Functional interactions between the VRP1–LAS17 and RHO3–RHO4 genes involved in actin cytoskeleton organization in Saccharomyces cerevisiae

The RGD1 gene from Saccharomyces cerevisiae, which encodes a GTPase-activating protein for the Rho3 and Rho4 small G proteins, exhibits synthetic lethality with the VRP1 and LAS17 genes. Their products are proline-rich proteins that interact with both actin and myosins to ensure polarized growth. By testing functional links, we found that the VRP1 and LAS17 genes are potent suppressors of the rho3Delta mutation. In particular, they restore the polarization of actin patches in rho3Delta cells. Moreover, the vrp1Delta and las17Delta mutations were found to display a similar pattern of genetic interactions with specific actin-linked genes. These mutations also increase the sensitivity to activated forms of both Rho3p and Rho4p. These data support our working model, in which the VRP1 and LAS17 genes define a cellular complex that works in concert with the RHO3-RHO4 signaling pathway in yeast polarized growth. In addition, other observations lead us to propose that Rvs167p may act as a linking protein between the two cellular elements.     

Electrical properties of gap junction channels in guinea-pig ventricular cell pairs revealed by exposure to heptanol

Cell pairs were isolated from adult guinea pig ventricles to study the electrical properties of gap junction channels. The experiments involved a double voltage-clamp approach and whole-cell, tight-seal recording. Heptanol decreased the intracellular current, In, in a dose-dependent fashion. Before complete uncoupling, In showed fluctuations suggesting the operation of gated channels. In the presence of 3 mM heptanol, In showed quantal steps arising from spontaneous opening and closing of single channels. The IV-relationship of the channels was linear (range: +/- 95 mV). Analysis of current records revealed the following single-channel conductances, gamma n: Mean value = 37 pS; median value = 33 pS. gamma n was insensitive to the non-junctional membrane potential (range: -90 to +10 mV). 3 mM ATP4- in the pipette solution had no effects on gamma n, 6 mM ATP4- produced a small decrease, and 6 mM ATP + 0.1 mM cAMP- an increase in gamma n. Channel transitions from closed to open state were variable (range of apparent time constants: 2.5-32 ms; mean: 11 ms).     

Monte Carlo calculation of the sensitivity of a commercial dose calibrator to gamma and beta radiation

The detection process used in a commercial dose calibrator was modeled using the GEANT 3 Monte Carlo code. Dose calibrator efficiency for gamma and beta emitters, and the response to monoenergetic photons and electrons was calculated. The model shows that beta emitters below 2.5 MeV deposit energy indirectly in the detector through bremsstrahlung produced in the chamber wall or in the source itself. Higher energy beta emitters (E > 2.5 MeV) deposit energy directly in the chamber sensitive volume, and dose calibrator sensitivity increases abruptly for these radionuclides. The Monte Carlo calculations were compared with gamma and beta emitter measurements. The calculations show that the variation in dose calibrator efficiency with measuring conditions (source volume, container diameter, container wall thickness and material, position of the source within the calibrator) is relatively small and can be considered insignificant for routine measurement applications. However, dose calibrator efficiency depends strongly on the inner-wall thickness of the detector.     

Disruption of the Aspergillus niger argB gene: a tool for transformation

We disrupted the Aspergillus niger gene argB, encoding ornithine transcarbamylase. Full characterisation of the argB deletion was performed by Southern blot analysis, growth tests and by means of mitotic recombination, complementation and transformation. The argB locus was found to be physically removed, thus creating an auxotrophic mutation. The latter can be supplemented by addition of arginine into the culture medium. The argB gene and its disruption do not correlate to the argI13 (formerly argB13) allele described. The delta argB is on chromosome I whereas argI13 is on V. In addition, the argI13 mutation can only be complemented by the A. nidulans argB gene, whereas the new argB deletion can be complemented by both the A. niger and A. nidulans argB genes. The delta argB strain has been used to generate several strains in a breeding programme and to study the expression of important genes, such as areA and kexB.     

Somatic mosaicism for a MECP2 mutation associated with classic Rett syndrome in a boy

Rett syndrome is a severe neurodevelopmental disorder that arises from mutations in the X-linked MECP2 gene. It is almost exclusively seen in girls due to the predominant occurrence of the mutations on the paternal X-chromosome, and also the early postnatal lethal effect of the disease causing mutations in hemizygous boys. We identified a boy with features of classic Rett syndrome who is mosaic for the truncating MECP2 mutation R270X. Chromosome analysis showed normal karyotype. These results indicate that a MECP2 mutation associated with Rett syndrome in females could lead to a similar phenotype in males as a result of somatic mosaicism.     

Infective agents in fixed human cadavers: a brief review and suggested guidelines

Cadavers remain a principal teaching tool for anatomists and medical educators teaching gross anatomy. Infectious pathogens in cadavers that present particular risks include Mycobacterium tuberculosis, hepatitis B and C, the AIDS virus HIV, and prions that cause transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease (CJD) and Gerstmann-Straussler-Scheinker syndrome (GSS). It is often claimed that fixatives are effective in inactivation of these agents. Unfortunately cadavers, even though they are fixed, may still pose infection hazards to those who handle them. Specific safety precautions are necessary to avoid accidental disease transmission from cadavers before and during dissection and to decontaminate the local environment afterward. In this brief review, we describe the infectious pathogens that can be detected in cadavers and suggest safety guidelines for the protection of all who handle cadavers against infectious hazards.     

Role of granulocyte colony-stimulating factor in the treatment of mucormycosis

Several problems in the management of life-threatening mucormycosis remain unresolved, necessitating new methods of management. Four patients with histopathologically proven rhinocerebral mucormycosis were treated with high cumulative doses of granulocyte colony-stimulating factor (G-CSF). All had multiple predisposing factors for mucormycosis, particularly leukemia and neutropenia. Two patients refractory to fluconazole therapy were treated with liposomal amphotericin B. The improvement in clinical manifestations was closely related to neutrophil recovery, and all patients were alive at the end of therapy. In addition to surgical debridement and antifungal therapy, G-CSF seems to have played a role in their survival.