The use of cell lethal mutations in the study of Drosophila development

Cell-lethal mutations are currently being used to study the role of cell death in the development of normal and mutant phenotypes, and in highly detailed studies of pattern formation. Histological studies of certain “position-specific” cell-lethals suggest that programmed cell death may be important in the development of normal imaginal discs, and that many mutations may be producing an abnormal phenotype by amplifying this normal process. Somatic mosaic studies using temperature-sensitive cell-lethals have provided much information about the development of pattern duplications, including the number of cells involved, their growth rate, and compartmentalization during duplication. Further work in this area may, when combined with genetic analyses of the loci involved, reveal much about the nature of the processes controlling pattern determination and differentiation.     

Some observations on habituation of the flexor reflex in the rat: the influence of strychnine, bicuculline, spinal transection, and decerebration

The involvement of inhibition in habituation of the flexor reflex was investigated in intact, spinal, and decerebrate rats. Strychnine and bicuculline were administered in order to determine the contribution of certain forms of central inhibition to the development of habituation. Both strychnine and bicuculline reduced habituation in the intact rat but did not do so in the spinal preparation. Strychnine, in fact, caused a facilitation of habituation in the spinal rat. The impairment of habituation by strychnine was related to the intensity of stimulation used to elicit the reflex. Thus, the effect of strychnine was only demonstrable when relatively high intensities were used. Flexor reflex habituation was shown to be more pronounced in the decerebrate than in the spinal preparation. This difference could be demonstrated only when stimuli of high intensity were given. It is concluded that, in the absence of supraspinal influences, habituation of the flexor reflex does not require inhibitory mechanisms. However, inhibition may play a role in habituation of the component of the reflex that utilizes descending influences.     

Bendectin and fetal malformations.

Mortality among 172 workers who received workmen''s compensation for asbestosis in Ontario was investigated and the causes of death were compared with those for the general male population in that province. The workers were found to have increased rates of death, relative to the general populations, for nonmalignant respiratory diseases, lung cancer and pleural and peritoneal mesothelioma. In comparison with the general population, the proportion of workers that survived was 69% of that expected 5 years after they were awarded compensation and 53% at 10 years.     

Ionic currents across pancreatic acinar cell membranes and their role in fluid secretion

Fluid and enzyme secretion from a number of mammalian exocrine glands is controlled by the action of neurotransmitters and hormones on acinar cell membranes. Sustained stimulation evoking sustained fluid and enzyme secretion also evokes sustained membrane depolarization and increase in conductance. Mouse and rat pancreatic fluid and enzyme secretion, as well as membrane depolarization and conductance increase evoked by sustained stimulation with acetylcholine or cholecystokinin-gastrin peptides, are acutely dependent on extracellular calcium. However, the initial stimulant-evoked conductance increase and secretion appear to be triggered by calcium released from inside the cells. Direct measurement of membrane current during sustained stimulation in voltage-clamp experiments with resolution of the total current into its Na, Cl and K components has allowed calculations of stimulant-evoked Na and Cl uptake into the acinar cells. The NaCl uptake is quantitatively sufficient to account for the stimulant-evoked fluid secretion. The role of the stimulant-evoked transmembrane ionic current appears to be the supply of salt for the fluid secretion. Calcium derived from intracellular sources in the initial phase of secretion, and from the extracellular fluid in the sustained phase, couples fluid and enzyme secretion to hormone-receptor interaction.     

An in vitro morphological study of the mouse visceral yolk sac and possible yolk sac immunocyte precursors

Summary Mouse visceral yolk sac has been organ cultured from 9 days of gestation, a time prior to the thymus being lymphoid, until 12 days of gestation, a time after which the thymus is lymphoid. During the culture period the endodermal epithelial cells survived well, erythropoiesis diminished, endothelial-lined cavities formed in the mesodermal mass, and cells developed which have been classified as large, medium and small immunocyte precursors. The cytoplasm of the immunocyte precursors contains polysomes, spherical mitochondria, a few profiles of rough endoplasmic reticulum, occasional granules and a large Golgi complex. This study offers morphological support for the yolk sac origin of immunocyte precursors in the mouse which may seed the thymus and liver.Supported by NIH Grant AI 13486-01     

Innervation of the cultured fetal rat pancreas

Summary The fetal rat pancreas, explanted at 18 days of gestation and cultured up to ten days, contains numerous acetylcholinesterase-positive neurons. These nerves usually appear in small ganglia although single nerve cells are encountered. The axons of these intrapancreatic nerves appear to terminate only in the islet tissue and not on any exocrine components of the expiant. It is concluded that the fetal rat pancreas contains an islet-specific group of cholinergic neurons.We gratefully acknowledge the skilled technical assistance of Dan Whitehead and the secretarial assistance of Mary Pat Brady     

Plants interact with microbial polysaccharides

Plants are resistant to almost all of the microorganisms with which they come in contact. In response to invasion by a fungus, bacterium, or a virus, many plants produce low molecular weight compounds, phytoalexins, which inhibit the growth of microorganisms. Phytoalexins are produced whether or not the invading microorganism is a pathogen. The production of phytoalexins appears to be a widespread mechanism by which plants attempt to defend themselves against pests. Molecules of microbial origin which trigger phytoalexin accumulation in plants are called elicitors. Structural polysaccharides from the mycelial walls of several fungi elicit phytoalexin accumlation in plants. Approximately 10 ng of the polysaccharide elicits the accumulation in plants of more than sufficient amounts of phytoalexin to stop the growth of microorganisms in vitro. The best characterized elicitors have been demonstrated to be β-1,3-glucans with branches to the 6 position of some of the glucosyl residues. Oligosaccharides, produced by partial acid hydrolysis of the mycelial wall glucans, are exceptionally active elicitors. The smallest oligosaccharide which is still an effective elicitor is composed of about 8 sugar residues. Bacteria also elicit phytoalexin accumulation in plants, but the Rhizobium symbionts of legumes presumably have a mechanism which allows them to avoid either eliciting phytoalexin accumulation or the effects of the phytoalexins if they are accumulated. The lectins of legumes bind to the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It is not known whether the lectin-lipopolysaccharide interaction is involved with the establishment of symbiosis. However, evidence will be presented that suggests that lectins are, in fact, enzymes capable of modifying the structurs of the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It will also be shown that the lipopolysaccharides isolated from different Rhizobium species and from different strains of individual Rhizobium species have different sugar compositions. Thus, the different strains of a single Rhizobium species are as different from one another as the different species of Salmonella and other gram-negative bacteria. This conclusion is substantiated by experiments demonstrating that antibodies to the lipopolysaccharide from a single Rhizobium strain can differentiate that strain from other strains of the same species as well as from other Rhizobium species. The role in symbiosis of the strain-specific O-antigens is unknown.     

Effects of Cycloate on Development of Heterodera schachtii and Growth of Three Beta Species

Greenhouse tests were set up to evaluate the effects of the herbicide, cycloate (S-ethyl cydohexylethylthiocarbamate), oil development of Heterodera schachtii and growth of three Beta species. Cycloate added to infested soil enhanced cyst development/gm root on B. vulgaris and larvae/gm of root in B. patellaris and B. procumbens at 4, 16, and 16 μg(a.i.)/gm of soil, respectively. Total numbers of nematodes/individual root system decreased because of poor root growth of seedlings in cycloate-amended soil. Penetration and larval development through stage three did occur in the wild Beta species in any treatment. Thus, resistance of B. patellaris and B. pocumbens to development of H. schachtii was not altered by cycloate. Cycloate also retarded growth (P = 0.05) of the sugarbeet cultivars and B. patellaris at 4 μg(a.i.)/gm and B. procumbens at 16 μg(a.i.)/gm of soil. Higher concentrations of nematodes/gm root in plants growing in cycloate-amended soil may be attributed to factors such as fewer roots available for penetration, possible effects of cycloate on egg hatch, greater attraction of nematodes to roots, and increased susceptibility of roots to larval penetration. Suppression of seedling growth in cycloate-amended soil may be attributed in part to higher nematode density and in part to direct root damage from cycloate.     

Metabolism of phenylalanine and tyrosine in tobacco cell lines resistant and sensitive to p-fluorophenylalanine

Chromatography of soluble polyphenols of p-fluorophenylalanine-sensitive and -resistant tobacco cells revealed that the 10-fold increased level found in the resistant line was largely due to the accumulation of two unidentified polyphenols. The uptake of Phe-[U-¹⁴C] and Tyr-[U-¹⁴C] by the resistant line was ca 10 % that by the sensitive line. About 90 % of the phenylalanine-[¹⁴C] which was taken up by both cell lines could be accounted for as free phenylalanine in protein, soluble polyphenols or CO₂. The fate of Tyr-[¹⁴C] was similar to that of phenylalanine except that the incorporation was into insoluble polymeric forms of polyphenols rather than into soluble polyphenols. The resistant line incorporated 9-times more phenylalanine-[¹⁴C] into soluble polyphenols than did the sensitive line. The different ¹⁴C-aromatic amino acid accumulation and incorporation patterns noted with the two cell lines indicates that there are different active pools. Differential uptake rates by the two cell lines might affect the distribution of the absorbed amino acid among the different pools.     

Paraquat ingestion and pulmonary injury.

Ventricular aneurysm is usually a complication of acute transmural myocardial infarction. The development of cardiac aneurysm represents a process of continued thinning and fibrosis of the necrotic tissue of the ventricular wall. Survival allows the development of a solid fibrous scar which of itself does not affect global ventricular function substantially. Hence, ventricular aneurysms can be present for up to 18 years without production of serious symptoms. The cases were reviewed of 45 patients in whom aneurysmectomy and myocardial revascularization were carried out. Surgical mortality was low (6.6 percent, 30 days); survival one year after operation was 76 percent, but at three years had fallen to 47 percent. Cause of late death was dominantly cardiac. In 19 patients post-operative study was done; although graft patency was observed in 98 percent, substantive improvement in ventricular performance was seen in a minority of patients. The outcome in patients with ventricular aneurysm is primarily related to the status of the residual myocardium and to the status of the vessels which supply it. The mechanism of clinical improvement after aneurysmectomy has not been clarified. However, the long-term results appear to be similar to those in patients with extensive myocardial infarction.