Search PubMed⌕ Search

Biomedical subjects

Sheng Li

Publications and source records attributed to Sheng Li.

At least 19 recordsLinked to original sources

Sex pheromone communication and its regulation by the sex determination pathway in cockroaches.

Sexual communication in animals orchestrates a series of interactive behaviors from locating and recognizing potential partners to courtship and final mating decisions and is thus critical for sexual reproduction and population fitness. Highly efficient communication between the sexes requires not only the production and emission of species-specific signals but also their precise detection and interpretation by the receiving individuals. Cockroaches, as one of the most evolutionarily ancient and successful group of insects, are quintessential chemical communicators that rely heavily on sex pheromones for sexual communication. They have long served as excellent model organisms in studies of chemical ecology. Although the biochemical characterization of sex pheromones in several species was largely accomplished during the last century, the past two decades have witnessed remarkable progress in understanding the molecular genetics of sex pheromone communication and its regulation, particularly driven by functional genomics. This review first provides an updated comparative survey of the pheromone components identified across distinct taxa. We then synthesize, but not limited to, recent advances in identification of key molecules controlling sex pheromone production, characterization of candidate chemosensory receptors and their neural processing pathways, and the regulatory roles of the sex determination cascade in shaping sexually dimorphic traits in both pheromone production and perception. Finally, we highlight key scientific questions that remain unsolved and propose future directions aimed at extending our mechanistic understanding of cockroach pheromone communication, as well as at developing behavior-based pest management strategies.

biosynthetic pathway↗

Dendrimer disassembly by benzyl ether depolymerization.

The disassembly of dendritic structures was realized by a cascade cleavage reaction triggered by an initially stimulated group in the dendrimer periphery. A depolymerizable backbone was engineered into prototypical dendritic structures. Evidence for the completion of the disassembly process is provided by the absorbance peak of the p-nitrophenoxide ion that was intentionally installed at the focal point of the dendrons. Observation of the UV spectra during the disassembly process supports a stepwise cascade cleavage proceeding from the periphery into the core.

Delayed-Action Preparations↗

Association of APOE gene with schizophrenia in Chinese: a possible risk factor in times of malnutrition.

Five hundred and seventy nine Chinese patients with schizophrenia who met DSMIV criteria for the disorder were genotyped for alleles epsilon 2,3,4 of apolipoprotein E (APOE) gene. All were recruited from inpatients and outpatients attending a large mental health centre in Shanghai. Results were compared to APOE data on 1528 controls drawn from the same area. Major differences in APOE genotype ratios and allele frequencies were observed between the patients and controls. The patients with schizophrenia had highly significantly (p<0.0001) increased epsilon 4/-genotypes and allele frequencies, and decreased epsilon 3/3 genotypes and epsilon 3 allele frequencies compared to controls. The effect was independent of sex and/or age of onset of illness, but strongly influenced by date of birth. Significant differences were restricted to individuals with schizophrenia born either before 1949 or during the period 1958-1967. Both were times of severe food shortages and malnutrition. We suggest that APOE may operate as an additional risk factor for schizophrenia in individuals subjected to fetal and/or early postnatal malnutrition.

Adult↗

Finger interaction during multi-finger tasks involving finger addition and removal.

The purpose of this study was to investigate changes in finger forces and their interactions in one-hand multi-finger force production tasks involving finger addition and removal. Eight male subjects were instructed to produce maximal (MVC) forces with explicitly instructed ('master') fingers. After reaching maximal force with a set of master fingers, the subjects added/removed one master finger while continuing to produce the MVC with the new group of master fingers. The non-instructed ('slave') fingers also produced forces (enslaving). Finger addition/removal led to changes in the forces of individual master fingers expected from earlier studies of maximal force production by different finger groups acting synchronously. A significant increase in the forces of remaining master fingers was observed after finger removal and a close-to-significant drop in the forces of previously recruited master fingers was observed after finger addition. These effects were larger when subjects started the task with a smaller number of explicitly involved fingers. The enslaving effects increased after finger addition while they did not change after finger removal. Forces produced by the same group of master fingers acting in different tasks showed no history-dependent effects. However, significant effects of history were seen in enslaving. These observations speak against hypotheses of more independent behaviour of effectors during their asynchronous involvement. They show that finger interaction may show effects of the history of finger involvement in a task.

Adult↗

Regulation of protein tyrosine phosphatase 1B in intact cells by S-nitrosothiols.

Protein tyrosine phosphatases (PTPases) contain an active site cysteine which when oxidized leads to loss of phosphatase activity and accumulation of phosphoproteins. For example, oxidants produced following EGF stimulation inhibit PTP1B and enhance EGF receptor phosphorylation. Because NO-derived species also modify reactive thiols, we postulated that NO would reversibly inhibit PTP1B. In our studies we exposed A431 or Jurkat cells to NO donors and measured PTP1B activity or used 3-maleimidylpropionylbiocytin (MPB) to measure thiol redox status. Nitrosothiols led to a rapid inhibition of PTP1B through a mechanism that was greatly enhanced by addition of cysteine to the medium. Analysis of thiol oxidation status using immunoprecipitated PTP1B showed modification consistent with loss of activity. Both enzyme inhibition and modification were reversible in intact cells or after addition of DTT to cell lysates. While DTT reversed oxidation, ascorbate did not, suggesting that formation of a mixed disulfide (possibly glutathionylation) rather than S-nitrosylation accounts for PTP1B inhibition. Importantly, PTP1B inhibition by nitrosothiols led to EGF receptor phosphorylation even in the absence of exogenously added EGF. These findings suggest an important role for NO in modulating signaling pathways since inhibition of PTPases could potentially enhance or prolong activity of phosphoproteins.

Cell Line↗

A mode hypothesis for finger interaction during multi-finger force-production tasks.

Finger forces are known to change involuntarily during multi-finger force-production tasks, even when a finger's involvement in a task is not consciously changed (the enslaving effect). Furthermore, during maximal force-production (MVC) tests, the force produced by a given finger in a multi-finger task is smaller than the force generated by this finger in its single-finger MVC test (the force-deficit effect). A set of hypothetical control variables - modes - is introduced. Modes can be estimated based on individual finger forces during single-finger MVC tests. We show that a simple formal model based on modes with only one free parameter accounts for finger forces during a variety of multi-finger MVC tests. The free parameter accounts for the force-deficit effect, and its value depends only on the number of explicitly involved fingers. This approach offers a simple framework for the analysis of finger interaction during multi-finger actions.

Biomechanical Phenomena↗

Finger interactions studied with transcranial magnetic stimulation during multi-finger force production tasks.

OBJECTIVE: We used transcranial magnetic stimulation (TMS) to investigate interactions among neuromuscular complexes involved in force production by individual fingers of a hand during single- and multi-finger tasks. METHODS: Subjects were asked to press with the fingertips at various levels of force using different finger combinations. TMS was applied over the M1 cortical hand area during constant force production. TMS-induced increments in fingertip forces were analyzed, as well as motor evoked potentials (MEPs) in flexor digitorum superficialis. RESULTS: Both MEP size and individual force increments had inverted U-shaped dependences on the background force (peak responses were seen at about 50% of the maximal force). Similar relationships were obtained when subjects were asked to produce different forces with the same finger combination or the same total force with different finger combinations. The relationships were similar when the force was produced by explicitly instructed fingers or by other fingers of the hand. Effects of TMS on the force of a finger showed a strong dependence on the background force produced by this finger and minimal or no dependence on forces produced by other fingers of the hand. CONCLUSIONS: Overall, TMS applied over M1 revealed little interaction among fingers. This supports the notion of digit-specific compartments in multi-digit extrinsic muscles of the hand and suggests that these compartments possess a high degree of physiological independence.

Adult↗

The effects of stroke and age on finger interaction in multi-finger force production tasks.

OBJECTIVE: The main purpose of this study was to investigate changes in finger interaction after stroke with strongly unilateral motor effects. Effects of age on finger interaction were also analyzed. METHODS: Sixteen stroke subjects and 16 control subjects produced maximal voluntary contractions with different finger combinations by one hand and by two hands simultaneously. Individual finger forces were measured. In multi-finger tasks, force deficit (FD) was quantified as the difference between the peak finger forces in single-finger tasks and in multi-finger tasks, while enslaving (ENSL) was quantified as forces produced by fingers that were not required to produce force. RESULTS: In stroke subjects, the peak forces produced by the fingers of the impaired hand (IH) were about 36% less than those produced by the unimpaired hand. Stroke resulted in higher ENSL and decreased FD in the IH, particularly when the index and middle fingers produced force together, while aging led to higher FD and no change in ENSL. Two-hand tasks were accompanied by an additional drop in the force of individual fingers, i.e. bilateral deficit (BD). No changes in BD were observed with age or after stroke. CONCLUSIONS: We conclude that IH function in persons after stroke is accompanied not only by a general loss of finger force but also by changes in indices of multi-finger interaction. The contrast between the significantly changed indices of one-hand multi-finger interaction and unchanged BD implies that cortical neurons mediating interhemispheric inhibition are relatively spared in unilateral stroke. SIGNIFICANCE: The study shows that stroke leads to changes not only in finger force but also in finger interaction. The conclusion on relatively spared interhemispheric projections is potentially important for therapy of hand function in stroke survivors.

Adult↗

Coupling phenomena during asynchronous submaximal two-hand, multi-finger force production tasks in humans.

We studied asynchronous two-hand multi-finger force production at submaximal levels. Subjects produced constant levels of force with one hand (F(REF)), and started ramp force production with the other hand (F(RAMP)) 3 s later. The zero-maximal force-zero ramp lasted 10 s. Visual feedback was provided only for F(REF) during the first 3 s and only for F(RAMP) during the rest of the trial. The initiation of F(RAMP) induced a transient overshoot by F(RAMP) and a drop in F(REF); both scaled with F(REF). Later into the trial, F(REF) dropped slowly, while F(RAMP) undershot maximal force by about 15%. Two regimes of bimanual interaction are hypothesized, 'strong interaction' when an effector is added to a one-hand task, and 'weak interaction' during two-hand force production.

Adult↗

Localization of electromagnetic waves in a two-dimensional random medium.

Motivated by previous investigations on the radiative effects of the electric dipoles embedded in structured cavities, localization of electromagnetic waves in two dimensions is studied ab initio for a system consisting of many randomly distributed two-dimensional dipoles. A set of self-consistent equations, incorporating all orders of multiple scattering of the electromagnetic waves, is derived from first principles and then solved numerically for the total electromagnetic field. The results show that spatially localized electromagnetic waves are possible in such a simple but realistic disordered system. When localization occurs, a coherent behavior appears and is revealed as a unique property differentiating localization from either the residual absorption or the attenuation effects.

Journal Article↗

Effects of age and gender on finger coordination in MVC and submaximal force-matching tasks.

The objective of the study is to examine the effects of age and gender on finger coordination. Twelve young (24 +/- 8 yr; 6 men and 6 women) and 12 elderly (75 +/- 5 yr; 6 men and 6 women) subjects performed single-finger maximal contraction [maximal voluntary contraction (MVC)], four-finger MVC, and four-finger ramp force production tasks by pressing on individual force transducers. A drop in the force of individual fingers during four-finger MVC tasks compared with single-finger MVC tasks (force deficit) was larger, whereas unintended force production by other fingers during single-finger MVC tasks (enslaving) was smaller, in elderly than in young subjects and in women than in men. Force deficit was smaller and enslaving was larger in subjects with higher peak force. During the ramp task, the difference between the variance of total force and the sum of variances of individual forces showed a logarithmic relation to the level of total force, across all subject groups. These findings suggest that indexes of finger coordination scale with force-generating capabilities across gender and age groups.

Adult↗

Relations between surface EMG of extrinsic flexors and individual finger forces support the notion of muscle compartments.

The goal of this experiment was to investigate the relationship between individual fingertip forces and the surface EMG of multi-digit muscles. The surface EMG of the hand extrinsic flexors (flexor digitorum profundis and superficialis) was recorded in eight subjects during multi-digit force production tasks. In one session, subjects pressed with all four fingers (IMRL, I = index, M = middle, R = ring, and L = little finger) with the total force ranging from 10% and 90% of their maximum force (MVC). Results showed a close linear relationship between an integrated EMG index and force. In another session, subjects produced constant total force of either 10% or 30% of their IMRL MVC, with different finger combinations such that the degree of involvement of each finger was manipulated (15 finger combinations were tested). The EMG level of the flexors depended greatly on the finger combination (P < 0.001). Multi-variable regression made it possible to describe the flexor EMG as a linear function of individual fingertip forces. These results suggest that: (1) hand extrinsic flexors muscles are arranged in functional compartments serving individual fingers, and (2) each compartment has a force/EMG relationship that is close to being linear.

Adult↗

Central mechanisms of finger interaction during one- and two-hand force production at distal and proximal phalanges.

In this study we used changes in the relative involvement of different muscle groups during force production at the distal (DT) and proximal (PR) phalanges to test and modify a hypothesis on the central organization of multi-finger control for tasks involving non-homologous elements in the two hands. Ten subjects produced maximal force with different finger combinations. Two symmetrical (PR/PR and DT/DT) and two asymmetrical (PR/DT and DT/PR) combinations of force application sites in the two hands were used. During one-hand tasks, higher forces were produced at the PR site. In multi-finger tasks, total peak force was smaller than the sum of peak forces in single-finger tasks by the involved fingers (force deficit). Force production by some fingers of a hand was accompanied by involuntary force production by other fingers (enslaving). Force deficit and enslaving were both higher at the PR site. Two-hand tasks were accompanied by an additional drop in the force of individual fingers, i.e., bilateral deficit (BD). When symmetrical sites of force production were used in the two hands, BD was lower for symmetrical finger groups than for asymmetrical groups. During tests at asymmetrical sites, BD was higher and did not depend on symmetry of involved finger groups. We conclude that within-a-hand force deficit and enslaving are likely to be of a central, neural origin. An earlier introduced hypothesis has been expanded assuming that excitatory projections to contralateral finger representations exist only for homologous elements (sub-synergies) of a multi-finger force production synergy, while only inhibitory projections connect non-homologous elements.

Adult↗

Viral vectors for gene transfer of micro-, mini-, or full-length dystrophin.

Gene therapy for Duchenne muscular dystrophy will require methods to deliver gene constructs encoding functional versions of dystrophin to the vast majority of a patient's musculature. Obstacles to achieving these goals include identifying which forms of dystrophin would be effective in a clinical setting and developing gene delivery shuttles capable of carrying and expressing dystrophin cassettes without toxic or adverse immunologic consequences. We review here recent work from our laboratory to identify sequences within dystrophin that are required to prevent development of dystrophic changes in muscle or which might be able to correct pre-existing damage. We also describe work aimed at developing viral shuttle vectors able to carry and express these dystrophin cassettes at high levels and in a muscle-specific fashion. While great challenges remain in developing methods for systemic gene delivery, we show that a variety of viral vectors are able to carry and express therapeutic levels of dystrophin when delivered directly to mouse skeletal muscle.

Adenoviridae↗

The eukaryotic two-component histidine kinase Sln1p regulates OCH1 via the transcription factor, Skn7p.

The yeast "two-component" osmotic stress phosphorelay consists of the histidine kinase, Sln1p, the phosphorelay intermediate, Ypd1p and two response regulators, Ssk1p and Skn7p, whose activities are regulated by phosphorylation of a conserved aspartyl residue in the receiver domain. Dephospho-Ssk1p leads to activation of the hyper-osmotic response (HOG) pathway, whereas phospho-Skn7p presumably leads to activation of hypo-osmotic response genes. The multifunctional Skn7 protein is important in oxidative as well as osmotic stress; however, the Skn7p receiver domain aspartate that is the phosphoacceptor in the SLN1 pathway is dispensable for oxidative stress. Like many well-characterized bacterial response regulators, Skn7p is a transcription factor. In this report we investigate the role of Skn7p in osmotic response gene activation. Our studies reveal that the Skn7p HSF-like DNA binding domain interacts with a cis-acting element identified upstream of OCH1 that is distinct from the previously defined HSE-like Skn7p binding site. Our data support a model in which Skn7p receiver domain phosphorylation affects transcriptional activation rather than DNA binding to this class of DNA binding site.

Aspartic Acid↗

Antisocial alcoholism and serotonin-related polymorphisms: association tests.

Central serotonin dysfunction appears to be related to a subtype of alcoholism with antisocial impulsive features (type II; antisocial alcoholism). The serotonergic deficit may be associated with greater impulsivity, which in turn facilitates both alcohol dependence and antisocial behavior. The present study tested association of antisocial impulsive alcoholism with candidate genes related to serotonergic neurotransmission, using families. Eight markers were assayed using polymerase chain reaction: tryptophan hydroxylase (intron 7), the serotonin transporter SLC6A4 (VNTR 9/12), HTTLPR, the three serotonin receptor types HTR1B (G861C), HTR2A (T102C) and HTR2C (Cys23Ser), monoamine oxidase A (T1460C), and (CA)(n). Eligible probands had early age of onset of alcoholism, child conduct disorder, and two or more symptoms of adult Antisocial Personality Disorder. This sample included 35 probands, their parents, and some siblings (n = 116). Association tests were conducted using the Haplotype Relative Risk method for antisocial alcoholism diagnosis and the George-Elston regression method (the S.A.G.E. program ASSOC) for quantitative antisocial alcoholism severity. Haplotype Relative Risk analyses were not significant at the 0.05 level for any of the markers. Trends suggestive for future research occurred for tryptophan hydroxylase and HTR2A. Quantitative ASSOC analyses showed significant marker effects (P < 0.05) for both monoamine oxidase A markers, which were in linkage disequilibrium. Antisocial alcoholism symptom severity was higher with monoamine oxidase A C homozygotes or hemizygotes, indicating that low monoamine oxidase activity may be important. Future studies are needed to examine joint and interactive effects of serotonin-related markers.

Adult↗