Viscoelastic properties of acid- and alkaline-treated human dermis: a correlation between total surface charge and elastic modulus

BACKGROUND: One of the major mechanical functions of collagenous tissues is the storage, transmission and dissipation of elastic energy during mechanical deformation. In skin, mechanical energy is stored during loading and then is transmitted and dissipated, which protects skin from mechanical failure. Thus energy storage (elastic properties) and dissipation (viscous properties) are important characteristics of extracellular matrices. METHODS: A uniaxial incremental stress relaxation test method has been used to characterize the time-dependent (viscous) and time-independent (elastic) properties of human dermis. Viscoelasticity was investigated in processed human dermis that was equilibrated at pHs of 3.0, 7.4 and 11.0 in an effort to study the link between electrostatic interactions within the collagen matrix and macroscopic tissue properties. RESULTS: Our results show that the solution pH and the charge on collagen significantly affected the high-strain elastic behavior of dermis; the elastic behavior of skin has previously been shown to be directly correlated with axial stretching of the collagen triple helix in crosslinked collagen fibrils. A positive linear correlation existed between the high-strain elastic modulus and both pH (R(2)=0.96) and the total number of charged residues on collagen (R(2)=0.93). These results provide in vitro/ex vivo evidence that charged groups on the surface of collagen molecules in processed human skin influence the high-strain elastic properties of dermis and are likely to be involved in elastic energy storage. CONCLUSION: It is proposed that the pH and charged residue dependency of the elastic modulus suggests that charged pair interactions and repulsions within and between collagen molecules are involved in elastic energy storage during stretching at high strains. It is hypothesized that elastic energy storage is associated with the stretching of pairs of charged amino acid residues that are found primarily in the flexible regions of collagen molecules.     

脱细胞异体皮肤细胞外基质——医用组织补片在美容外科的应用

目的介绍脱细胞异体皮肤细胞外基质医用组织补片在美容外科中的临床应用经验。方法自2002年3月至2005年10月,应用脱细胞异体皮肤细胞外基质医用组织补片,对患者不同部位进行填充的美容手术,其中头面部填充于皮下浅筋膜层,唇部、颏部、唇裂合并牙槽裂部填充于皮下深筋膜层或肌肉浅层,隆乳术中用于胸大肌减张。结果本组115例患者经1~27个月随访,1例唇裂合并牙槽裂者因补片填充量不足凹陷未完全矫正;1例鼻唇沟填充者其左侧出现血肿、局部出现硬结,于2个月后将左侧假体取出重新填充,但术后6个月仍有不平整,其余患者均获得良好的美容效果。结论脱细胞异体皮肤细胞外基质医用组织补片可以广泛地应用于美容外科的临床填充术。     

An improved and highly standardised transformation procedure allows efficient production of single and multiple targeted gene-knockouts in a moss,<Emphasis Type="Italic"> Physcomitrella patens</Emphasis>

The moss Physcomitrella patens is the only land plant known to date with highly efficient homologous recombination in its nuclear DNA, making it a unique model for plant functional genomics approaches. For high-throughput production of knockout plants, a robust transformation system based on polyethylene glycol-mediated transfection of protoplasts was developed and optimised. Both the DNA conformation and pre-culture of plants used for protoplast isolation significantly affected transformation efficiencies. Employing a newly developed PCR high-throughput method, the gene-targeting efficiency in more than 1,000 plants transformed with different cDNA-based knockout constructs was determined and analysed with regard to the length and intron/exon structure of the homologous gene locus. Different targeting constructs, each containing an identical selectable marker gene, were applied as batch DNA in a single transformation experiment and resulted in double-knockout plants. Thus, the fast and efficient generation of multiple targeted gene-knockouts is now feasible in Physcomitrella.Communicated by U. Kück     

Skin ligaments: regional distribution and variation in morphology

Skin ligaments (SL) (L. retinacula cutis) are present extensively in the face, hands, feet, and in breast tissue, but have seldom been reported elsewhere in the body. The traditional histological view of the subcutaneous region is that it comprises a matrix of loose connective tissue devoid of fibrous specializations. The purpose of this study was to determine the structure and distribution of skin ligaments. Eight embalmed cadavers (3 males, 5 females, 69-90 years of age) were used in this study. Tissue was prepared using the E12 plastination technique. Macroscopic and microscopic examination demonstrated the widespread presence in the limbs and most of the rest of the body of fibrous strands linking the base of the dermis and the superficial fibers of the underlying deep fascia. The morphology and distribution of these skin ligaments were similar in the individuals examined. Variations in the structure of the skin ligaments depended on the presence of underlying muscle, neurovascular bundles, intermuscular septa and adipose tissue. We conclude that skin ligaments are complex fibrous structures that are present over most of the body. They form an extensive peripheral network in the subcutaneous fat. These 'ligaments' seem to provide an anchorage of skin to deep fascia that is flexible and yet resistant to mechanical loading from multi-directional forces. The use of the E12 plastination technique coupled with fluorescent confocal microscopy has been of benefit in visualizing and delineating SLs from other soft tissue structures in three planes.     

Studies on homologous recombination in the green alga Chlamydomonas reinhardtii

The introduction of exogenous DNA into the nuclear genome of Chlamydomonas reinhardtii occurs predominantly via non-homologous (illegitimate) recombination and results in integration at apparently-random loci. Using truncated and modified versions of the C. reinhardtii ARG7 gene in a series of transformation experiments, we demonstrate that homologous recombination between introduced DNA molecules occurs readily in C. reinhardtii, requires a region of homology of no more than 230 bp, and gives rise to intact copies of ARG7 in the nuclear genome. Evidence is presented for homologous recombination between introduced ARG7 DNA and the resident copy of the gene, and for the de-novo synthesis of the ARG7 sequence during transformation.     

Ⅰ型胶原膜、胞外基质提取物膜体外构建人工真皮能力比较

比较Ⅰ型胶原与胞外基质(extracellularmatrix,EM)提取物冻干后形成的膜(EM膜)在体外构建人工真皮的能力,以选择一种更有利于人工真皮形成的支架材料。方法分别使用小牛真皮部分提取的Ⅰ型胶原蛋白和胞外基质提取物冻干后制备基质网架,植入皮肤成纤维细胞,形成人工真皮。用扫描电镜观察I型胶原膜和EM膜的表面形态结构;选取不同的时间点,对种植于两种支架材料上的细胞进行计数,并利用间接ELISA方法检测人工真皮复合物中的细胞Ⅰ型胶原分泌情况,通过统计学的分析手段,对细胞的生长情况做出判断;用组织学方法观察人工真皮的形成情况。结果扫描电镜观察结果,两种膜在外观形态上无明显差异;细胞在EM膜上的增殖速度较Ⅰ型胶原膜快;ELISA分析显示,EM-细胞复合物中的成纤维细胞能够分泌更多的Ⅰ型胶原;与Ⅰ型胶原膜相比,EM在培养液中的降解更为缓慢,种植后的成纤维细胞在EM膜上生长旺盛,细胞层次明显多于前者,形成了较为明显的真皮样组织。结论EM膜适于成纤维细胞的生长,体外降解速率慢,是一种较Ⅰ型胶原膜更为理想的真皮支架材料。     

Homologous recombination in the fission yeast Schizosaccharomyces pombe: different requirements for the rhp51+, rhp54+ and rad22+ genes

The Schizosaccharomyces pombe rhp51 ⁺ , rad22 ⁺ and rhp54 ⁺ genes are homologous to RAD51, RAD52 and RAD54 respectively, which are indispensable in the recombinational repair of double-strand breaks (DSBs) in Saccharomyces cerevisiae. The rhp51Δ and rhp54Δ strains are extremely sensitive to ionizing radiation; the rad22Δ mutant turned out to be much less sensitive. Homologous recombination in these mutants was studied by targeted integration at the leu1-32 locus. These experiments revealed that rhp51Δ and rhp54Δ are equally impaired in the integration of plasmid molecules (15-fold reduction), while integration in the rad22Δ mutant is only reduced by a factor of two. Blot-analysis demonstrated that the majority of the leu⁺ transformants of the wild-type and rad22Δ strains have integrated one or more copies of the vector. Gene conversion events were observed in less than 10% of the transformants. Interestingly, the relative contribution of gene conversion events is much higher in a rhp51Δ and a rhp54Δ background. Meiotic recombination is hardly affected in the rad22Δ mutant. The rhp51Δ and rhp54Δ strains also show minor deficiencies in this type of recombination. The viability of spores is 46% in the rad22Δ strain and 27% in the rhp54Δ strain, as compared with wild-type cells. However, in the rhp51Δ mutant the spore viability is only 1.7%, suggesting an essential role for Rhp51 in meiosis. The function of Rhp51 and Rhp54 in damage repair and recombination resembles the role of Rad51 and Rad54 in S. cerevisiae. Compared with Rad52 from S. cerevisiae, Rad22 has a much less prominent role in the recombinational repair pathway in S. pombe. Received: 20 July 1996     

The <Emphasis Type="Italic">rpl5</Emphasis>–<Emphasis Type="Italic">rps14</Emphasis> mitochondrial region: a hot spot for DNA rearrangements in <Emphasis Type="Italic">Solanum</Emphasis> spp. somatic hybrids

Southern analysis with rpl5 and rps14 mtDNA gene probes of Solanum tuberosum, S. commersonii and a sample of somatic hybrids detected polymorphisms between parents and the appearance of a novel restriction fragment in various hybrids. In one of them, detailed mtDNA analyses revealed various configurations of the rpl5–rps14 region present at different stoichiometries. Multiple inter-parental recombination events across homologous sequences were assumed to have caused these rearrangements. Sequence similarity searches detected one sequence putatively involved in the recombination upstream of the rpl5 gene. The presence of a second recombinogenic sequence was inferred. We propose two models to explain the mechanism responsible for obtaining the different rpl5–rps14 arrangements shown after somatic hybridization. Variability in the rpl5–rps14 region observed in both the parental species and their somatic hybrids suggests this region is a hot spot for mtDNA rearrangements in Solanum spp.Contribution no. 39 from the Institute of Plant Genetics, Research Division of Portici.Communicated by A. Brennicke     

Membrane attack complex of complement and 20 kDa homologous restriction factor (CD59) in myocardial infarction

In order to investigate the mechanism of deposition of the complement membrane attack complex (MAC) in cardiomyocytes in areas of human myocardial infarction, the 20 kDA homologous restriction factor of complement (HRF20; CD59) and complement components (C1q, C3d and MAC) were analysed immunohistochemically using specific antibodies. Myocardial tissues obtained at autopsy from nine patients who died of acute myocardial infarction were fixed in acetone and embedded in paraffin. The ages of the infarcts ranged from about 3.5 h to 12 days. In cases of myocardial infarction of 20 h or less, MAC deposition was shown in the infarcted cardiomyocytes without loss of HRF20. Where the duration was 4 days or more, the cardiomyocytes with MAC deposition in the infarcted areas also showed complete loss of HRF20. Outside the infarcts, HRF20 in the cardiomyocytes was well preserved without MAC deposition. The present study suggests that the initial MAC deposition in dead cardiomyocytes can occur as a result of degradation of plasma-membrane by a mechanism independent of complement-mediated injury to the membrane. Loss of HRF20 from dead cardiomyocytes may not be the initial cause of MAC deposition, but may accelerate the deposition process of MAC in later stages of infarction.