Instantaneous force-velocity-length relationship in diaphragmatic sarcomere

Coirault, Catherine, Denis Chemla, Jean-Claude Pourny,Francine Lambert, and Yves Lecarpentier. Instantaneousforce-velocity-length relationship in diaphragmatic sarcomere.J. Appl. Physiol. 82(2): 404-412, 1997.The simultaneous analysis of muscle force, length, velocity, andtime has been shown to precisely characterize the mechanicalperformance of isolated striated muscle. We tested the hypothesis thatthe three-dimensional force-velocity-length relationship reflectsmechanical properties of sarcomeres. In hamster diaphragm strips,instantaneous sarcomere length (SL) and muscle length were simultaneously measured during afterloaded twitches. SL was measured by means of laser diffraction. Wealso studied the influence of initialSL, abrupt changes in total load, and2 × 10⁷ M dantrolene.Baseline resting SL at the apex of thelength-active tension curve was 2.2 ± 0.1 µm, whereasSL at peak shortening was 1.6 ± 0.1 µm in the preloaded twitch and 2.1 ± 0.1 µm in the "isometric" twitch. Over the whole load continuum and at anygiven level of isotonic load, there was a unique relationship between instantaneous sarcomere velocity and instantaneousSL. Part of this relationship was timeindependent and initial SL independent and was markedly downshifted after dantrolene. When five different muscle regions were considered, there were no significant variations ofSL and sarcomere kinetics along themuscle. These results indicate that the time- and initiallength-independent part of the instantaneous force-velocity-lengthrelationship previously described in muscle strips reflects intrinsicsarcomere mechanical properties.

     

Proteolytic activity of proteasome on myofibrillar structures

The physiologic function of proteasome remains unclear. Evidence suggests a role in degradation of ubiquitin-protein conjugates, MHC antigen presentation, and some specificity of substrate within certain cell types. To explore further the properties of proteasome we have examined its effect on a well defined structure, the myofibril. We find that despite its large size (20S) proteasome is able to degrade myofibrils and intact, permeabilized muscle fibrils. The proteins degraded showed some specificity because actin, myosin and desmin were degraded faster than -actinin, troponin T and tropomyosin. Changes in ultrastructure were slow and included a general loss of structure with Z and I bands effected before the M band and costameres.     

Molecular basis and PCR-DNA typing of the Fya/fyb blood group polymorphism

Spondyloepiphyseal dysplasia tarda (SEDL) is an X-linked recessive disorder characterized in affected males by short stature resulting from a growth defect of the vertebral bodies. We have extended our earlier studies by analyzing 15 families with newly identified microsatellite DNA markers; analysis of recombination events with these markers indicates that the gene responsible for SEDL is located in Xp22 between DXS 16 and DXS 987 on an interval spanning approximately 2 Mb.     

Population structure and mycelial phenotypic variability of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton

Mating type allele distribution and phenotypic variability were investigated in field populations of Laccaria bicolor. Sporophores associated with Norway spruce (Picea abies), colonized by natural sources of inoculum and growing in a seed orchard, were sampled to obtain dikaryotic strains and assay their phenotypic variability for traits important to the symbiosis. Basid-iospores were also collected for mating type analysis of different mycelia. Four sporophore mating types were identified containing seven A and five B factors. Out-breeding efficiency was estimated at 73.8% and the population was slightly inbred. Crosses with previously characterized L. bicolor strains from two nearby populations identified in total six sporophore mating types and ten A and nine B factors, for an estimated outbreeding efficiency (85.7%) similar to previous studies of more spatially disparate Laccaria spp. populations. Dikaryotic strains were tested for mycelial growth rate, as a measure of their competitive ability, on agar media containing a soluble (NaH₂PO₄), or an insoluble (CaHPO₄) phosphate source. Their ability to solubilize the latter was also tested to assess their relative capacity to access insoluble, inorganic phosphate. In most cases, significant variation was detected among strains from the same site for all variables. On three sites (VC4, VC5 and VC7), each determined previously to possess a uniform mycelial genotype, phenotypic variability was likely due to epigenetic variation among different strains of the same genotype. Possible evidence for dikaryon-monokaryon crosses was observed in vivo on one sample site (VC2) where adjacent mycelia shared two mating factors. The phenotypic variability of different mycelial genotypes reflected their genetic variability observed as mating type allele diversity and underlined the importance of basidiospore dispersal in introducing new genotypes into the population. The reproductive strategies of L. bicolor are discussed and compared to those of other basidiomycete species.     

A cellulase/xylanase-negative mutant of Streptomyces lividans 1326 defective in cellobiose and xylobiose uptake is mutated in a gene encoding a protein homologous to ATP-binding proteins

Centre de Recherche en Microbiologie Appliquée, Institut Armand-Frappier, Université du Québec, Ville de Laval, Québec H7N 4Z3, Canada.     

Structure-function relationships and molecular genetics of the 3β-hydroxysteroid dehydrogenase gene family

The isoenzymes of the 3β-hydroxysteroid dehydrogenase/5-ene-4-ene-isomerase (3β-HSD) gene family catalyse the transformation of all 5-ene-3β-hydroxysteroids into the corresponding 4-ene-3-keto-steroids and are responsible for the interconversion of 3β-hydroxy- and 3-keto-5-androstane steroids. The two human 3β-HSD genes and the three related pseudogenes are located on the chromosome 1p13.1 region, close to the centromeric marker D1Z5. The 3β-HSD isoenzymes prefer NAD⁺ to NADP⁺ as cofactor with the exception of the rat liver type III and mouse kidney type IV, which both prefer NADPH as cofactor for their specific 3-ketosteroid reductase activity due to the presence of Tyr³⁶ in the rat type III and of Phe³⁶ in mouse type IV enzymes instead of Asp³⁶ found in other 3β-HSD isoenzymes. The rat types I and IV, bovine and guinea pig 3β-HSD proteins possess an intrinsic 17β-HSD activity psecific to 5-androstane 17β-ol steroids, thus suggesting that such “secondary” activity is specifically responsible for controlling the bioavailability of the active androgen DHT. To elucidate the molecular basis of classical form of 3β-HSD deficiency, the structures of the types I and II 3β-HSD genes in 12 male pseudohermaphrodite 3β-HSD deficient patients as well as in four female patients were analyzed. The 14 different point mutations characterized were all detected in the type II 3β-HSD gene, which is the gene predominantly expressed in the adrenals and gonads, while no mutation was detected in the type I 3β-HSD gene predominantly expressed in the placenta and peripheral tissues. The mutant type II 3β-HSD enzymes carrying mutations detected in patients affected by the salt-losing form exhibit no detectable activity in intact transfected cells, at the exception of L108W and P186L proteins, which have some residual activity (1%). Mutations found in nonsalt-loser patients have some residual activity ranging from 1 to 10% compared to the wild-type enzyme. Characterization of mutant proteins provides unique information on the structure-function relationships of the 3β-HSD superfamily.     

Double helical arrangement of spread dinoflagellate chromosomes

Dinoflagellate chromosomes observed in thin section show regular patterns which have been shown to correspond to a liquid crystalline helicoidal arrangement of DNA. Peripheral DNA filaments form a system of loops in the surrounding nucleoplasm. When such chromosomes (studied in Prorocentrum micans) are in presence of water, they extend considerably and form a double helical bundle. At the periphery of these bundles, one observes numerous filaments, which are smooth and devoid of nucleosomes; their diameter is constant.This study, in phase contrast and in electron microscopy, allows statistical measurements. A geometrical model is proposed and shows the simplest way to pass from the intact to the extended form. The liquid crystalline character of the chromosome is probably involved in the extension mechanisms.     

Influence of some gastrointestinal hormones on adipose tissue lipoprotein lipase activity in vitro: Evidence of a stimulatory effect of pancreozymin and gastrin

At concentrations corresponding to the levels usually reported in the blood of different species in the fed state, gastrin and pancreozymin but not secretin and vasoactive intestinal peptide, stimulate the lipoprotein lipase activity of adipose tissue from fasted rats. The enzyme response to gastrin is, like that to insulin, dependent on the presence of glucose and is not additive with the enzyme response to insulin. On the contrary, the effect of pancreozymin on lipoprotein lipase is glucoseindependent and is additive with the enzyme response to insulin. Both the effects of gastrin and pancreozymin depend on protein synthesis as shown by their suppression by cycloheximide. With isolated fat cells, gastrin increases both the releasable and non-releasable lipase activities whereas pancreozymin increases almost exclusively the non-releasable activity. The mechanisms and the possible physiological significance of these findings are discussed in relationship with the influence of insulin and the nutritional state on adipose tissue lipoprotein lipase.     

Histone - induced changes in the cellular growth of synchronized chlamydomonas reinhardii are due to histone H1

The cellular growth ofChlamydomonas reinhardii is modified by the addition of a total exogenous histone fraction. These modifications may be related to chloroplast DNA replication; they are different according to the different classes of histones. The H₁ subfraction seems to be responsible for the effect of the total histone fraction.