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1 Department of Biology, Program in Neuroscience, University of Massachusetts, Amherst, MA, USA
* To whom correspondence should be addressed. E-mail: elb{at}bio.umass.edu.
Circadian rhythms are generated by a mechanism which involves the oscillating expression ofPer1 and Per2. These genes are expressed not only in the central brain pacemaker which is localized to the suprachiasmatic nucleus, but also in peripheral tissues. Hormones are likely to function as informational signals to coordinate physiological function in time. As a first step to determining possible functional roles of per homologs in endocrine tissues, we performed in situ hybridization to localize mPer1 and mPer2 mRNA to particular cell types and tissue compartments in adrenal, thyroid and testis of BALB/c mice. Animals maintained in 12L:12D were rapidly killed at one of four times during the day and night. In situ hybridization revealed that mPer1 was prominently expressed in the adrenal medulla. Although labeled cells were detected at all times of day, mPer1 signal was most intense in late afternoon and early night. In contrast, mPer2 labeling was more intensely expressed in adrenal cortex; signal was again highest in afternoon and evening. mPer1 mRNA was detected in both the follicular and interstitial tissue of the thyroid. mPer1 was abundantly expressed in some, but not all, of the seminiferous tubules of each mouse, regardless of the time of day. Further quantitative studies were carried out in C57BL/6 mice, in which a slight but significant increase in the number of seminiferous tubules with high grain densities was detected during the early night. Labeled cells lie within the seminiferous epithelium intermediate between the basement membrane and the tubular lumen. Immunocytochemical staining using two different antibodies showed a corresponding distribution of PER1 protein within the seminiferous tubules, with PER1-ir appearing most prominently in spermatocytes and in spermatids. Staining in spermatogonia and interstitial cells was also detected, but was less consistent. Double label studies in which mice were injected with the thymidine analog 5'-bromodeoxyuridine (BrdU) indicate that intense PER1 expression first occurs approximately 5 days after the completion of DNA replication. These results indicate that mPer1 and to a lesser extent mPer2 are expressed in particular compartments of peripheral endocrine glands. Central regulation, adenohypophyseal control, and functional importance of expression and phase remain to be elucidated.
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