration of the primary mesenchyme in vitro.

Primary mesenchyme cells used in this study were isolated from Lytechinus pictus mesenchyme blastulae by their ability to preferentially adhere to the surface of a tissue culture dish in the presence of serum. Once isolated, primary mesenchyme cells were found to form thin, elongated, active filopodia which closely resemble the filopodia seen in vivo. The filopodia formed in vitro can move as stiffened bristles, bend gradually or very sharply, or be slowly withdrawn. The integrity of the filopodia is not affected by nocodazole but is totally disrupted by cytochalasin D. Filopodia exhibit several apparent functions in vitro: as organelles involved in contacting the external environment, as anchoring appendages that hold the cell bodies in place, and as intercellular connectives that can join cell bodies. The filopodia of primary mesenchyme cells appear to have similar roles within the embryo. The function of the filopodia has been explored by watching the behavior of isolated primary mesenchyme cells in close proximity to deposits of extracellular material (ECM) prepared from mesenchyme blastulae. When the filopodium from a mesenchyme cell makes contact with the nearby ECM, a response is initiated which causes the cell body to move in a directed manner toward the ECM deposit. The use of this type of response as a model system for the study of the migration of primary mesenchyme cells within the embryo is considered.

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PubMed1985

In vitro fusion and separation of sea urchin primary mesenchyme cells.

Time-lapse videomicroscopy of cultured primary mesenchyme cells from mesenchyme blastulae of the sea urchin Lytechinus pictus demonstrates the dramatic ability of these cells to undergo cell fusion and cell separation. Although this plasticity of cell associations is presumed to play a role in the formation of the syncytial cables that secrete the larval skeleton, the surfaces of these cells must be specialized for fusion and cell separation.

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PubMed1984

Chemotactic behavior of myoblasts.

Earlier studies have suggested that myogenic cells of somite origin migrate into the developing limb, but little is known about the factors affecting the pattern of migration. In order to understand the migratory behavior of myogenic cells, embryonic skeletal muscle cells were tested for their ability to migrate chemotactically using a modified Boyden chamber assay system. It is shown here, for the first time, that embryonic skeletal muscle cells have the capacity to migrate toward a gradient of platelet-derived growth factor (PDGF) and PDGF-like factors present in serum and chick embryo extract (CEE). On the other hand, nonmyogenic limb mesenchyme cells do not exhibit such a response. A hypothesis is proposed here that chemotactic factors from the already patterned vasculature might influence the distribution of skeletal muscle cells during early limb development.

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PubMed1984

The migratory capacity of myogenic cells in vitro.

Time-lapse films of micromass cultures prepared from stage 19-24 chick embryo wing buds indicate that the majority of the mesenchymal cells present undergo little net movement, even during the formation of prechondrogenic aggregates. Rather, these cells undergo mitosis and pulsatile movements in place. In the same cultures, round or elongate myoblasts could be observed migrating as single cells on or between the mesenchymal cells. These in vitro observations are consistent with the suggestion that migratory myoblasts may establish the myogenic pattern in the limb by extensive migration through the nonmigrating limb mesenchyme.

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PubMed1984

Extracellular matrix mediates epithelial effects on chondrogenesis in vitro.

It has been previously observed that single chick embryonic limb mesenchymal cells can differentiate into chondrocytes without cell-cell interactions when cultured in collagen or agarose gels. In the present study, limb ectoderm, but not dermis, inhibits chondrogenesis when placed on such collagen gel cultures. The inhibitory influence can be transmitted extensive distances in the gel, even when the ectoderm is placed on a porous filter. Collagen gels, preconditioned with limb ectoderms, are also inhibitory to chondrogenesis. On the other hand, chondrogenesis is less inhibited by ectoderm when the mesenchymal cells are placed in agarose. These results suggest that the antichondrogenic effect of limb ectoderm is mediated through alterations of the collagenous extracellular matrix and support the idea that the extracellular matrix must be considered as an organized, functional unit capable of regulating cell differentiation.

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PubMed1984

Adhesive and migratory behavior of normal and sulfate-deficient sea urchin cells in vitro.

Dissociated cells from different stage embryos of the sea urchin Lytechinus pictus were compared in their adhesion to various substrates. Micromeres from 16-cell stage embryos bind to tissue culture and Petri dishes but not to Petri dishes coated with human plasma fibronectin. Other cell types did not adhere to any of the substrates tested. By hatched blastula stage, about 28% of the cells adhered to fibronectin as well as to tissue culture dishes. By the mesenchyme blastula stage, there was a further increase in the proportion of cells adhering to these substrates. At no stage did cells adhere to native rat tail collagen. Primary mesenchymal cells were isolated by their selective adhesion to tissue culture dishes in the presence of horse serum. These cells were then examined for their migratory capacity. Cell spreading and migration followed adhesion and occurred on fibronectin but not on the other substrates tested. Based on analysis of video tapes, greater than 60% of these cells moved faster than 1 micron/min. On the other hand, cells from sulfate-deprived embryos, in which primary mesenchyme migration is blocked in situ, failed to spread and migrated little on the same substratum. This defect was reversed by a 6 h pretreatment of the cells in normal sea water. Thus, the in vitro migratory behavior parallels that observed in vivo. These results support the hypothesis that the primary mesenchymal cells produce a sulfate-dependent component that is required for cell spreading and migration.

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PubMed1984

Ectoderm as a determinant of early tissue pattern in the limb bud.

This review considers the hypothesis that the limb bud ectoderm establishes the initial pattern of the various mesodermal components within the limb bud. The evidence reviewed supports the hypothesis that the ectoderm establishes a peripheral, non-chondrogenic, avascular sleeve around the limb bud. The ectodermal influence is a diffusible factor that acts by altering the collagenous extracellular matrix so that cell flattening and fibrogenic differentiation are promoted. It is hypothesized that just within this sleeve is a vascular-rich zone where myogenic cells migrate in response to a chemotactic influence. In the center of the limb bud is the prechondrogenic core, whose size determines the number of skeletal elements which subsequently form. The dimensions of the developing limb bud are established during distal limb outgrowth by the reciprocal interaction between the apical ectodermal ridge, which has a mitogenic influence, and the underlying mesoderm.

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PubMed1984

Induction of chondrogenesis in limb mesenchymal cultures by disruption of the actin cytoskeleton.

Cell shape is known to influence the chondrogenic differentiation of cultured limb bud mesenchyme cells (Solursh, M., T. F. Linsenmayer, and K. L. Jensen, 1982, Dev. Biol., 94: 259-264). To test whether specific cytoskeletal components mediate this influence of cell shape, we examined different cytoskeleton disrupting agents for their ability to affect chondrogenesis. Limb bud cells cultured at subconfluent densities on plastic substrata normally become flattened, contain numerous cytoplasmic microtubules and actin bundles, and do not undergo spontaneous chondrogenesis. If such cultures are treated with 2 micrograms/ml cytochalasin D during the initial 3-24 h in culture, the cells round up, lose their actin cables, and undergo chondrogenesis, as indicated by the production of immunologically detectable type II collagen and a pericellular Alcian blue staining matrix. Cytochalasin D also induces cartilage formation by high-density cultures of proximal limb bud cells, which normally become blocked in a protodifferentiated state. In addition, cytochalasin D was found to reverse the normal inhibition by fibronectin of chondrogenesis by proximal limb bud cells cultured in hydrated collagen gels. Agents that disrupt microtubules have no apparent effect on the shape or chondrogenic differentiation of limb bud mesenchymal cells. These results suggest an involvement of the actin cytoskeleton in controlling cell shape and chondrogenic differentiation of limb bud mesenchyme. Interactions of the actin cytoskeleton and extracellular matrix components may provide a regulatory mechanism for mesenchyme cell differentiation into cartilage or fibrous connective tissue in the developing limb.

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PubMed1984

Inhibition of limb chondrogenesis by fibronectin.

This study compares the chondrogenic capacity of high density cultures prepared from either the developmentally younger, distal region or more advanced proximal region of stage 23/24 limb mesenchyme in high density cultures. Distal cultures undergo extensive chondrogenesis whether in F12 medium supplemented with 10% fetal calf serum, 5% fetal calf serum, or fibronectin. On the other hand, proximal cultures fail to undergo chondrogenesis in medium containing 10% fetal calf serum or fibronectin, but do form cartilage in medium containing a decreased serum concentration or no serum. Furthermore, if the cells are cultured at low densities in native type I collagen gels, proximal cells have a reduced chondrogenic capacity in the presence of fibronectin, while chondrogenesis by distal cells is unaffected by the addition of fibronectin. The results demonstrate that proximal and distal cells respond differentially to serum and to fibronectin, and they suggest that the response of the cell to prevalent components of the extracellular matrix might change with development.

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PubMed1984

Epithelial enhancement of connective tissue differentiation in explanted somites.

This paper examines the differentiation of somites from stage-16 or -17 chick embryos cultured with or without notochord in explant cultures. Histological sections of the cultures were stained with a trichrome stain to identify the different kinds of connective tissues formed. Both anterior and posterior (epithelial) somites made muscle, cartilage and loose connective tissue in explant culture. The extent of cartilage differentiation was enhanced by the presence of the notochord, confirming earlier studies. The presence of 1 mM-dibutyryl cAMP in the culture medium increased the amount of muscle found in the explants but by histological criteria did not inhibit chondrogenesis, contrary to earlier reports. The addition of quail ectoderm to the explants stimulated loose connective tissue to form directly beneath it, suggesting for the first time a role of the ectoderm in dermatome differentiation. These results suggest that the epithelial somite has the capacity to differentiate into all three connective tissue types even before it has separated into sclerotome and dermamyotome. The relative amount of different connective tissue types can be influenced by environmental factors, such as adjacent epithelia like the notochord or ectoderm.

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PubMed1983

Two distinct classes of prechondrogenic cell types in the embryonic limb bud.

Differences are demonstrated in the chondrogenic potential of cells derived from the distal and proximal halves of chick wing buds from as early as stage 23, prior to the appearance of overt cartilage differentiation. In high cell density cultures, cells obtained from the distal portions of stage 23 or 24 limb buds are spontaneously chondrogenic in micromass cultures. Cells obtained from the proximal portions, however, become blocked in their differentiation as protodifferentiated cartilage cels, since these cells in micromass cultures make detectable type II collagen, but fail to synthesize significant levels of cartilage proteoglycan or to accumulate an extracellular matrix that will stain for sulfated glycosaminoglycans. Such cultures of proximal limb bud cells can be stimulated to form alcian blue staining nodules by the addition of 1 mM dbcAMP or 50 micrograms/ml ascorbate, or by mixing proximal cells with small numbers of distal cells (1 distal cell to 10 proximal cells). These results demonstrate the existence of two distinct stages among prechondrogenic mesenchyme cells. The earlier stage appears to be able to provide a chondrogenic stimulus to proximal cells.

Animals↗
PubMed1983

Accelerated maturation of limb mesenchyme by the BrachypodH mouse mutation.

Mesenchyme cell populations prepared from proximal and distal halves of stage 20 mouse forelimb buds are shown to behave under in vitro micromass culture conditions like analogous cell populations obtained from chick embryo limb buds. While the distal cells are spontaneously chondrogenic, the proximal cells make aggregates which are only potentially chondrogenic after treatment with dibutyryl cyclic AMP. In addition, stage 20 mouse whole limb bud cells homozygous for the brachypodismH (bpH) mutation are shown to behave similarly to 'normal' proximal cells. Both make fewer aggregates and nodules and both have faster aggregation rates (determined as the rate of disappearance of single cells over time) in rotation cultures than 'normal' distal or whole limb bud cells. These results support the hypothesis that the bpH mutation specifically decreases the proportion of spontaneously chondrogenic mesenchyme cells (that is, distal-like cells) present at certain developmental stages in the limb bud, resulting in a prematurely high proportion of proximal-like cells.

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