LARK activates posttranscriptional expression of an essential mammalian clock protein, PERIOD1

*Laboratory of Chronogenomics, Mitsubishi Kagaku Institute of Life Sciences, 11 Minamiooya, Machida, Tokyo 194-8511, Japan;
^‡Department of Anatomy and Neurobiology, Kinki University School of Medicine, 377-2 Ohno-Higashi, Osaka-Sayama, Osaka 589-8511, Japan;
^§Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan;
^¶Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan;
^†Department of Biology, University of Virginia, Charlottesville, VA 22904-4328; and
^‖Genomic Science Center, RIKEN, The Institute of Physical and Chemical Research, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan

Edited by Joseph S. Takahashi, Northwestern University, Evanston, IL, and approved December 5, 2006 (received for review September 1, 2006)

Abstract

The mammalian molecular clock is composed of feedback loops to keep circadian 24-h rhythms. Although much focus has been on transcriptional regulation, it is clear that posttranscriptional controls also play important roles in molecular circadian clocks. In this study, we found that mouse LARK (mLARK), an RNA binding protein, activates the posttranscriptional expression of the mouse Period1 (mPer1) mRNA. A strong circadian cycling of the mLARK protein is observed in the suprachiasmatic nuclei with a phase similar to that of mPER1, although the level of the Lark transcripts are not rhythmic. We demonstrate that LARK causes increased mPER1 protein levels, most likely through translational regulation and that the LARK1 protein binds directly to a cis element in the 3′ UTR of the mPer1 mRNA. Alterations of mLark expression in cycling cells caused significant changes in circadian period, with mLark knockdown by siRNA resulting in a shorter circadian period, and the overexpression of mLARK1 resulting in a lengthened period. These data indicate that mLARKs are novel posttranscriptional regulators of mammalian circadian clocks.

Footnotes

**To whom correspondence should be addressed. E-mail: tei{at}mitils.jp
Author contributions: H.T. designed research; S.K., K.M., M.H., M.S., M.N., Y. Shigeyoshi, and H.T. performed research; M.N., S.-i.H., K.U.-T., and K.S. contributed new reagents/analytic tools; S.K., K.M., M.N., Y. Shigeyoshi, C.B.G., Y. Sakaki, and H.T. analyzed data; and S.K., C.B.G., and H.T. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0607567104/DC1.
Abbreviations:

Per,

Period;

mPer,

mouse Per;

SCN,

suprachiasmatic nucleus;

DD,

constant dark;

LD,

light–dark;

CT,

circadian time;

ZT,

Zeitgeber time;

IRES,

internal ribosome entry site;

Cry,

cryptochrome;

dper,

Drosophila per;

mLARK,

mouse LARK;

dLARK,

Drosophila LARK;

mRbm4,

mouse Rbm4;

IR,

immunoreactive;

RMSA,

RNA mobility-shift assay;

F-luc,

firefly luciferase;

R-luc,

Renilla luciferase.