Regulation of phenotype in somatic cell hybrids derived by fusion of teratocarcinoma cell lines with normal or tumor-derived mouse cells

The phenotypes of somatic cell hybrids between murine embryonal carcinoma cell lines, F9 BrdU 7C12 and PCC4 aza 1, and normal murine splenic lymphocytes or thymoma-derived cell lines were compared. Analysis of morphology in vivo and in vitro of cell surface markers and of the karyotype of these cloned hybrid cells did not reveal any simple mechanism for the regulation of the phenotype of such hybrids. Hybrids of either the embryonal carcinoma cell phenotype or of a differentiated morphology (resembling neither parental cell) but not of lymphoid morphology can be derived from fusions of this type. Moreover, transition from one phenotype to the other (ECC → differentiated cell and differentiated cell → ECC) can be found with passage of clonally derived hybrid cell lines. Coordinate control of the phenotypic markers of the state of differentiation in these hybrid cells was found.     

Relative activities of linear and cyclic electron flows during chloroplast CO2-fixation

Evolution of oxygen and turnover of cytochromes b-563 and ? were measured upon illumination of isolated intact spinach chloroplasts with a series of flashes. The flash yield of cytochrome ? oxidation approximated the sum of the yields of cytochrome b-563 reduction and electron transfer through Photosystem II, regardless of whether HCO^?₃, 3-phosphoglycerate or O₂ served as the terminal electron acceptor. No absorbance contribution from cytochrome b-559 was discerned within the time range studied. Some pseudocyclic electron flow occurred when both HCO^?₃ and 3-phosphoglycerate were omitted, and possibly also during induction of photosynthesis; however, the flash yield data suggest that O₂ is not reduced at a significant rate during steady state photosynthesis. The maximum rate of cytochrome ? turnover (1000 μequiv./mg chlorophyll per h) was adequate to support the highest rates of photosynthesis observed in isolated chloroplasts.These results agree with the concept that cytochrome ? is a component both of the linear and cyclic pathways whereas cytochrome b-563 functions only in the cyclic pathway. NH₄Cl decreased the half time of cytochrome b-563 oxidation from 11.6 to 8.2 ms and decreased the half time of cytochrome ? reduction from 7.2 to 2.8 ms. The cyclic and linear pathways thus seem to be jointly regulated by a transthylakoid H⁺ gradient through a common control point on the reducing side of cytochrome ?. Cyclic turnover also increased during the induction phase of photosynthesis, when linear throughput is limited by the rate of utilization of NADPH. The slow rise in the P-518 transient correlated with increased cyclic activity under the above conditions.It is proposed that flexibility in the utilization of linear and cyclic pathways allows the chloroplast to generate ATP and NADPH in ratios appropriate to varying needs.     

The intracellular location of adenylyl cyclase in the cellular slime molds Dictyostelium discoideum and Polysphondylium pallidum

Adenylyl cyclase activity was low or not detectable on intact cells and in isolated plasma membranes, phagocytic vacuoles and nuclei of the two slime mold species examined. The entire activity of homogenates was sedimentable and concentrated in a light membrane fraction. When this fraction was centrifugated through sucrose density gradients the adenylyl cyclase activity sedimented differently from all other enzymes measured. The gradient fractions with the highest specific activity of adenylyl cyclase consisted mainly of small vesicles. No changes in adenylyl cyclase distribution were associated with development. The possibility that cellular slime mold adenylyl cyclase activity is associated with vesicles in vivo, as already suggested by Maeda & Gerisch [10], is discussed.     

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.     

Differentiation in cultures derived from embryonic chicken muscle: I. Muscle-specific enzyme changes before fusion in EGTA-synchronized cultures

It is known that myoblast fusion fails to occur in cultures containing EGTA (a calcium-specific chelator) but occurs very rapidly after EGTA medium is replaced with standard high-calcium medium. On the basis of a careful analysis of the time course of fusion in cultures switched from EGTA to standard medium, it is proposed that this method of synchronization be used routinely in studies of the timing of different processes during in vitro myogenesis. The kinetics of accumulation of total enzyme activity for creatine kinase and fructose diphosphate aldolase indicate that the increases characteristic of terminal muscle differentiation begin prior to the experimentally imposed onset of fusion in EGTA-synchronized cultures. Additionally, the accumulation of M-creatine kinase subunits, also typical for muscle differentiation, is shown by microcomplement fixation to begin before the switch from EGTA to standard medium. Creatine kinase isoenzyme patterns also show that the transition from B- to M-subunit-containing creatine kinases occurs in EGTA cultures not switched to standard medium. Like EGTA, 5-bromodeoxyuridine (BrdUrd) reversibly prevents myoblast fusion. By adding EGTA and BrdUrd in different sequences to muscle cell cultures, it is shown that they act at different stages in the course of in vitro myogenesis. Cells cultured in EGTA from 23 to 69 hr after plating fused very rapidly when switched to medium containing BrdUrd. In the reverse experiment, in which BrdUrd preceded EGTA, no fusion occurred. Parallel experiments with 5-fluorodeoxyuridine suggest that cell division is necessary to reverse the inhibitory effect of BrdUrd, but not that of EGTA; this is consistent with the observed kinetics of fusion after switching to standard medium. These data strongly support a model of myogenesis in vitro in which two processes (one BrdUrd-sensitive, the other EGTA-sensitive) occur sequentially. In the first process, myogenic cells give rise to cells capable of producing molecules necessary for (terminal) skeletal muscle differentiation, including both those required for cell fusion and specific isoenzymes. The second process, fusion itself, can occur in the presence of BrdUrd or in the absence of cell division.     

Differentiation in cultures derived from embryonic chicken muscle: II. Phosphorylase histochemistry and fluorescent antibody staining for creatine kinase and aldolase

The presence or absence of five proteins (glycogen phosphorylase, aldolase A, aldolase C, creatine kinase M, creatine kinase B) in the various classes of cells found in primary cultures derived from embryonic chick breast muscle was investigated using cytological staining methods. Histochemical staining for phosphorylase and indirect fluorescent antibody staining for aldolase A and C as well as for creatine kinases M and B showed the following: All five proteins were found in the many myotubes present in standard medium cultures and in the very few myotubes found in cultures containing 5-bromodeoxyuridine (10^?5M). The elongated bipolar cells prevented from fusing in medium containing EGTA also contain all five proteins. The flattened myogenic cells that predominate in the 5-bromodeoxyuridine-treated cultures contain no phosphorylase or creatine kinase M, though many of them contain creatine kinase B and aldolases A and C. These results are interpreted as indicating that: (1) phosphorylase and creatine kinase M, but not aldolase A, are suitable all-or-none markers for terminal muscle differentiation; (2) the small amounts of creatine kinase M detected in electrophoreses of 5-bromodeoxyruridine-treated cultures can be accounted for by the few myotubes present and are not due to “protodifferentiation” of large numbers of cells; (3) proteins typical of differentiated muscle are produced only in cells that have passed through the last step in myogenesis that is susceptible to 5-bromodeoxyuridine inhibition, and (4) if fusion is blocked by reducing the concentration of calcium ions, accumulation of characteristic muscle proteins can continue in those cells that have initiated terminal differentiation.     

Protoprimulagenin a Als Aglykon des Hauptsaponins von Primula elatior

It was shown that the aglycone of the main saponin of Primula elatior (L.) Hill is not primulagenin A but protoprimulagenin A with an oxide ring between C-13 β and C-28 in the β amyrin ring system.     

Calf articular cartilage in organ culture in a chemically defined medium

In Vitro Cellular &; Developmental Biology - Plant - Articular cartilage from 6-month-old calves was maintained in organ culture in Eagle's minimum essential medium at different oxygen...