The in vitro cell fusion of embryonic chick muscle without DNA synthesis

A system has been developed for the in vitro development of chick skeletal muscle monolayers, in which a burst of synchronous fusion occurs, such that some 40% of the spindle-shaped cells fuse in a 10-hr period. Cells inhibited from synthesizing DNA by ara-C do fuse, but at a later time than the normal burst. If ara-C is added to cultures 6 hr or more before the normal fusion time, fusion is delayed, but no delay results when the drug is added after this time. A medium change will delay the fusion if done 4 hr or more before fusion, but gives no delay if done later. Cells grown in conditioned medium fuse some 10 hr earlier than controls, even in the presence of ara-C, as do cultures prepared at higher than normal cell densities. The data suggest that muscle cell fusion is independent of DNA synthesis in vitro, but depends upon a modification of the culture medium to a sufficient degree required for initiating the synthetic program for fusion.     

Osmotic alterations of the lysosomal system during rat liver perfusion: Reversible suppression by insulin and amino acids

Livers from nonfasted rats were perfused in situ under conditions known from previous studies in this laboratory to increase or decrease overall endogenous proteolysis. At the termination of the experiments, lysosomal alterations were evaluated by the increase in free acid phosphatase or N-acetyl-β-D-glucosaminidase that occurred when tissue homogenates were subjected to osmotic shock in hypotonic sucrose. In control perfusions, osmotic sensitivity increased spontaneously over unperfused values, reaching maximum by 60 min or earlier. Additions of insulin, amino acid mixtures, or cycloheximide in amounts known to suppress proteolysis prevented this spontaneous perfusion effect or, when added at 60 min, rapidly reversed it. Glucagon alone during perfusion did not increase osmotic sensitivity further; however, stimulation with glucagon was observed when the perfusion effect was suppressed by insulin or cycloheximide. Anoxia, induced by gassing with nitrogen instead of oxygen, markedly reduced the perfusion effect and also doubled the amount of free acid phosphatase in the initial isotonic homogenates. Total acid phosphatase activities in the perfusion experiments were not significantly different from unperfused values and, with the exception of the anoxia perfusions, the amounts of free enzyme present in the initial isotonic sucrose homogenates did not change.     

Ribonucleic Acid Synthesis of Vesicular Stomatitis Virus: I. Species of Ribonucleic Acid Found in Chinese Hamster Ovary Cells Infected with Plaque-forming and Defective Particles

Plaque-forming B particles of vesicular stomatitis virus (VSV) induce the synthesis of virus-specific ribonucleic acid (RNA) in Chinese hamster ovary cells, whereas defective T particles do not. Infection with low input multiplicities of B results in the formation of four species of RNA. During infection with high multiplicities, RNA synthesis begins with mainly these four species of RNA but gradually shifts to a new pattern of RNA synthesis involving five other species of RNA. The change can also be induced by superinfection with T at 2.5 hr after infection with a low multiplicity of B. T added at the same time as B prevents virtually all RNA synthesis. Synthesis of the first group of RNA species correlates with the formation of B particles, whereas synthesis of the second group correlates with the formation of T particles. The various species of RNA formed after infection with VSV particles include single-stranded RNA, a completely double-stranded RNA, and RNA with partially double-stranded regions. These observations begin to establish a molecular basis for understanding the ability of T particles to interfere with the growth of B particles.     

Rapid Fluorescent-Antibody Staining Technique

The rapid fluorescent-antibody staining technique described by Kellogg and Deacon for staining Neisseria gonorrhoeae and Treponema pallidum was applied to fluorescent-antibody tests for group A streptococci and enteropathogenic Escherichia coli. Results obtained with this staining technique were compared with results using the conventional staining procedure; excellent correlation was obtained. Considerable time and materials were saved by using the rapid method; it was also found completely satisfactory.     

BIOSYNTHESIS OF RIBONUCLEIC ACID IN RAT BRAIN SLICES

The incorporation of uridine into RNA in brain slices was studied. Optimal conditions for uridine incorporation were determined. The characteristics of the product suggest that de novo DNA-directcd synthesis of fairly high molecular weight material takes place. Incorporation into RNA of several areas of brain was studied. The incorporation was also studied as a function of the age of the animal. Finally, an apparent correlation was observed between the decrease in uridine incorporation with age and the increase of the enzyme uridine nucleosidase which hydrolyses uridine to uracil, a material which cannot be incorporated into RNA.     

Morphogenetic studies of a genetically controlled tumor-like condition in Lycopersicon hybrids

Summary A dominant tumor-like condition recently isolated in a tomato hybrid is described from the viewpoint of morphogenesis. Tumors, consisting of masses of enlarged parenchymatous cells, generally appear on the ventral surface of the third leaf and the subsequently formed leaves of the hybrid derivatives. These outgrowths do not differentiate into teratomas. Abortive floral buds develop under greenhouse conditions and the tumorous plants are much dwarfed compared to the normal segregants of the same population. the same tumor genotype behaves differently under the field conditions: it grows and blossoms like the normal plants, setting fruits with viable seeds, and tumors fail to develop. Thus, tumor expression and general morphology of the tumor plants are greatly modified by environmental conditions.Tissue culture studies employing a variety of media have shown that tissues excised from tumor-producing plants are not autonomous with respect to growth hormones, nor are tissues from the non-tumorous segregants. Nevertheless, tissues from tumor and non-tumor genotypes show different growth requirements. Tumor and non-tumor tomatoes can thus be distinguished on the basis of in vitro growth responses, a result consistent with their different genetic constitution. Differentiation of buds or roots was not observed in either type of tissue.Abbreviations used GA gibberellic acid - IAA 3-indoleacetic acid - 2.4-D 2.4-dichlorophenoxyacetic acid Work Supported by National Science Foundation Grant GB-3198 and funds from The Cairncrest Foundation.     

The Photosynthetic Electron Transport Chain of Chlamydomonas reinhardi. VII. Photosynthetic Phosphorylation by a Mutant Strain of Chlamydomonas reinhardi Deficient in Active P700

Electron transport activity and absorbance changes associated with P700 were investigated in a mutant strain of Chlamydomonas reinhardi with impaired photosynthesis. This mutant strain, ac-8oa, cannot reduce NADP with electrons from either water or dye and ascorbate, but it has considerable Hill activity. The mutant strain shows none of the absorbance changes characteristic of P700. Although unable to carry out cyclic photosynthetic phosphorylation, ac-8oa is able to synthesize ATP when ferricyanide is provided as an electron acceptor.

These observations lead to the conclusion that a site for the coupling of photosynthetic phosphorylation with electron transport must exist between the 2 photochemical systems.