ayout 1 - EMBL Grenoble

EMBL Research at a Glance 2009
Small non-coding RNA function in development
and physiology
Dónal O’Carroll
PhD 1999, Research Institute
of Molecular Pathology,
Vienna.
Postdoctoral research at The
Rockefeller University, New
York.
Group leader at EMBL
Monterotondo since 2007.
Previous and current research
MicroRNAs (miRNAs) are small non-coding RNA molecules that have been identified as potent
negative regulators of gene expression. miRNA-mediated gene silencing is executed by the multiprotein
RNA–induced silencing complex (RISC). At the core of RISC are Dicer and an Argonaute
(Ago) protein that interact to generate miRNA and execute their function. Dicer cleaves miRNA
from its precursors whereas Ago proteins (Ago1-4) bind miRNA and mediate gene silencing.
Using hematopoiesis in mice as a model system to study the physiological function of RISC components
and the mechanism of miRNA-mediated gene silencing in vivo, we inactivated components
of this complex using conditional alleles of Dicer (Dcr) and Argonaute (Ago1-4) genes.
While Dcr function is absolutely required for early hematopoiesis, we found that Ago2 selectively
controls early development of B lymphoid and erythroid cells. We showed that the unique and
defining feature of Ago2, the Slicer endonuclease activity, is dispensable for hematopoiesis. Instead,
we have identified Ago2 as a key regulator of miRNA homeostasis, with deficiency in Ago2
impairing miRNA biogenesis from precursor-miRNAs.
The major foci of the laboratory are to understand how miRNAs regulate gene expression in vivo
and to contribute to the development and homeostasis of hematopoiesis and spermatogenesis. The analysis of Ago2 deficiency during
hematopoietic development has uncovered the processes of early erythroid and B lymphocyte development as being sensitive to miRNA
dosage. The identity and mechanism of the miRNAs that control these developmental transitions are currently being investigated. Similar approaches
are being applied to determine the dependence of spermatogenesis on miRNA function. By identifying the miRNAs that control these
various developmental systems and their network of targets, we strive to understand the physiological merits of this gene-silencing pathway.
In the pursuit of these goals we currently employ genetic, biochemical and miRNA profiling/sequencing, as well as pharmacological approaches.
Future projects and goals
• To determine the physiological mechanism of Ago2 function in miRNA biogenesis and the execution of miRNA function.
• To identify the miRNAs and their respective targets that control early erythropoiesis and B cell development.
• To explore the function of small RNAs during spermatogenesis.
Selected references
O’Carroll, D., Mecklenbrauker, I., Das, P.P., Santana, A., Koenig, U.,
Enright, A.J., Miska, E.A. & Tarakhovsky, A. (2007). A Slicerindependent
role for Argonaute 2 in hematopoiesis and the
microRNA pathway. Genes Dev., 21, 1999-200
Schaefer, A., O’Carroll, D., Tan, C.L., Hillman, D., Sugimori, M.,
Llinas, R. & Greengard, P. (2007). Cerebellar neurodegeneration in
the absence of microRNAs. J. Exp. Med., 20, 1553-8
Tang, F., Kaneda, M., O’Carroll, D., Hajkova, P., Barton, S.C., Sun,
Y.A., Lee, C., Tarakhovsky, A., Lao, K. & Surani, M.A. (2007).
Maternal microRNAs are essential for mouse zygotic development.
Genes Dev., 21, 6-8
Yi, R., O’Carroll, D., Pasolli, H.A., Zhang, Z., Dietrich, F.S.,
Tarakhovsky, A. & Fuchs, E. (2006). Morphogenesis in skin is
governed by discrete sets of differentially expressed microRNAs.
Nat. Genet., 38, 356-62
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