770 research outputs found
C.T. Vivian, Joseph E. Lowery, and Tom Brown, circa 1980
No full textSouthern Christian Leadership Conference President Joseph E. Lowery is shown standing outside with C.T. Vivian (left) and Tom Brown (right) at Paschal's Motor Hotel.The Atlanta University Center Robert W. Woodruff Library acknowledges the generous support of the Joseph & Evelyn Lowery Institute for Justice and Human Rights, the Joseph Echols Lowery Irrevocable Trust, and other donors in supporting the processing and digitization of Morehouse College's Joseph Echols and Evelyn Gibson Lowery Collection
Chondrocyte dedifferentiation down regulates mechano-responsiveness and hedgehog signalling associated with changes in primary cilia structure
No full textPurpose: with the limited availability of human chondrocytes for tissue engineering applications, passaging is used to increase cell yield. However, this 2D expansion leads to a loss of chondrogenic phenotype associated with changes in actin organisation. Primary cilia are microtubule structures that act as a signalling hub controlling a variety of signalling pathways including mechanotransduction and hedgehog signalling, both of which are involved in differentiation and osteoarthritis. Primary cilia structure and function are known to be regulated by changes in actin tension. Thus the present study tests the hypothesis that chondrocyte dedifferentiation during monolayer expansion leads to alterations in mechano-responsiveness and hedgehog signalling mediated by changes in primary cilia structure.Methods: chondrocytes were isolated from the metacarpophalangeal joints of 18-24 month old steers. Primary chondrocytes at passage 0 (P0) were cultured in monolayer up to passage 5 (P5) using DMEM containing 10% FBS, 1.9 mM L-glutamine, 96 U/ml penicillin, 96 mg/ml streptomycin, 20 mM HEPES buffer, and 0.74 mM L-ascorbic acid.For mechano-responsiveness, primary (P0) and dedifferentiated (P5) chondrocytes were cultured on collagen I-coated Bioflex plates and subjected to cyclic tensile strain (10%, 0.33 Hz, 1 hour) via the Flexcell 4000T system, prior to analysis of collagen II, aggrecan, ADAMTS5, and MMP13 gene expression. For hedgehog signalling, P0 and P5 chondrocytes were treated with 1 μg/ml Indian hedgehog (Ihh) for 24 hours. Hedgehog pathway activation was then quantified by analysis of Gli1 and Ptch1 gene expression. Controls were maintained in parallel for both studies. Total RNA was isolated using RNeasy Kit (Qiagen). Quantitect Reverse Transcription Kit (Qiagen) was used to covert 1 μg RNA to cDNA and real-time PCR was performed using KAPA SYBR® FAST qPCR Kit (KAPA Biosystems).Cells at P0 to P5 were also fixed with 4% paraformaldehyde and labelled for acetylated α-tubulin and Ki67, with DAPI counterstaining. Confocal microscopy was used to determine the percentage of Ki67 positive cells as well as primary cilia prevalence and length.Results: at P0, cyclic tensile strain significantly upregulated aggrecan, type II collagen and ADAMTS5 gene expression and downregulated MMP13 expression (Fig. 1). This response to loading was completely lost in the P5 chondrocytes. When chondrocytes at P0 were treated with Ihh, pathway activation was confirmed by a 5-fold increase in Gli1 and Ptch1 gene expression (Fig. 2). However both Gli1 and Ptch1 responses to Ihh were significantly reduced at P5 with a complete suppression of Ptch1 up-regulation.Cell proliferation, as indicated by Ki67, remained less than 30% although there was a significant increase by passage 3 (Fig. 3A). The percentage of ciliated cells increased significantly after the first passage and remained constant at 40-50% with subsequent passaging (Fig. 3B). Chondrocyte primary cilia length increased continuously with passage, doubling in length from P0 to P5 (Fig. 3C and D).Conclusions: changes in primary cilia length affects cilia function including mechanotransduction and hedgehog signalling and may also affect other cilia signalling pathways. As hypothesized, the reduction in mechano-responsiveness and hedgehog signalling with extended 2D culture is due to the associated elongation of primary cilia. To further identify the underpinning mechanisms, ongoing studies are using super resolution microscopy to examine whether cilia elongation at P5 is associated with alterations in cilia expression of ARL13B, and putative mechanoreceptors polycystin 2 and TRPV4. The observed reductions in mechano-responsiveness and ligand-induced hedgehog signalling with passage have important implications for the success of cartilage tissue engineering. Future work will investigate whether modulation of cilia length can maintain or rescue mechano- and hedgehog-responsiveness during expansion of chondrocytes for cartilage tissue engineering
Extracellular matrix synthesis and degradation in functionally distinct tendons
No full textTendon injury is common in humans and horses, and incidence increases with age. The high-strain energy storing equine superficial digital flexor (SDFT) is injured more frequently than the low-strain positional common digital extensor (CDET). However, previous work indicated that matrix turnover is greater in the CDET than in the SDFT. It was hypothesised that matrix turnover is programmed by the cells’ strain environment; therefore high-strain energy storing tendons would have a lower rate of matrix turnover than low-strain positional tendons and the rate of matrix turnover would decrease with increasing age. The rate of matrix turnover was investigated by measuring the potential of the cells to synthesise and degrade matrix proteins, measuring the half-life of the collagenous and non-collagenous matrix proteins and assessing collagen turnover at the protein level. In vitro cell phenotype was also assessed in 2D and 3D culture and the effect of load on cells within native tissue was determined. The results show that turnover of collagenous and non-collagenous matrix proteins is differentially regulated in the functionally distinct SDFT and CDET. CDET tenocytes show greater potential for collagen turnover, whereas SDFT tenocytes have a greater potential for proteoglycan turnover; differences that are also present at the protein level. The differences in cell phenotype identified in vivo were lost in 2D and 3D culture, but tendon organ culture resulted in the maintenance of tenocyte phenotype. The cells’ ability to turnover the matrix does not decrease with increasing age, but collagen within the SDFT appears to become more resistant to degradation with ageing. This results in the accumulation of partially degraded collagen within the SDFT which may have a detrimental effect on tendon mechanical properties. These findings will help to elucidate the mechanisms behind the development of age-related tendinopathy and will be of use when developing treatment regimes
Pectin - Xyloglucan linkages in type I primary cell walls of plants
No full textEvidence for covalent pectin - xyloglucan linkages in the cell wall of growing cells and maturing tissues has been reported. In-vitro studies using isolated Golgi membranes, and pulse-labelling studies in vivo, indicate that pectin - xyloglucan linkages form in the Golgi apparatus. The structure and biological significance of these complexes are discussed. © 2005 Società Botanica Italiana.Abdel-Massih RM, 2003, PLANTA, V216, P502, DOI 10.1007-s00425-002-0861-y; Brett C.T., 1996, PHYSL BIOCH PLANT CE; BRETT CT, 2004, 10 CELL WALL M 2004, P66; Femenia A, 1999, CARBOHYD POLYM, V39, P151, DOI 10.1016-S0144-8617(99)00003-X; KEEGSTRA K, 1973, PLANT PHYSIOL, V51, P188, DOI 10.1104-pp.51.1.188; MCCANN MC, 1990, J CELL SCI, V96, P323; POPPER ZA, 2004, 10 CELL WALL M 2004, P85; Thompson JE, 2000, PLANTA, V211, P275, DOI 10.1007-s004250000287; Vincken JP, 2003, PLANT PHYSIOL, V132, P1781, DOI 10.1104-pp.103.022350; WALDRON KW, 1992, PHYTOCHEMISTRY, V31, P1931, DOI 10.1016-0031-9422(92)80336-D89
Contribuicao para o estudo da epidemiologia molecular e da patogenia das infeccoes causadas por Chlamydia trachomatis
No full textThe study determined Chlamydia trachomatis (C.t.) genotype E as predominant, in the biological products of Lisbon citizens infected by C.t.. The author developed an experimental model of chronic infection, using mice of different haplotypes, inoculated (once or more) in the uterus (through the vagina) with one E C.t. strain. C.t. was isolated, by culture, after the first inoculation, but C.t. DNA was detected during the six months period of experiments; C.t. remained in tubal tissues in a nonviable biological state. The humoral immune response of infected animals indicated a chronic C.t. infection. The evaluation of the genetic expression of different cytokines produced by Th1 or Th2 cells, couldn't determine a profile specifically related with the chronic C.t. infection; however, the IFN_#gamma# production by illiac node cells, only occured during the acute infection. The production of isotype IgG2a or IgG1 showed a Th1 profile in C3H/He mice and a Th2 profile in C57BL/6 mice. C3H/He mice produced antibodies to the C.t HSP60 (CHSP60) during both acute and chronic C.t. infection; C57BL/6 mice only reacted to CHSP60 when submitted to several C.t. infection episodes. Mice carrying a chronic C.t. infection didn't exhibit any histological changes suggesting episodes. Mice carrying a chronic C.t. infection didn't exhibit any histological changes suggesting the establishment of a chronic inflammatory processAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga
An Auto-Zero Stabilized Voltage Buffer with a Trimmed Input Current of 0.2pA
No full textThis paper presents an input-current trimming scheme for auto-zero amplifiers. Since their input current is mainly due to charge injection,the scheme operates by trimming the clock swing,and hence the charge injection,of two dummy input switches. At room temperature,the trimming scheme reduces the maximum input current of an auto-zero stabilized voltage buffer from 1pA to 0.2pA (13 samples) over its full input voltage range (0 to 1.3V). This increases to 0.4pA over temperature (0 to 85°C),which is well below the leakage of typical ESD diodes,and is the lowest input current ever reported for an auto-zero amplifier.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
An Auto-Zero-Stabilized Voltage Buffer With a Quiet Chopping Scheme and Constant Sub-pA Input Current
No full textThis article describes an auto-zero stabilized voltage buffer that achieves low offset and low noise with sub-pA input current. A high gain stabilization loop is used to periodically cancel the buffer’s offset. The loop itself is periodically disconnected from the buffer and auto-zeroed, during which its bandwidth is reduced to reduce the associated noise folding. However, this also reduces its offset correction range, and so to avoid overloading, its initial offset is digitally trimmed. To break up the correlation between the residual low-frequency (LF) noise of the auto-zero and stabilization phases, the loop is periodically chopped, which significantly reduces the buffer’s LF noise. Finally, the duty-cycle of the two phases is optimized to bring the buffer’s LF noise density close to 2–√ times its white noise density (14 nV/ Hz−−−√ ), which is the fundamental limit of an AZ amplifier. The buffer also achieves a constant and low input current (0.8 pA), as well as a state-of-the-art offset (0.4 μV ).Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
A Quiet Digitally Assisted Auto-Zero-Stabilized Voltage Buffer with 0.6pA Input Current and 0.6μV Offset
No full textThe readout of high impedance sensors and sampled voltage references [1]requires amplifiers with both low offset and low input current. Chopper amplifierscan achieve low offset, but the switching of their input chopper gives rise tosignificant input current (40 to 110pA) [2-4]. Auto-zero (AZ) amplifiers requireless input switching, but exhibit more voltage noise. However, ping-pongamplifiers continuously swap two auto-zeroed input stages, leading to moreswitching [5,7]. In this work, an AZ stabilized topology is proposed, in which asingle amplifier is always present in the signal path. Only one input switch isrequired, resulting in an input current of 0.6pA (max), a 66× improvement on thestate-of-the art [4]. Furthermore, a digitally assisted offset-reduction schemereduces its low-frequency (LF) noise to the theoretical √5× limit. It also achievesa state-of-the-art maximum offset of 0.6μV.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
An Exploratory Analysis of the Timing of Job Reentry for Married Women in Taiwan
No full text本研究之特點在於採用事件史分析法來探討已婚婦女再就業之時機及其解釋因素。採用行政院主計處「婦女婚育與就業調查」1983與1993兩年資料，本研究先針對20-26歲已婚婦女再就業型態加以分類並描述其人口特質，其次針對「曾因結婚離職」與「曾因生育離職」者，分析其再就業時間之分布。研究指出，在離職後之20年間，「曾因結婚離職者」再就業之可能性比「曾因生育離職者」低，而且再就業可能性1993年比1983年高。尤值得注意的，離職後第三年與第十年均為再就業之高峰期，這個現象又以「曾因生育離職者」最為明顯。採用「卡克斯模型」分析，發現影響婦女「再就業」的解釋因素中「年齡」與「配偶教育」在兩類復職與各年間均有一致的負效應，即不利於再就業。另外，在「曾因生育離職」婦女中，須照顧小孩者不利於再就業，也在1983與1993兩年資料中一致出現。研究結果說明著台灣婦女再就業仍受到家庭生命週期的影響，隱含對於傳統性別角色專業化說法的支持，以及家庭經濟理性的考量仍重於婦女個人薪資效益的考量。由於在1983至1993年間，婦女個人教育的效應從不顯著轉變為顯著且正面的淨影響，即婦女個人教育高有助於再就業，意含著婦女個人因素的重要性隨時間增加中。This research examined the timing of job reentry for married women who had ever quitted from job market due to marriage or birth. Using 1983 and 1993 waves of Fertility and Employment of Married Women Survey conducted by DGBAS, the author converted the retrospective information in the survey into women’s work histories. This paper reported that these women were more likely to reenter job market in the third and the tenth years after quitting than any other time. The peaks of the curve were of particular prominence in 1993 sample and for the birth-quitting women. By employing the Cox Model, the author further analyzed the factors that might be used to interpret the event of job reentry while censoring was taken into account. Both models of marriage-quitting and of birth-quitting commonly revealed that age and spouse’s schooling were negatively related to the job reentry. Childcare was another factor that negatively affected the job reentry for birth-quitting women in both survey years. Besides, schooling was getting important in 1993 when compared with that in 1983
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