Mammalian folliculogenesis is a complex process in which primordial follicles 
develop into pre-ovulatory follicles, followed by ovulation to release mature 
oocytes. In this study, we explored the role of miR-144 in ovulation. miR-144 
was one of the differentially expressed microRNAs, which showed 5.59-fold 
changes, in pre-ovulatory ovarian follicles between Large White and Chinese 
Taihu sows detected by Solexa deep sequencing. We demonstrated that 
overexpression of miR-144 significantly decreased the luciferase reporter 
activity under the control of the cyclooxygenase-2 (COX-2) or mothers against 
decapentaplegic homologue 4 (Smad4) 3'-untranslated region (3'-UTR) and 
suppressed COX-2 and Smad4 expression. In contrast, a miR-144 inhibitor 
increased COX-2 and Smad4 expression in mouse granulosa cells (mGCs). Meanwhile, 
Smad4 upregulated COX-2 expression, but this effect was abolished when the mGCs 
were treated with the transforming growth factor beta signalling pathway 
inhibitor SB431542. Moreover, luciferase reporter, chromatin immunoprecipitation 
and electrophoretic mobility shift assay results showed that the transcription 
factor CP2 upregulated miR-144 expression, which partially contributed to the 
suppression of COX-2 in mGCs. Both CP2 and miR-144 alter prostaglandin E2 (PGE2) 
production by regulating COX-2 expression. In addition, miR-144 regulated mGC 
apoptosis and affected follicular atresia, but these activities did not appear 
to be through COX-2 and Smad4. Taken together, we revealed an important 
CP2/miR-144/COX-2/PGE2/ovulation pathway in mGCs.