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Biomedical subjects

A MacLeod

Publications and source records attributed to A MacLeod.

At least 37 records · Page 2Linked to original sources
PubMed1998

Chondrocytes in culture produce a mechanically functional tissue.

A mechanically testable tissue was grown in vitro from rabbit chondrocytes that were initially plated at high density (approximately 80,000 cells/cm2). The DNA, collagen, and proteoglycan content, as well as the tissue thickness, tensile stiffness, and synthesis rates, were measured at 4, 6, and 8 weeks. The biochemical properties were similar to those for immature cartilage, with predominantly type-II collagen produced; this indicated that the cells retained their chondrocytic phenotype. The tissue formed a coherent mechanical layer with testable tensile stiffness as early as 4 weeks. The tensile elastic modulus reached 1.3 MPa at 8 weeks, which is in the range of values for native cartilage from the midzone. Collagen density was approximately 24 mg/ml at 8 weeks, which is about one-half the value for native cartilage, and the collagen fibril diameters were smaller. Chondrocytes in culture responded to culture conditions and were stimulated by cytokine interleukin-1beta. When culture conditions were varied to RPMI nutrient medium with lower fetal bovine serum and higher ascorbic acid concentrations, the thickness decreased and the modulus increased significantly. Interleukin-1beta, added to the 8-week culture for 2 weeks, caused a decrease of 60% in thickness, a decrease of 81% in proteoglycan content, and a decrease of 31% in collagen content; this is similar to the response of cartilage explants to interleukin-1beta. This cartilage analog may be useful as a model system to study structure-function relationships in cartilage or as cartilage-replacement tissue.

Animals↗
PubMed1998

Streptomyces griseus protease B: secretion correlates with the length of the propeptide.

Streptomyces griseus protease B, a member of the chymotrypsin superfamily, is encoded by a gene that express a pre-pro-mature protein. During secretion the precursor protein is processed into a mature, fully folded protease. In this study, we constructed a family of genes which encode deletions at the amino-terminal end of the propeptide. The secretion of active protease B was seen to decrease in an exponential manner according to the length of the deletion. The results underscore the intimate relationship between folding and secretion in bacterial protease expression. They further suggest that the propeptide segment of the zymogen stabilizes the folding of the mature through many small binding interactions over the entire surface of the peptide rather than through a few specific contacts.

Binding Sites↗
PubMed1996

Surveillance of vascular incisions: outcomes a four-year unit-based quality-improvement program.

In a health care climate that emphasizes improving patient outcomes as well as reducing costs of care, the quality improvement process can be an effective tool to identify changes in practice that affect both of these factors in positive directions. Nursing staff members on our vascular surgical ward recognized incisional healing as critical to both cost of care and outcome. Infections and non-healing vascular incisions were problems that resulted in lengthy hospitalizations, the use of expensive antibiotics, and many read missions. Beginning in fiscal year 1992, nurses began monitoring incisional healing in vascular patients as part of the unit-based quality-improvement program. For 3 years nurses collected and analyzed data related to incisional healing in patients with postoperative groin, leg, and amputation incisions. They communicated with interdisciplinary colleagues about ways to improve outcomes and identified and implemented changes in practice that resulted in improvements. A formalized research program is underway to increase knowledge related to incisional healing and factor that affect healing in this specialty population.

Hospital Units↗
PubMed1994

Complex gene conversion events in germline mutation at human minisatellites.

Mutation at the human minisatellites MS32, MS205 and MS31A has been investigated by characterizing mutant alleles in pedigrees and in the case of MS32 by direct analysis of mutant molecules in single sperm. Most mutations at all three loci are polar, involving the preferential gain of a few repeat units at one end of the tandem repeat array. Incoming repeats can be derived from the same allele or the homologous chromosome, through they are frequently rearranged during mutation. Lack of exchange of flanking markers suggests the involvement of complex conversion-like events in the generation of mutant alleles. At MS32, high frequency mutation processes in sperm appear to be largely germline specific and to occur at a constant rate irrespective of allele size. Together with mutational polarity, this implies that germline instability is controlled by elements outside the tandem repeat array.

Alleles↗
PubMed1994

Minisatellite mutation rate variation associated with a flanking DNA sequence polymorphism.

Human minisatellite mutation in the male germline frequently involves complex interallelic gene conversion events restricted to one end of the tandem repeat array. Some alleles at minisatellite MS32 show reduced variability in human populations and are associated with a G to C transversion upstream of the array. Analysis of single sperm demonstrated a frequently profound reduction in mutation rate at alleles carrying the C variant. This mutation suppression acts in cis, but does not affect the ability of an allele to act as sequence donor during gene conversion. This mutation rate polymorphism provides strong evidence for elements near the minisatellite that regulate tandem repeat instability.

Africa↗
PubMed1993

Minisatellite variant repeat mapping: application to DNA typing and mutation analysis.

Most DNA typing systems assay allele length variation at tandemly repeated loci such as minisatellites and microsatellites. Allele length measurements are approximate, which impedes the use of such loci in forensic analysis and in studies of allelic variability at hypervariable loci. We now review progress in the development of alternative DNA typing systems based on allelic variation in the interspersion patterns of variant repeat units along minisatellite alleles. Minisatellite variant repeat mapping by PCR (MVR-PCR) not only provides a powerful new digital approach to DNA typing, but also for the first time allows investigation of the true level of allelic variability at minisatellite loci and of the mutational mechanisms that generate ultravariability.

Alleles↗
PubMed1993

Four-state MVR-PCR: increased discrimination of digital DNA typing by simultaneous analysis of two polymorphic sites within minisatellite variant repeats at D1S8.

Minisatellite variant repeat mapping by PCR (MVR-PCR) provides a digital approach to DNA typing that can reveal huge levels of variation at minisatellite loci. MVR-PCR has so far been applied to three human minisatellites, including the hypervariable locus D1S8. Previous analysis at D1S8 was based on the discrimination of repeat unit types that differ by a single base substitution. We now show that a second polymorphic site within D1S8 repeats may be assayed simultaneously with the first to define four classes of repeat units ('four-state MVR-PCR'). This approach can also be applied to the other end of D1S8 alleles in 'reverse four-state MVR-PCR'. Both of these procedures substantially increase the informativeness of MVR analysis at D1S8 and should prove useful in studies of minisatellite biology and potentially in forensic DNA typing.

Alleles↗
PubMed1993

Allele-specific MVR-PCR analysis at minisatellite D1S8.

Minisatellite variant repeat mapping by the polymerase chain reaction (MVR-PCR) provides a digital approach to DNA typing of great potential use both in forensic medicine and, by mapping single alleles, for exploring allelic variability and mutation processes at minisatellites. The MVR haplotypes of single alleles can be determined either from physically separated alleles or by pedigree analysis of digital diploid codes generated from both alleles simultaneously. We now show that single alleles can be rapidly mapped from total genomic DNA using allele-specific PCR primers directed to polymorphic sites in the DNA flanking the minisatellite. This approach can also be used to dissect mixed DNA samples such as those often encountered in forensic DNA analysis.

Alleles↗
PubMed1992

Minisatellite variant repeat (MVR) mapping: analysis of 'null' repeat units at D1S8.

Minisatellite variant repeat mapping by PCR (MVR-PCR) is a new approach to studying variation in human DNA which analyses interspersion patterns of variant repeats within minisatellite arrays. MVR-PCR has been applied to the hypervariable human minisatellite D1S8 which contains two major classes of variant 29bp repeat units designated a-type and t-type. The MVR-PCR assay uses a- or t-type specific primers, together with an amplimer at a fixed site in the DNA flanking the minisatellite, to reveal the interspersion patterns of variant repeats along an allele. Extreme levels of variation are seen both in the internal structures of individual alleles and in the digital code generated from the two superimposed alleles in total genomic DNA. However, occasional repeat units fail to amplify in MVR-PCR, signifying the existence of further repeat sequence variants termed 'null' or O-type repeats. Although not significant in individual identification, correct genotyping of null repeats is important when using MVR digital codes in parentage analysis. We have therefore characterised these null repeats and show that most null repeats share a common variant repeat sequence. We discuss the possible origins of null repeats and their application to paternity testing and the analysis of minisatellite evolution.

Alleles↗