Induction of Lambda-Bacteriophage in Escherichia coli as a Screening Test for Potential Antitumor Agents

A simple, rapid, quantitative test procedure to measure induction of phage production in lysogenic Escherichia coli K-12 (λ) was described. This test was used in a study of 209 substances, including antibiotics, pyrimirines, purines, alkylating agents, thiols, amino acids, vitamins, and miscellaneous compounds. Minimal inducing concentrations for the 26 (12.5% of total tested) substances found to be effective inducing agents, as well as a listing of the inactive compounds, are presented. Since 21 of the 26 active agents reportedly have antineoplastic activity in rodent tumor systems, it was concluded that the induction test may provide a useful screen for the detection of potentially useful antitumor compounds.     

SPORE GERMINATION AND DEVELOPMENT OF THE YOUNG GAMETOPHYTE OF THE OSTRICH FERN (MATTEUCCIA STRUTHIOPTERIS)

Light is required for the germination of spores of Matteuccia struthiopteris. Histochemical studies show that dormant spores contain no starch, but have an abundance of storage protein granules. Starch accumulates in the numerous chloroplasts of the spore on exposure to light and becomes gradually more extensive. Protein granules disappear as germination progresses. Following this, the centrally located nucleus migrates toward the proximal spore face. Concomitant with the nuclear migration, an increase of cytoplasmic RNA surrounding the nucleus occurs. An equal nuclear division and unequal cell division give rise to a 2-celled gametophyte consisting of a large prothallial cell and smaller rhizoidal cell. A new peripheral wall forms around the entire protoplast at the time of nuclear migration, while a transverse wall forms after nuclear division. The rhizoid emerges through the split raphe along the proximal spore face; it is rich in cytoplasmic RNA but contains very few chloroplasts and little starch. Electron microscopy of the 2-celled stage revealed a greater concentration of mitochondria, Golgi bodies, and a more extensive endoplasmic reticulum in the rhizoid than was found in the prothallial cell, which, however, was far richer in chloroplasts and lipid bodies. As the rhizoid elongates and becomes more vacuolated, cytoplasmic RNA decreases as cytoplasmic protein increases. The rhizoid undergoes no cell divisions, while the prothallial cell retains the potential for further cell division. The possible significance of the distribution of storage products, cell organelles, and other cell components were considered in relation to the non-equational cell division and differentiation of the 2 cells.     

Growth of epithelium from a preneoplastic mammary outgrowth in response to mammary adipose tissue

Summary We investigated the effects of conditioned media derived from mouse mammary fat pads on the proliferation of CL-S1 cells, an epithelial cell line originally isolated from a preneoplastic mammary outgrowth line. Cell proliferation in vitro in serum-free defined medium was compared to that in this medium conditioned using intact mammary fat pad pieces or isolated fat pad adipocytes. Culture medium was conditioned by incubating the conditioning material in defined culture medium for 24 h at 37°C. Conditioned medium induced CL-S1 proliferation as much as 10- to 20-fold above the minimal levels of growth in control cultures after 13 d of culture. The growth-stimulatory factor(s) had an apparent molecular weight of greater than 10 kDa. This growth-stimulatory activity was both heat and trypsin stable. Because the role of adipose tissue is to store and release lipids, we next tested whether lipids are released during medium conditioning. The lipid composition of the fat pad conditioned medium was characterized using both thin layer and gas liquid chromatography. These lipid analyses indicated that the fat pad pieces released significant amounts of fatty acids and phospholipids into the medium during the conditioning period. The free fatty acid composition included both saturated and unsaturated molecules, and about 80% of the total fatty acids consisted of palmitate, stearate, oleate, and linoleate. These same fatty acids were a structural component of the majority of phospholipid found in the medium. The addition of palmitate or stearate to defined medium had no effect or was inhibitory for CL-S1 proliferation, depending on the concentration used. Defined medium supplemented with oleate, arachidonate, or linoleate induced CL-S1 proliferation, and the inhibitory effects of palmitate and stearate were overcome by addition of oleate and linoleate. These data indicate that both unsaturated and saturated fatty acids are released from intact adipose cells of the mouse mammary fat pad and that fatty acids can influence the growth of prenoplastic mouse mammary epithelium. Thus, unsaturated fatty acids, perhaps in conjunction with other substances released simultaneously, are candidate molecules for the substances that mediate the effect of adipose tissue on growth of epithelium. This work was supported in part by a grant from the American Institute for Cancer Research; grant CA 46885 from the National Institutes of Health, Bethesda, MD; and by State of Washington initiative 171.