A protein homologous to the 27,000 dalton liver gap junction protein is present in a wide variety of species and tissues

The species and tissue specificities of gap junction polypeptides were investigated with antibodies raised against the 27,000 dalton rat liver gap junction protein. Cross-reacting 27,000 dalton polypeptides were detected in liver from mammalian, fish, and avian species by immunoreplica analyses and were localized to punctate regions of the plasma membrane by indirect immunofluorescence. They were also found in homogenates of other rat tissues, including pancreas, heart, brain, kidney, stomach, and adrenal gland, but not in lens fiber material. Localization of antibody binding in pancreas was similar to that of liver, while in heart ventricle the immunofluorescence pattern was consistent with binding to the intercalated disc. These findings indicate that homologous gap junction polypeptides may be widely distributed among vertebrate tissues.     

Reduced extracellular pH reversibly inhibits oligomerization, intracellular transport, and processing of the influenza hemagglutinin in infected Madin-Darby canine kidney cells

Incubation of Madin-Darby canine kidney cells infected with influenza virus in medium of pH 5.8-6.0 blocks transport of newly synthesized hemagglutinin and processing of the hemagglutinin oligosaccharides to a form resistant to endo H digestion. Upon restoration of the culture medium to pH 7.4, arrested hemagglutinin is processed and then appears on the cell surface, indicating that exclusively transport and not oligosaccharide processing is inhibited. Based upon kinetic data and localization of blocked hemagglutinin by immunofluorescence, the point of inhibition appears to be a discrete step in transport located in a pre-Golgi compartment. This conclusion is supported by the observation that trimerization of hemagglutinin, which is believed to occur in the endoplasmic reticulum, is also inhibited by acidic medium.     

Sister chromatid cohesion role for CDC28-CDK in Saccharomyces cerevisiae

High-fidelity chromosome segregation requires that the sister chromatids produced during S phase also become paired during S phase. Ctf7p (Eco1p) is required to establish sister chromatid pairing specifically during DNA replication. However, Ctf7p also becomes active during G(2)/M in response to DNA damage. Ctf7p is a phosphoprotein and an in vitro target of Cdc28p cyclin-dependent kinase (CDK), suggesting one possible mechanism for regulating the essential function of Ctf7p. Here, we report a novel synthetic lethal interaction between ctf7 and cdc28. However, neither elevated CDC28 levels nor CDC28 Cak1p-bypass alleles rescue ctf7 cell phenotypes. Moreover, cells expressing Ctf7p mutated at all full- and partial-consensus CDK-phosphorylation sites exhibit robust cell growth. These and other results reveal that Ctf7p regulation is more complicated than previously envisioned and suggest that CDK acts in sister chromatid cohesion parallel to Ctf7p reactions.     

Multiple actins in drosophila melanogaster

The tissue and developmental specificities of the three Drosophila isoactins, originally identified in primary myogenic cultures and in the permanent Schneider L-2 cell line, have been investigated. Of these three isoactins (I, II, and III), actins I and II are stable and actin III is unstable. Two-dimensional polyacrylamide gel electrophoretic analyses of total cellular extracts after 1-h [(35)S]methionine pulses were performed on a large variety of embryonic, larval, and adult muscle and nonmuscle tissues. The results suggest that isoactins II and III are generalized cellular actins found in all drosophila cell types. Actin I, on the other hand, is muscle-associated and is found exclusively in supercontractile muscle (such as larval body wall and larval and adult viscera) including primary myogenic cell cultures. Although actin I synthesis is not detectable during very early embryogenesis, it is detectable by 25 h and actin I is a major stable actin in all larval muscle tissues. Actin I is synthesized in reduced amounts relative to the other actins in late third instar larvae but is again a major product of actin synthesis in the adult abdomen. A stable actin species with the same pI as actin III has been identified in the adult thorax and appears to be unique to flight muscle tissue. This new stable form of thoracic actin may be the result of a stabilization of the actin III found in other tissues or may be an entirely separate gene product.     

How the transition frequencies of microtubule dynamic instability (nucleation, catastrophe, and rescue) regulate microtubule dynamics in interphase and mitosis: analysis using a Monte Carlo computer simulation.

Microtubules (MTs) in newt mitotic spindles grow faster than MTs in the interphase cytoplasmic microtubule complex (CMTC), yet spindle MTs do not have the long lengths or lifetimes of the CMTC microtubules. Because MTs undergo dynamic instability, it is likely that changes in the durations of growth or shortening are responsible for this anomaly. We have used a Monte Carlo computer simulation to examine how changes in the number of MTs and changes in the catastrophe and rescue frequencies of dynamic instability may be responsible for the cell cycle dependent changes in MT characteristics. We used the computer simulations to model interphase-like or mitotic-like MT populations on the basis of the dynamic instability parameters available from newt lung epithelial cells in vivo. We started with parameters that produced MT populations similar to the interphase newt lung cell CMTC. In the simulation, increasing the number of MTs and either increasing the frequency of catastrophe or decreasing the frequency of rescue reproduced the changes in MT dynamics measured in vivo between interphase and mitosis.     

Unzipped and loaded: the role of DNA helicases and RFC clamp-loading complexes in sister chromatid cohesion

It is well known that the products of chromosome replication are paired to ensure that the sisters segregate away from each other during mitosis. A key issue is how cells pair sister chromatids but preclude the catastrophic pairing of nonsister chromatids. The identification of both replication factor C and DNA helicases as critical for sister chromatid pairing has brought new insights into this fundamental process.     

Regulated assembly of the mitotic spindle: a perspective from two ends

Chromosome segregration and cell division requires the regulated assembly of the mitotic spindle apparatus. This mitotic spindle is composed of condensed chromosomes attached to a dynamic array of microtubules. The microtubule array is nucleated by centrosomes and organized by associated structural and motor proteins. Mechanical linkages between sister chromatids and microtubules are critical for spindle assembly and chromosome segregation. Defects in either chromosome or centrosome segregation can lead to aneuploidy and are correlated with cancer progression. In this review, we discuss current models of how centrosomes and chromosomes organize the spindle for their equal distribution to each daughter cell.     

Change in Brain Magnetic Resonance Spectroscopy after Treatment during Acute HIV Infection

Objective

Single voxel proton magnetic resonance spectroscopy (MRS) can be used to monitor changes in brain inflammation and neuronal integrity associated with HIV infection and its treatments. We used MRS to measure brain changes during the first weeks following HIV infection and in response to antiretroviral therapy (ART).

Methods

Brain metabolite levels of N-acetyl aspartate (NAA), choline (tCHO), creatine (CR), myoinositol (MI), and glutamate and glutamine (GLX) were measured in acute HIV subjects (n = 31) and compared to chronic HIV+individuals (n = 26) and HIV negative control subjects (n = 10) from Bangkok, Thailand. Metabolites were measured in frontal gray matter (FGM), frontal white matter (FWM), occipital gray matter (OGM), and basal ganglia (BG). Repeat measures were obtained in 17 acute subjects 1, 3 and 6 months following initiation of ART.

Results

After adjustment for age we identified elevated BG tCHO/CR in acute HIV cases at baseline (median 14 days after HIV infection) compared to control (p = 0.0014), as well as chronic subjects (p = 0.0023). A similar tCHO/CR elevation was noted in OGM; no other metabolite abnormalities were seen between acute and control subjects. Mixed longitudinal models revealed resolution of BG tCHO/CR elevation after ART (p = 0.022) with tCHO/CR similar to control subjects at 6 months.

Interpretation

We detected cellular inflammation in the absence of measurable neuronal injury within the first month of HIV infection, and normalization of this inflammation following acutely administered ART. Our findings suggest that early ART may be neuroprotective in HIV infection by mitigating processes leading to CNS injury.     

Sister-chromatid telomere cohesion is nonredundant and resists both spindle forces and telomere motility

It is well documented that inactivation of essential cohesion proteins results in precocious sister-chromatid separation. On average, however, only approximately 55% of cohesin-deficient budding yeast cells arrested prior to anaphase contain separated sister chromatids , suggesting that cohesin-independent factors also contribute to sister-chromatid pairing. Recently, redundant pairing mechanisms were found to occur at both rDNA and centromeres . Here, we tested whether redundant mechanisms also function to pair telomeres or whether cohesins provide sole pairing activity. Results from both mcd1 and ctf7 mutant cells show that nearly 100% of telomeres separate prior to anaphase, twice the cohesion defect reported for centromeres. Such complete loci separation reveals that cohesins are singularly responsible for maintaining telomere cohesion, in contrast to other loci. We also found that sister telomeres moved 141% farther apart than centromeres. Telomere separation occurred in the absence of spindle microtubules and an actin cytoskeleton and persisted in cells abrogated for Mps3p function-an integral nuclear envelope protein previously shown to function in cohesion . These findings are consistent with numerous studies that telomeres translocate along the nuclear periphery and provide new evidence that telomere dynamics can contribute to sister-chromatid separation, independent of centromere motility.