Actin cytoskeleton in intact and wounded coenocytic green algae

Summary The subcellular distribution of actin was investigated in two related species of coenocytic green algae, with immunofluorescence microscopy. Either no, or fine punctate fluorescence was detected in intact cells of Ernodesmis verticillata (Kützing) Børgesen and Boergesenia forbesii (Harvey) Feldmann. A reticulate pattern of fluorescence appears throughout the cortical cytoplasm of Ernodesmis cells shortly after wounding; this silhouettes chloroplasts and small vacuoles. Slender, longitudinal bundles of actin become evident in contracting regions of the cell, superimposed over the reticulum. Thicker portions of the bundles were observed in well-contracted regions, and the highly-convoluted appearance of nearby cortical microtubules indicates contraction of the bundles in these thicker areas. Bundles are no longer evident after healing; only the reticulum remains. In Boergesenia, a wider-mesh reticulum of actin develops in the cortex of wounded cells, which widens further as contractions continue. Cells wounded in Ca²⁺-free medium do not contract, and although the actin reticulum is apparent, no actin bundles were ever observed in these cells. Exogenously applied cytochalasins have no effect on contractions of cut cells or extruded cytoplasm, and normal actin-bundle formation occurs in treated cells. In contrast, erythro-9-[3-(2-hydroxynonyl)]adenine (EHNA) completely inhibits longitudinal contractions in wounded cells, and few uniformly slender actin bundles develop in inhibited cells. These results indicate that wounding stimulates a Ca²⁺-dependent, hierarchical assembly of actin into bundles, whose assembly and functioning are inhibited by EHNA. Contraction of the bundles and concomitant wound healing are followed by cessation of motility and disassembly of the bundles. The spatial and temporal association of the bundles with regions of cytoplasmic contraction, indicates that the actin bundles are directly involved in wound-induced cytoplasmic motility in these algae.Abbreviations EHNA erythro-9-[3-(2-hydroxynonyl)]adenine - MT(s) microtubule(s)     

Direct adhesion to type I and homotrimer collagens by breast carcinoma and embryonic epithelial cells in culture: a comparative study

A continuous cell line of neoplastic cells derived from ductal infiltrating carcinoma of the human breast (8701-BC), was assayed for its ability to adhere to collagen substrates. The collagens used were regular type I and type I homotrimer isolated from primary breast carcinomas. Comparative studies were performed using an embryonic epithelial cell line derived from human intestine (Int. 407). The neoplastic cells adhere equally well to both collagens, while the embryonic epithelial cells recognized only the homotrimer. Some receptor diversity was recognized in the adhesion of the two cell lines to homotrimer collagen. The data demonstrate a functional difference between type I and homotrimer collagen with regard to cellular recognition and attachment. In addition, the data suggest that oncogenic transformation of breast epithelial cells promotes their adhesive properties to interstitial collagens and that this may be relevant to their increased potential to invade host tissue.     

Binding of flunitrazepam to differentiating neurons cultured in a chemically defined,hormone-supplemented medium

[³H]Flunitrazepam (FNZ) binding to cortical neurons from fetal rat brain was investigated in vitro. The use of a synthetic medium specific for neurons made it possible to plot a developmental curve of³H-FNZ binding in an almost pure neuronal culture. Detectable specific binding was present in vitro at time 0 (that is, the 16th gestational day). A progressive increase of binding, due to an increment in the number of recognition sites, was observed on the subsequent days. The affinity of the specific binding sites to³H-FNZ was enhanced by the addition of exogenous GABA, whereas the density was not affected.