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Results for “quantitative genetics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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57 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Cytogenetic effects of space radiation in lymphocytes of MIR-18 crews

For assessing health risk, the measurement of physical dose received during a space mission, as well as the LETs, energies and charges of particles is important. It is also important to obtain quantitative information regarding the effectiveness of space radiation in causing damage to critical biological targets, e.g., chromosomes, since at present the estimated uncertainty of biological effects of space radiation is more than a factor of two. Such large uncertainty makes accurate health risk assessment very difficult. For this very reason, a study on cytogenetic effects of space radiation in human lymphocytes was proposed and done for MIR-18 mission. This study used FISH technique to score chromosomal translocations and C-banding method to determine dicentrics. Growth kinetics of cells and SCE were examined to ensure that chromosomal aberrations were scored in first mitosis and were induced not by chemical mutagens. Our results showed that chromosomal aberration frequency of post-flight samples was significantly higher than that of pre-flight ones and that SCE frequency was similar between pre- and post-flight samples. Based on a dose-response curve of preflight samples exposed to gamma rays, the absorbed dose received by crews during the mission was estimated to be about 14.5 cSv. Because the absorbed dose measured by physical dosimeters is 4.16 cGy for the entire mission, the RBE is about 3.5.

Mir Project↗
NASA NTRS2002

Size distribution of retrovirally marked lineages matches prediction from population measurements of cell cycle behavior

Mechanisms that regulate neuron production in the developing mouse neocortex were examined by using a retroviral lineage marking method to determine the sizes of the lineages remaining in the proliferating population of the ventricular zone during the period of neuron production. The distribution of clade sizes obtained experimentally in four different injection-survival paradigms (E11-E13, E11-E14, E11-E15, and E12-E15) from a total of over 500 labeled lineages was compared with that obtained from three models in which the average behavior of the proliferating population [i.e., the proportion of cells remaining in the proliferative population (P) vs. that exiting the proliferative population (Q)] was quantitatively related to lineage size distribution. In model 1, different proportions of asymmetric, symmetric terminal, and symmetric nonterminal cell divisions coexisted during the entire developmental period. In model 2, the developmental period was divided into two epochs: During the first, asymmetric and symmetric nonterminal cell divisions occurred, but, during the second, asymmetric and symmetric terminal cell divisions occurred. In model 3, the shifts in P and Q are accounted for by changes in the proportions of the two types of symmetric cell divisions without the inclusion of any asymmetric cell divisions. The results obtained from the retroviral experiments were well accounted for by model 1 but not by model 2 or 3. These findings demonstrate that: 1) asymmetric and both types of symmetric cell divisions coexist during the entire period of neurogenesis in the mouse, 2) neuron production is regulated in the proliferative population by the independent decisions of the two daughter cells to reenter S phase, and 3) neurons are produced by both asymmetric and symmetric terminal cell divisions. In addition, the findings mean that cell death and/or tangential movements of cells in the proliferative population occur at only a low rate and that there are no proliferating lineages "reserved" to make particular laminae or cell types. Copyright 2002 Wiley-Liss, Inc.

NASA Discipline Developmental Biology↗
NASA NTRS1993

Post-translational control of collagen fibrillogenesis in mineralizing cultures of chick osteoblasts

Cultured osteoblasts from chick embryo calvaria were used as a model system to investigate the post-translational extracellular mechanisms controlling the macroassembly of collagen fibrils. The results of these studies demonstrated that cultured osteoblasts secreted a collagenous extracellular matrix that assembled and mineralized in a defined temporal and spatial sequence. The assembly of collagen occurred in a polarized fashion, such that successive orthogonal arrays of fibrils formed between successive cell layers proceeding from the culture surface toward the media. Mineralization followed in the same manner, being observed first in the deepest and oldest fibril layers. Collagen fibrillogenesis, the kinetics of cross-link formation, and collagen stability in the extracellular matrix of the cultures were examined over a 30 day culture period. Between days 8 and 12 in culture, collagen fibril diameters increased from < 30 nm to an average of 30-45 nm. Thereafter, diameters ranged in size from 20 to 200 nm. Quantitation of the collagen cross-linking residues, hydroxylysyl pyridinoline (HP) and lysyl pyridinoline (LP), showed that these mature cross-links increased from undetectable levels to concentrations found in normal chick bone. Analysis of the kinetics of their formation by pulse-chase labeling the cultures with [3H]lysine showed a doubling time of approximately 5 days. The relationships between cross-link formation, fibrillogenesis, and collagen stability were examined in cultures treated with beta-aminopropionitrile (beta-APN), a potent inhibitor of lysyl oxidase and cross-link formation. In beta-APN-treated cultures, total collagen synthesis was increased twofold, with no change in mRNA levels for type I collagen, whereas the amount of collagen accumulated in the cell layer was decreased by 50% and mineral deposition was reduced. The rate of collagen retention in the matrix was assessed by pulse-chase analysis of [3H]proline over a 16 day period in control and beta-APN-treated cultures. In control cultures, about 20% of the labeled collagen was lost from the cell layers over a 16 day period compared with > 80% in the presence of beta-APN. The beta-APN-treated cultures also showed a wider diversity of fibril diameters with a median in the > 45-60 nm range. In summary, these data suggest that cross-linking and assembly of collagen fibrils secreted by osteoblasts in vitro occur in a fashion similar to that found in vivo. The rate of cross-link formation is relatively constant and may be correlated with increasing collagen mass.(ABSTRACT TRUNCATED AT 400 WORDS).

NASA Discipline Musculoskeletal↗