Numerical analysis of a unique mode of locomotion: vertical climbing by Pacific lamprey

Pacific lampreys are capable of climbing vertical wetted surfaces through a two-phase (bending and stretching) locomotion mode using the oral disc for adherence. We investigate the physical mechanism and performance of this process by using a continuous beam model. Two mechanisms, one akin to the jumping process and the other related to the fast stretching of the body, have been identified. This locomotion mode may inspire biomimetic designs of anguilliform swimming devices capable of overcoming steep obstacles. By using a genetic algorithm simulation we identify the combination of kinematic parameters corresponding to optimal efficiency (defined as the gravitational potential energy gained in each climbing step divided by the energy spent to activate the motion). These parameters are similar to laboratory observations of lamprey motion, suggesting that this type of locomotion has been optimized for maximum efficiency through evolution.

Snail shape and growth rates: Evidence for plastic shell allometry in Littorina littorea

The periwinkle Littorina littorea exhibits morphological variation among southern New England populations that appear to be genetically continuous. In dense populations, individuals have relatively elongate shells in comparison to individuals in sparse populations, which have rounder, globose shells. We experimentally demonstrate that this shell variation is a function of snail growth rate. Rapidly growing snails develop thin, globose shells that accommodate more body mass than thicker, more elongate shells. The implications of these results are discussed in relation to interpreting morphological variation in extant gastropods and in the molluscan fossil record.

Role of Ucp1 enhancer methylation and chromatin remodelling in the control of Ucp1 expression in murine adipose tissue

AIMS/HYPOTHESIS

Increasing the expression of the brown adipose tissue-specific gene uncoupling protein-1 (Ucp1) is a potential target for treating obesity. We investigated the role of DNA methylation and histone modification in Ucp1 expression in adipose cell lines and ex vivo murine adipose tissues.

METHODS

Methylation state of the Ucp1 enhancer was studied using bisulphite mapping in murine adipose cell lines, and tissue taken from cold-stressed mice, coupled with functional assays of the effects of methylation and demethylation of the Ucp1 promoter on gene expression and nuclear protein binding.

RESULTS

We show that demethylation of the Ucp1 promoter by 5-aza-deoxycytidine increases Ucp1 expression while methylation of Ucp1 promoter-reporter constructs decreases expression. Brown adipose tissue-specific Ucp1 expression is associated with decreased CpG dinucleotide methylation of the Ucp1 enhancer. The lowest CpG dinucleotide methylation state was found in two cyclic AMP response elements (CRE3, CRE2) in the Ucp1 promoter and methylation of the CpG in CRE2, but not CRE3 decreased nuclear protein binding. Chromatin immunoprecipitation assays revealed the presence of the silencing DiMethH3K9 modification on the Ucp1 enhancer in white adipose tissue and the appearance of the active TriMethH3K4 mark at the Ucp1 promoter in brown adipose tissue in response to a cold environment.

CONCLUSIONS/INTERPRETATION

The results demonstrate that CpG dinucleotide methylation of the Ucp1 enhancer exhibits tissue-specific patterns in murine tissue and cell lines and suggest that adipose tissue-specific Ucp1 expression involves demethylation of CpG dinucleotides found in regulatory CREs in the Ucp1 enhancer, as well as modification of histone tails.

Survey of pigs' kidneys with lesions consistent with PMWS and PDNS and ochratoxicosis. Part 1: concentrations and prevalence of ochratoxin A

One thousand condemned pigs' kidneys were collected in February 2002 from two pig abattoirs in England to assess the possible contribution of ochratoxicosis to postweaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS); 250 of the kidneys with macroscopic lesions consistent with nephrosis/nephritis (pale or white cortical lesions) were selected, and the concentration of ochratoxin A was measured in samples of renal cortex by high-performance liquid chromatography (HPLC). Low concentrations were detected in 230 (92 per cent) of the kidneys tested, and in 41 (16.4 per cent) of them the concentration was below the limit of quantification of 0.2 microg/kg. In 187 (74.8 per cent) of the kidneys, the concentration was more than 0.2 microg/kg, and the highest concentration detected was 2.3 microg/kg. The mean (sd) concentration was 0.31 (0.33) microg/kg. The identification of ochratoxin A was confirmed by mass spectrometry. The concentrations of ochratoxin A did not exceed the threshold assessed by the Food Standards Agency to be safe for human food.

Survey of pigs' kidneys with lesions consistent with PMWS and PDNS and ochratoxicosis. Part 2: pathological and histological findings

One thousand condemned pigs' kidneys were collected in February 2002 from two pig abattoirs in England to assess the lesions due to postweaning multisystemic wasting syndrome (pmws) and porcine dermatitis and nephropathy syndrome (pdns) and the possible contribution of ochratoxicosis; 174 of the kidneys were pale, 295 were swollen and 81 were abnormally firm with the gross appearance of fibrosis. The main macroscopic finding was the presence of multifocal pale cortical lesions, observed in 446 of the kidneys, and there were large cysts in 266 of them. Histopathological lesions of non-suppurative tubulointerstitial nephritis, with degeneration and fibrosis of renal tubules, were identified in 213 of 250 (85.2 per cent) of the kidneys examined. These lesions were consistent with those reported in cases of pmws and pdns. The tubular degeneration and fibrosis were also consistent with ochratoxicosis. A higher mean concentration of ochratoxin A was significantly (P=0.020) associated with the presence of multifocal pale cortical lesions consistent with ochratoxicosis, but a causal relationship was not confirmed because histochemistry was not used to detect ochratoxin in the lesions directly. There was no significant correlation between the microscopic lesions and the concentration of ochratoxin. The degenerative lesions may have been caused by previous exposure to ochratoxin that had subsequently been excreted, but the microscopic lesions also included non-suppurative interstitial nephritis, which was unlikely to have been caused by ochratoxicosis.

Genomic Analysis of Bacteriophages SP6 and K1-5, an Estranged Subgroup of the T7 Supergroup

We have determined the genome sequences of two closely related lytic bacteriophages, SP6 and K1-5, which infect Salmonella typhimurium LT2 and Escherichia coli serotypes K1 and K5, respectively. The genome organization of these phages is almost identical with the notable exception of the tail fiber genes that confer the different host specificities. The two phages have diverged extensively at the nucleotide level but they are still more closely related to each other than either is to any other phage currently characterized. The SP6 and K1-5 genomes contain, respectively, 43,769 bp and 44,385 bp, with 174 bp and 234 bp direct terminal repeats. About half of the 105 putative open reading frames in the two genomes combined show no significant similarity to database proteins with a known or predicted function that is obviously beneficial for growth of a bacteriophage. The overall genome organization of SP6 and K1-5 is comparable to that of the T7 group of phages, although the specific order of genes coding for DNA metabolism functions has not been conserved. Low levels of nucleotide similarity between genomes in the T7 and SP6 groups suggest that they diverged a long time ago but, on the basis of this conservation of genome organization, they are expected to have retained similar developmental strategies.

Effects of water deficit on Mediterranean and temperate cultivars of tall fescue

Two glasshouse experiments were carried out to evaluate the morphological and physiological responses to water deficit of Mediterranean and temperate tall fescue (Festuca arundinacea Schreb.) cultivars. In Expt 1, 3 cultivars were studied: 2 temperate cultivars, Grasslands Advance (GA) and El Palenque (EP); and a Mediterranean cultivar, Maris Kasba (MK). Water deficit was induced in containers of 4 plants of a single cultivar by withholding water. In Expt 2, plants of EP and MK were grown together in the same container and received water daily with gradation in intensity of water deficit achieved by varying the daily water ration per container. All cultivars in each experiment exhibited commonly reported responses to water deficit, characterised by diminished evaporative surface area and increased root : shoot ratio. The response of MK was primarily morphological and MK plants had smaller plant size, higher root : shoot ratio, and a lower growth rate compared with temperate cultivars. By contrast, response of temperate cultivars was primarily physiological; stomatal conductance of temperate cultivars was lower and these cultivars had a greater tendency for leaf lamina osmotic adjustment than MK under the most stressful water deficit conditions studied. The morphological adaptations of MK were very effective in delaying the onset of water deficit in Expt 1 when plants were grown with others of the same cultivar, but rendered MK plants uncompetitive and more susceptible to water deficit in Expt 2 where plants of MK where interspersed with plants of a temperate cultivar.

Stretch-induced alternative splicing of serum response factor promotes bronchial myogenesis and is defective in lung hypoplasia

Smooth muscle (SM) develops only in organs and sites that sustain mechanical tensions. Therefore, we determined the role of stretch in mouse and human bronchial myogenesis. Sustained stretch induced expression of SM proteins in undifferentiated mesenchymal cells and accelerated the differentiation of cells undergoing myogenesis. Moreover, bronchial myogenesis was entirely controlled in lung organ cultures by the airway intraluminal pressure. Serum response factor (SRF) is a transcription factor critical for the induction of muscle-specific gene expression. Recently, a SRF-truncated isoform produced by alternative splicing of exon 5 has been identified (SRFDelta5). Here we show that undifferentiated mesenchymal cells synthesize both SRF and SRFDelta5 but that SRFDelta5 synthesis is suppressed during bronchial myogenesis in favor of increased SRF production. Stretch induces the same change in SRF alternative splicing, and its myogenic effect is abrogated by overexpressing SRFDelta5. Furthermore, human hypoplastic lungs related to conditions that hinder cell stretching continue to synthesize SRFDelta5 and show a marked decrease in bronchial and interstitial SM cells and their ECM product, tropoelastin. Taken together, our findings indicate that stretch plays a critical role in SM myogenesis and suggest that its decrease precludes normal bronchial muscle development.

The internal head protein Gp16 controls DNA ejection from the bacteriophage T7 virion

A wild-type T7 virion ejects about 850 bp of the 40 kb genome into the bacterial cell by a transcription-independent process. Internalization of the remainder of the genome normally requires transcription. Inhibition of transcription-independent DNA translocation beyond the leading 850 bp is not absolute but the time taken by a population of phage genomes in overcoming the block averages about 20 minutes at 30 degrees C. There are additional blocks to transcription-independent translocation and less than 20 % of infecting DNA molecules completely penetrate the cell cytoplasm after four hours of infection. Mutant virions containing an altered gene 16 protein either prevent the blocks to transcription-independent DNA translocation or effect rapid release from blocking sites and allow the entire phage DNA molecule to enter the cell at a constant rate of about 75 bp per second. This rate is likely the same at which the leading 850 bp is ejected into the cell from a wild-type virion. All mutations fall into two clusters contained within 380 bp of the 4 kb gene 16, suggesting that a 127 residue segment of gp16 controls DNA ejection from the phage particle. We suggest that this segment of gp16 acts as a clamp to prevent transcription-independent DNA translocation.

Small ribosomal RNA content in marine Proteobacteria during non-steady-state growth

Nine strains of marine Proteobacteria were assayed for nucleic acid content during non-steady-state growth to assess whether a species-specific growth rate based on rRNA content is feasible for environmental samples. The large and small ribosomal subunits and genomic DNA were quantified using image analysis. It was found that the maximal intracellular concentration of 16S rRNA during batch growth for the bacteria averaged 155 fg+/-60 (S.D.) per cell for eight of the nine marine bacteria in the exponential phase (with the exception of one strain, Pac 218). The dilution/decay of 16S rRNA/cell was rapid with a return to pre-shift up values within 6-12 h for all strains except Vibrio fisherii. An overall relationship between the RNA:DNA ratio and the specific growth rate for non-steady-state growth for all bacterial strains was not observed as previously described for other Proteobacteria during steady-state growth. However, a predictable relationship between rRNA content and growth rate for many isolates during batch growth was observed. Furthermore, the rapid kinetics of intracellular rRNA levels indicates it will be feasible to assess whether specific bacteria are in steady state or non-steady state in the marine environment. If the condition of steady state is met for a specific Proteobacterial group in an environmental sample, it will be possible to estimate species-specific growth rates by measuring rRNA content.

The DNA translocation and ATPase activities of restriction-deficient mutants of Eco KI

Eco KI, a type I restriction enzyme, specifies DNA methyltransferase, ATPase, endonuclease and DNA translocation activities. One subunit (HsdR) of the oligomeric enzyme contributes to those activities essential for restriction. These activities involve ATP-dependent DNA translocation and DNA cleavage. Mutations that change amino acids within recognisable motifs in HsdR impair restriction. We have used an in vivo assay to monitor the effect of these mutations on DNA translocation. The assay follows the Eco KI-dependent entry of phage T7 DNA from the phage particle into the host cell. Earlier experiments have shown that mutations within the seven motifs characteristic of the DEAD-box family of proteins that comprise known or putative helicases severely impair the ATPase activity of purified enzymes. We find that the mutations abolish DNA translocation in vivo. This provides evidence that these motifs are relevant to the coupling of ATP hydrolysis to DNA translocation. Mutations that identify an endonuclease motif similar to that found at the active site of type II restriction enzymes and other nucleases have been shown to abolish DNA nicking activity. When conservative changes are made at these residues, the enzymes lack nuclease activity but retain the ability to hydrolyse ATP and to translocate DNA at wild-type levels. It has been speculated that nicking may be necessary to resolve the topological problems associated with DNA translocation by type I restriction and modification systems. Our experiments show that loss of the nicking activity associated with the endonuclease motif of Eco KI has no effect on ATPase activity in vitro or DNA translocation of the T7 genome in vivo.

Molecular cloning of the human HAND2 gene

We have cloned and characterized the coding sequence of the human HAND2 basic helix-loop-helix transcription factor. The amino acid sequence includes an amino-terminal polyalanine repeat which is precisely conserved in the rat HAND2 gene. Northern analysis indicates that the HAND2 transcript is 2.3 kb in length and strongly expressed in the human heart.

Expression and distribution of transforming growth factor-beta isoforms and their signaling receptors in growing human bone

Transforming growth factors type beta (TGF-beta1, -beta2, and -beta3) are potent stimulators of bone formation and have been shown to regulate chondrocyte, osteoblast, and osteoclast formation and function. However, the distribution of the different isoforms and their signaling receptors in human bone in vivo has not previously been reported. Using samples of normal (neonatal rib) and pathological (osteophytic) developing human bone, we have investigated the expression of the different TGF-beta isoforms and their signaling receptors (TGF-betaRI and RII) at the messenger ribonucleic acid (mRNA) and protein levels by in situ hybridization and immunolocalization to establish the sites of TGF-beta production and their possible sites of action during human bone development in vivo. All three TGF-beta isoforms and the receptors were detected at sites of endochondral and intramembranous ossification. At sites of endochondral ossification, TGF-beta2 was detected in all zones of the cartilage, with the highest expression seen in the hypertrophic and mineralizing zones. TGF-beta3 was detected in proliferative and hypertrophic zone chondrocytes, while TGF-beta1 expression was restricted to the proliferative and upper hypertrophic zones. TGF-betaRI and RII exhibited similar distributions with maximum expression in the hypertrophic and mineralizing zones in the neonatal rib but in the resting/proliferative zone in the developing osteophyte. At sites of intramembranous ossification TGF-beta3 was the most widely distributed isoform and showed both matrix- and cell-associated staining. TGF-beta2 and -beta1 were expressed almost exclusively at sites of mineralization. These observations demonstrate that the different TGF-beta isoforms and their receptors exhibit distinct but overlapping patterns of expression, and support the hypothesis that they are involved in the regulation of endochondral and intramembranous ossification during human bone development in vivo.

The enemy within: diarrheal rates among British and Australian troops in Iraq

British and Australian medical teams working in Northern Iraq in 1991 providing primary care to refugees and the war wounded were subjected to a descriptive retrospective survey, 5 weeks after arriving in Iraq. The aim was to document different rates of diarrhea in British and Australian troops. The British, who were not taking daily doxycycline and did not enforce a plate- and hand-washing routine, experienced higher rates of diarrhea (69% of British troops compared with 36% of Australian troops), which was more severe and of a longer duration (p < 0.001) and resulted in twice as many days being lost (p < 0.001) in spite of the British team being half the size of the Australian contingent, and the region having enteropathogens with a high rate of antibiotic resistance. Vigorous hand- and plate-washing routines along with doxycycline prophylaxis appear to significantly reduce incapacitation from diarrhea in this military setting and have an important implication for operational effectiveness.

Distribution of platelet-derived growth factor (PDGF) A chain mRNA, protein, and PDGF-alpha receptor in rapidly forming human bone

Platelet-derived growth factors (PDGFs) are potent bone cell mitogens which stimulate the proliferation of osteoblastic cells, may also be involved in the regulation of osteoclastic bone resorption, and indirectly induce vascular endothelial cell proliferation and angiogenesis. In view of the established relationship between angiogenesis and osteogenesis, the production of PDGFs by both osteoblastic and vascular endothelial cells suggests that they may play a role in bone formation during skeletal development. We have used two human models of rapid bone formation, heterotopic bone and osteophytic bone, to investigate the expression of PDGF-A mRNA and protein and the PDGF-alpha receptor protein in vivo using in situ hybridization and immunohistochemistry. PDGF-A mRNA and protein were widely distributed throughout heterotopic and osteophytic bone. Within the cartilaginous tissue PDGF-A mRNA and protein were most strongly expressed by mature chondrocytes with decreased expression in the hypertrophic zone and almost no staining in the mineralizing and mineralized zones. PDGF mRNA and protein were also expressed in cells of small blood vessels within fibrous and cartilaginous tissue. In contrast, PDGF-alpha receptor expression was restricted to a minority of hypertrophic chondrocytes and sites of vascular invasion. Within the bone and fibrous tissue the growth factor and the receptor were widely distributed, being detected on most cells at sites of bone formation or in remodeling sites; no receptor was detected on osteoclasts. These data demonstrate the widespread expression of PDGF-A and its receptor in forming human bone and indicate that this growth factor may exert autocrine and paracrine effects to regulate osteogenesis during skeletal development.

Streptomycin- and rifampin-resistant mutants of Escherichia coli perturb F exclusion of bacteriophage T7 by affecting synthesis of the F plasmid protein PifA

Certain alleles of rpsL that confer resistance to the antibiotic streptomycin almost completely relieve F exclusion of bacteriophage T7. Introduction of a specific rpoB allele conferring resistance to rifampin into the rpsL strain restores the ability of the F-containing strain to exclude T7. This variation in the severity of F exclusion is reflected in the levels of the F-encoded inhibitor protein PifA: F'-containing cells that harbor specific rpsL alleles are phenotypically Pif-, but become Pif+ by the further acquisition of a specific rpoB allele. F-containing cells harboring the gyrA43(Ts) mutation also appear phenotypically Pif-, possibly because repression of the pif operon is enhanced by an altered DNA conformation in the gyrase mutant strain.

Activation of MAP kinase kinase is necessary and sufficient for PC12 differentiation and for transformation of NIH 3T3 cells

The MAP kinase pathway is activated by a wide variety of external signals leading to cell proliferation or differentiation. However, it is not clear whether activation of this pathway is required for cellular responses or whether it is only one branch point in signal transduction. To investigate these questions, we generated constitutively activated and interfering mutants of MAP kinase kinase 1. The activated mutants stimulated PC12 cell neuronal differentiation and transformed NIH 3T3 cells. The interfering mutants inhibited growth factor-induced PC12 differentiation, growth factor stimulation of proliferation, and reverted v-src- and ras-transformed cells. These results therefore show that, depending on cellular context, activation of MAP kinase kinase is necessary and sufficient for cell differentiation or proliferation.

Genes 1.2 and 10 of bacteriophages T3 and T7 determine the permeability lesions observed in infected cells of Escherichia coli expressing the F plasmid gene pifA

Infections of F plasmid-containing strains of Escherichia coli by bacteriophage T7 result in membrane damage that allows nucleotides to exude from the infected cell into the culture medium. Only pifA of the F pif operon is necessary for "leakiness" of the T7-infected cell. Expression of either T7 gene 1.2 or gene 10 is sufficient to cause leakiness, since infections by phage containing null mutations in both of these genes do not result in permeability changes of the F-containing cell. Even in the absence of phage infection, expression from plasmids of either gene 1.2 or 10 can cause permeability changes, particularly of F plasmid-containing cells. In contrast, gene 1.2 of the related bacteriophage T3 prevents leakiness of the infected cell. In the absence of T3 gene 1.2 function, expression of gene 10 causes membrane damage that allows nucleotides to leak from the cell. Genes 1.2 and 10 of both T3 and T7 are the two genes involved in determining resistance or sensitivity to F exclusion; F exclusion and leakiness of the phage-infected cell are therefore closely related phenomena. However, since leakiness of the infected cell does not necessarily result in phage exclusion, it cannot be used as a predictor of an abortive infection.

Recipes for reconstituting skin

Reconstituted Living Skin Equivalent (LSE) is made up of a dermal equivalent (DE) on which keratinocytes are plated where they give rise to a multilayered differentiated epidermis. The dermal equivalent develops through interactions between fibroblasts and collagen fibrils that begin to form after the cell-matrix precursor is cast. The gel that forms as a result of collagen polymerization and fluid trapping is contracted uniformly in all dimensions. By securing it at ends and edges in the mold in which it is cast, the final dimensions, strength and morphology of the forming tissue are altered. The same phenomena are seen in casting tubular tissues for the fabrication of small caliber blood vessel equivalents. The cells of the dermal equivalent are biosynthetically active and enrich the matrix to different degrees with secretory products, depending on how the cells are stimulated and on the presence or absence of an epidermis. Collagen biosynthesis by dermal cells in the DE is sensitive to growth factors, ascorbate concentrations and amino acid pools. Both ascorbate and TGF beta 1 increase total collagen biosynthesis at least two-fold by one week after tissue formation. With TGF beta 1 present, the capacity of cells in the DE to synthesize collagen increases with time, over a two-week period. If ascorbate (200 micrograms/ml) is added just after the tissue is cast and daily thereafter, contraction lattice is blocked, and collagen biosynthesis is enhanced relative to contracted controls that had received 200 micrograms/ml ascorbate once. The increase was nearly an order of magnitude over that of controls and was coordinate with a comparable increase in hyaluronate and sulfated glycosaminoglycan (GAG) production as shown by TCA-precipitable glucosamine in the intercellular matrix of the DE. Both the LSE and the Living Dermal Equivalent (LDE) exhibit complex responses to UV radiation and to various chemicals that are greatly different from responses given by monolayered cells.(ABSTRACT TRUNCATED AT 250 WORDS)