Introduction:Drosha is an RNAase III enzyme that interacts with the RNA binding protein DGCR8 and forms amicrocomplex in the nucleus to process primary miRNAs (pri-miRNAs) into recursor miRNAs (pre-miRNAs),which are subsequently cleaved by Dicer in the ytoplasm to produce mature miRNA. Accumulatingexperimental evidence suggests that miRNAs control gene expression through RNA-induced silencing complex(RISC) at the osttranscriptional level and regulates cell apoptosis, proliferation, and differentiation The miRNA biogenesis pathway is tightly controlled through different molecular mechanisms includingmethylation, RNA editing, and a self-regulatory feedback loop between Drosha and GCR8 in thephysiological condition [5]. Disruption of the miRNA biogenesis pathway causes aberrant expression profilesof miRNA genes, thus leading to various human diseases and developmental retardation.

DGCR8 specifically processes miRNA, whereas Dicer functions in other small RNAs such as siRNA or shRNA. in addition to miRNAs. Recent studies indicated that some splicing-independent mirtron-like miRNA(simtrons) maturation does not require the canonical miRNA biogenesis pathway, which skips the processing ofDGCR8, exportin-5, Dicer, and Ago2, but is Drosha-dependent [6,7,8]. In our previous studies, we showed that disruption of DGCR8 in VSMCs results in embryonic death 2–3 days earlier than that of Dicer, although bothDGCR8 and Dicer cKO embryos share some phenotypic similarity [9,10]. Our studies demonstrated thatDGCR8 plays a more important role than does Dicer in maintaining the VSMC functions by participating in themiRNA process in the upstream biogenesis pathway. Drosha and Dicer are two RNAase III enzymes and sharethe structural and functional similarity that both cleave the double-stranded RNA and have two RNAase IIIdomains, a/b and an RNA binding domain. However, DGCR8 is an RNA binding protein whose structurediffers from Dicer and Drosha, which do not have RNAase III domains but have two RNA binding domains.Drosha, DGCR8, and Dicer are key components of the miRNA biogenesis pathway and contribute to miRNAmaturation by participating in this pathway.

In our previous studies , we have shown that DGCR8 and Dicer are required for vasculardevelopment. However, the roles of Drosha in VSMCs are largely unknown. To investigate the role of Droshain VSMC function, we generated conditional Drosha knockout mice (cKO) by crossing Droshaloxp/loxp with VSMC-specific SM22-cre mice. Disruption of Drosha in VSMCs of mice results in embryonic mortality. Inaddition, we also generated KO VSMCs by using adeno-cre virus and knockdown (KD) VSMCs usingretroviral shRNA vector. By characterizing Drosha cKO mice, KO, and KD VSMCs, we found that loss ofDrosha in VSMCs reduces VSMC proliferation and differentiation by compromising miRNA biogenesispathways and attenuating cellular survival pathways ERK1/2 and AKT.

    作者：Pei Fan, Zixuan Chen, Peng Tian, Wen Liu, Yan Jiao,YiXue, Anindya Bhattacharya, Jianmin Wu, Meifen Lu, Yuqi Guo, Yan Cui, Weikuan Gu, Weiwang Gu, Junming Yue

    作者单位：1.Department of Pathology, University of Tennessee Health Science Center, Memphis,Tennessee, United States of America, 2.Center for Cancer Research, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America, 3.Department of Orthopaedic Surgery–Campbell Clinic, University of Tennessee Health Science Center, Memphis,Tennessee, United States of America, 4.Department of Neurology, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America, .Southern Medical University, Guangzhou, Guangdong, P. R. China, 6.The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, P. R. China, 7.Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America, 8.Veterinary Research Institute, Nanning, Guangxi, P. R. China

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