Sarcolemmal organization in skeletal muscle lacking desmin: evidence for cytokeratins associated with the membrane skeleton at costameres

The sarcolemma of fast-twitch muscle is organized into "costameres," structures that are oriented transversely, over the Z and M lines of nearby myofibrils, and longitudinally, to form a rectilinear lattice. Here we examine the role of desmin, the major intermediate filament protein of muscle in organizing costameres. In control mouse muscle, desmin is enriched at the sarcolemmal domains that lie over nearby Z lines and that also contain beta-spectrin. In tibialis anterior muscle from mice lacking desmin due to homologous recombination, most costameres are lost. In myofibers from desmin -/- quadriceps, by contrast, most costameric structures are stable. Alternatively, Z line domains may be lost, whereas domains oriented longitudinally or lying over M lines are retained. Experiments with pan-specific antibodies to intermediate filament proteins and to cytokeratins suggest that control and desmin -/- muscles express similar levels of cytokeratins. Cytokeratins concentrate at the sarcolemma at all three domains of costameres when the latter are retained in desmin -/- muscle and redistribute with beta-spectrin at the sarcolemma when costameres are lost. Our results suggest that desmin associates with and selectively stabilizes the Z line domains of costameres, but that cytokeratins associate with all three domains of costameres, even in the absence of desmin.     

The effects of high-dose glutamine ingestion on weightlifting performance

The purpose of this study was to determine if high-dose glutamine ingestion affected weightlifting performance. In a double-blind, placebo-controlled, crossover study, 6 resistance-trained men (mean +/- SE: age, 21.5 +/- 0.3 years; weight, 76.5 +/- 2.8 kg(-1)) performed weightlifting exercises after the ingestion of glutamine or glycine (0.3 g x kg(-1)) mixed with calorie-free fruit juice or placebo (calorie-free fruit juice only). Each subject underwent each of the 3 treatments in a randomized order. One hour after ingestion, subjects performed 4 total sets of exercise to momentary muscular failure (2 sets of leg presses at 200% of body weight, 2 sets of bench presses at 100% of body weight). There were no differences in the average number of maximal repetitions performed in the leg press or bench press exercises among the 3 groups. These data indicate that the short-term ingestion of glutamine does not enhance weightlifting performance in resistance-trained men.     

Hypothesis: hyperstructures regulate initiation in Escherichia coli and other bacteria

Hyperstructures or modules have been proposed to constitute a level of organisation intermediate between macromolecules and whole cells. In this model of intracellular organisation, hyperstructures compete and collaborate for existence within the membrane and cytoplasm. Those directly involved in the cell cycle include initiation, replication and division hyperstructures based on DnaA, SeqA and the 2-minute cluster, respectively. During the run-up to initiation, the mass to DNA ratio increases and, we contend, differential gene expression leads to some hyperstructures becoming more active and stable than others. This results in a drop in the diversity of hyperstructures, some of which release DnaA as they dissociate, and a DnaA-initiation hyperstructure forms. Subsequent DNA replication and cell division generate different daughter cells containing different hyperstructures. This has the advantage of increasing the phenotypic diversity of the population. In developing this model, we also invoke hyperstructures in the partitioning of origins of replication.     

Competent dendritic cells derived from CD34+ progenitors express CMRF-44 antigen early in the differentiation pathway

Differentiation of CD34(+) haematopoietic stem cells into functional dendritic cells (DC) was investigated using the mAb CMRF-44 and other mAb against DC-associated markers. GM-CSF mobilized peripheral blood stem cells were obtained from healthy donors by leukapheresis. CD34(+) cells were purified using CD34(+)-positive selection,and subsequent immunomagnetic depletion of CD14 and CD2 cells. CD34(+) cells were cultured in medium supplemented with one or more of GM-CSF,TNF-alpha, IL-4 or IL-6. CMRF-44 Ag expression was monitored by flow cytometry, and DC function by allogeneic MLR and tetanus toxoid(TT) presentation assays. CD34(+) cells quickly acquired the CMRF-44 Ag when cultured in the presence of TNF-alpha.By day 3, more than 50% of the cells were double-positive for CD34 and CMRF-44. CD34 expression was gradually lost, so that by day 9, the majority of the cells were CD34(-)/CMRF-44(+).GM-CSF and TNF-alpha also induced CD40 expression, and up-regulation of CD54 and MHC class II on CD34(+) cells; their expression was correlated to the CMRF-44 Ag. Day 3 CD34(+)/CMRF-44(+) cells,but not CD34(+)/CMRF-44(-) cells, become potent APC when cultured further with GM-CSF plus TNF-alpha. These CMRF-44(+) cells were potent inducers of Th1-type immune response in the primary allogeneic MLR and present TT to autologous CD4(+) T cells. TNF-alpha alone is sufficient to induce CMRF-44 expression on CD34(+) cells, but in combination with GM-CSF expands the CMRF-44(+) population. CMRF-44 expression correlates with DC function and may be a useful early marker for commitment of CD34(+) cells to the DC differentiation pathway.     

Biological activity and enrichment of spermatogonial stem cells in vitamin A-deficient and hyperthermia-exposed testes from mice based on colonization following germ cell transplantation

Spermatogenesis is a complex process in which spermatogonial stem cells divide and subsequently differentiate into spermatozoa. This process requires spermatogonial stem cells to self-renew and provide a continual population of cells for differentiation. Studies on spermatogonial stem cells have been limited due to a lack of unique markers and an inability to detect the presence of these cells. The technique of germ cell transplantation provides a functional assay to identify spermatogonial stem cells in a cell population. We hypothesized that vitamin A-deficient (VAD) and hyperthermically treated testes would provide an enriched in vivo source of spermatogonial stem cells. The first model, hyperthermic treatment, depends on the sensitivity of maturing germ cells to high temperatures. Testes of adult mice were exposed to 43 degrees C for 15 min to eliminate the majority of differentiating germ cells. Treated donor testes were 50% of normal adult testis size and, when transplanted into recipients, resulted in a 5.3- and 19-fold (colonies and area, respectively) increase in colonization efficiency compared to controls. The second model, VAD animals, also lacked differentiating germ cells, and testes weights were 25% of control values. Colonization efficiency of germ cells from VAD testes resulted in a 2.5- and 6.2-fold (colonies and area, respectively) increase in colonization compared to controls. Hyperthermically treated mice represent an enriched source of spermatogonial stem cells. In contrast, the low extent of colonization with germ cells from VAD animals raises important questions regarding the competency of stem cells from this model.     

Paradoxical effects of chemicals in the diet on health

In 1992, Block et al. published a summary of 200 epidemiological investigations which indicated that a diet that was high in fruit and vegetables cut cancer risks approximately in half. These investigations used conventionally farmed produce that contained traces of synthetic pesticides and mycotoxins as well as an estimated 10,000 secondary products (i.e. natural pesticides). Dietary consumption of fruits and vegetables also reduces risks of cardiovascular disease, cataracts and brain dysfunction. Before genetic manipulation is undertaken to elevate or diminish any individual constituent of fruits and vegetables, the contribution of each of these constituents to health must be better understood, as in many cases their effects on health can be paradoxical.