Diploidy

Publication Title: 
Proceedings of the National Academy of Sciences of the United States of America

Inclusion of vitamin E (DL-alpha-tocopherol) in the culture medium for human diploid cells greatly prolongs their in vitro lifespan. The addition of 100 mug of DL-alpha-tocopherol per ml of medium has allowed us to culture WI-38 cells for more than 100 population doublings to date. (These cells normally have an in vitro lifespan of 50 +/- 10 population doublings.) Cells at the 100th population doubling have a normal diploid karyotype, appear to behave in all other respects like young WI-38 cells, and are still actively dividing.

Author(s): 
Packer, L.
Smith, J. R.
Publication Title: 
Proceedings of the National Academy of Sciences of the United States of America

Previously we reported [Packer, L. & Smith, J.R. (1974) Proc. Natl. Acad. Sci. USA 71, 4763-4767] that the lifespan of WI-38 human diploid fibroblasts in vitro was significantly increased by continuously growing the cell cultures in the presence of vitamin E(dl-alpha-tocopherol), but in 19 subsequent subcultivation series we were unable to reproduce these findings. While vitamin E is incorporated into the cells and is able to act effectively as an antioxidant, apparantly is intracellular antioxidant properties alone do not routinely result in an increase of cell lifespan.

Author(s): 
Packer, L.
Smith, J. R.
Publication Title: 
Mutation Research

Human diploid fibroblasts, strain MRC-5, were sequentially irradiated with 60Co gamma rays at intervals during their in vitro lifespan. The results indicate that 3 or 6 doses of 1 Gy can increase lifespan, and the same was true for cells treated with 3 doses of 3 Gy. Higher doses (5 x 3 Gy) did reduce growth potential, suggesting either that mid-late passage cells become more sensitive to radiation, or that doses beyond a given threshold reduce population lifespan by multiple cellular hits. The life extension induced by gamma rays might be due to an induced hypermethylation of DNA.

Author(s): 
Holliday, R.
Publication Title: 
Biochemical and Biophysical Research Communications

Telomere is the repetitive DNA sequence at the end of chromosomes, which shortens progressively with cell division and limits the replicative potential of normal human somatic cells. L-carnosine, a naturally occurring dipeptide, has been reported to delay the replicative senescence, and extend the lifespan of cultured human diploid fibroblasts. In this work, we studied the effect of carnosine on the telomeric DNA of cultured human fetal lung fibroblast cells.

Author(s): 
Shao, Lan
Li, Qing-Huan
Tan, Zheng
Publication Title: 
Genes & Development

The ribonucleoprotein enzyme telomerase adds telomeric DNA to chromosomal ends. In most eukaryotes the telomeric repeat units are repeated precisely, consistent with the action of a telomerase that faithfully copies its RNA template. In contrast, Saccharomyces cerevisiae telomeric repeats are degenerate, suggesting that its telomerase has unusual mechanistic properties. We mutated the S. cerevisiae telomerase RNA (TLC1) with a series of 3-base (GUG) substitutions in and next to the 17-nucleotide templating domain.

Author(s): 
Prescott, J.
Blackburn, E. H.
Publication Title: 
Science (New York, N.Y.)

Hamilton's theory of inclusive fitness showed how natural selection could lead to behaviors that decrease the relative fitness of the actor and also either benefit (altruism) or harm (spite) other individuals. However, several fundamental issues in the evolution of altruism and spite have remained contentious.

Author(s): 
West, Stuart A.
Gardner, Andy
Publication Title: 
Proceedings of the National Academy of Sciences of the United States of America

The evolution of life on earth has been driven by a small number of major evolutionary transitions. These transitions have been characterized by individuals that could previously replicate independently, cooperating to form a new, more complex life form. For example, archaea and eubacteria formed eukaryotic cells, and cells formed multicellular organisms. However, not all cooperative groups are en route to major transitions. How can we explain why major evolutionary transitions have or haven't taken place on different branches of the tree of life?

Author(s): 
West, Stuart A.
Fisher, Roberta M.
Gardner, Andy
Kiers, E. Toby
Publication Title: 
Age (Dordrecht, Netherlands)

Sirtuin 3 (SIRT3) is one of the seven mammalian sirtuins, which are homologs of the yeast Sir2 gene. SIRT3 is the only sirtuin reported to be associated with human life span. Many recent studies have indicated that SIRT3 levels are elevated by exercise and caloric restriction, but whether SIRT3 influences cell senescence under stressed conditions in human diploid fibroblasts has not been established.

Author(s): 
Zhang, Bin
Cui, Shaoyuan
Bai, Xueyuan
Zhuo, Li
Sun, Xuefeng
Hong, Quan
Fu, Bo
Wang, Jianzhong
Chen, Xiangmei
Cai, Guangyan
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