Hormones Tick on Epigenetic Clock

    The reproductive cycle of mammals is controlled by reversible changes in DNA.  Siberian hamsters breed during the longest days of the year and the shortest days trigger hormonal changes, thus causing their gonads to shrink.  It has been unclear how melatonin, a nocturnal hormone, alters gene activity. 
   
    Tyler Stevenson of University of Aberdeen and Brian Prendergast of University of Chicago discovered that shorter days and changes in melatonin reduce a key gene, methylation which is in the hypothalamus, to activate the gonad shrinking.  This study that was performed was the first to show cycles of DNA modification underlie seasonal changes.  I found this very interesting because just a slight change in a hormone can trigger a whole cascade of events.  I personally didn't know that melatonin had that much of an impact on mammals. 

http://doi.org/nz8
http://www.newswise.com/articles/siberian-hamsters-show-what-helps-make-seasonal-clocks-tick
http://www.jstor.org/discover/10.1086/652243?uid=3739808&uid=2&uid=4&uid=3739256&sid=21102847425247