Nocturnin is a deadenylase involved in the posttranscriptional control of circadian gene expression

GARBARINO PICO E. AND GREEN CB.

Villa Carlos Paz, Argentina

Congreso; XLIV Reunión Anual Soc. Argentina de Investigación en Bioquímica y Biología Molecular; 2008

Soc. Argentina de Investigación en Bioquímica y Biología Molecular

5-10% of the transcripts expressed in a given tissue show daily oscillations. Presumably, this is largely generated by changes in the transcription of those genes. However, the relative importance of mRNA decay has not been established. We have characterized in mouse the unique ribonuclease reported which expression is circadian regulated, Nocturnin (mNoc). We showed that recombinant GST-mNOC is a deadenylase, a poly(A)-specific ribonuclease. Deadenylation triggers degradation or translational silencing of mRNAs. We then studied mNoc expression in NIH3T3 cells in response to stimuli that synchronize circadian clocks in cultures. mNoc was acutely induced by FBS and TPA, whereas forskolin and dexamethasone had no effect. This induction exhibited a typical immediately-early gene response. We generated an antibody and found that mNOC has a robust circadian expression pattern in mouse liver and kidney peaking at night. We then studied the subcellular localization and showed that mNOC is present in the cytoplasm and did not co-localize with P-bodies or stress granules, subcellular domains where a number of factors involved in mRNA cytoplasmic processing accumulate. Polysome analysis showed that mNOC is not associated with ribosomes or polyribosomes. Our data suggest that mNOC is involved in the posttranscriptional regulation of mRNAs whose levels decline at night or in response to stimuli.