Malignant transformation of rat thyroid cells transfected with the human TSH receptor cDNA.

Growth and function of well differentiated FRTL-5 thyroid cells depend on thyrotropin as its main regulatory hormone. We demonstrate here that stable transfection of FRTL-5 cells with the human thyrotropin receptor cDNA results in cellular transformation of these cells with altered cell shape and loss of contact inhibition. The transformed cells replicate in soft agar and form invasive tumors when cell suspensions are implanted onto nude mice. They have lost their thyrotropin dependent growth and their ability to concentrate iodide and synthesize thyroglobulin. But they still express the rat thyrotropin receptor mRNA and accumulate cAMP in response to thyrotropin stimulation. However, although the full length human thyrotropin receptor cDNA is integrated into their genome, transformed cells do not express the human thyrotropin receptor mRNA.     

Modulation of K+ channels by hydrogen peroxide.

External application of hydrogen peroxide (H2O2) was found to inhibit the time-dependent fast inactivation process of three cloned voltage-gated K+ channels expressed in Xenopus oocytes: KShIIIC, KShIIID and HukII. As expected from kinetic models where some channels are still opening while a significant fraction of channels is already inactivated there was a large increase in current magnitude concomitant to inactivation block. The channels otherwise functioned normally. The effects of H2O2 were specific (other cloned voltage-gated K+ channels were not affected), and reversible, the currents returned to normal upon removal of the H2O2. H2O2 is produced during normal metabolism; it could act as a modulator of excitability through effects on K+ channels if effective local concentrations are reached in neuronal regions close to the channel. KShIIIC and KShIIID currents are very similar to an O2-sensitive K+ current present in type I cells of the carotid body which is believed to underlie the modulation of excitability of these cells by changes in arterial O2 pressure. H2O2 has been proposed as an intermediary between O2 and cellular response in the carotid body; our results provide support for this model.     

Characterization of the pH-mediated solubility of Bacillus thuringiensis var. san diego native delta-endotoxin crystals.

Native crystals of Bacillus thuringiensis var. san diego, a coleopteran-specific delta-endotoxin, were metabolically labelled with [35S]methionine. Specific activity was 82,000 CPM/micrograms (2.44 Ci/mmol). Using a universal buffer formulated with the same ionic strength at every pH, we determined that native crystals dissolve above pH 10 and below pH 4. At the acidic pH, the rate of solubilization was substantially slower than at the alkaline pH. Recrystallization rates for the toxin were similar regardless of solubilization conditions. The banding patterns in denatured polyacrylamide gel electrophoresis were unaffected by solubilization conditions. Toxicity was higher for soluble toxin compared to crystal toxin, but virtually identical for the acidic and alkaline produced solutions. Acid solubilization is significant because of the acidic midgut of susceptible Coleoptera.     

Induction of adventitious buds on the cotyledons ofAbies concolor x Abies grandis hybrid seedlings

Possibilities of adventitious buds induction on the cotyledons obtained from sterile seedlings ofAbies concolor xAbies grandis hybrid were investigated. The following variables influencing bud induction and their further development were studied: the effect of expiant age, the effect of different growth regulators and their concentrations and duration of their application. The most suitable expiants proved to be the cotyledons of 7 d old seedlings. The most efficient cytokinin was benzylaminopurine (S mg l^?1) in combination with napthaleneacetic acid (0.01 mg l^?1). The most optimal duration of treatment was 17 to 21 d culture of explants on induction medium. Shoot growth was achieved on basal medium to which 14 mg 1^?1 spermidine was added.     

Introduction to the Symposium: What is Computational Neurobiology?

SYNOPSIS. Current advances in computational biology are derivedfrom two sets of ideas established in the work of Santiago Ramóny Cajal. One is the neuron doctrine, which holds that neuronsare the functional units of the nervous system, and has ledto detailed models of neuronal properties based on increasinginformation on the physical and chemical properties of neurons.The second is the idea of networks of neurons with specificpatterns of interconnections that has led to a variety of mathematicalmethods of analyzing such networks. Future work in computationalneurobiology promises to be a blend of these two modeling approaches.     

Bivariate flow cytometry of farm animal chromosomes: a potential tool for gene mapping

Bivariate flow karyotypes of chromosomes from sheep, cattle and pig lymphocytes and from a cattle-mouse somatic cell hybrid line were obtained using a dual laser fluorescence-activated cell sorter (FACS). Pig chromosomes were resolved into 19-20 peaks, indicating that most, if not all, pig chromosomes could be separated by this technique. Sheep chromosomes showed incomplete separation but three clear peaks, presumably representing the three large metacentric chromosomes, plus five other clusters were obtained. Cattle chromosomes showed poor separation but about four peaks could be distinguished, indicating that certain chromosomes could be sorted in this species. The use of cattle-mouse hybrids may enable other individual cattle chromosomes to be obtained. It is concluded that FACS separation will be a useful additional tool for gene mapping.     

The unique headpore of Monospilus dispar (Cladocera,Chydoridae) is not lonesome: new record of minute lateral pores

The headshield of Monospilus dispar (Cladocera, Chydoridae, Aloninae) was characterized by the presence of a unique headpore. Scanning Electron Microscopy shows the occurrence of minute pores close to the main headpore. The intimate structure of the main headpore is formed by concentric lamellae. This new information leads to new considerations about phylogeny.     

Primary sequence and functional expression of a novel ouabain-resistant Na,K-ATPase. The beta subunit modulates potassium activation of the Na,K-pump.

In order to understand the molecular mechanism of ouabain resistance in the toad Bufo marinus, Na,K-ATPase alpha and beta subunits have been cloned and their functional properties tested in the Xenopus laevis oocyte expression system. According to sequence comparison between species, alpha 1, beta 1, and beta 3 isoforms were identified in a clonal toad urinary bladder cell line (TBM 18-23). The sequence of the alpha 1 isoform is characterized by two positively charged amino acids (Arg, Lys) at the N-terminal border of the H1-H2 extracellular loop and no charged amino acid at the C terminus, a pattern distinct from the ouabain-resistant rat alpha 1 isoform. The coexpression of alpha 1 beta 1 or alpha 1 beta 3 TBM subunits in the Xenopus oocyte resulted in the expression of identical maximum Na,K-pump currents with identical inhibition constant for ouabain (Ki) (alpha 1 beta 1: 53 +/- 3 microM; n = 7 vs. alpha 1 beta 3: 57 +/- 3.0 microM; n = 8) but distinct potassium half activation constant (K1/2) (alpha 1 beta 1: 0.87 +/- 0.08 mM, n = 16; alpha 1 beta 3: 1.29 +/- 0.07 mM, n = 17; p less than 0.005). We conclude that (i) the TBM alpha 1 isoform is necessary and sufficient to confer the ouabain resistant phenotype; (ii) the beta 3 or beta 1 subunit can associate with the alpha 1 equally well without affecting the ouabain-resistant phenotype; (iii) some specific sequence of the beta subunit can modulate the activation of the Na,K-pump by extracellular potassium ions.