Tuesday, May 23, 2006

Clock in the primate adrenal

From Afarensis, I got a new paper about circadian rhythms in primates: Twenty-four hour rhythmic gene expression in the rhesus macaque adrenal gland (PDF), by Dario Lemos, Jodi Downs and Henryk Urbanski.

The way the study is presented in the press release (now offline!), it sounds like this is a big surprising breakthrough, but I am not too impressed. The work is good and useful, but the findings are far from Earth-shattering.

Using microarrays, they have shown that expression of many genes cycle in a circadian manner in the adrenal glands of monkeys. The work is in vivo, and we have known for more than ten years that every cell in the body contains a clock and that clock genes cycle in every cell in our body. There was even a curious old study showing that there is a rhythm in red blood cells - no nucleus there!

Also, people have done time-series analysis of gene expression in various tissues using microarrays, and in each tissue those genes that code for proteins that are essential for that tissue's function show a circadian profile of expression (while the housekeeping genes do not). So, genes for liver enzymes cycle in the liver, genes that code for proteins involved in muscle contraction show circadian patterns of expression in muscle cells, etc. Genes that are not involved in that organ's main function are either expressed constituitively (at a constant level) or not expressed at all.

If you take any tissue out of the body and culture it, the rhythms persist, at least for several days, showing that all cells in our body are competent clocks, not just driven into rhythmicity by a daily signal from the SCN. This has been done with a number of tissues to date, including heart, lung, liver and fibroblasts.

I'd get really excited if, in their next study, they transplant an adrenal from one monkey to another and force all rhythms of the (SCN-lesioned) host to adopt the period and phase of the transplant - that would show that the adrenal is not just a clock (which is boring - every cell is a clock), but a pacemaker of the circadian system.

People in the field of chronobiology have targeted the adrenal as a potential pacemaker for a long time (since 1948 work by Curt Richter) and many experiments have been performed in the past in rodents and chickens (a friend of mine did his PhD dissertation on this topic) and all the results were always negative - adrenal is functioning as a peripheral clock, but not a pacemaker.


Blogger Nick Anthis said...

This is definitely an interesting topic, although I think you're right that this isn't really that new, as the existence of peripheral clocks is well-known, and I wrote something about it last year for my college's student paper (and today on my blog). One of the researchers I interviewed for the article made the case that biological clock research is unique among the neurosciences in its ability to fully bridge the gap from genetics to understanding behavior. Cool.

7:53 PM  

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