A continuous-flow method of organ culture

Summary A method of perfusion organ culture is described in which explants cultured at the airmedium interface are bathed by a continuous flow of nutrient medium. Morphological studies on the fetal rat lung indicate that explant development in this system is comparable to that obtained using standard organ-culture dishes. Medium supply is easily manipulated and continuous sampling of the effluent stream is possible without disturbing the immediate explant environment. The basic design facilitates secretory-response studies on cultured organ explants as demonstrated by a study of glucose-stimulated insulin release by the neonatal rat pancreas. This work was supported by U. S. Public Health Service Training Grant No. GM 00114.     

Suppression of lymphocyte proliferation by a nonspecific factor produced by the burkitt lymphoma-derived lymphoblast cell line

Summary The DAUDI lymphoblast cell line derived from a patient with Burkitt lymphoma was obtained from two different sources. One of these (DAUDI-I) produced a factor that inhibited lymphocyte proliferation in both human and mouse regardless of the stimulator, i.e. allogeneic lymphocytes or mitogens. Glutaraldehyde treatment eliminated production of the factor and demonstrated that DAUDI-I was capable of stimulating normal lymphocytes in MLR. A second DAUDI cell line (DAUDI-S) did not produce the inhibitory factor and was capable of MLR stimulation. Supported by the Children's Leukemia Foundation of Michigan, NIH Grants AI 11013 and AI 11335, and the Kidney Foundation of Michigan.     

Influence of low temperature on phosphatase in roots of Verbascum thapsus,a biennial weed

The temperature peak (15 °C) of acid and alkaline phosphatase in this study coincides with a peak in alpha-amylase as seen in an earlier study of roots of Verbascum thapsus. It is speculated that one of the results of higher phosphatase activities may be increased amount of orthophosphate which can be utilized in phosphorylation of soluble carbohydrates which in turn are in greater supply due to the higher activities of the starch-degrading enzymes.A second peak in activities of acid and alkaline phosphatase was seen in plants which were returned to the greenhouse following cold treatment. This increase in enzymatic activities is also similar to increases in activities of three starch degrading enzymes studied earlier. Alkaline phosphatase showed greater activities than did acid phosphatase at lower temperatures (10 and 4 °C) and under greenhouse conditions following cold treatment.     

The polyadenylated RNA of zoospores and growth phase cells of the aquatic fungus,Blastocladiella

The stored poly(A) + RNA from zoospores of the aquatic fungus Blastocladiella emersonii represents 2.5% of the total RNA and has a model MW of 425,000 daltons and an average poly(A) isostich of 32 bases. The poly(A) + RNA also represents 2.5% of the total RNA from early growth phase cells and has a modal MW of 360,000 daltons and an average poly(A) isostich of 38 bases. The poly(A) + RNA from spores and 2-hr plants contains a structure resistant to RNases T₁, T₂, and A, which can be labeled with ³²PO₄ and which will bind to DBAE-cellulose. These characteristics strongly suggest that both the zoospore poly(A) + RNA and the 2-hr cell poly(A) + RNA are capped at the 5′ end; and, hence, it is unlikely that capping is involved in the control of protein synthesis during germination.Approximately 80% of the poly(A) + RNA of the spore is located in the membrane-enclosed ribosomal nuclear cap, and more than 90% of the poly(A) + RNA within the cap is found in the 80S monoribosome and heavier fractions.Synthesis of new poly(A) + RNA occurs very early during zoospore germination, and the labeled poly(A) + RNA rapidly enters the newly organized polysomes. The labeling data for early germination also suggest that cytoplasmic polyadenylation occurs.     

Repetitive DNA in Cichorieae (Compositae)

Thermally denatured DNA of 11 species of Cichorieae (Compositae) was allowed to renature at 69° C in 0.8 M Na⁺. Two distinct fractions of repetitive DNA (fast: 10⁵ repetitions, intermediate: 10³ repetitions) were found in all species. The remaining (slow) fraction comprises 26 to 58% of the genome. The relative amounts of fast and intermediate fractions maintain constant proportions to the slow fraction except for saltatory changes, especially halvings in species with reduced genome sizes.     

Cell attachment to collagen: The ionic requirements

This study is concerned with three aspects of the ionic requirements for cell attachment to collagen; namely (a) the divalent, (b) monovalent cation specificities and (c) pH optima for cell interaction with collagen. The divalent cation requirement for cell attachment to collagen can be sufficed by Ca²⁺, Mg²⁺ and certain transition group metals; whereas Ba²⁺, Sr²⁺, and polyamines are inactive. The pH optimum for cell attachment in this system occurs in the physiological range. The monovalent cation requirement for cell attachment to collagen is satisfied by isotonic NaCl, KCl, LiCl, NH₄Cl, sucrose, and glucose. Pronounced inhibition of cell attachment occurs under both hypertonic and hypotonic conditions.     

A Model of Functional Epistasis and Linkage Disequilibrium in Populations with Overlapping Generations

A model of functional epistasis is proposed in which it is assumed that coupling and repulsion genotypes differ in metabolic efficiency and thus in development time and net fecundity. The implications of this model are investigated for iteroparous populations with fluctuating rates of increase. It is found that the fluctuations in rate of increase can lead to large fluctuations in gamete frequency and D, the coefficient of linkage disequilibrium, but that D will almost always have a value of zero at some point during the populations' demographic cycle. Some of the model populations would be expected to be in a state of linkage disequilibrium only fleetingly: others would exhibit D-cycles interpretable as random fluctuation. Implications of the model for interpretations of existing data on linkage disequilibrium among enzyme loci in Drosophila are discussed.