Half-lives of messenger RNA species during growth and differentiation of Dictyostelium discoideum

The half-lives of functional messenger RNAs were determined by a method employing the drugs actinomycin D and daunomycin for the inhibition of mRNA synthesis; the activity of extracted mRNAs was determined by an in vitro translation assay. Several controls indicated that this method yielded reliable values for mRNA half-lives; in particular, the declining rate of protein synthesis in the presence of the drugs is due predominantly to the decay of translatable mRNA. This method was used to determine the half-lives of two specific mRNAs—encoding actin and a protein of MW 51,000—as well as that of total cytoplasmic mRNA activity during growth and at several times in differentiation. The half-lives of at least these two mRNAs were shown to be distinctly different from that of the total mRNA population—about 4 hr. However, no significant change in any of these half-lives was observed between growing and developing cells. Therefore wholesale alterations in the degradation rates of total and at least specific messages do not appear to play a role in the regulation of gene expression during Dictyostelium development.     

The evolution of conspicuous coloration: Some experiments in bad taste

Unpalatable species are often brightly coloured. Such aposematic coloration may have evolved because predators can learn to avoid conspicuous prey more readily than cryptic prey. Experiments on young male chicks are described and the results are consistent with this hypothesis.     

Primary induction of metallothionein by dexamethasone in cultured rat hepatocytes

Dexamethasone or Zn⁺⁺ increase the rate of synthesis of the metal-binding protein metallothionein in hepatocyte cultures. Dexamethasone induction of the capacity to synthesize metallothionein is not blocked by cycloheximide. In contrast, the dexamethasone stimulated increase in Zn⁺⁺ uptake is inhibited by cycloheximide. Like Zn⁺⁺, dexamethasone is a “primary inducer” of metallothionein. The glucocorticoid induction of metallothionein in primary cultures of rat hepatocytes is not mediated through elevation of Zn⁺⁺ uptake.     

Effects of Cd++ on short-circuit current across epithelial membranes

Summary Cadmium ion (Cd⁺⁺) was found not to inhibit active sodium transport across the isolated frog skin when added in 10^–3 m concentration to the basal-lateral surface. The same Cd⁺⁺ concentration similarly had no effect on Na⁺ transport across the isolated epithelial cell layer from the frog skin, although this dose of Cd⁺⁺ did inhibit Na⁺ transport across the frog urinary bladder and large intestine. When 10^–3 m Cd⁺⁺ was added to the apical surface of the isolated frog skin or to the isolated epithelial cells from the frog skin, sodium transport was reversibly stimulated, in contrast to the irreversible inhibition noted above. If equimolar cysteine was added with Cd⁺⁺ to the apical surface of the skin, however, active Na⁺ transport was irreversibly inhibited. In conjunction with the inhibition produced by equimolar Cd⁺⁺ and cysteine, isotopic Cd⁺⁺ permeation into the tissue was three times higher when added with cysteine than in the absence of cysteine. Thus, the effects of Cd⁺⁺ on epithelial Na⁺ transport is variable according to the epithelium studied and the presence of potential carrier molecules.     

IDENTIFICATION OF SEROTONIN WITHIN VITAL-STAINED NEURONS FROM LEECH GANGLIA

Abstract— We have measured serotonin (5-HT) within large and small neurosomata which are vitally stained by Neutral Red dye. A micro-radioenzymatic technique which is sensitive to 50fmol of 5-HT was employed on intact ganglia, 75 μm Retzius Cells (RZ) and a 10 μm ventro-lateral cell (VL) taken from the leech Macrobdella decora. The stain does not affect the levels of 5-HT in either ganglia or RZ. The VL cell body contains 5-HT at concentrations of at least 100 m m . Microspectrofluorometry of all the ganglionic neurosomata which fluoresce following the Falck-Hillarp formaldehyde condensation reaction detected rapidly-fading emission peaks of 509–523 nanometers. We conclude that all seven fluorescent neurons in the leech ganglion very probably contain serotonin.     

The role of microtubules and cell-wall deposition in elongation of regenerating protoplasts of Mougeotia

Protoplasts of the filamentous green alga Mougeotia sp. are spherical when isolated and revert to their normal cylindrical cell shape during regeneration of a cell wall. Sections of protoplasts show that cortical microtubules are present at all times but examination of osmotically ruptured protoplasts by negative staining shows that the microtubules are initially free and become progressively cross-bridged to the plasma membrane during the first 3 h of protoplast culture. Cell-wall microfibrils areoobserved within 60 min when protoplasts are returned to growth medium; deposition of microfibrils that is predominantly transverse to the future axis of elongation is detectable after about 6 h of culture. When regenerating protoplasts are treated with either colchicine or isopropyl-N-phenyl carbamate, drugs which interfere with microtubule polymerization, they remain spherical and develop cell walls in which the microfibrils are randomly oriented.     

Terminal distribution of retinal fibers in the tegu lizard (Tupinambis nigropunctatus)

Summary The retinal projections in the tegu lizard were traced using degeneration-silver methods. Bilateral projections were found to the dorsolateral geniculate and the posterodorsal nuclei. Unilateral, crossed projections were traced to the suprachiasmatic nucleus, the ventrolateral geniculate nucleus, the mesencephalic lentiform nucleus, nucleus geniculatus praetectalis, the ectomammillary nucleus, and the optic tectum. Some of these connections are distinctly different from those reported in other reptiles and suggest that important interspecific variations occur among reptiles.     

Size variation polymorphisms of the short arm of human acrocentric chromosomes determined by R-banding by fluorescence using acridine orange (RFA)

Summary One hundred normal Caucasians were studied by the RFA technique to estimate the frequencies of size variation of the short arm of acrocentric chromosomes. Each size variation was classified into one of five levels. The most frequent size level (code) was 3; therefore, this was regarded as the average size. If one excludes the average size, the frequencies of size variation by RFA for chromosome 13, 14, 15, 21, and 22 were 22.5, 19.5, 14.5, 19, and 17% respectively. There was no significant difference for the overall frequencies of size variation between sexes. Furthermore, the RFA technique detects more variation in the size of human acrocentric chromosomes than any other method.