Southern Illinois University Science E-Letter, published online 16 May 2011
(submitted in reply to:  Science, 15 April 2011, vol. 332, pp. 300-301).

Genetic Variation Among Developing Brain Cells

Reports that LINE-1 transposable elements (TEs) provide somatic genetic variation among cells in developing brains (G. Vogel, NewsFocus, 15 April 2011, p.300) offer an intriguing parallel to other recent evidence that simple sequence repeats (SSRs) also create genetic diversity among nerve cells, notably in cases of triplet-repeat expansion (1).  Upon their initial discovery, both TEs and SSRs were marginalized as "junk" or "selfish" DNA, unlikely to have significant genomic function.  Yet in recent years both TEs and SSRs have become appreciated as prolific sources of genetic variation that can be instrumental in evolutionary adaptation (2-5).  Curiously, the activity of TEs and SSRs are interrelated, such that TEs can generate new SSRs while SSRs provide sites for TE insertion.  These unexpected functional congruencies between two distinct forms of mutagenic "junk DNA," together with other well-established examples of adaptively advantageous somatic mutation such as hypermutability of antibody genes, demonstrate that Sturtevant's dismissive dictum, "Mutations are accidents" (6), has grown obsolete (7).  "Implicit protocols" (8) for the spontaneous, nonaccidental production of genetic variation are deeply embedded in genomic architecture.

DAVID G. KING
Departments of Anatomy and Zoology
Southern IllinoisUniversity Carbondale Carbondale, IL 62901, USA.
E-mail: dgking@siu.edu

References

  1. J. W. Fondon III, E. A.D. Hammock, A. J. Hannan, D. G. King, Trends Neurosci. 31, 328 (2008).
     
  2. A. R. Muotri, M. C. N. Marchetto, N. G. Coufal, F. H. Gage, Hum. Molec. Genet. 16, R159 (2007).
     
  3. Y. Kashi, D. King DG, Trends Genet. 22, 253 (2006).
     
  4. M. D. Vinces, M. Legendre, M. Caldara, M. Hagihara, K. J. Verstrepen, Science 324, 1213 (2009).
     
  5. K. R. Oliver, W. K. Greene, BioEssays 31:703 (2009).
     
  6. A. H. Sturtevant, Q. Rev. Biol. 12, 464 (1937).
     
  7. D. G. King, Y. Kashi, Heredity 99, 123 (2007).
     
  8. J. Doyle, M. Csete, L. H. Caporale, in L. H. Caporale, ed., The Implicit Genome, pp. 294-298, Oxford Univ. P. (2006).

David King portrait Comments and questions: dgking@siu.edu

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