.
\nThe genes that regulate the process called photoperiodism\u2014the seasonal responses induced
\nin organisms by changing day length\u2014have been found by researchers from the RIKEN Center
\nfor Developmental Biology, Kobe, and Kinki University, Osaka. Led by Koh-hei Masumoto
\nand Hiroki R. Ueda from RIKEN, the researchers also discovered how these genes can be
\nactivated within a single day1. The work bears relevance to seasonal human disorders,
\nsuch as winter depression, and symptoms associated with conditions such as bipolar
\ndisease.
\n.
\nOrganisms need to alter body functions and behavior to accommodate seasonal changes
\nin their environment. The measurement of day length is one obvious way of
\ndetermining the time of year. To this end, the body uses its internal circadian clock, and
\nagainst this background measures the extent and timing of light and dark.
\n.
\nThe team noted that an increase in day length induces activity in the gene for thyroid
\nstimulating hormone beta (TSH\u03b2) in the pars tuberalis (PT) region of the pituitary gland.
\nTSH\u03b2 plays a key role in the pathway that regulates photoperiodism in vertebrate animals.
\nHowever, the detailed mechanism that links information about day length with induction
\nof the production of TSH\u03b2 is unknown.
\n.
\nMasumoto, Ueda and colleagues found the genes that stimulate the activity of the TSH\u03b2
\ngene in mammals by observing the activity of genes in the PT of photoperiod-responsive
\nmice under chronic \u2019short-day\u2019 (eight hours of light) and \u2018long-day\u2019 (16 hours) conditions.
\nThey identified 57 genes stimulated by short days and 246, including TSH\u03b2, by long days.
\n.
\nThen, the researchers placed chronic short-day mice into a long-day regime\u2014they switched
\noff the lights eight hours later\u2014and observed that it took five days for TSH\u03b2 to become
\nfully active. They could, however, stimulate full activity of TSH\u03b2 within a single 24-hour
\nperiod if they subjected the mice to a short burst of light during a sensitive \u2018photo-inducible\u2019
\nperiod late at night. Thirty-four other long-day genes responded in the same way, including the
\ntranscription factor, Eya3, which seemed a likely candidate for regulating TSH\u03b2 activity. In
\nlaboratory studies, the researchers determined that Eya3 and its partner binding factor Six1
\ndo indeed act together to activate TSH\u03b2. And this activity is enhanced by two other genes,
\nTef and Hlf.
\n.
\n\u201cWe are next planning to identify the upstream gene of Eya3,\u201d Ueda says. \u201cAnd we are also hoping
\nto elucidate why the photo-inducible phase is late at night.\u201d
\n.<\/p>\n","protected":false},"excerpt":{"rendered":"
. The genes that regulate the process called photoperiodism\u2014the seasonal responses induced in organisms by changing day length\u2014have been found by researchers from the RIKEN Center for Developmental Biology, Kobe, and Kinki University, Osaka. Led by Koh-hei Masumoto and Hiroki R. Ueda from RIKEN, the researchers also discovered how these genes can be activated within … <\/p>\n