Implications of the human genome initiative for the primary care physician

... Despite the need for physicians to be knowledgeable about and open to advances in genetic technology, little is known about the level of preparedness of primary care physicians to offer new genetic tests. Evidence suggests that several barriers exist to physicians adopting genetic tests. These include lack of knowledge, inability to interpret probabilistic information, low tolerance for uncertainty, negative attitudes about their responsibility for genetic counseling and testing, lack of confidence in their clinical skills, and unfamiliarity with ethical issues raised by testing. This paper will explore some of these barriers in further depth, discuss the ethical impact of physician unpreparedness on both patient care and the diffusion of genetic tests, and describe a study that is currently underway to investigate some of these issues.     

Leaf growth of Betula and Acer in simulated shadelight

Summary Leaves of birch (Betula pendula Roth) and sycamore (Acer pseudoplatanus L.) were initiated and grown either in a simulated shadelight (80 mol m^-2 s^-1, R/FR ratio 0.28)/dark photoenvironment or a white light (250 mol m^-2 s^-1, R/FR>1)/dark photoenvironment. Until the leaves were more than 50% expanded, growth rates (measured every 24 h) were the same for both species in both environments. After this time, growth rate slowed and this correlated well with a decrease in wall extensibility (WEX). Birch leaves in shadelight showed reduced surface acidification and were the first to show reduced growth. WEX under these conditions was particularly low.Daily patterns of leaf growth of the two species were very different. Sycamore leaves showed a slightly higher growth rate in the dark than in shadelight, while birch leaves grew more rapidly in shadelight than in the dark. Limitation of growth of sycamore leaves in light may be explained by a very high yield threshold turgor for growth (Y). The daily pattern of leaf growth shown by birch is more difficult to explain but the importance of a possible limitation of growth by solute availability and a diurnal variation in Y are discussed.     

Why do anemonefishes inhabit only some host actinians?

Synopsis The 25 species ofAmphiprion and one ofPremnas (family Pomacentridae) are obligate symbionts of 10 species of facultatively symbiotic sea anemones. Throughout the tropical Indo-West Pacific range of the relationship, a fish species inhabits only certain of the hosts potentially available to it. This specificity is due to the fishes. Five fishes occupy six sea anemone species at Lizard Island, Great Barrier Reef, Australia.Entacmaea quadricolor harborsP. biaculeatus, A. melanopus andA. akindynos. Adults ofPremnas occur deeper than about 3 m in large, primarily solitary actinians; juveniles may occupy peripheral members ofEntacmaea clones in shallow water. Specimens ofA. melanopus live exclusively in clonal anemones, which are found no deeper than 3 m. Most individuals ofA. akindynos inEntacmaea are juveniles, occurring shallow and deep, in solitary anemones or at the margins of clones. Interspecific as well as intraspecific social control of growth may be responsible for keeping fish small at clone fringes. Conspicuous specimens ofE. quadricolor depend upon their anemonefish to survive. Actinians cleared of symbionts disappeared within 24 h, probably having been eaten by reef fishes.Entacmaea, the most abundant and widespread host actinian at Lizard Island and throughout the range of the association, is also arguably the most attractive to anemonefishes. I believe its vulnerability to predation was a factor in its evolving whatever makes it desirable to fishes. Experimental transfers pitted fish of one species against those of another, controlling for ecophenotype of host, and sex, size and number of fish. Competitive superiority was in the same order as abundance and over-all host specificity:P. biaculeatus, A. melanopus, A. akindynos. At least three factors are necessary to explain patterns of species specificity - innate or learned host preference, competition, and stochastic processes.     

Protoplast-derived streptomycin resistant plants of the forage legume Onobrychis viciifolia Scop. (sainfoin)

Approximately 10⁶ protoplast-derived cell colonies of sainfoin were stressed with streptomycin and two resistant colonies were recovered. Plants regenerated from these colonies could be recallused on streptomycin-containing medium three years after growth in the absence of the antibiotic.Ultrastructural studies showed cells of resistant callus grown in the presence of streptomycin to contain chloroplasts with internal thykaloids and grana. Such mutant plants should be useful in designing biochemical selection schemes to recover somatic hybrids and cybrids.Abbreviations BAP 6 - benzylamino purine - NAA - napthaleneacetic acid     

A high affinity,calmodulin-responsive (Ca2+ + Mg2+)-ATPase in isolated bone cells

Although acute alterations in Ca²⁺ fluxes may mediate the skeletal responses to certain humoral agents, the processes subserving those fluxes are not well understood. We have sought evidence for Ca²⁺-dependent ATPase activity in isolated osteoblast-like cells maintained in primary culture. Two Ca²⁺-dependent ATPase components were found in a plasma membrane fraction: a high affinity component (half-saturation constant for Ca²⁺ of 280 nM, $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ of 13.5 nmol/mg per min) and a low affinity component, which was in reality a divalent cation ATPase, since Mg²⁺ could replace Ca²⁺ without loss of activity. The high affinity component exhibited a pH optimum of 7.2 and required Mg²⁺ for full activity. It was unaffected by potassium or sodium chloride, ouabain or sodium azide, but was inhibited by lanthanum and by the calmodulin antagonist trifluoperazine. This component was prevalent in a subcellular fraction which was also enriched in 5′-nucleotidase and adenylate cyclase activities, suggesting the plasma membrane as its principal location. Osteosarcoma cells, known to resemble osteoblasts in their biological characteristics and responses to bone-seeking hormones, contained similar ATPase activities. Inclusion of purified calmodulin in the assay system caused small non-reproducible increases in the Ca²⁺-dependent ATPase activity of EGTA-washed membranes. Marked, consistent calmodulin stimulation was demonstrated in membranes exposed previously to trifluoperazine and then washed in trifluoperazine-free buffer. These results indicate the presence of a high affinity, calmodulin-sensitive Ca²⁺-dependent ATPase in osteoblast-like bone cells. As one determinant of Ca²⁺ fluxes in bone cells, this enzyme may participate in the hormonal regulation of bone cell function.     

Requirements for antiribosomal activity of pokeweed antiviral protein

It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K⁺ and 3 mM Mg²⁺ retards the reaction, while 20 mM K⁺ and 2 mM Mg²⁺ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The K_m for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pK_a value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity.     

Incidence of Infectious Drug Resistance Among Fecal Coliforms Isolated from Raw Sewage

Raw sewage was examined for the incidence of antibiotic-resistant coliforms present among both total and fecal coliforms. In both groups, it was found that approximately 3% of the coliform bacteria were resistant to two or more antibiotics. Of these organisms, 48% were capable of transferring all or part of their antibiotic resistance to an antibiotic-sensitive, F⁻, derivative of Escherichia coli K-12. Among the R factors identified, those conferring resistance to streptomycin-tetracycline, ampicillin-streptomycin-tetracycline, and ampicillin or ampicillin-streptomycin accounted for 23, 20, and 15%, respectively, of the total R factors detected. The data indicate a significant level of infectious drug resistance among the fecal coliforms of the urban population. The data indicate further that because of the high incidence of coliform bacteria found to be doubly resistant to streptomycin and tetracyline, the inclusion of these antibiotics in selective media used for routine total or fecal coliform counts may serve to identify domestic sources of pollution.     

The influence of sucrose, 2,4-D,and kinetin on the growth,fine structure,and lignin content of cultured sycamore cells

Summary When suspensions of sycamore cells are cultured in a synthetic medium containing 1.0 mg/l 2,4-D and 0.25 mg/l kinetin, maximum cell yield is obtained with an initial concentration of 6 per cent sucrose. There is a progressive increase in dry weight per cell, decline in extractive-free weight as a percentage of cell dry weight and increase in lignin content per cell as the initial sucrose concentration is increased from 1 per cent to 15 per cent. The percentage of lignin in the extractive-free cell residue is further enhanced by increasing the level of 2,4-D to 10 mg/l or by growing the cells in an auxin-free medium containing 10 mg/l kinetin.When the cell suspensions are treated with phloroglucinol/HCl it is found that only a proportion of the cells contain lignin, that this lignin occurs in the protoplasts and in plates between the cells, and that lignin is present in the culture medium.Electron micrographs confirmed the absence of any secondary wall such as is characteristic of tracheary elements. Cells cultured in the presence of 6 per cent sucrose or higher levels showed numerous amyloplasts and frequently the presence of electron opaque material. This occurs in the irregular but not frequent wall thickenings, as droplets in the vacuoles and as amorphous sheets between the cells. Pictures showing such electron opaque droplets clustered on the inner face of the tonoplasts suggest that this material is formed in the cytoplasm and released into the vacuoles. In addition these cells are characterised by the presence of fine electron opaque granular material in their vacuoles and external to their protoplasts. Cultures richest in lignin showed the highest content of electron opaque globules in, and amorphous sheets between, the cells and it is suggested that these correspond to lignin or a lignin-hemicellulose complex. In the presence of 15 per cent sucrose many cells showing breakdown of organised structure were observed; they were characterised by the persistence of mitochondria and particularly of the amyloplasts and by their high content of the electron opaque material equated with lignin. This material was also present in the dead cells.     

Molting in a parasitic nematode, Phocanema decipiens—VII. The mode of action of the ecdysial hormone

The cycle of aminopeptidase activity demonstrated by histochemical methods in the activated excretory gland could not be detected in homogenates. In the electron microscope, the secretory granules in dormant glands were dense and irregular in shape and the mitochondria elongate, relatively dense, and with a crenellated outer membrane. The excretory gland was activated when the neuroendocrine system was stimulated by farnesyl methyl ether. In activated glands the secretory granules became larger, less dense and the membranes began to fuse with membranes of the ductules which ramify through the gland. The mitochondria became swollen. Aminopeptidase activity was displayed by a large uniformly less dense granules but not by the denser granules, and was seen in the endoplasmic reticulum, Golgi apparatus and in the lumen of the ducts. It is suggested that the ecdysial hormone from the neurosecretory cells sets in train a sequence of events which leads to entry of water into the gland and consequent activation of the enzyme in the granules, and to changes in the membranes of the granules which facilitate fusion with the membrane lining the ducts.     

Genetic and Biophysical Study of R Plasmids Conferring Sulfonamide Resistance in Shigella Strains Isolated in 1952 and 1956

The conjugative plasmids determining sulfonamide resistance in five Shigella strains, each isolated from a different patient, have been characterized. One S. flexneri 2a strain, isolated in 1952, harbored an fi(+) plasmid of molecular weight 53 x 10(6), which specified synthesis of F-like pili and bore determinants for sulfonamide resistance (Su) and bacteriocinogeny (Col). This plasmid was compatible with plasmids of groups F(I), F(II), I(alpha), and P. A second S. flexneri 2a strain isolated in 1952 harbored an fi(-) plasmid of molecular weight 59 x 10(6), bearing the Su determinant and compatible with all plasmids tested. This strain also harbored an fi(+) group-F(II) plasmid of molecular weight 42 x 10(6), which bore the Col determinant and specified synthesis of F-like pili. Three S. dysenteriae 2 strains isolated in 1956 carried apparently identical fi(-) plasmids of molecular weight 58 x 10(6), which bore the Su determinant, could form transconjugants in Pseudomonas but not in Proteus, and were incompatible with the P-group plasmid RP4.