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Changes in Per1 and Per2 expression during early postnatal stage in rat masseters

ABSTRACT Numerous studies reported that the rhythmic expression of Period (Per) 1 and per2 are different depending on the tissues during postnatal ontogenesis. However, the changes of Per1 and Per2 expression in masticatory muscles remains unknown. The aim of the study was to explore the changes in Per1 and Per2 expression during early postnatal stage in rat masseters. Rat masseters were isolated in the light and dark frompostnatalday 1 (P1) to P21, then Per1 and Per2 were detected. At P21, rats were subjected to chew for 1, 5 and 10 min, then Per1 and Per2 were evaluated. The results showed that Per1 and Per2 showedsignificantly decreased expression from P1 to P21 in masseters. There was alight-dark significant difference in Per2 protein at P1, P21 and mRNA at P1, P7, P21. However, the significant difference in Per1 protein was only found at P1. Moreover, Per1 was mainly observed in the nucleus while Per2 was observed in the nucleus and cytoplasm. The expression of Per1 and Per2 were inhibited after chewing. Taken together, these findings demonstrate that the decreased expression of Per1 and Per2 during early postnatal stage may attribute to the feeding pattern change, from sucking to chewing, indicating progressive functional maturation of rat masseters.