title: Altered calmodulin response to light in the suprachiasmatic nucleus of PAC1 receptor knockout mice revealed by proteomic analysis.
abstract: In mammals circadian rhythms are generated by a light-entrainable oscillator located in the hypothalamic suprachiasmatic nucleus (SCN). Light signals reach the SCN via a monosynaptic neuronal pathway, the retinohypothalamic tract, originating in a subset of retinal ganglion cells. The nerve terminals of these cells contain the classical neurotransmitter glutamate and the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), and there is evidence that these two transmitters interact to mediate photoentrainment of the oscillator in the SCN. To elucidate light-provoked PACAP receptor signaling we used proteomic analysis. Wild-type mice and mice lacking the PAC1 receptor (PAC1-/-) were light stimulated at early night, and the SCN was examined for proteins that were differentially expressed using two-dimensional gel electrophoresis and identification by tandem mass spectrometry. The most striking finding, which was subsequently confirmed by Western blotting, was a significant reduction of calmodulin (CaM) in wild-type mice as compared with PAC1-/- mice. Analysis at the mRNA level by quantitative in situ hybridization histochemistry was inconclusive, indicating that a translational mechanism might be involved. The findings indicate that PAC1 receptor signaling in the SCN in response to light stimulation induces a down-regulation of CaM expression and that CaM is involved in the photic-entrainment mechanism.
authors.affiliation: Department of Clinical Biochemistry, Bispebjerg Hospital, University of Copenhagen, DK-2400 Copenhagen NV, Denmark. bbjanf@inet.uni2.dk
authors.forename: Jan
authors.initials: J
authors.lastname: Fahrenkrug
authors.forename: Jens
authors.initials: J
authors.lastname: Hannibal
authors.forename: Bent
authors.initials: B
authors.lastname: Honoré
authors.forename: Henrik
authors.initials: H
authors.lastname: Vorum
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001923:Brain Chemistry / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics; D002147:Calmodulin / Q000032:analysis / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D008029:Lighting; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010775:Photic Stimulation; D040901:Proteomics; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D013493:Suprachiasmatic Nucleus / Q000502:physiology*
chemical_list: C495504:Adcyap1r1 protein, mouse; D002147:Calmodulin; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases