In this study, we showed that the clock-controlled mir-142-3p can directly target its circadian activator, Bmal1.
Although mir-142-3p has been reported to be a potential Bmal1
-targeting miRNA based on a luciferase reporter assay
], the present report is the first confirmation that mir-142-3p can directly regulate the expression of Bmal1
both in mouse and human cells. By over-expression of mir-142-3p in NIH3T3 cells, we showed mir-142-3p can regulate the expression of Bmal1
. However, a further study on the effects of knocking down mir-142-3p in appropriate murine cell models (with high level of mir-142-3p) will help to confirm the relationship between mir-142-3p and its target at the physiological conditions. Feedback loops formed by clock genes are thought to be the basis of the molecular clock. To our knowledge, this is the first report suggesting a potential negative feedback loop formed by miRNAs and clock genes. Considering the important role of Bmal1
in circadian clock, we speculate that the molecular clock might be also fine tuned by the miRNA-mediated negative feedback.
was also predicted to be targeted by several miRNAs using three bioinformatic algorithms (Additional file
A). The results of our luciferase reporter assay showed that six candidates (mir-20a, mir-106a, mir-106b, mir-148a, mir-182 and mir-301a) could be Clock
-targeting miRNAs (Additional file
B and C). Among them, mir-182 was reported to be a modulator of CLOCK
in a recent study
]. Although we did not perform additional experiments to confirm the interaction between the miRNAs and Clock
, the regulation of Clock
by miRNAs deserves further study. Indeed, a similar regulatory network consisting of miRNAs and Clock
may exist, and a feedback loop involving mir-182/96 and Clock
has been hypothesized
In our study, we identified mir-142-3p as a regulator of Bmal1 both in human and mouse cells. Even though we showed that mir-142 is transcriptionally controlled by CLOCK/BMAL1 heterodimers only in a mouse fibroblast cell line (NIH3T3), the E-box in the upstream regulatory sequence of mir-142 gene is perfectly conserved among mammals (Figure
B). Thus, we hypothesize that this potential negative feedback mechanism could be conserved, at least between mice and human beings.
In our concise model, CLOCK/BMAL1 heterodimers enhance the transcription of mir-142
, the product of which, in turn, inhibits the expression of Bmal1
. In addition to Bmal1
, mir-142-3p was reported to target several genes, including ADCY9
, whose product controls cAMP levels
]. Other genes were also predicted to be targets of mir-142-3p (Additional file
), and two of them (foxo1
) are involved in the circadian clock
]. The other product of mir-142, mir-142-5p, was also predicted to target numerous genes, the most interesting one of which is Clock
, the other master regulator of the molecular clock (Additional file
). Further studies are needed to confirm these prediction results and to uncover the regulatory role of the mir-142 gene in the circadian clock.