Disruption of gene expression rhythms in mice lacking secretory vesicle proteins IA-2 and IA-2β

Abstract

Mice with targeted disruption of both IA-2 and IA-2␤ (double-knockout, or DKO mice) have numerous endocrine and physiological disruptions, including disruption of circadian and diurnal rhythms. In the present study, we have assessed the impact of disruption of IA-2 and IA-2␤ on molecular rhythms in the brain and peripheral oscillators. We used in situ hybridization to assess molecular rhythms in the hypothalamic suprachiasmatic nuclei (SCN) of wild-type (WT) and DKO mice. The results indicate significant disruption of molecular rhythmicity in the SCN, which serves as the central pacemaker regulating circadian behavior. We also used quantitative PCR to assess gene expression rhythms in peripheral tissues of DKO, single-knockout, and WT mice. The results indicate significant attenuation of gene expression rhythms in several peripheral tissues of DKO mice but not in either single knockout. To distinguish whether this reduction in rhythmicity reflects defective oscillatory function in peripheral tissues or lack of entrainment of peripheral tissues, animals were injected with dexamethasone daily for 15 days, and then molecular rhythms were assessed throughout the day after discontinuation of injections. Dexamethasone injections improved gene expression rhythms in liver and heart of DKO mice. These results are consistent with the hypothesis that peripheral tissues of DKO mice have a functioning circadian clockwork, but rhythmicity is greatly reduced in the absence of robust, rhythmic physiological signals originating from the SCN. Thus, IA-2 and IA-2␤ play an important role in the regulation of circadian rhythms, likely through their participation in neurochemical communication among SCN neurons. circadian; suprachiasmatic nucleus; vasoactive intestinal peptide; Prprn; Ptprn2 INSULINOMA-ASSOCIATED PROTEIN 2 (IA-2; also called islet antigen 2, ICA 512, and Prprn) and IA-2␤ (also called phogrin and Ptprn2) are transmembrane proteins with homology to protein tyrosine phosphatase but which lack phosphatase activity (29,35,36; for review, see Ref. 51). IA-2 and IA-2␤ are components of dense core vesicle membranes and play important roles in vesicle loading and release (11,14,17,29,44,49). Targeted disruption of these genes in mice leads to impaired secretion of hormones and neurotransmitters, which are more severe in mice lacking functional alleles of both genes (16, 22, 24 -26, 42, 48). These proteins are also of interest at the clinical level, since the majority of newly diagnosed diabetic patients have antibodies against these proteins, and antibodies appear years before disease development, identifying them as major autoantigens predictive of type 1 diabetes (30,36,49).A recent study to assess the cardiovascular impact of targeted disruption of IA-2 and IA-2␤ revealed that mice lacking these proteins did not have daily rhythms in blood pressure, heart rate, core body temperature, or spontaneous locomotor activity (21). Electrophysiological studies on the suprachiasmatic nuclei (SCN), the site of the brain's master cir...

The Circadian Clock Gene BMAL1 Coordinates Intestinal Regeneration

“…Consistent with previous reports,13, 14, 15, 16, 31 the undamaged intestine of BMAL1 +/+ mice exhibits a diurnal expression pattern of PER2 , BMAL1 , and REV-ERBα (Figure 4 A ). The sinusoidal, rhythmic expression profiles are consistent with rhythms seen in other mouse tissues, with BMAL1 expression peaking at ZT20, approximately antiphase to the time of peaks of PER2 (ZT8-12) and REV-ERBα (ZT8) 32 . The BMAL1 -/- intestine shows no rhythms in the expression of these genes under the same conditions, confirming the clock is dysfunctional when BMAL1 is absent.…”

“…The sinusoidal, rhythmic expression profiles are consistent with rhythms seen in other mouse tissues, with BMAL1 expression peaking at ZT20, approximately antiphase to the time of peaks of PER2 (ZT8-12) and REV-ERBα (ZT8). 32 The BMAL1 -/- intestine shows no rhythms in the expression of these genes under the same conditions, confirming the clock is dysfunctional when BMAL1 is absent. The gene TBP , which is not clock-regulated, 33 shows no rhythms in either genotype under LD photoperiod.…”

Pathophysiologic changes in IA-2/IA-2β null mice are secondary to alterations in the secretion of hormones and neurotransmitters

“…It is thought that this disruption in circadian rhythm caused by the deletion of IA-2/IA-2β is due to alterations in the release of one or more neurotransmitters (e.g., VIP) within the SCN that is required for the coordination of neuronal signaling within the SCN. The disruption of circadian rhythm leads to significant disruption of the clock genes in the SCN (e.g., Per1, Dbp) and also in several peripheral tissues of the DKO mice but not the single KO mice [24]. These findings add support to the idea that the effect of IA-2 and IA-2β on DCV secretion profoundly influences neurochemical communication among SCN neurons and that although peripheral tissues have a functioning circadian clockwork, the rhythmicity of this clockwork is greatly influenced by the SCN.…”

Hypothesis driven single cell dual oscillator mathematical model of circadian rhythms

“…For comparison, the individual time series were normalized to maximum 1 and the minimum 0. Experimental data points of per1 , per2 , and Bmal1 mRNA were extracted from [ 7 ], Rev-erbα from [ 35 ] and PER1, PER2 protein from [ 34 ]. (G) per expression in response light.…”