Multiple Body Clocks?

According to Science Daily the body may have more than one clock:

Our latest research suggests that a separate but likely related clock resides in the adrenal gland. The adrenal gland is involved in several important body functions, such as body temperature regulation, metabolism, mood, stress response and reproduction. The research also suggests that other peripheral clocks reside throughout the body and that these clocks are perhaps interconnected.”

(One version of the paper can be found here)
The methodology:

Specifically, researchers measured gene expression in the adrenal gland of monkeys during a 24-hour period (six times a day, four-hour intervals). In analyzing this information, researchers identified 322 genes in the adrenal gland with functions that varied rhythmically over a 24-hour period, meaning that each gene’s function peaked and diminished at the same time each day. Interestingly, the scientists also noted that a subgroup of these 322 genes also exist in the SCN — the home of the body’s master body clock. This suggests that the adrenal gland has its own timing mechanism that is related to, but separate from, the SCN body clock.


4 Responses

  1. I’ll have to take a closer look at this later. The first link does not work, but I downloaded the second one. So far, I do not see anything exciting – the work is in vivo, and we have known for more than 10 years now that every cell in the body contains a clock and that clock genes cycle in every cell in our body. There is even a curious 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 DNA-chips, 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).
    If you take any tissue out of the body and culture it, the rhythms persist, at least for several days, showing at all cells in our body are competent clocks, not just driven into rhythmicity by the SCN.
    I’d be excited if they transplanted an adrenal from one monkey to another and forced all rhythms of the 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 have suspected the adrenal for a long time 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 a peripheral clock, but not a pacemaker.

  2. The first link does not work

    Yeah, I don’t know what my problem (extremely short attention span lately) is lately, but if it’s not messed up links it’s tons of typos…blech!
    As I was reading the paper (haven’t completely finished yet) and the Science Daily article (the link is fixed now) I couldn’t help thinking that they had not really made the case. I kept thinking that the fact that adrenal genes were expressed in a 24 hour rhythm was interesting but didn’t make it – in your terms – a pacemaker. It didn’t seem like theyt ( case in point – it should be “they” – afarensis) had established the independence of the adrenal rhythm (but I could be wrong, I haven’t finished the paper yet). On the other hand, I did give them the benefit of the doubt because this is an area I don’t know much about (recommended reading would be fun). Consequently, I was hoping you’d respond with a few thoughts…

  3. This definitely is an interesting topic, and it’s too bad that the paper doesn’t seem to live up to the hype. The existence of peripheral clocks is well-known, and from what I understand, it’s the existence of these other clocks that actually leads to the health issues (jet lag, seasonal affective disorder) associated with biological clocks.

  4. Yes, perhaps the paper is not a huge novelty in the circadian field, however, three main breakthroughs are made for endocriologists: if you noticed, the implication is that the clock oscillates in the core of this organ (chromaffin cells), not in the cortex (were cortisol would be the great target. Second, these are monkeys, with physiological characteristics that are much closer to humans than a rodent (i.e. secretion of DHEAS). Meaning: the study tries to push the circadian field one step further, and give it relevance in a physiological context.
    Third: by being a gland, the adrenal allows to measure its functions, so in a future study the authors could culture an adrenal cell type in vitro, and play with clock genes and secretions, similarly to what has been done in GnRH neurons.
    The three points made remark the same issue: science and experiments (and theories particularly), are made step by step, involving patience, lots of details and thinking, and even more money. Try not to trust super fancy studies. An example: check the last Dr Reppert’s paper in Neuron saying that Clock (the big clock component) is not an essential component of the clock actually. And check the last Dr Sassone-Corsi’s paper too. So what do we do now with all the fancy stuff about the relevance of Clock for the clock written before?
    The lesson: we still don’t know what the clock genes do, even in the SCN. Regarding this, I recommend to follow Dr Antoch’s papers.

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