Cytoplasmic localization of mPER1 clock protein isoforms in the mouse retina

The Per-1 Short Isoform Inhibits de novo HIV-1 Transcription in Resting CD4+ T-cells

Background:

Understanding of the restriction of HIV-1 transcription in resting CD4+ T-cells is critical to find a cure for AIDS. Although many negative factors causing HIV-1 transcription blockage in resting CD4+ T-cells have been found, there are still unknown mechanisms to explore.

Objective:

To explore the mechanism for the suppression of de novo HIV-1 transcription in resting CD4+ T-cells.

Methods:

In this study, a short isoform of Per-1 expression plasmid was transfected into 293T cells with or without Tat's presence to identify Per-1 as a negative regulator for HIV-1 transcription. Silenc-ing of Per-1 was conducted in resting CD4+ T-cells or monocyte-derived macrophages (MDMs) to evaluate the antiviral activity of Per-1. Additionally, we analyzed the correlation between Per-1 expres-sion and viral loads in vivo, and silenced Per-1 by siRNA technology to investigate the potential anti-HIV-1 roles of Per-1 in vivo in untreated HIV-1-infected individuals.

Results:

We found that short isoform Per-1 can restrict HIV-1 replication and Tat ameliorates this in-hibitory effect. Silencing of Per-1 could upregulate HIV-1 transcription both in resting CD4+ T-cells and MDMs. Moreover, Per-1 expression is inversely correlated with viral loads in Rapid progressors (RPs) in vivo.

Conclusion:

These data together suggest that Per-1 is a novel negative regulator of HIV-1 transcrip-tion. This restrictive activity of Per-1 to HIV-1 replication may contribute to HIV-1 latency in resting CD4+ T-cells.

Nucleolar localization and circadian regulation of Per2S, a novel splicing variant of the Period 2 gene

In this work, we show for the first time that a second splicing variant of the core clock gene Period 2 (Per2), Per2S, is expressed at both the mRNA and protein levels in human keratinocytes and that it localizes in the nucleoli. Moreover, we show that a reversible perturbation of the nucleolar structure acts as a resetting stimulus for the cellular clock. Per2S expression and periodic oscillation upon dexamethasone treatment were assessed by qRT-PCR using specific primers. Western blot (WB) analysis using an antibody against the recombinant human PER2 (abRc) displayed an intense band at a molecular weight of ~55 kDa, close to the predicted size of Per2S, and a weaker band at the expected size of Per2 (~140 kDa). The antibody raised against PER2 pS662 (abS662), an epitope absent in PER2S, detected only the higher band. Immunolocalization studies with abRc revealed a peculiar nucleolar signal colocalizing with the nucleolar marker nucleophosmin, whereas with abS662 the signal was predominantly diffuse all over the nucleus and partially colocalized with abRc in the nucleolus. The analysis of cell fractions by WB confirmed the enrichment of PER2S and the presence of PER2 in the nucleolar compartment. Finally, a pulse (1 h) of actinomycin D (0.01 μg/ml) induced reversible nucleolar disruption, PER2S de-localization and circadian synchronization of clock and Per2S genes. Our work represents the first evidence that the Per2S splicing isoform is a clock component expressed in human cells localizing in the nucleolus. These results suggest a critical role for the nucleolus in the process of circadian synchronization in human keratinocytes.

The absence of melanopsin alters retinal clock function and dopamine regulation by light

The retinal circadian clock is crucial for optimal regulation of retinal physiology and function, yet its cellular location in mammals is still controversial. We used laser microdissection to investigate the circadian profiles and phase relations of clock gene expression and Period gene induction by light in the isolated outer (rods/cones) and inner (inner nuclear and ganglion cell layers) regions in wild-type and melanopsin-knockout (Opn 4 (-/-) ) mouse retinas. In the wild-type mouse, all clock genes are rhythmically expressed in the photoreceptor layer but not in the inner retina. For clock genes that are rhythmic in both retinal compartments, the circadian profiles are out of phase. These results are consistent with the view that photoreceptors are a potential site of circadian rhythm generation. In mice lacking melanopsin, we found an unexpected loss of clock gene rhythms and of the photic induction of Per1-Per2 mRNAs only in the outer retina. Since melanopsin ganglion cells are known to provide a feed-back signalling pathway for photic information to dopaminergic cells, we further examined dopamine (DA) synthesis in Opn 4 (-/-) mice. The lack of melanopsin prevented the light-dependent increase of tyrosine hydroxylase (TH) mRNA and of DA and, in constant darkness, led to comparatively high levels of both components. These results suggest that melanopsin is required for molecular clock function and DA regulation in the retina, and that Period gene induction by light is mediated by a melanopsin-dependent, DA-driven signal acting on retinal photoreceptors.

Expression and light sensitivity of clock genes Per1 and Per2 and immediate-early gene c-fos within the retina of early postnatal Wistar rats

Mammalian retina contains a circadian clock that is composed of components similar to those of the master circadian clock within the suprachiasmatic nuclei of the hypothalamus. The aim of the present study was to elucidate whether, when, and where the transcripts of the clock genes Per1 and Per2 and the immediate early gene c-fos are spontaneously expressed and/or induced by light in the newborn rat retina. At postnatal day 1 (P1), P3, P5, and P10, Wistar rat pups were released into constant darkness, and a 30-minute light pulse was administered during the subjective day or during the first or second part of subjective night. Gene expression was determined 30 minutes, 1 hour, 2 hours, and 4 hours after the light pulse by in situ hybridization followed by emulsion autoradiography. Endogenous expression of Per1 was detected in the neuroblastic retina, and Per2 expression was detected in the inner part of the neuroblastic retina from birth. Light pulses induced c-fos expression in ganglion cells from P1. Until P5, the cells were localized in the dorsal part of the retina, but, at P10, they were already distributed across the entire retinal circumference. Light pulses also induced the expression of c-fos and Per1 in the retinal pigment epithelium until P3, but not afterward. Expression of the Per2 gene was not photoresponsive until P10. These data demonstrate that the rat retina is light-sensitive immediately after birth. During early postnatal development, the spatial distribution of spontaneous and light-induced gene expression within the retinal layers changes gradually.

Elevated mPer1 gene expression in tumor stroma imaged through bioluminescence

The tumor stroma has significant effects on cancer cell growth and metastasis. Interactions between cancer and stromal cells shape tumor progression through poorly understood mechanisms. One factor regulating tumor growth is the circadian timing system that generates daily physiological rhythms throughout the body. Clock genes such as mPer1 serve in molecular timing events of circadian oscillators and when mutated can disrupt circadian rhythms and accelerate tumor growth. Stimulation of mPer1 by cytokines suggests that the timing of circadian oscillators may be altered by these tumor-derived signals. To explore tumor and stromal interactions, the pattern of mPer1 expression was imaged in tumors generated through subcutaneous injection of Lewis lung carcinoma (LLC) cells. Several imaging studies have used bioluminescent cancer cell lines expressing firefly luciferase to image tumor growth in live mice. In contrast, this study used non-bioluminescent cancer cells to produce tumors within transgenic mice expressing luciferase controlled by the mPer1 gene promoter. Bioluminescence originated only in host cells and was significantly elevated throughout the tumor stroma. It was detected through the skin of live mice or by imaging the tumor directly. No effects on the circadian timing system were detected during three weeks of tumor growth according to wheel-running rhythms. Similarly, no effects on mPer1 expression outside the tumor were found. These results suggest that mPer1 activity may play a localized role in the interactions between cancer and stromal cells. The effects might be exploited clinically by targeting the circadian clock genes of stromal cells.

Localization of a circadian clock in mammalian photoreceptors

Several studies have demonstrated that the mammalian retina contains an autonomous circadian clock. Dopaminergic and other inner retinal neurons express many of the clock genes, whereas some of these genes seem to be absent from the photoreceptors. This observation has led to the suggestion that in mammalian retina the circadian pacemaker driving retinal rhythms is located in the inner nuclear layer. However, other evidence points to the photoreceptor layer as the site of the mammalian retinal clock. The goal of the present study was to demonstrate the presence of a functional circadian clock in photoreceptors. First, using laser capture microdissection and reverse transcriptase-polymerase chain reaction, we investigated which of the clock genes are expressed in rat photoreceptors. We then prepared photoreceptor layer cultures from the retina to test whether these isolated cultures were viable and could drive circadian rhythms. Our data indicated that Per1, Per3, Cry1, Cry2, Clock, Bmal1, Rev-erb alpha, and Rora RNAs were present in the photoreceptors, whereas we were unable to amplify mRNA for Per2 and Npas2. Photoreceptor layers obtained from Period1-luciferase rats expressed a robust circadian rhythm in bioluminescence and melatonin synthesis. These results demonstrate that mammalian photoreceptors contain the circadian pacemaker driving rhythmic melatonin synthesis.