Biomedical subjects

Sheng Li

Publications and source records attributed to Sheng Li.

At least 19 recordsLinked to original sources

PubMed2026

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↗

PubMed2006

Effects of changing wrist positions on finger flexor hypertonia in stroke survivors.

We sought to establish whether spastic hypertonia results from changes in intrinsic muscle properties or from altered stretch reflex properties. We hypothesized that finger flexor spastic hypertonia is primarily of neural origin, and that the dynamics of spastic muscle responses to stretch should therefore reflect the dynamics of muscle spindle receptor responses. In 12 stroke survivors, we recorded torque and electromyographic (EMG) responses of extrinsic finger flexors to constant-velocity rotation of the metacarpophalangeal (MCP) joints of the affected hand, over a range of initial muscle lengths. Stretch velocity was set to 6 degrees, 50 degrees, 150 degrees, or 300 degrees per second. Muscle length changes were imposed by changing wrist angle between 0 degree, 25 degrees, and 50 degrees of flexion. We found that reflex torque and EMG responses exhibited both velocity and length dependence, and there were significant interactions between velocity and length, replicating known characteristics of muscle spindle receptors. Our results support the hypothesis that finger flexor hypertonia is primarily of neural origin, and that it accurately reflects spindle receptor firing properties.

Adult↗

PubMed2005

Bright cyclic light accelerates photoreceptor cell degeneration in tubby mice.

Photoreceptor cell death is an irreversible, pathologic event in many blinding retinal diseases including retinitis pigmentosa, age-related macular disease, and retinal detachment. Light exposure can exacerbate a variety of human retinal diseases by increasing the rate of photoreceptor cell death. In the present study, we characterize the kinetics of photoreceptor cell death in Tubby (homozygous tub/tub, which have inherited, progressive retinal degeneration) mice born and raised in a bright cyclic light environment. Our data show that raising tub/tub mice in a bright cyclic light environment induces rapid loss of photoreceptors. This effect can be slowed, but not prevented, by raising animals in constant darkness, which suggests the involvement of phototransduction in the accelerated death of photoreceptors in this animal. We further demonstrated that the activities of cytosolic cytochrome c and caspases-3 and -9 were significantly increased in the retinas of tub/tub mice. Raising animals in darkness significantly reduced the increased activities of caspases-3 and -9, as well as cytosolic cytochrome c. We also observed that rhodopsin, a phototransduction protein, is not restricted to the rod outer segment, but is distributed throughout the rod cell, including the inner segments, cell bodies, and synapses. In addition, the light-dependent translocation and compartmentalization of arrestin and transducin are affected by the tubby mutation. Our results support the interpretation that problems in protein trafficking in the photoreceptors of the tub/tub mouse may contribute to retinal degeneration.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Donor origin of multipotent adult progenitor cells in radiation chimeras.

Multipotent adult progenitor cells (MAPCs) are bone marrow-derived stem cells that have extensive in vitro expansion capacity and can differentiate in vivo and in vitro into tissue cells of all 3 germinal layers: ectoderm, mesoderm, and endoderm. The origin of MAPCs within bone marrow is unknown. MAPCs are believed to be derived from the bone marrow stroma compartment as they are isolated within the adherent cell component. Numerous studies of bone marrow chimeras in the human and the mouse point to a host origin of bone marrow stromal cells. Mesenchymal stem cells (MSCs), which coexist with stromal cells, have also been proven to be of host origin after allogeneic bone marrow transplantation in numerous studies. We report here that following syngeneic bone marrow transplants into lethally irradiated C57BL6 mice, MAPCs are of donor origin.

Animals↗

PubMed2005

Characterization of the PR domain of RIZ1 histone methyltransferase.

RIZ1 (PRDM2) and PRDI-BF1 (PRDM1) are involved in B cell differentiation and the development of B cell lymphomas. These proteins are expressed in two forms that differ by the presence or absence of a PR domain. The protein product that retains the PR domain is anti-tumorigenic while the product that lacks the PR domain is oncogenic and over-expressed in tumor cells. The conserved PR domain is homologous to the SET domain from a family of histone methyltransferases. RIZ1 is also a histone methyltransferase and methylates lysine 9 in histone H3. This activity has been mapped to the PR domain. In the present study, deuterium exchange mass spectrometry was used to define the structural boundaries of the RIZ1 PR domain and to map sites of missense mutations that occur in human cancers and reduce methyltransferase activity. Flexible segments were selectively deleted to produce protein products that crystallize for structural studies. Segments at the carboxyl terminus of the PR domain that are involved in methylation of H3 were shown to be flexible, similar to SET domains, suggesting that the PR and SET methyltransferases may belong to an emerging class of proteins that contain mobile functional regions.

Amino Acid Sequence↗

PubMed2005

Juvenile hormone diol kinase, a calcium-binding protein with kinase activity, from the silkworm, Bombyx mori.

Juvenile hormone (JH) diol kinase (JHDK) is an important enzyme involved in the JH degradation pathway. Bombyx mori (Bommo)-JHDK cDNA (637bp) contains an open reading frame encoding a 183-amino acid protein, which reveals a high degree of identity to the two previously reported JHDKs. JHDK is similar to GTP-binding proteins with three conserved sequence elements involved in purine nucleotide binding, contains eight alpha-helices and three EF-hand motifs, and resembles the three-dimensional model of 2SCP and some other calcium-binding proteins. The Bommo-JHDK gene has only a single copy in the silkworm haploid genome, contains only one exon, and its 5'-upstream sequence does not have a JH response element. Although Bommo-JHDK is highly expressed in the gut of the silkworm, its mRNA expression remains at a constant level during larval development suggesting this enzyme is constitutive and not regulated by JH, at least at the transcriptional level. Recombinant Bommo-JHDK catalyzed the conversion of 10S-JH diol into JH diol phosphate, confirming its enzymatic function. Recombinant enzyme formed a dimer and had biochemical characteristics similar to other JHDKs. Bommo-JHDK, a calcium-binding protein with kinase activity, provides unique insights on how JH levels are regulated in the silkworm.

Amino Acid Sequence↗

PubMed2005

Immunization of mice with concentrated liquor from male zooid of Antheraea pernyi.

AIM: To study the effects of concentrated liquor from male zooid of Antheraea pernyi on immunological mice. METHODS: For each experiment, 40 mice were randomly divided into normal saline group (control group) and three tested groups that were administered different dosages of concentrated liquor from male zooid of A. pernyi and food for 15 d. The typical FSR and HC(50) value, monocyte-phagocytic exponent K and emendated monocyte-phagocytic exponent alpha were determined and calculated respectively. RESULTS: After 24 and 48 h, the FSR values of the three tested groups improved significantly in comparison to the control group by variance analysis. The HC(50) values showed a significant difference between the high dosage group and the control group, as well as between the high dosage group and other two tested groups. The monocyte-phagocytic exponent K and emendated exponent alpha showed rising tendencies, but no significant differences were found by variance analysis. CONCLUSION: The concentrated liquor from male zooid of A. pernyi can significantly enhance cellular and humoral immune function in mice, but has no distinct influence on the monocyte-phagocytic system in mice.

Animals↗

PubMed2005

Redox regulation of PTEN by S-nitrosothiols.

PTEN (phosphatase with sequence homology to tensin) is a phosphatidylinositol 3,4,5-trisphosphate phosphatase that regulates many cellular processes. Activity of the enzyme is dependent on the redox state of the active site cysteine such that oxidation by H2O2 leads to inhibition. Because S-nitrosothiols are known to modify enzymes containing reactive cysteines, we hypothesized that S-nitrosothiols would oxidize PTEN and inhibit its phosphatase activity. In the present study, we show that S-nitrosocysteine (CSNO), S-nitrosoglutathione (GSNO), and S-nitroso-N-acetylpenicillamine (SNAP) reversibly oxidized recombinant PTEN. In addition, CSNO led to concentration- and time-dependent oxidation of endogenous cellular PTEN. However, in contrast, GSNO and SNAP were effective only when coincubated with cysteine, suggesting that these nitrosothiols must react with cysteine to form CSNO, which can be transferred across cell membranes. Oxidation of cellular PTEN resulted from thiol modification and led to reversible inhibition of phosphatase activity. Although oxidation of PTEN by H2O2 led to formation of an intramolecular disulfide, oxidation of PTEN by CSNO seemed to lead to formation of a mixed disulfide. Glutathionylation of cellular proteins by incubating cells with diamide or incubating cellular extracts with GSSG oxidized PTEN in a manner similar to that of CSNO. Overall, these data demonstrate for the first time that S-nitrosothiols oxidatively modify PTEN, leading to reversible inhibition of its phosphatase activity, and suggest that the oxidized species is a mixed disulfide.

Base Sequence↗

PubMed2005

Lentiviral transduction of microglial cells.

Microglial cells are the resident immune cells of the central nervous system. Their function resembles that of tissue macrophages and, as such, they share many properties with both peripheral macrophages and monocytes. One striking similarity is the difficulty with which these cells can be genetically manipulated via transfection or transduction. We have sought to overcome this challenge and generate stably transduced microglial cell lines. Based on encouraging results from macrophages, we hypothesized that lentiviral vectors might provide a valuable tool in the transduction of microglial cells. Using a lentiviral-based vector system expressing enhanced green fluorescent protein (eGFP) under the control of the murine stem cell virus promoter (MSCV), we found that multiplicities of infection (MOIs) of 1, 10, and 100 transduce >70%, >88%, and >95% of the cells, respectively. From the pool of transduced cells, we established lines of N9 and BV-2 microglial cells with distinct fluorescence intensities. Using real time-polymerase chain reaction (PCR), we correlated the integrated eGFP copy numbers to eGFP fluorescence measured by flow cytometry. When mixed, up to three lines with different eGFP intensities could be separated by flow cytometry and fluorescence microscopy. Neither infection nor transgene expression influenced microglial activation as assessed by nitric oxide (NO) production, cytokine release, and surface antigen expression. Our findings that microglial cells are easily transduced by lentiviral based vectors will facilitate research depending on genetic manipulation and help generate transgenic cell lines. In addition, the availability of microglial cell lines with defined fluorescence properties could replace elaborate staining procedures for microglial identification in co-culture experiments.

Animals↗

PubMed2005

Identification of stereoselective transporters for S-nitroso-L-cysteine: role of LAT1 and LAT2 in biological activity of S-nitrosothiols.

Many of the biological effects of nitric oxide are mediated by S-nitrosothiols. However, the mechanisms by which S-nitrosothiols transduce their activity across cell membranes are unclear. We show that the pathway responsible for the cellular effects of S-nitrosothiols is specific for S-nitrosocysteine (CSNO), is stereoselective, and requires direct uptake of intact L-CSNO. Transport is independent of extracellular sodium, competitively inhibited by leucine, and blocked by 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid, a specific inhibitor of the system L amino acid transporter family. Other nitrosothiols such as S-nitrosoglutathione are not substrates for transport and require reaction with L-cysteine for activity. To show that system L family members mediate uptake, we expressed two members, LAT1 and LAT2, in Xenopus oocytes. Both LAT1 and LAT2, when co-expressed with 4F2 heavy chain, were found to efficiently transport L-CSNO. Mammalian cells were shown to express LAT1 and LAT2. A431 cells express both proteins, whereas T24 cells express only LAT1. Overexpression of LAT1 in T24 cells using recombinant adenoviruses led to increased uptake of L-CSNO, whereas knockdown using a specific small interfering RNA led to decreased uptake. These data definitively identify LAT1 and LAT2 as members of system L that mediate transmembrane movement of l-CSNO and suggest that system L family members are involved in the cellular activity of small molecular weight nitrosothiols.

Amino Acid Transport System y+↗

PubMed2005

Structural basis for the unique biological function of small GTPase RHEB.

The small GTPase Rheb displays unique biological and biochemical properties different from other small GTPases and functions as an important mediator between the tumor suppressor proteins TSC1 and TSC2 and the mammalian target of rapamycin to stimulate cell growth. We report here the three-dimensional structures of human Rheb in complexes with GDP, GTP, and GppNHp (5'-(beta,gamma-imide)triphosphate), which reveal novel structural features of Rheb and provide a molecular basis for its distinct properties. During GTP/GDP cycling, switch I of Rheb undergoes conformational change while switch II maintains a stable, unusually extended conformation, which is substantially different from the alpha-helical conformation seen in other small GTPases. The unique switch II conformation results in a displacement of Gln64 (equivalent to the catalytic Gln61 of Ras), making it incapable of participating in GTP hydrolysis and thus accounting for the low intrinsic GTPase activity of Rheb. This rearrangement also creates space to accommodate the side chain of Arg15, avoiding its steric hindrance with the catalytic residue and explaining its noninvolvement in GTP hydrolysis. Unlike Ras, the phosphate moiety of GTP in Rheb is shielded by the conserved Tyr35 of switch I, leading to the closure of the GTP-binding site, which appears to prohibit the insertion of a potential arginine finger from its GTPase-activating protein. Taking the genetic, biochemical, biological, and structural data together, we propose that Rheb forms a new group of the Ras/Rap subfamily and uses a novel GTP hydrolysis mechanism that utilizes Asn1643 of the tuberous sclerosis complex 2 GTPase-activating protein domain instead of Gln64 of Rheb as the catalytic residue.

Amino Acid Sequence↗

PubMed2005

Molecular and biochemical characterization of juvenile hormone epoxide hydrolase from the silkworm, Bombyx mori.

One major route of insect juvenile hormone (JH) degradation is epoxide hydration by JH epoxide hydrolase (JHEH). A full-length cDNA (1536 bp) encoding a microsomal JHEH was isolated from the silkworm, Bombyx mori. Bommo-JHEH cDNA contains an open reading frame encoding a 461-amino acid protein (52 kDa), which reveals a high degree of similarity to the previously reported insect JHEHs. The residues Tyr298, Tyr373, and the HGWP motif corresponding to the oxyanion hole of JHEHs and the residues Asp227, His430, and Glu403 in the catalytic triad are well conserved in Bommo-JHEH. Bommo-JHEH was highly expressed in the fat body, where its mRNA expression pattern was in contrast to the pattern of hemolymph levels of JH during the larval development, suggesting that Bommo-JHEH plays an important role in JH degradation. Recombinant Bommo-JHEH (52 kDa) expressed in Sf9 insect cells was membrane-bound and had a high level of enzyme activity (300-fold over the control activity). This Bommo-JHEH study provides a better understanding of how JH levels are regulated in the domesticated silkworm.

Amino Acid Sequence↗

PubMed2005

Allatotropin regulation of juvenile hormone synthesis by the corpora allata from the lubber grasshopper, Romalea microptera.

The in vitro synthesis of juvenile hormone (JH) by corpora allata (CA) from the lubber grasshopper (Romalea microptera) was stimulated by low concentrations of brain extract and this effect was reduced at higher concentrations, suggesting the presence of allatotropin (AT) and allatostatin (AST) factors in the brain. The AT activity of brain extracts caused a rapid and reversible stimulation and appeared to be a peptide(s). Reversed phase (C18) HPLC analysis of brain extracts disclosed two peaks of AT activity but no significant AST activity. Manse-AT, Schgr-NPF, and Locmi-FLRF had no effect on JH synthesis by lubber CA, indicating that the Rommi-AT factors are distinct from these peptides. High concentrations of Dippu-AST-7 and Grybi-AST-1 inhibited JH synthesis, implying that AST factors might be present in lubber grasshoppers. CA response to AT activity of brain extracts varied during the oviposition cycle ( approximately 35 days), with the maximum response occurring on days 16-18. AT activity of brain extracts also varied during the cycle, being highest on day 25. Our data suggest that the lubber CA is largely regulated by AT activity, and that JH synthesis reflects both CA response to AT activity and the level of AT activity in the brain.

Animals↗

PubMed2005

The movement-specific effect of motor imagery on the premotor time.

The purpose of this study was to investigate the effect of motor imagery on the premotor time (PMT). Twelve healthy adults performed reaction time movements in response to external visual signals at rest, when holding an object (muscle activation), or performing different background imagined movements (motor imagery). When compared to rest, muscle activation reduced the PMT; imagined finger extension of the right hand and imagined finger flexion of the left hand elongated the PMT; imagined finger flexion of the right hand had no effect on the PMT. This movement-specific effect is interpreted as the sum of the excitatory effect caused by enhanced corticospinal excitability specifically for the primary mover of the imagined movement and an overall inhibition associated with increased task complexity during motor imagery. Our results clearly demonstrate that motor imagery has movement-specific effects on the PMT.

Electrodes↗

PubMed2005

[Different histological changes of hard palates in rats with different areas of denudated bone].

PURPOSE: To explore the relationship between the histological changes of the denudated bone in the hard palate of rats and its sizes. METHODS: Sixteen three-week-old SD male rats were randomly divided into 4 groups (a control group and 3 experimental groups). In the three experimental groups, one and two and three quarters of the bilateral palatal mucoperiosteum were excised respectively. One animal in each group was sacrificed every two weeks and the histological differences were observed. RESULTS: Different histological changes were found among the groups. When the denuded part was over half of the palate, tight connections between scar tissues and both the palatal bone and the periodontal fibers were observed. Many necrotic bone tissues appeared in the mid-palate if more than three quarters of areas were exposed. CONCLUSION: Different sizes of denuded bone may lead to different histological appearances. Structures and tissues change more when denuded part of the bone is larger.

Animals↗

PubMed2004

The effect of motor imagery on spinal segmental excitability.

The purpose of this study was to investigate the effect of motor imagery on spinal segmental excitability by recording the reflex responses to externally applied stretch of the extrinsic finger flexors and extensors during the performance of an imaginary task. Nine young healthy subjects performed a series of imagined flexion-extension movements of the fingers. Muscle stretch was imposed concurrently by applying rotations of the metacarpophalangeal joints at 100, 300, or 500 degrees /sec. Three of the nine tested subjects also generated 0.2 Newton meter voluntary flexion torque in preloading tasks before stretch. At 300 degrees /sec stretch, electromyogram (EMG) and torque reflex responses, which were observed in the finger flexors in four of nine subjects during motor imagery, were activated at a short latency (38.6 +/- 10.6 msec). This latency was similar to that recorded during a stretch of preactivated flexor muscles (34.4 +/- 3.6 msec), in which motoneurons are already suprathreshold and in which monosynaptic effects of muscle afferents are likely to be discernable. In a similar manner, for stretches imposed at 500 degrees /sec, responses to stretch of the flexors were observed in all five tested subjects in imaginary flexion tasks at very short latencies (26.4 +/- 3.7 msec), again similar to those induced by tendon taps (22.8 +/- 1.2 msec). No EMG response was observed at rest during stretches. These observations support the view that effects must have been mediated by imagery-related subthreshold activation of spinal motoneurons and/or interneurons, rather than by long-latency transcortical reflex responses. We conclude that motor imagery has a potent effect on the excitability of spinal reflex pathways.

Adult↗

PubMed2004

Expression, purification, crystallization and preliminary structural characterization of the GTPase domain of human Rheb.

Ras homologue enriched in brain (Rheb) represents a unique group of small GTPases and shares moderate sequence identity with the Ras/Rap subfamily. It acts downstream of nutrient signalling as the direct target of the tuberous sclerosis complex (TSC) and upstream of mTOR/S6K1/4EBP in the insulin-signalling pathway. The GTPase domain of human Rheb (hRheb) has been recombinantly expressed in Escherichia coli, purified and cocrystallized in complexes with GDP, GTP and GppNHp using the hanging-drop vapour-diffusion method. Crystals of the hRheb-GDP complex belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 44.5, b = 52.3, c = 70.6 A. The hRheb-GppNHp complex crystallized in two crystal forms: one has the same space group and unit-cell parameters as the hRheb-GDP complex and the other belongs to space group C222(1), with unit-cell parameters a = 102.9, b = 99.2, c = 48.0 A. The hRheb-GTP complex also crystallized in two crystal forms: one belongs to space group C222(1), with unit-cell parameters a = 102.4, b = 98.3, c = 47.9 A, and the other belongs to space group P2(1), with unit-cell parameters a = 77.3, b = 47.9, c = 71.9 A, beta = 89.0 degrees. All these crystals diffract X-rays to better than 2.8 A resolution and at least one diffraction data set has been collected for each crystal form using an in-house R-AXIS IV++ diffractometer. Structural studies of hRheb in complexes with various substrates may provide insights into the recognition and specificity of substrate and the catalytic mechanism of mammalian Rhebs and shed light on the biological functions of Rhebs in the mTOR signalling pathway.

Brain↗

PubMed2004

The lobster mandibular organ produces soluble and membrane-bound forms of 3-hydroxy-3-methylglutaryl-CoA reductase.

In a previous study [Li, Wagner, Friesen and Borst (2003) Gen. Comp. Endocrinol. 134, 147-155], we showed that the MO (mandibular organ) of the lobster Homarus americanus has high levels of HMGR (3-hydroxy-3-methylglutaryl-CoA reductase) and that most (approx. 75%) of the enzyme activity is soluble. In the present study, we report the biochemical and molecular characteristics of this enzyme. HMGR had two forms in the MO: a more abundant soluble form (66 kDa) and a less abundant membrane-bound form (72 kDa). Two cDNAs for HMGR were isolated from the MO. A 2.6-kb cDNA encoded HMGR1, a 599-amino-acid protein (63 kDa), and a 3.2-kb cDNA encoded HMGR2, a 655-amino-acid protein (69 kDa). These two cDNAs had identical 3'-ends and appeared to be products of a single gene. The deduced amino acid sequences of these two proteins revealed a high degree of similarity to other class I HMGRs. Hydropathy plots indicated that the N-terminus of HMGR1 lacked a transmembrane region and HMGR2 had a single transmembrane segment. Recombinant HMGR1 expressed in Sf9 insect cells was soluble and had kinetic characteristics similar to native HMGR from the MO. Treatment with phosphatase did not affect HMGR activity, consistent with the observation that neither HMGR1 nor HMGR2 has a serine at position 490 or 546, the position of a conserved phosphorylation site found in class I HMGR from higher eukaryotes. Other lobster tissues (i.e. midgut, brain and muscles) had low HMGR activities and mRNA levels. MO with higher HMGR activities had higher HMGR mRNA levels, implying that HMGR is regulated, in part, at the transcription level.

Adenosine Triphosphate↗