A computational model of limb impedance control based on principles of internal model uncertainty

Efficient human motor control is characterized by an extensive use of joint impedance modulation, which is achieved by co-contracting antagonistic muscles in a way that is beneficial to the specific task. While there is much experimental evidence available that the nervous system employs such strategies, no generally-valid computational model of impedance control derived from first principles has been proposed so far. Here we develop a new impedance control model for antagonistic limb systems which is based on a minimization of uncertainties in the internal model predictions. In contrast to previously proposed models, our framework predicts a wide range of impedance control patterns, during stationary and adaptive tasks. This indicates that many well-known impedance control phenomena naturally emerge from the first principles of a stochastic optimization process that minimizes for internal model prediction uncertainties, along with energy and accuracy demands. The insights from this computational model could be used to interpret existing experimental impedance control data from the viewpoint of optimality or could even govern the design of future experiments based on principles of internal model uncertainty.     

Radiation effects of poly(l-glutamic acid) and poly(l-lysine) in the helix-coil transitional state

Summary The degradation of poly(l-glutamic acid) and poly(l-lysine) by X-rays and ultraviolet radiation has been studied at variouspH values, including the helix-coil transition region. It was found that X-rays cause maximum degradation in the transition region for both polypeptides, indicating that the efficiency of degradation is affected not only by the secondary structure but also by some other factors related to the transition. On the contrary, the degradation by monochromatic ultraviolet 2537 radiation showed a strong dependence on helix content of PLGA, suggesting that degradation occurs more effectively in the helical form than in the coil form. Theoretical calculations were made to approximate thepH dependence of degradation, assuming different cross sections for the peptide bonds in helix, coil, and junctions between helical and coil regions.     

Dysregulation of the Bmi‐1/p16Ink4a pathway provokes an aging‐associated decline of submandibular gland function

Bmi‐1 prevents stem cell aging, at least partly, by blocking expression of the cyclin‐dependent kinase inhibitor p16^Ink4a. Therefore, dysregulation of the Bmi‐1/p16^Ink4a pathway is considered key to the loss of tissue homeostasis and development of associated degenerative diseases during aging. However, because Bmi‐1 knockout (KO) mice die within 20 weeks after birth, it is difficult to determine exactly where and when dysregulation of the Bmi‐1/p16^Ink4a pathway occurs during aging in vivo. Using real‐time in vivo imaging of p16^Ink4a expression in Bmi‐1‐KO mice, we uncovered a novel function of the Bmi‐1/p16^Ink4a pathway in controlling homeostasis of the submandibular glands (SMGs), which secrete saliva into the oral cavity. This pathway is dysregulated during aging in vivo, leading to induction of p16^Ink4a expression and subsequent declined SMG function. These findings will advance our understanding of the molecular mechanisms underlying the aging‐related decline of SMG function and associated salivary gland hypofunction, which is particularly problematic among the elderly.     

Molecular cloning and functional expression of soybean allene oxide synthases

A plant allene oxide synthase (AOS) reacting with 13S-hydroperoxy-9Z,11E,15Z-octadecatrienoic acid (13-HPOT), a lipoxygenase product of alpha-linolenic acid, provides an allene oxide which functions as an intermediate for jasmonic acid (JA) synthesis, making AOS a key enzyme regulating the JA level in plants. Although AOSs in various plants have been investigated, there is only limited information about AOSs in soybean (Glycine max). In this study, we cloned and characterized two soybean AOSs, GmAOS1 and GmAOS2, sharing 95% homology in the predicted amino acid sequences. GmAOS1 and GmAOS2 were composed of 564 and 559 amino acids respectively, with predicted N-terminal chloroplast-targeting signal peptides. Both AOSs expressed in Escherichia coli were selective for 13S-hydroperoxides of alpha-linolenic and linoleic acids, suggesting the potential of GmAOS1 and GmAOS2 to contribute to JA synthesis. GmAOS1 and GmAOS2 were expressed in leaves, stems, and roots, suggesting broad distribution in a soybean plant.     

Recessive Mutations in the Putative Calcium-Activated Chloride Channel Anoctamin 5 Cause Proximal LGMD2L and Distal MMD3 Muscular Dystrophies

The recently described human anion channel Anoctamin (ANO) protein family comprises at least ten members, many of which have been shown to correspond to calcium-activated chloride channels. To date, the only reported human mutations in this family of genes are dominant mutations in ANO5 (TMEM16E, GDD1) in the rare skeletal disorder gnathodiaphyseal dysplasia. We have identified recessive mutations in ANO5 that result in a proximal limb-girdle muscular dystrophy (LGMD2L) in three French Canadian families and in a distal non-dysferlin Miyoshi myopathy (MMD3) in Dutch and Finnish families. These mutations consist of a splice site, one base pair duplication shared by French Canadian and Dutch cases, and two missense mutations. The splice site and the duplication mutations introduce premature-termination codons and consequently trigger nonsense-mediated mRNA decay, suggesting an underlining loss-of-function mechanism. The LGMD2L phenotype is characterized by proximal weakness, with prominent asymmetrical quadriceps femoris and biceps brachii atrophy. The MMD3 phenotype is associated with distal weakness, of calf muscles in particular. With the use of electron microscopy, multifocal sarcolemmal lesions were observed in both phenotypes. The phenotypic heterogeneity associated with ANO5 mutations is reminiscent of that observed with Dysferlin (DYSF) mutations that can cause both LGMD2B and Miyoshi myopathy (MMD1). In one MMD3-affected individual, defective membrane repair was documented on fibroblasts by membrane-resealing ability assays, as observed in dysferlinopathies. Though the function of the ANO5 protein is still unknown, its putative calcium-activated chloride channel function may lead to important insights into the role of deficient skeletal muscle membrane repair in muscular dystrophies.     

Pressure activates rat pancreatic stellate cells

Pancreatic stellate cells (PSCs) play a central role in development of pancreatic fibrosis. In chronic pancreatitis, pancreatic tissue pressure is higher than that of the normal pancreas. We here evaluate the effects of pressure on the activation of rat PSCs. PSCs were isolated from the pancreas of Wistar rat using collagenase digestion and centrifugation with Nycodenz gradient. Pressure was applied to cultured rat PSCs by adding compressed helium gas into the pressure-loading apparatus to raise the internal pressure. Cell proliferation rate was assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation. MAPK protein levels and alpha-smooth muscle actin (alpha-SMA) expression were evaluated by Western blot analysis. Concentration of activated transforming growth factor-beta1 (TGF-beta1) secreted from PSCs into culture medium was determined by ELISA. Collagen type I mRNA expression and collagen secretion were assessed by quantitative PCR and Sirius red dye binding assay, respectively. Application of pressure significantly increased BrdU incorporation and alpha-SMA expression. In addition, pressure rapidly increased the phosphorylation of p44/42 and p38 MAPK. Treatment of PSCs with an MEK inhibitor and p38 MAPK inhibitor suppressed pressure-induced cell proliferation and alpha-SMA expression, respectively. Moreover, pressure significantly promoted activated TGF-beta1 secretion, collagen type I mRNA expression, and collagen secretion. Our results demonstrate that pressure itself activates rat PSCs and suggest that increased pancreatic tissue pressure may accelerate the development of pancreatic fibrosis in chronic pancreatitis.     

Class VI myosin moves processively along actin filaments backward with large steps.

Among a superfamily of myosin, class VI myosin moves actin filaments backwards. Here we show that myosin VI moves processively on actin filaments backwards with large ( approximately 36 nm) steps, nevertheless it has an extremely short neck domain. Myosin V also moves processively with large ( approximately 36 nm) steps and it is believed that myosin V strides along the actin helical repeat with its elongated neck domain that is critical for its processive movement with large steps. Myosin VI having a short neck cannot take this scenario. We found by electron microscopy that myosin VI cooperatively binds to an actin filament at approximately 36 nm intervals in the presence of ATP, raising a hypothesis that the binding of myosin VI evokes "hot spots" on actin filaments that attract myosin heads. Myosin VI may step on these "hot spots" on actin filaments in every helical pitch, thus producing processive movement with 36 nm steps.     

Phylogenetic analysis of the human gut microbiota using 16S rDNA clone libraries and strictly anaerobic culture-based methods

The human gut microbiota from three healthy subjects were compared by the use of a sequence analysis of 16S rDNA libraries and a culture-based method. Direct counts ranged from 1.9 X 10" to 4.0 X 10" cells/g (wet weight), and plate counts totaled 6.6 X 10(10) to 1.2 X 10(11) CFU/g (wet weight). Sixty to seventy percent of the bacteria in the human intestinal tract cannot be cultured with currently available methods. The 16S rDNA libraries from three subjects were generated from total community DNA in the intestinal tract with universal primer sets. Randomly selected clones were partially sequenced. All purified colonies detected from the surface of the agar plate were used for a partial sequencing of 16S rDNA. On the basis of sequence similarities, the clones and colonies were classified into several clusters corresponding to the major phylum of the domain Bacteria. Among a total of 744 clones obtained, approximately 25% of them belonged to 31 known species. About 75% of the remaining clones were novel "phylotypes" (at least 98% similarity of clone sequence). The predominant intestinal microbial community consisted of 130 species or phylotypes according to the sequence data in this study. The 16S rDNA libraries and colonies included the Bacteroides group, Streptococcus group, Bifidobacterium group, and Clostridium rRNA clusters IV, IX, XIVa, and XVIII. Moreover, several previously uncharacterized and uncultured microorganisms were recognized in clone libraries and colonies. Our results also showed marked individual differences in the composition of intestinal microbiota.     

Three-dimensional structure of a new enzyme, O-phosphoserine sulfhydrylase, involved in l-cysteine biosynthesis by a hyperthermophilic archaeon, Aeropyrum pernix K1, at 2.0A resolution

O-Phosphoserine sulfhydrylase is a new enzyme found in a hyperthermophilic archaeon, Aeropyrum pernix K1. This enzyme catalyzes a novel cysteine synthetic reaction from O-phospho-l-serine and sulfide. The crystal structure of the enzyme was determined at 2.0A resolution using the method of multi-wavelength anomalous dispersion. A monomer consists of three domains, including an N-terminal domain with a new alpha/beta fold. The topology folds of the middle and C-terminal domains were similar to those of the O-acetylserine sulfhydrylase-A from Salmonella typhimurium and the cystathionine beta-synthase from human. The cofactor, pyridoxal 5'-phosphate, is bound in a cleft between the middle and C-terminal domains through a covalent linkage to Lys127. Based on the structure determined, O-phospho-l-serine could be rationally modeled into the active site of the enzyme. An enzyme-substrate complex model and a mutation experiment revealed that Arg297, unique to hyperthermophilic archaea, is one of the most crucial residues for O-phosphoserine sulfhydrylation activity. There are more hydrophobic areas and less electric charges at the dimer interface, compared to the S.typhimurium O-acetylserine sulfhydrylase.