Somatic+Cell+Turnover

Somatic Cell Turnover:
Somatic cells are any biological cells forming the body of a multicellular organism. The average somatic cell has only a limited number of times that it is able to replicate itself, it can only divide itself so much before it is unable to continue and they undergo replicative senescence., meaning they are incapable of further division.

Turnover in relationship to Telomeres:
In a report detailed in the Journal of Experimental Medicine it is stated that "Rufer et al. find that in granulocytes as well as T lymphocytes telomere length decreases as a function of age. Consistent with and extending the previous report of Frenck et al., the rate of telomere loss as a function of age is greatest in early childhood for granulocytes as well as for naive and memory CD4 and CD8 T cell subpopulations (1,000–3,000 bp/yr). In each of these populations, the rate of telomere shortening then continues at a much lower rate of loss (30–60 bp/yr) for the remainder of life." [1]

It is telling that these two reports, from Frenck et al. and Rufer et al., favor different interpretations of their very similar findings. Frenck et al. suggest that the difference in rate of telomere loss during early childhood and later life most probably reflects a difference in the rate of telomere loss per cell division during different stages of life. In contrast, Rufer et al. favor a model in which each postnatal division of somatic cells results in “more or less constant losses of telomere repeats.” In the context of this latter model, the more rapid rate of telomere loss observed in early childhood is interpreted as reflecting a correspondingly rapid rate of cellular turnover during this time.

From reading both the reports it is clear that thought both cases had remarkably similar findings, they favor widely varying interpretations of these results. Frenck et al. seems to be suggesting the the fact that there is a difference in the rate at which telomeres are lost during childhood and adulthood is merely a reflection on the rate at which a person looses telomeres per cell division during these two very different stages of their lives. However Rufer et al. conclusion seems to be leaning towards the fact that each somatic cell division that occurred after birth results in "more or less constant losses of telomere repeats." [2]

By Joshua Campe

References:
[1] Frenck , R.W., E.H. Blackburn , K.M. Shannon ( 1998 ) The rate of telomere sequence loss in human leukocytes varies with age. Proc. Natl. Acad. Sci. USA. 95 :5607–5610 pmid: 9576930

Hodes, R.J. (1999) ‘Telomere Length, Aging, and Somatic Cell Turnover’ [Online]. __The Rockefeller University Press__. Available: [] [Accessed 29 September 2011].

[2] Rufer, N. , T.H. Brummendorf , S. Kolvraa , C. Bischoff , K. Christensen , L. Wadsworth , M. Schulzer , P.M. Lansdorp ( 1999 ) Telomere fluorescence measurements in granulocytes and T lymphocyte subsets point to a high turnover of hematopoietic stem cells and memory T cells in early childhood. J. Exp. Med. 190 : 157 – 167 pmid: 10432279.