NPAS2: An Analog of Clock Operative in the Mammalian Forebrain
Martin Reick,1
Joseph A. Garcia,2
Carol Dudley,1
Steven L. McKnight1*
Neuronal PAS domain protein 2 (NPAS2) is a transcription
factor expressed primarily in the mammalian forebrain. NPAS2 is highly related in primary amino acid sequence to Clock, a transcription factor
expressed in the suprachiasmatic nucleus that heterodimerizes with
BMAL1 and regulates circadian rhythm. To investigate the biological
role of NPAS2, we prepared a neuroblastoma cell line capable of
conditional induction of the NPAS2:BMAL1 heterodimer and identified
putative target genes by representational difference analysis, DNA
microarrays, and Northern blotting. Coinduction of NPAS2 and BMAL1
activated transcription of the endogenous Per1, Per2, and Cry1 genes, which encode negatively
activating components of the circadian regulatory apparatus, and
repressed transcription of the endogenous BMAL1 gene.
Analysis of the frontal cortex of wild-type mice kept in a 24-hour
light-dark cycle revealed that Per1, Per2, and
Cry1 mRNA levels were elevated during darkness and reduced
during light, whereas BMAL1 mRNA displayed the opposite pattern. In situ hybridization assays of mice kept in constant darkness
revealed that Per2 mRNA abundance did not oscillate as a
function of the circadian cycle in NPAS2-deficient mice. Thus, NPAS2
likely functions as part of a molecular clock operative in the
mammalian forebrain.
1 Department of Biochemistry,
2 Department of Internal Medicine, University of
Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas,
TX 75390, USA.
*
To whom correspondence should be addressed. E-mail:
smckni{at}biochem.swmed.edu
