The role of introns in evolution

What are the roles of 'classical' introns in the evolution of nuclear genes, and what was the origin of these introns? Exon shuffling has been important in the evolution of cell surface and extracellular proteins, but the evidence for it in respect of intracellular proteins is weak. Intron distributions imply that some introns have been removed while others have been inserted in the course of evolution: ancestral patterns of introns may thus have been obscured. Recent evidence on the self-splicing and reverse-splicing abilities of Group II introns supports the hypothesis that these could have been the ancestors of classical introns.     

Can zoosporic true fungi grow or survive in extreme or stressful environments?

Zoosporic true fungi are thought to be ubiquitous in many ecosystems, especially in cool, moist soils and freshwater habitats which are rich in organic matter. However, some of the habitats where these fungi are found may periodically experience extreme conditions, such as soils in extremely dry, hot and cold climates, acidic and alkaline soils, polluted rivers, anaerobic soil and water, saline soil and water, periglacial soils, oligotrophic soils, tree canopies and hydrothermal vents. It is clear that many ecotypes of zoosporic true fungi have indeed adapted to extreme or stressful environmental conditions. This conclusion is supported by studies in both the field and in the laboratory. Therefore, in our opinion, at least some true zoosporic fungi can be considered to be extremophiles.     

Fragile X expression in thymidine-prototrophic and auxotrophic human-mouse somatic cell hybrids under low and high thymidylate stress conditions

Expression of the fragile X site fra(X)(q27.3) was studied in thymidine-prototrophic and auxotrophic human-mouse somatic cell hybrids. In these cells, low thymidylate stress, achieved by 5-fluoro-2'-deoxyuridine (FdU) treatment and by limiting the exogenous supply of thymidine (dT), induced fragile X expression. High thymidylate stress, produced by supplying excess amounts of dT, was also effective in inducing fragile X expression, even in a hybrid clone that retained a fragile X chromosome as the only human chromosome; addition of deoxycytidine (dC) completely abolished this effect. In contrast, 5-bromo-2'-deoxyuridine (BrdU) did not induce fragile X expression. Cell-cycle analysis of BrdU-deprived thymidine-auxotrophic hybrid cells indicated that one round of DNA replication under thymidylate stress conditions is sufficient for fragile X expression. Our results suggest that the expression is an intrinsic property of the fragile site itself, which is believed to be composed of replicon clusters with pyrimidine-rich DNA sequence(s).     

What's new in cerebral palsy

Among new researches bearing on cerebral palsy are the growth of brain cells in tissue cultures for experimentation; the use of polysaccharides to prevent the formation of a glial barrier to nerve growth after injury; observation of changes in reactions of neurons at various stages of development; the finding of hypernatremia and hyperchloremia in lesions of the frontal lobe and the thalamus; stimulation of cerebral blood flow by injection of sodium bicarbonate and retardation with ammonium chloride; and studies of serial sections of brains of palsied children who died. Study of development in the early months of life has made possible the detection of significant abnormalities in behavior early in life. Loss of hearing may be tested in very young children by measuring minute variations in electrical resistance of the skin upon auditory stimulation of the sympathetic nervous system. Conditions which have been described as having been confused with cerebral palsy are dislocation of a cervical vertebra, hereditary spastic paraplegia, transverse myelopathy, injury to the spinal cord or cauda equina by anomalous growths of the spine, and also encephalitis and meningitis. Sedation has proved a valuable adjunct to electroencephalographic study of cerebral palsy. Better criteria for abnormality in the young child should be determined and the application of them more clearly standardized. Simple exercises are useful for early training of palsied children to stimulate development. "Crossed laterality"-the dominant eye being contralateral to the preferred hand-has been counteracted by special training with great success in eliminating emotional and behavior problems and accelerating development.Recent studies indicate that only 50 per cent of cerebral palsy patients have normal or better intelligence. Subluxation of the hip joint, a common deformity associated with cerebral palsy, can sometimes be corrected by operation if detected at an early stage. Radical ablation of epileptogenic foci in the cortex is also being done in young patients if drug control of seizures fails. Frontal topectomy, cingulate gyrectomy or prefrontal labotomy may be advisable in cases in which proper response to drug therapy is not obtained. Improvement in behavior as well as control of seizures may follow the use of Benzedrine,(R) Dexedrine,(R) Dilantin(R) sodium, Mebaral(R) and phenobarbital. Alcohol, paraldehyde and chloral hydrate have been effective as relaxants.     

The small hospital's role in poliomyelitis

Medical skills should be developed by the staffs of smaller hospitals for the differential study of patients with symptoms resembling those of poliomyelitis in order to provide the rudiments of care for the occasional patient with mild poliomyelitis, to recognize the indications which point to the necessity of superior technical assistance, and to decide when it is appropriate to move patients to better equipped centers. The impetuous acquisition of mechanical aids for the treatment of special problems will be effective in small communities only to the extent that this equipment is kept serviceable and is operated by persons of sufficient skill. Epidemic situations in a small community can be met only by mobilization of facilities under adequate direction and by integration of care with that provided by larger treatment centers.     

Commitment to Ploidy Conversion of 3y1 Cells During Metaphase Arrest By Colcemid

Abstract. Diploid rat 3Y1 fibroblasts proliferate to a saturation density, where they are arrested with a 2N DNA content. After treatment to induce ploidy conversion, the conversion rate can be estimated by determining the fraction of cells with a 4N DNA content in the confluent culture using flow cytometry. Using this method it was found that during mitotic inhibition with colcemid, 3Y1 cells were converted to tetraploids with a high efficiency (above 80%); the optimum colcemid concentration and exposure period were 40 ng/ml and 8 hr, respectively. When metaphase cells were reseeded with 40 ng/ml of colcemid, they delayed anchorage to a dish; 6 hr was required for complete adhesion (in the absence of colcemid only 1 hr was required). When reseeded metaphase cells were exposed to 40 ng/ml of colcemid for 5 hr followed by its removal, a greater fraction of the cells anchored to the substratum were converted to tetraploids, whereas most of the floating cells were not. A greater fraction of the anchored cells had formed nuclei, whereas most of the floating cells preserved condensed metaphase chromosomes. These results indicate that the cells which have formed nuclear structure without chromosome separation during mitotic inhibition are irreversibly committed to ploidy conversion, with restoration of anchorage.