neurodudes

The NYT has a nice summary of a recent Cell paper, where investigators from the Karolinska Institute used a wonderfully innovative technique to determine the age of many cells, including neurons from visual cortex and the cerebellum.

The general idea is this: Up until 1963, above ground nuclear weapons testing was allowed, dispersing radioactive carbon (14C) into the atmosphere. This “tagged” carbon was integrated into all plants and animals at that time and, since 1963, at an exponentially decreasing amount. Thus, calibrated with pine tree trunk rings (which are produced every year), the scientists are able to judge the age of cells by seeing how much of the genomic DNA of the cell contains 14C. Genomic DNA is created during cell division and, as the authors show, it appears not to be regenerated since preserved cell specimens from different years show the characteristic exponential decay of 14C post-1963.

The neat finding is that several neurons, from cortex and cerebellum, are very old… in 50-60 year old cadavers, neurons were found that were just as old or nearly just as old as the cadavers. So, even if there is neurogenesis occuring, it is now almost certain that some of our neurons are with us throughout life.

This research suggests that neuronal variety within a single person may be partly due to “jumping genes” which change their position from cell to cell.

Alysson R. Muotri, Vi T. Chu, Maria C. N. Marchetto, Wei Deng, John V. Moran and Fred H. Gage. Somatic mosaicism in neuronal precursor cells mediated by L1 retrotransposition p903. Nature 435, 903-910 (16 June 2005). doi: 10.1038/nature03663

News and Views

Looks like spinal cord regeneration might be the first target for embryonic stem cell therapy trials in humans. More info in the Science article.

It looks like Geron has developed a protocol to reliably induce ES cells to become oligodendrocytes, the glial cells that produce the myelin sheath. Here’s the details from the article:

For newly injured rats, the results are promising. In animals that received oligodendrocyte precursors 7 days after their injury, the cells survived and apparently helped repair the spinal cord’s myelin. Within 2 weeks, treated rats scored significantly better on standardized movement tests than control animals, which had received human fibroblasts or a cell-free injection.

“…a difference in concentration of a single molecule across the tip of an axon can measurably impact the direction in which the axons grow”

Press release: http://gumc.georgetown.edu/communications/releases/release.cfm?ObjectID=2670

Journal article:

• actual article
• Pubmed entry with link to commentary and errata

No, we haven’t fallen off the face of the earth… just busy. (well, I can’t speak for Bayle)

Interesting news in the AOP section of Nature Medicine. Looks like a combined therapy of cAMP and schwann cells can aid in spinal cord regeneration. This study shows that inhibition of cyclic AMP signaling is a major problem in axon regeneration. (Definitely some connections here with the MM Poo work on growth cone turning in response to cAMP from a pipette.)

Read on for the abstract….
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