骨软骨复合支架的研究进展

软骨的修复是当前医学界十分棘手的难题,人们采取若干手段均收效甚微。由于软骨缺损时,其下的软骨下骨常出现硬化、退变,而新生软骨是无法与病变的软骨下骨进行整合的,所以在修复软骨的同时,必须重视软骨下骨的修复。近十几年来,人们开始发明和利用各种骨软骨复合支架,进行同时修复软骨与软骨下骨的动物实验研究。在正常骨软骨组织中,软骨与软骨下骨被钙化层所相连,此外钙化层也将软骨与软骨下骨分隔在不同的生存环境中。根据仿生学原理,人们又设计出一种带有隔离层的新型骨软骨复合支架,并取得了较为理想的实验结果。本文就国内外骨软骨复合支架的研完进展作一综述。     

功能矫形前伸青春期大鼠下颌后浅层嚼肌细胞凋亡的研究

目的：研究功能矫形前伸大鼠下颌后浅层嚼肌细胞凋亡的变化规律,探讨功能矫形的肌肉改建机理。方法：选用50只5周龄Sprague-Dawley（SD）雄性大白鼠,随机分为实验组和对照组各25只。实验组大鼠戴自制上颌功能矫治嚣,引导下颌前伸,并打开咬合。利用RT-PCR方法检测两组大鼠浅层嚼肌Bcl-2和Bax基因表达情况,利用TUNEL方法检测浅层嚼肌细胞凋亡情况。结果：①Bcl-2和Bax基因表达随大鼠戴用矫治器时间的延长而升高,至第3周开始下降但仍高于对照组,但Bax的表达高于Bcl-2。Bax/Bcl-2比值随大鼠戴用矫治器时间的延长而升高,至第4周开始下降。②TUNEL实验结果显示浅层嚼肌细胞在戴用矫治器1天后,开始出现凋亡,随着时间延长而增加,至第3周达到顶峰,第4周开始下降。结论：①Bax/Bcl-2比值升高促进浅层嚼肌细胞凋亡。②功能矫形可引起浅层嚼肌细胞凋亡,导致肌肉的结构和功能发生适应性改建。     

RELATIVE PERFORMANCE OF SELFED AND OUTCROSSED PROGENY IN IMPATIENS CAPENSIS

This study compares survival and growth of progeny derived from chasmogamous (CH) and cleistogamous (CL) flowers in Impatiens capensis, a forest annual. When progeny were grown in the field, CH seeds had significantly higher survival rates over winter (64% versus 56%), and the survival advantage of outcrossed progeny was not attributable to seed weight differences. No differences in seedling growth were detected. Greenhouse comparisons revealed no difference in seed survival but a 30% growth advantage to CH seedlings. We found no changes in developmental homeostasis of three leaf shape characters between inbred and outbred progeny, nor was there any difference in variability within CH and CL families. The outcrossing advantage observed in these experiments could not have been caused by avoidance of sib competition. Theory predicts that self-pollinated progenies may be more variable than outcrossed progenies if rare, recessive alleles are important contributors to genetic variances. Electrophoretic markers indicate that progeny derived from CH flowers are predominantly outcrossed (at least 54-97%).     

Enhanced level and metabolic regulation of methionyl-transfer ribonucleic acid synthetase in different strains of Escherichia coli K-12.

The methionyl-transfer ribonucleic acid (tRNA) synthetase of Escherichia coli K-12 eductants carrying P2-mediated deletions in the region of the structural gene of this enzyme was investigated. No structural alteration of this enzyme was observed in three eductants examined. These were isolated from strain AB311, which had a threefold higher level of methionyl-tRNA synthetase than most haploid strains examined. In two of the three eductants studied, the level of this enzyme was twofold higher than in their parental strain regardless of growth conditions used. In contrast, isoleucyl-, leucyl-, and valyl-tRNA synthetases had similar levels in all strains examined. Like valyl-tRNA synthetase, but to a lesser extent, methionyl-tRNA synthetase was subject to metabolic regulation. Coupling between the level of methionyl-tRNA synthetase and growth rate was observed even in strains that had an enhanced level of methionyl-tRNA synthetase. These results suggest that the formation of methionyl-tRNA synthetase remains subject to metabolic regulation even when the repression-like mechanism that controls the synthesis of this enzyme is altered. In addition, we report that in the merodiploid strain EM20031, which was haploid for the valyl-tRNA synthetase structural gene and diploid for the structural genes of methionyl-tRNA synthetase and D-serine deaminase, the levels of these latter two enzymes varied to a minor yet significant extent with the phosphate concentration of the culture medium; under the same conditions, the level of valyl-tRNA synthetase remained unchanged. Moreover, no variation of the levels of these three enzymes in response to phosphate was observed in the haploid strain HfrH. These results indicate that in the merodiploid strain EM20031, which carries the episome F32, the number of episomes per chromosome varies to some extent according to the phosphate concentration of the culture medium.     

Predicting the Efficacy of Polycyclic Aromatic Hydrocarbon Bioremediation in Creosote-Contaminated Soil Using Bioavailability Assays

Nonexhaustive extraction (propanol, butanol, hydroxypropyl-β-cyclodextrin [HPCD]), persulfate oxidation and biodegradability assays were employed to determine the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soil. After 16 weeks incubation, greater than 89% of three-ring compounds (acenaphthene, anthracene, fluorene, and phenanthrene) and 21% to 79% of four-ring compounds (benz[a]anthracene, chrysene, fluoranthene, and pyrene) were degraded by the indigenous microorganisms under biopile conditions. No significant decrease in five- (benzo[a]pyrene, benzo[b+k]fluoranthene) and six-ring compounds (benz[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) was observed. Desorption of PAHs using propanol or butanol could not predict PAH biodegradability: low-molecular-weight PAH biodegradability was underestimated whereas high-molecular-weight PAH biodegradability was overestimated. Persulfate oxidation and HPCD extraction of creosote-contaminated soil was able to predict three- and four-ring PAH biodegradability; however, the biodegradability of five-ring PAHs was overestimated. These results demonstrate that persulfate oxidation and HPCD extraction are good predictors of PAH biodegradability for compounds with octanol-water partitioning coefficients of < 6.     

Gap junction structures: Analysis of the x-ray diffraction data

Models for the spatial distribution of protein, lipid and water in gap junction structures have been constructed from the results of the analysis of X-ray diffraction data described here and the electron microscope and chemical data presented in the preceding paper (Caspar, D. L. D., D. A. Goodenough, L. Makowski, and W.C. Phillips. 1977. 74:605-628). The continuous intensity distribution on the meridian of the X-ray diffraction pattern was measured, and corrected for the effects of the partially ordered stacking and partial orientation of the junctions in the X-ray specimens. The electron density distribution in the direction perpendicular to the plane of the junction was calculated from the meridional intensity data. Determination of the interference function for the stacking of the junctions improved the accuracy of the electron density profile. The pair-correlation function, which provides information about the packing of junctions in the specimen, was calculated from the interference function. The intensities of the hexagonal lattice reflections on the equator of the X-ray pattern were used in coordination with the electron microscope data to calculate to the two-dimensional electron density projection onto the plane of the membrane. Differences in the structure of the connexons as seen in the meridional profile and equatorial projections were shown to be correlated to changes in lattice constant. The parts of the junction structure which are variable have been distinguished from the invariant parts by comparison of the X-ray data from different specimens. The combination of these results with electron microscope and chemical data provides low resolution three- dimensional representations of the structures of gap junctions.