RESEARCH ARTICLE SUMMARY
Loss of a mammalian circular RNA
locus causes miRNA deregulation
and affects brain function
Monika Piwecka,* Petar Glažar,* Luis R. Hernandez-Miranda,* Sebastian Memczak,
Susanne A. Wolf, Agnieszka Rybak-Wolf, Andrei Filipchyk, Filippos Klironomos,
Cledi Alicia Cerda Jara, Pascal Fenske, Thorsten Trimbuch, Vera Zywitza, Mireya Plass,
Luisa Schreyer, Salah Ayoub, Christine Kocks, Ralf Kühn, Christian Rosenmund,
Carmen Birchmeier, Nikolaus Rajewsky†
INTRODUCTION: Recently, a special class of
RNAs has excited researchers and triggered
hundreds of now-published studies. Known as
circular RNAs (circRNAs), these RNAs are produced by regular transcription from genomic
DNA, but the two ends of the (usually) exonic
transcripts are covalently closed, probably in
most cases by noncanonical splice reactions.
Most circRNAs are expressed in the cytoplasm
and are unusually stable, suggesting that they
may have functions that diverge from those of
canonical messenger RNAs (mRNAs) or long
noncoding RNAs (lncRNAs).
CircRNAs tend to be weakly expressed, but
there are exceptions in animal brains. For
example, in the mouse brain, a few hundred
circRNAs are highly expressed, often with de-
velopmentally specific expression patterns that
are conserved in the human brain. We previous-
ly proposed that circRNAs may, at least some-
times, serve as regulatory RNAs. A circRNA
discovered by the Kjems laboratory, CDR1as,
caught our attention because it was covered
with >70 binding sites for the microRNA
(miRNA) miR-7. Our data suggested that
CDR1as might serve to alter the free concen-
tration of miR-7. But what really is the func-
tion of CDR1as?
RATIONALE: We first determined which
miRNAs specifically bind Cdr1as in postmortem human and mouse brains and characterized Cdr1as expression patterns. Once we
had that information, we removed Cdr1as
from the mouse genome to study the molecular and behavioral consequences.
RESULTS: We show that Cdr1as is, in the human
brain, directly and massively bound by miR-7
and miR-671. In fact, Cdr1as is one of the most
common transcripts targeted by miRNAs out of
all brain mRNAs or lncRNAs. The expression of
miRNAs was generally unperturbed in Cdr1as
knockout (KO) mice, with the exception of
the two miRNAs that directly interact with Cdr1as,
miR-7 and miR-671, which
were respectively down-regulated and up-regulated.
This perturbation was post-transcriptional, consistent
with a model in which Cdr1as interacts with
these miRNAs in the cytoplasm. We show that
Cdr1as is highly expressed (hundreds of copies
within neurons) in somas and neurites, but not
in glial cells.
The expression of many immediate early genes
(IEGs), which are markers of neuronal activity,
was consistently up-regulated in KO animals.
For example, c-Fos and a few other miR-7 targets were up-regulated, suggesting that IEG up-regulation can in part be explained by miR-7
down-regulation and that Cdr1as modulates
neuronal activity. Cdr1as KO mice showed a
strong deficit in prepulse inhibition of the
startle response, a sensorimotor gating phenotype that is impaired in several human neuropsychiatric disorders. Electrophysiological
measurements indicated an increase in spontaneous vesicle release in Cdr1as KO neurons,
suggesting that Cdr1as plays a role in regulating synaptic transmission.
CONCLUSION: Mechanistically, our data indicate that Cdr1as regulates miR-7 stability or
transport in neurons, whereas miR-671 regulates Cdr1as levels. Functionally, our data suggest that Cdr1as and its direct interactions
with miRNAs are important for sensorimotor
gating and synaptic transmission. More generally, because the brain is an organ with exceptionally high and diverse expression of circRNAs,
our data suggest the existence of a previously
unknown layer of biological functions carried
out by circRNAs. ▪
The list of author affiliations is available in the full article online.
*These authors contributed equally to this work.
†Corresponding author. Email: firstname.lastname@example.org
Cite this article as M. Piwecka et al., Science 357,
eaam8526 (2017). DOI: 10.1126/science.aam8526
Cdr1as is a brain-enriched circular RNA, expressed in hundreds of copies within neurons
and essential for maintaining normal brain function. Genetic ablation of the Cdr1as locus in
mice led to deregulation of miR-7 and miR-671 in the brain, up-regulation of immediate early
genes, synaptic malfunctions, and a deficit in prepulse inhibition of the startle reflex, a behavioral
phenotype associated with neuropsychiatric disorders.
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