Genotypic Differences of Candida albicans and C. dubliniensis Isolates Related to Ethnic/Racial Differences within the Same Geographic Area

Candida albicans and C. dubliniensis genotype differences among Israeli ethnic groups were assessed. Isolates from Jews (51), Arabs (35) and Druze (25) were genotyped. The distributions among ethnic groups were not different, however they differed (p = 0.002) from global populations. Therefore, C. albicans and C. dubliniensis genotype distribution differences in Israel are related to changes in all ethnic groups.     

Apatite as a P source in mycorrhizal and non-mycorrhizal Pinus sylvestris seedlings

The objectives of the study are firstly to test the ability of ectomycorrhizal pine seedlings to use apatite as a P source in comparison with non-mycorrhizal pine seedlings and secondly, to determine if there is a relation between exudation of organic acids and the ability to use apatite as a P source. Non-mycorrhizal Pinus sylvestris (L.) seedlings and seedlings ectomycorrhizal with 4 different isolates of ectomycorrhizal fungi were grown for 220 days in sand/peat filled pots with apatite (Ca₅(F,OH)(PO₄)₃) as the sole P source. In an additional experiment, non-mycorrhizal Pinus sylvestris (L.) seedlings and seedlings ectomycorrhizal with 2 different isolates of ectomycorrhizal fungi were grown without any P source for 250 days. All other nutrients were supplied in a balanced nutrient solution.Ectomycorrhizal seedlings grew less than non-mycorrhizal seedlings but ectomycorrhizal seedlings produced a large external mycelium not included in the biomass estimates. All seedlings in the present study had low shoot:root ratios compared to seedlings growing under optimal conditions. All seedlings grown with apatite as P source had higher foliar P concentrations (0.71–2.11 mg/g) than seedlings growing without any P source (0.57–0.75 mg/g) indicating a significant ability to use apatite as a P source. Seedlings colonized by Suillus variegatus and Paxillus involutus had higher concentrations and total contents of P in shoots compared with non-mycorrhizal seedlings, indicating significant improvement of P uptake by these fungi in comparison with non-mycorrhizal seedlings or seedlings colonized Piloderma croceum.No clear relationship between exudation of organic acids and uptake of P was found. Seedlings colonized by S. variegatus reduced the pH of the soil more than seedlings colonized by P. involutus or non-mycorrhizal seedlings. It is suggested that S. variegatus colonization improves the P uptake by reducing the pH of the soil while P. involutus improves P uptake by having a greater ability to absorb dissolved phosphate than non-mycorrhizal roots or roots colonized by the other fungi used in the study.     

Propagation of Tau Misfolding from the Outside to the Inside of a Cell

Tauopathies are neurodegenerative diseases characterized by aggregation of the microtubule-associated protein Tau in neurons and glia. Although Tau is normally considered an intracellular protein, Tau aggregates are observed in the extracellular space, and Tau peptide is readily detected in the cerebrospinal fluid of patients. Tau aggregation occurs in many diseases, including Alzheimer disease and frontotemporal dementia. Tau pathology begins in discrete, disease-specific regions but eventually involves much larger areas of the brain. It is unknown how this propagation of Tau misfolding occurs. We hypothesize that extracellular Tau aggregates can transmit a misfolded state from the outside to the inside of a cell, similar to prions. Here we show that extracellular Tau aggregates, but not monomer, are taken up by cultured cells. Internalized Tau aggregates displace tubulin, co-localize with dextran, a marker of fluid-phase endocytosis, and induce fibrillization of intracellular full-length Tau. These intracellular fibrils are competent to seed fibril formation of recombinant Tau monomer in vitro. Finally, we observed that newly aggregated intracellular Tau transfers between co-cultured cells. Our data indicate that Tau aggregates can propagate a fibrillar, misfolded state from the outside to the inside of a cell. This may have important implications for understanding how protein misfolding spreads through the brains of tauopathy patients, and it is potentially relevant to myriad neurodegenerative diseases associated with protein misfolding.Tau filament deposition in Alzheimer disease (AD),² frontotemporal dementia (FTD), and other tauopathies correlates closely with cognitive dysfunction and cell death (1). Mutations in the tau gene cause autosomal dominant tauopathy, implicating Tau as the proximal cause (2–4). Specific disease phenotypes are defined by the early sites of pathology. For example, AD is characterized by memory loss that derives from involvement of hippocampal neurons, whereas FTD is characterized by personality changes that result from frontal lobe involvement (5). Pathology ultimately spreads to involve much larger regions of brain. Studies on patients with AD show a progressive, stereotyped spread of Tau deposits from the transentorhinal cortex to the hippocampus, and eventually to most cortical areas (6–8). Others have correlated the distribution of neurofibrillary tangles of Tau in AD brains with trans-synaptic distance from the affected areas (9). A similar spread affecting different subsets of neurons has been observed in other sporadic tauopathies, such as progressive supranuclear palsy (10). It is unknown why Tau misfolding progresses through the brain, whether it is a sequence of cell autonomous processes or whether a toxic factor is involved. Loss of synaptic connections and cell death may expose healthy cells to toxic factors and decrease available neurotrophins (11, 12). Another possibility is that the Tau protein itself serves as the agent of trans-cellular propagation. For example, it has been shown that extracellular Tau is toxic to cultured neuronal cells (13, 14). This is consistent with the observation that immunotherapy against Tau reduces pathology in a mouse model (15).Tau is well known as an intracellular protein that stabilizes microtubule filaments (16); however, it is readily detected in cerebrospinal fluid (17) and as extracellular aggregates, termed “ghost tangles,” in diseased brain. These are comprised predominantly of the microtubule-binding region (MTBR), the functional and pathogenic core of the Tau protein (18). We hypothesize that Tau aggregates present in the extracellular space enter naive cells and induce misfolding of intracellular Tau. We have tested this idea using cellular studies, biochemistry, and atomic force microscopy (AFM).     

RB signaling prevents replication-dependent DNA double-strand breaks following genotoxic insult

Cell cycle checkpoints induced by DNA damage play an integral role in preservation of genomic stability by allowing cells to limit the propagation of deleterious mutations. The retinoblastoma tumor suppressor (RB) is crucial for the maintenance of the DNA damage checkpoint function because it elicits cell cycle arrest in response to a variety of genotoxic stresses. Although sporadic loss of RB is characteristic of most cancers and results in the bypass of the DNA damage checkpoint, the consequence of RB loss upon chemotherapeutic responsiveness has been largely uninvestigated. Here, we employed a conditional knockout approach to ablate RB in adult fibroblasts. This system enabled us to examine the DNA damage response of adult cells following acute RB deletion. Using this system, we demonstrated that loss of RB disrupted the DNA damage checkpoint elicited by either cisplatin or camptothecin exposure. Strikingly, this bypass was not associated with enhanced repair, but rather the accumulation of phosphorylated H2AX (γH2AX) foci, which indicate DNA double-strand breaks. The formation of γH2AX foci was due to ongoing replication following chemotherapeutic treatment in the RB-deficient cells. Additionally, peak γH2AX accumulation occurred in S-phase cells undergoing DNA replication in the presence of damage, and these γH2AX foci co-localized with replication foci. These results demonstrate that acute RB loss abrogates DNA damage-induced cell cycle arrest to induce γH2AX foci formation. Thus, secondary genetic lesions induced by RB loss have implications for the chemotherapeutic response and the development of genetic instability.     

Activity of pre-entral neurones in conscious monkeys: effects of deafferentation and cerebellar ablation.

After limb deafferentation, there was no gross alteration in the initiation and performance of a sound-triggered ballistic movement. The pattern of neuronal discharge in the arm area of the motor cortex was not significantly modified. In the absence of cerebellum, the reaction time of motor cortex cells was about 150 msec longer than the reaction time observed in normal and deafferented animals. This was associated with an equal retardation in the onset of ENG changes in the limb muscles. This observation is compatible with the idea that the motor cortex is normally situated downstream to the cerebellum in the initiation of some movements. However, the motor cortex is necessary for the initiation and execution of simple sound-triggered movements since its removal results in a permanent inability to perform the task. Finally, in the absence of peripheral feedback, the pattern of motor output to the agonistic and antagonistic muscles was initiated normally and thus appeared to be preprogrammed centrally. The importance of the motor cortex as a "reflex center" in the control of slower movements is obviously not challenged by these observations since the motor task that we have used depends very little or not at all on sensory feedback (Stark, 1968). What these results indicate, however, is that the execution of some voluntary fast ballistic movements can be entirely preprogrammed independently of peripheral and cerebellar influences, and that the program, which is mainly concerned with generating velocity signals, appears to require the integrity of the motor cortex for its execution.