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Biomedical subjects

A P Swan

Publications and source records attributed to A P Swan.

10 recordsLinked to original sources
PubMed1986

The migration of amphibian primordial germ cells in the chick embryo.

A fibrous band of extracellular materials on the chick embryo area pellucida/area opaca border is a preferential migratory pathway for chick embryo primordial germ cells (PGC). This band contains fibronectin, collagen Type I and sulphated glycosaminoglycans. It is known that PGCs from Xenopus laevis interact with fibronectin as they undergo migration in the embryo from their site of origin to the gonads. To establish whether this pathway is species specific in chick embryos it was decided to transplant PGC from Xenopus laevis embryos stage 48 on to chick embryos stage 4 fibrous band. Their rapid migration on this extracellular matrix and their subsequent re-orientation of the basement membrane has been studied by scanning electron microscopy.

Animals↗
PubMed1984

Mononuclear phagocytes and collagen matrices--a review.

Mononuclear phagocytes comprise populations of both stationary and wandering cells in vivo, and play many important roles, including major ones in host defence and the regulation of the immune response. They also interact with fibroblasts in the production and degradation of collagen and are therefore responsible in part for the modelling of connective tissue. Motile macrophages in vivo can use this connective tissue as a substrate for their migration, moving over and through dense collagenous matrix in the process. They adhere readily to collagenous substrates in vitro but there are distinct differences between the morphology and behaviour of macrophages on these substrates and those on glass or plastic. The locomotory behaviour of macrophages can be manipulated in vitro by the use of MIF (migration inhibition factor), a soluble lymphokine produced by sensitised T-lymphocytes, which inhibits macrophage motility. MIF also affects the morphology of macrophages and their behaviour on collagenous substrates. When their motility is suppressed by MIF macrophages become activated to enhanced levels of phagocytic, cytotoxic and microbicidal activities, but lose their marked propensity to invade collagenous matrices.

Animals↗
PubMed1981

Primordial germ cells of Xenopus embryos: the role of fibronectin in their adhesion during migration.

Primordial germ cells (PGCs) of Xenopus laevis are highly migratory. The last section of their migratory pathway is through the dorsal mesentery of the tadpole gut. This in vivo pathway is rich in fibronectin, a glycoprotein that promotes cell adhesion and migration in vitro. Isolated PGCs are associated with cells from the mesentery and with fibronectin. Treatment with trypsin removes both the mesentery cells and the fibronectin. The PGCs do not appear to resynthesize detectable fibronectin in vitro. In contrast, cultured adult mesentery epithelial cells synthesize large amounts of fibronectin and lay it down in subcellular fibrils that align with intracellular microfilament bundles. PGCs plated on cultured mesentery cell layers adhere to them, elongate and align with the microfilament bundles of the mesentery cells. PGCs adherent to mesentery cell layers are closely associated with fibronectin; moreover, F(ab)2 fragments of anti-Xenopus fibronectin IgG inhibit the adhesion and spreading of PGCs on the mesentery. These results indicate that PGCs can adhere to mesentery cells via fibronectin produced by the latter cells and suggest that fibronectin may be involved in the migration of PGCs in vivo.

Animals↗
PubMed1981

The invasion of cultured cell layers and intact epithelia.

This paper concerns the invasive behaviour of a migratory embryonic cell type, the primordial germ cell (PGC) of the anuran amphibian Xenopus laevis. Scanning electron microscopy of isolated PGCs shows that they invade layers of cells derived from adult Xenopus mesentery, and the epithelium of the intact mesentery itself. This invasion is at least partly due to the stimulation by the PGCs of process formation in both cultured and intact epithelial cells. These broad lamellipodia move over the surface of the PGCs and eventually enclose them. We have documented previously that active invasion by the PGC also takes place, though the relative roles of these two components of the invasive process are unknown. We also demonstrate that these properties are not mediated by any contaminating cellular or extracellular material on the isolated PGCs, since their removal by trypsin does not alter the invasive behaviour.

Animals↗
PubMed1979

A ligand-receptor model for the cohesive behaviour of Dictyostelium discoideum axenic cells.

Axenically grown cells of D. discoideum Ax-2 harvested in the log phase of growth, cohere rapidly when shaken in phosphate buffer. After 3.5 days in the stationary phase of growth, cells become completely non-cohesive. Although they do not stick to each other, stationary phase cells do stick to both log phase cells and aggregation-competent cells. The cohesion of stationary phase cells with these other 2 cell types is inhibited by both EDTA and the low-molecular-weight factor which we have previously demonstrated in stationary-phase growth medium. There is a decline in the sensitivity of slime mould cell cohesion to the low-molecular-weight inhibitory factor as the cells become aggregation-competent. This effect parallels the developmentally-regulated decline in sensitivity to EDTA. The low-molecular-weight inhibitor is not a chelating agent, however. The effect of the inhibitor seems to be specifically against contact sites-B mediated cohesion. We suggest that the simplest cohesive mechanism which can explain our results, is that the EDTA-sensitive cohesion of log phase cells could be dependent on a ligand-receptor system.

Adhesiveness↗
PubMed1977

An inhibitor of cell cohesion from axenically grown cells of the slime mould, Dictyostelium discoideum.

Medium from a stationary phase culture of axenically grown D. discoideum cells contains an inhibitor of cohesion of log phase cells. The inhibitor is a heat-stable, low molecular weight substance. Its biological effects include inhibition of cohesion of aggregation-competent cells, of cells of other slime mould species, the blocking of development on Millipore filters and a reduction in adhesiveness of slime mould cells to glass. Present evidence suggests that the inhibitor may bind to the cell surface.

Adhesiveness↗