Regulation of the contact behaviour of cells

The green hydra symbiosis. V. Stages in the intracellular recognition of algal symbionts by digestive cells

Aposymbiotic (alga-free) green hydra may be reinfected by injecting a suspension ofChlorellasymbionts into their coelenterons. Digestive cells could phagocytose a wide range ofChlorellatypes, but transport to the cell base, where the symbionts normally reside, was limited to algae that release detectable amounts of maltose. Transport of their own symbionts was inhibited when maltose release was curtailed by prolonged pretreatment with a photosynthetic inhibitor. After phagocytosis, only about half of their own symbionts were transported, the rest remaining at the digestive cell apex where they disintegrated. This phenomenon was termed sorting. It was not due to damage of algae during isolation, nor to saturation of the transport mechanism. A further stage of discrimination was observed to take place up to 5 days after injection; some symbionts that had been transported to the cell bases were removed to the apices and disintegrated or were ejected (re-sorting). It is concluded that recognition of suitable algae is unlikely to involve identification of a single algal character by the European digestive cells. The establishment of the symbiosis may depend upon a number of algal properties and interactions within the host cell.

Cell interactions during the in vitro neoformation of fetal rat pancreatic islets

As shown by scanning electron microscopy, transmission electron microscopy and membrane labeling analysis, the in vitro neoformation of rat pancreatic islets arose from two main processes: a budding from explants containing duct cells, and a competition between endocrine monolayers and fibroblasts on the culture substratum. The stronger cytoskeleton of fibroblasts and their higher adhesive properties, probably related to their more homogeneous distribution of membrane charges, may explain the spherization of the islets. The pure endocrine cell population of neoformed islets was composed mainly of insulin-secreting cells, and the other types of endocrine cells were distributed in the periphery. Preformed extracellular matrices of osmotically disrupted fibroblasts enhanced the yield of the cultures by increasing the anchorage of endocrine cells and slowing down the fibroblastic growth.

Surface coats of pore tubules and olfactory sensory dendrites of a silkmoth revealed by cationic markers

Negatively charged surface coats have been demonstrated on the pore tubules and dendritic membranes of olfactory hairs of male Antheraea polyphemus silkmoths by application of the cationic markers lanthanum (La3+), ruthenium red (RR), and cationized ferritin (CF). Lanthanum and RR diffused readily into the apically opened hairs, whereas CF penetrated only for a relatively short distance. Deposits of the markers are distributed as follows: the inner surfaces of the hair walls are stained by RR and to a small degree by CF; the surfaces of the pore tubules and the dendritic membranes are stained by all three markers. The pore tubules have the strongest affinity for CF. The number of pore tubule-membrane contacts seems to be increased by the cationic dyes. The dendrites are often penetrated by RR, which forms deposits on the inner membrane leaflets, the cytoplasmic microtubules, and microfilaments, and by La3+, but never by CF. The observations provide support for the assumption that, first, the pore tubule-membrane contacts are formed via surface coats of both structures, possibly influenced by cations and, second, that the dendrites remain intact after pinching off the hair tips.

Rotation-mediated aggregation of skin fibroblasts in Duchenne muscular dystrophy. Effects of monensin

Rotation-mediated aggregation of human skin fibroblasts has been studied and the patterns of aggregation compared between cultures obtained from 9 patients with Duchenne muscular dystrophy and from 10 normal controls. The rate of aggregation was dependent on the growth state of the cells, with growing cells aggregating more rapidly than growth-arrested cells. There was considerable variation between individuals in the rate at which cells aggregated but no differences were detected in the aggregation of normal and DMD cells measured by this method. The monovalent cation ionophore monensin, which inhibits the transport of cellular proteins to the extracellular medium, reduced aggregation of all cells. The data suggest that after initial cell-cell contact continued aggregation is dependent on the secretion of materials to the cell surface. The aggregation of normal and DMD cells was affected similarly by this treatment.

Intercellular contacts between migrating blood cells and cells of the sinusoidal wall of bone marrow. An ultrastructural study using tannic acid

The migration of blood cells across the sinusoidal wall of murine bone marrow was studied following fixation with tannic acid-glutaraldehyde. Electron microscopic examination showed regions of close membrane apposition (referred to in this study as "intercellular contacts") between migrating blood cells and cells of the sinusoidal wall (adventitial and endothelial cells). Ultrastructurally the intercellular contacts are pentalaminar structures resembling gap junctions of other organs after tannic-acid fixation. The possibility that these contacts are regions of intercellular communication and/or sites of membrane attachment utilized for locomotion of the migrating blood cells is discussed.