Adenosine deaminases acting on RNA (ADARs) are involved in adenosine (A) - to - inosine (I) RNA editing and are implicated in development and diseases. Three ADAR gene family members (ADAR1-3) are found in mammals. ADAR1 and ADAR2 are widely expressed and catalytically active in mammals, while ADAR3 is considered to be inactive. Importantly, ADAR1 is an essential protein and ADAR1-deficient mice were embryonically lethal. In addition, mutations in human ADAR1 gene were shown to be associated with Aicardi-Goutières syndrome, an early-onset encephalopathy that often results in severe and permanent neurological damage, indicating that ADAR1 may play an important role during neural development in humans.
To gain insights into the role of ADAR1 in embryonic stem cell (ESC) differentiation and neural induction in a human context, human ESCs (hESCs) lacking ADAR1 were generated and were examined their ability to differentiate into specific types of neurons, followed by RNA-sequencing to systematically compare RNA editing, mRNA and miRNA changes between wild-type (WT) and ADAR1-deficient cells at several differentiation time points.
A team of scientists led by Prof. CHEN Lingling from the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences of Chinese Academy of Sciences, in collaboration with Prof. YANG Li from CAS-MPG Partner Institute for Computational Biology, found that ADAR1 deficiency in hESCs significantly affected hESC differentiation and neural induction with widespread changes in mRNA and miRNA expression, including up regulation of self-renewal-related miRNAs, such as miR302s. Global editing analyses revealed that ADAR1 editing activity contributes little to the altered miRNA/mRNA expression in ADAR1-deficient hESCs upon neural induction. Genome-wide iCLIP studies identified that ADAR1 binds directly to pri-miRNAs to interfere with miRNA processing by acting as an RNA-binding protein. Importantly, aberrant expression of miRNAs and phenotypes observed in ADAR1-depleted hESCs upon neural differentiation could be reversed by an enzymatically inactive ADAR1 mutant, but not by the RNA-binding-null ADAR1 mutant. These findings reveal that ADAR1, but not its editing activity, is critical for hESC differentiation and neural induction by regulating miRNA biogenesis via direct RNA interaction.
This work entitled “ADAR1 is required for differentiation and neural induction by regulating microRNA processing in a catalytically independent manner” was published in Cell Research on Feb 24th, 2015. This study was supported by the grants from the Chinese Academy of Sciences (the Strategic Priority Research Program), the Ministry of Science and Technology, and the National Natural Science Foundation of China.
AUTHOR CONTACT:
CHEN Lingling;
Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences
Shanghai 200031, China.
E-mail: linglingchen@sibcb.ac.cn;
Fig. A model for the non-enzymatic role of ADAR1 in hESC self-renewal and differentiation.
(Image provided by Prof. CHEN Lingling’s group)
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