clock news
clock | July 13, 2006This is so basic that I even teach it in Intro Bio:
Wherever the master clock may be located (SCN, pineal or retina) in any particular species, its main function is to coordinate the timing of peripheral circadian clocks which are found in every single cell in the body. Genes that code for proteins that are important for the function of a particular tissue (e.g., liver enzymes in liver cells, neurotransmitters in nerve cells, etc.) show a daily rhythm in gene expression. As a result, all biochemical, physiological and behavioral functions exhibit daily (circadian) rhythms, e.g., body…
clock | July 4, 2006
I got several e-mails yesterday about a new study about the molecular mechanism underlying circadian rhythms in mammals ("You gotta blog about this!"), so, thanks to Abel, I got the paper (PDF), printed it out, and, after coming back from the pool, sat down on the porch to read it.
After reading the press releases, I was in a mind-frame of a movie reviewer, looking for holes and weaknesses so I could pounce on it and write a highly critical post, but, even after a whole hour of careful reading of seven pages, I did not find anything deeply disturbing about the paper. Actually, more I read…
clock | June 29, 2006This is in the bread-mold Neurospora crassa. It is unlikely to be universal. I expect to see the connection in some protists and fungi, perhaps in some animals. I am not so sure about plants, and I am pretty sure it is not like this in Cyanobacteria in which the cycle of cell division is independent from circadian timing:
Novel connection found between biological clock and cancer
Hanover, NH--Dartmouth Medical School geneticists have discovered that DNA damage resets the cellular circadian clock, suggesting links among circadian timing, the cycle of cell division, and the propensity for…
clock | June 29, 2006The absence of light-dark cycles in space (e.g., on the shuttle or space station) results in disruptions of sleep. It has been proposed that humans who spend prolonged time in space are suffering from jet-lag - the internal desynchronization of clocks in various tissues.
A new experiment on the space station will take a somewhat different strategy than usual. Instead of measuring EEG (brain activity), it will monitor EKG (heart activity) over a period of 150 days.
The idea, brought by Irish researchers, is that EEG monitoring is not capable of measuring internal desynchronization of the…
clock | June 26, 2006
In the beginning, there was period.
Before 1995, the only known circadian clock genes were period (Per) in Drosophila melanogaster (wine fly) and frequency (Frq) in Neurospora crassa (bread mold). Some mutations, though not characterized at the molecular level, were also known in Chlamydomonas, Euglena as well as the famous Tau-mutation in hamsters.
I still remember the strained mathematical models attempting to account for a 24-hour rhythm with just a single gene controlling its own expression. We now know that multiple genes are involved in circadian function in invertebrates and…
clock | June 26, 2006
The persistence of circadian rhythmicity during long bouts of hibernation in mammals has been a somewhat controversial topic in the literature. While some studies suggest that circadian clock is active during hibernation, other studies dispute this. Apparently, the truth is somewhere in-between - it differs between species:
Not all hibernating animals retain apparent circadian rhythmicity during the hibernation season. Whereas some species, such as bats and golden-mantled ground squirrels, maintain circadian rhythmicity in Tb throughout the hibernation season when held in constant…
clock | June 19, 2006
Melatonin is secreted in human mother's milk with a daily rhythm - high at night, undetectable during the day (see the figure under the fold):
It has been known for a long time that mother's melatonin entrains the circadian rhythms in the SCN (suprachiasmatic nucleus) of the embryos - thus they are born with a correct phase (time of day). However, a study in rats suggests that melatonin in mother's milk is unlikely to be able to entrain the pups circadian rhythms after they are born.
So, the appearance of melatonin in the milk of breastfeeding humans may either be:
a) just a by-product…
clock | June 16, 2006Interesting:
Melatonin may be found in grapes
MILAN, Italy, June 16 (UPI) -- Scientists in Italy say they have discovered that the grapes used in popular red wines may contain high levels of the sleep hormone melatonin.
Melatonin is naturally secreted by the pineal gland in the brain, especially at night, and it tells the body when it is time to sleep, according to researcher Iriti Marcello at the University of Milan.
Hey, hey, what do you say:
Until recently, melatonin was thought to be exclusively produced by mammals, but has recently been discovered in plants.
Excuse me, but we've known…
clock | June 12, 2006
This post is perhaps not my best post, but is, by far, my most popular ever. Sick and tired of politics after the 2004 election I decided to start a science-only blog - Circadiana. After a couple of days of fiddling with the templae, on January 8, 2005, I posted the very first post, this one, at 2:53 AM and went to bed. When I woke up I was astonished as the Sitemeter was going wild! This post was linked by BoingBoing and later that day, by Andrew Sullivan. It has been linked by people ever since, as recently as a couple of days ago, although the post is a year and a half old.…