Yoshiki Ishida

Phase-dependent responses of Per1 and Per2 genes to a light-stimulus in the suprachiasmatic nucleus of the rat.

Single brief and discrete light treatments are sufficient to reset the overt mammalian rhythms of nocturnal rodents. In the present study, we examined the phase-dependent response of the mammalian clock genes, Per1 and Per2, to a brief strong light-stimulus (1000 lux) in the circadian oscillator center, the suprachiasmatic nucleus (SCN) of rats. Light-induced elevation of Per1 mRNA was observed through the subjective night (CT16, CT20 and CT0 (=CT24)) with a marked peak at the subjective dawn (CT0). However, the light influence was very limited for the induction of Per2; only weak elevation of Per2 mRNA was detected at CT16. The effect of light-stimulus on the Per1 gene was transient, and the effect was restricted to ventrolateral SCN neurons in both CT0 and CT16 after light exposure. Since it is known that these rats show a light-induced behavioral phase-shift throughout the subjective night with being strongest at subjective dawn, the present results suggest that the transient induction of Per1 in ventrolateral SCN neurons is a critical step in the resetting of the biological clock to environmental light-dark schedule.

View of a mouse clock gene ticking

Circadian clocks consist of an ingenious autoregulatory feedback loop whereby the cyclically expressed products of the clock gene are able to inhibit their own expression<. Here we follow the rhythmic expression of the clock gene mPer1 in the brain of a living mouse. This model system enables real-time gene expression to be monitored in the intact brain under physiological conditions.

Expression of the Per1 gene in the hamster: Brain atlas and circadian characteristics in the suprachiasmatic nucleus

Recent progress in study on the molecular component of mammalian clocks has claimed that mammals and Drosophila share the similar fundamental clock oscillating system. In the present study, we investigated expression of Per1, the first gene of the mammalian homolog of the Drosophila clock gene period, in the hamster brain, and we also examined its circadian expression pattern in the mammalian clock center, the suprachiasmatic nucleus (SCN). In situ hybridization using isotope‐labeled cRNA probes revealed a wide and region‐specific distribution of Per1 in the hamster brain and spinal cord. High levels of Per1 were found in the internal granular layer of the granular cells of the olfactory bulb, anterior olfactory nuclei, tenia tecta, olfactory tubercle, piriform cortex, suprachiasmatic nucleus, and gyrus dentatus of hippocampus. Moderate levels of expression were detected in many brain regions including the granular layer of the cerebellum, anterior paraventricular thalamic nucleus, caudate‐putamen, inferior colliculus, pontine nuclei, inferior olive, and nucleus of the solitary tract. We examined the circadian profile of hamster Per1 mRNA in the SCN in constant darkness and found that Per1 expression showed a peak at subjective day (circadian time [CT] 4) and formed a trough at subjective night (CT16–CT20). A brief exposure of light at CT16 could acutely induce large quantities of Per1 mRNA in the hamster SCN, except for its dorsomedial subdivision. These findings suggest that the characteristics of Per1 gene expression in the mammalian circadian center (showing a peak in the daytime and a trough in the nighttime and a rapid inducibility by light) are common among mammalian species. Lastly, in hamster brain, Per1 gene is also inducible in extra‐SCN brain nuclei, since light at night also elicited Per1 mRNA in neurons of the hypothalamic paraventricular nucleus. J. Comp. Neurol. 430:518–532, 2001.

Rev‐erbα gene expression in the mouse brain with special emphasis on its circadian profiles in the suprachiasmatic nucleus

Rev‐erbα is an orphan nuclear receptor that constitutively suppresses gene transcription. In the present study, the expression of Rev‐erbα was investigated in the mouse brain by in situ hybridization using antisense cRNA probe. Positive Rev‐erbα mRNA signals were detected widely in the brain with the highest expression in the suprachiasmatic nucleus (SCN). In the constant dark condition, the circadian expression profiles of Rev‐erbα m RNA in the SCN showed a peak at early daytime (CT4) and a trough at early night time (CT16). The environmental lighting condition (light–dark environmental condition and exposure in the subjective night) did not alter the expression profiles. These findings indicate that Rev‐erbα gene is a transcription factor intimately related to the circadian clock in the SCN.

Tumor-doubling time and onset of pulmonary metastasis from adenoid cystic carcinoma of the salivary gland

Adenoid cystic carcinoma (ACC), an uncommon malignancy in the head and neck region, invades diffusely and often metastasizes to the lung, although the growth rate is very slow. A retrospective study was conducted in 30 patients with ACC to ascertain the frequency of pulmonary metastasis, the doubling time of metastatic tumor deposits, and the time of onset for pulmonary metastasis. The following results were obtained: (1) Of 30 patients with ACC, 21 had pulmonary metastases (4 initially and 17 during observation), 7 were free of metastases but have not been observed for 5 years, and 2 were free of metastases for more than 5 years but less than 10 years after the initial treatment. The cumulative metastasis rate at 5 and 10 years for this group of patients was 70% and 100%, respectively. (2) Patients with T1 or T2 tumors that have a tubular or cribriform histopathologic pattern showed pulmonary metastases about 20 months later than those with T3 or T4 tumors and a solid pattern. However, the final metastasis rate did not differ between the 2 groups after a long period. (3) The tumor doubling time of the metastatic deposits of ACC was 86 to 1064 days with an average of 393 days, which was much longer than that of most other malignant neoplasms reported previously. (4) The time of onset of pulmonary metastasis was calculated to be much earlier (average of 227 months) before the first visit. These findings suggest that the treatment method for ACC should be chosen with the consideration that many of the patients may have occult pulmonary metastases at the time of their initial evaluation.

Rhythmic expression of RORβ mRNA in the mice suprachiasmatic nucleus

Abstract The expression of the brain rich orphan nuclear receptor RORβ (retinoid-related orphan receptor beta) was investigated in the mouse brain by in situ hybridization using antisense cRNA probe. Positive RORβ mRNA signals were detected in various parts of the brain with high expression in the suprachiasmatic nucleus (SCN). In the SCN, RORβ mRNA signals showed a peak at early daytime (ZT/CT4) and a trough at early nighttime (ZT/CT16) in both light–dark and constant dark conditions. Light exposure at subjective night did not alter the expression level. These findings suggest that RORβ is a new member of a transcription factor possibly related to the circadian pacemaking system.

Circadian rhythm of aromatic L -amino acid decarboxylase in the rat suprachiasmatic nucleus: gene expression and decarboxylating activity in clock oscillating cells

Background: Aromatic l‐amino acid decarboxylase (AADC) is the enzyme responsible for the decarboxylation step in both the catecholamine and indoleamine synthetic pathways. In the brain, however, a group of AADC containing neurones is found outside the classical monoaminergic cell groups. Since such non‐monoaminergic AADC is expressed abundantly in the suprachiasmatic nucleus (SCN), the mammalian circadian centre, we characterized the role of AADC in circadian oscillation.

Constitutive expression and delayed light response of casein kinase Iϵ and Iδ mRNAs in the mouse suprachiasmatic nucleus

Casein kinase Iϵ (CKIϵ) and casein kinase Iδ (CKIδ) phosphorylate clock oscillating mPER proteins, and play a key role in the transcription (post)translation feedback loop that generates circadian rhythm. In the present study, the expression profiles of CKIϵ and CKIδ mRNAs were examined in the mice clock center, suprachiasmatic nucleus (SCN). Moderate levels of CKIϵ and CKIδ mRNAs were constantly expressed in the SCN in both light:dark and constant dark conditions. This finding supports the hypothesis that CKI may form a constant threshold to the nuclear entry of mPER proteins as in the Drosophila homologue, double‐time. Further, we demonstrated that the light exposure at subjective night induced a delayed increase in CKIϵ and CKIδ mRNAs in the SCN. CKIϵ and CKIδ proteins may play a role on light‐induced phase‐shift. J. Neurosci. Res. 64:612–616, 2001.