Cryptochromes regulate the circadian clock in animals and plants. Humans and mice have two cryptochrome (Cry) genes. A previous study showed that mice lacking the Cry2 gene had reduced sensitivity to acute light induction of the circadian gene mPer1 in the suprachiasmatic nucleus (SCN) and had an intrinsic period 1 hr longer than normal. In this study, Cry1 ؊͞؊ and Cry1 ؊͞؊ Cry2 ؊͞؊ mice were generated and their circadian clocks were analyzed at behavioral and molecular levels. Behaviorally, the Cry1 ؊͞؊ mice had a circadian period 1 hr shorter than wild type and the Cry1 ؊͞؊ Cry2 ؊͞؊ mice were arrhythmic in constant darkness (DD). Biochemically, acute light induction of mPer1 mRNA in the SCN was blunted in Cry1 ؊͞؊ and abolished in Cry1 ؊͞؊ Cry2 ؊͞؊ mice. In contrast, the acute light induction of mPer2 in the SCN was intact in Cry1 ؊͞؊ and Cry1 ؊͞؊ Cry2 ؊͞؊ animals. Importantly, in double mutants, mPer1 expression was constitutively elevated and no rhythmicity was detected in either 12-hr light͞12-hr dark or DD, whereas mPer2 expression appeared rhythmic in 12-hr light͞12-hr dark, but nonrhythmic in DD with intermediate levels. These results demonstrate that Cry1 and Cry2 are required for the normal expression of circadian behavioral rhythms, as well as circadian rhythms of mPer1 and mPer2 in the SCN. The differential regulation of mPer1 and mPer2 by light in Cry double mutants reveals a surprising complexity in the role of cryptochromes in mammals.gene targeting ͉ photoreceptor ͉ suprachiasmatic nucleus C ircadian rhythms are oscillations with daily periodicities in physiological and behavioral functions of organisms (1-3). The rhythms are generated by a cell-autonomous circadian oscillator (4) that is synchronized with the environment by light. Recently, it was proposed that, in mammals, the nonopsin pigments, cryptochrome blue-light photoreceptors (5, 6), may be the photoactive pigments that synchronized the molecular oscillator and, ultimately, the organismic circadian rhythm with the daily light-dark cycle (7,8). In humans and mice there are two genes encoding the apoproteins of the cryptochromes: CRY1 and CRY2 in humans and Cry1 and Cry2 in mice (6,8,9). Both genes are expressed throughout the body (8-11). Of particular interest, both Cry1 and Cry2 are expressed at high levels in the ganglion cells and the inner nuclear layer of the retina, which are known to be important for circadian photoreception, and Cry1 is expressed with a robust circadian rhythm in the suprachiasmatic nucleus (SCN) (8).In a previous study (12), we found that mice lacking a functional Cry2 gene (i) had reduced sensitivity to acute light induction of the clock gene mPer1 (mouse period gene 1) in the SCN, (ii) had an intrinsic circadian period about 1 hr longer than normal, and (iii) exhibited high amplitude phase shifts in response to light pulses administered at circadian time (CT) 17. These data, and related findings in cryptochrome mutants of Drosophila melanogaster (13) and Arabidopsis thaliana (14), supported the notion that cr...

In this study, we performed small RNA library sequencing using human placental tissues to identify placenta-specific miRNAs. We also tested the hypothesis that human chorionic villi could secrete miRNAs extracellularly via exosomes, which in turn enter into maternal circulation. By small RNA library sequencing, most placenta-specific miRNAs (e.g., MIR517A) were linked to a miRNA cluster on chromosome 19. The miRNA cluster genes were differentially expressed in placental development. Subsequent validation by real-time PCR and in situ hybridization revealed that villous trophoblasts express placenta-specific miRNAs. The analysis of small RNA libraries from the blood plasma showed that the placenta-specific miRNAs are abundant in the plasma of pregnant women. By real-time PCR, we confirmed the rapid clearance of the placenta-specific miRNAs from the plasma after delivery, indicating that such miRNAs enter into maternal circulation. By using the trophoblast cell line BeWo in culture, we demonstrated that miRNAs are indeed extracellularly released via exosomes. Taken together, our findings suggest that miRNAs are exported from the human placental syncytiotrophoblast into maternal circulation, where they could target maternal tissues. Finally, to address the biological functions of placenta-specific miRNAs, we performed a proteome analysis of BeWo cells transfected with MIR517A. Bioinformatic analysis suggests that this miRNA is possibly involved in tumor necrosis factor-mediated signaling. Our data provide important insights into miRNA biology of the human placenta.