The effects of antimicrotubule agents on cell motility in fibroblast aggregates

Spherical aggregates of chick heart, sclera and skin fibroblasts were fused with tritiated thymidine-labelled aggregates of the identical cell type. After being placed in contact, the two aggregates cohered and broadened the area of contact to form a single aggregate with a planar interface between the labelled and unlabelled halves. The motility of cells in the aggregate was determined by measuring the movement of labelled cells across the boundary into the unlabelled half. Exposure to pharmacological doses of antimicrotubule agents resulted in a significant reduction in fibroblast motility in the three-dimensional aggregates.     

Contact guidance in vitro : A light, transmission, and scanning electron microscopic study

Contact guidance was studied in cultures of chick heart fibroblasts and kidney epithelium by observing the relation of these cells to fine grooves ruled in plastic culture dishes, and also to ridges or grooves in plastic replicas moulded from rulings made in metal. The relation of the cells to the regularly arranged collagen fibers of fish scales was also studied by scanning and transmission electron microscopy (SEM and TEM). On the rulings with groove periodicity in the range of 5 μm about 75% of the cells were aligned, but on grooves separated about 30 μm only 60% of cells were aligned. Cytoplasmic components of the cells such as microfilaments maintained a constant relation to the axis of the cell as a whole, but they, and also any cytoplasmic extensions, such as filopodia, bore no consistent relation to any features of the substratum, whether or not the cells were aligned. The cells were not guided to become aligned by filopodia or lamellipodia. The most remarkable and consistent finding was that cells bridged over grooves without contacting their surfaces, whether the grooves were 2 or 10 μm wide. The bridging was a characteristic of cells growing on any of the substrates, including those with grooves or ridges, and also of collagen substrates made from fish scales. A hypothesis is proposed to explain the contact guidance seen on ridged or grooved substrata and on the orientated collagen fibers involving the observed cell bridging and the fact that linear cell-to-substrate contacts (focal contacts) are known to be vital for cell movement. The cell is considered to be stiff so that as it bridges over much of the substratum there is only a limited area available for contact. Assuming that focal contacts need to be of a certain length to provide adhesion, a cell orientation that presents the maximum linear contact would be favoured. An examination of the results of this study and of the reports in the literature shows that cells on these types of substrata take on an orientation such that linear contacts would be expected to predominate.     

Complex genetic effect of B10.D2 (M504) (H-2dm1) mutation

Serological and capping experiments show that the strain B10.D2 (M504) carrying the mutant haplotypeH-2 ^dm1 has two molecules in the products of theD region: H-2D^dm1 and H-2L^dm1 which are detectable by anti-H-2.4 and by anti-H-2.28 sera, respectively. Both these molecules differ serologically from the H-2D^d and H-2L^d molecules of the original (nonmutant) strain B10.D2. A third molecule, different from H-2D and H-2L, was detected inH-2 ^d ,H-2 ^dm2 but not inH-2 ^dm1 products.     

Freeze-fracture study of taste bud pores in the foliate papillae of the rabbit

Summary In freeze-fractured specimens of taste buds from the foliate papillae of rabbits, the intercellular spaces are separated from the pore of the taste bud by zonulae occludentes of the tight-type. Below these tight junctions numerous desmosomes are found at irregular intervals. The epithelial cells adjacent to the pore are also joined by single strands of fusion. The microvilli arising from the neck of the type I cells have a high particle density. The microvilli of type II cells and especially the short microvilli of peripherally situated cells have a lower intramembranous particle density. The single microvillus of type III cells has a very large diameter and is longer than the other microvilli. It contains a few larger intramembranous particles and vesicle-like protrusions of the membrane facing the cytoplasm. Transverse fracturing reveals a filamentous fine structure in all microvilli. The physiological implications of these observations are discussed.Supported by grants from the Deutsche Forschungsgemeinschaft (Ja 205/5+6)     

Nickel,cobalt, and molybdenum requirement for growth of Methanobacterium thermoautotrophicum

Growth of Methanobacterium thermoautotrophicum on H₂ and CO₂ as sole energy and carbon sources was found to be dependent on Ni, Co, and Mo. At low concentrations of Ni (<100 nM), Co (<10 nM) and Mo (<10 nM) the amount of cells formed was roughly proportional to the amount of transition metal added to the medium; for the formation of 1 g cells (dry weight) approximately 150 nmol NiCl₂, 20 nmol CoCl₂ and 20 nmol Na₂MoO₄ were required. A dependence of growth on Cu, Mn, Zn, Ca, Al, and B could not be demonstrated. Conditions are described under which the bacterium grew exponentially with a doubling time of 1.8 h up to a cell density of 2 g cells (dry weight)/1.     

Analysis of nucleolus organizer regions (NORs) in mitotic and polytene chromosomes ofPhaseolus coccineus by silver staining and Giemsa C-banding

Chromosomes with active nucleolus organizer regions (NORs) were visualized in root tip metaphases ofPhaseolus coccineus using the silver staining technique. A mean number of 5.5 Ag-NORs per cell was observed in 54 cells from eight plants. In the endopolyploid nuclei of the suspensor the silver technique did not demonstrate the reported specificity for nucleolus organizer activity, because there was usually pale staining of nucleoli and preferential staining of heterochromatic regions in the polytene chromosomes including pericentromeric material, telomeres and NORs. The mean number of NORs per nucleolus as detected by this method was 5.8 (28 nucleoli analysed). Using a modified preparation technique, giant chromosomes stained pale, but nucleoli of suspensor cells displayed darkly silver staining internal domains, each of which originating from a nucleolus organizer.—Giemsa C-banding of endopolyploid suspensor nuclei revealed C-positive nucleolus organizers with darkly staining intranucleolar fibrils. The latter were frequently involved in inter-NOR associations. In 34 nucleoli analysed, the mean number of Giemsa C-positive NORs per nucleolus was 6.0.Dedicated to Professor Dr.Lothar Geitler on the occasion of his 80th birthday.