O'Carroll Group
Argonaute protein function in mammalian development and physiology
Figure 1: A. Single cell visualization of the miR-144/451 locus activity in E8.5 mouse embryos. A miR-144/451 EGFP BAC transgenic E8.5 mouse embryo is shown, DAPI in blue and EGFP in green. EGFP expression is found in the nascent blood islands.
B. Sylamer analysis of transcriptomes from wildtype and miR-144/451 -/- erythroblasts reveals miR-451 targets and the importance of miR-451 within the miR-144/451 locus (Collaboration with Enright Group).
C. Nuclear Miwi2 localization in gonadocytes from fetal testis of Slicer-inactive Mili ADH mice. DAPI in blue and Miwi2 in green.
Previous and current research
The aim of the group is to understand the mechanisms by which Argonaute proteins contribute to mammalian development and physiology with an emphasis on mouse hematopoiesis, embryology and germ cell development. We address our challenges using state-of-the-art mouse genetic strategies coupled with high throughput sequencing approaches.
Members of the Argonaute family are highly conserved small-RNA-binding proteins with diverse functions ranging from the regulation of post-transcriptional gene expression, anti-viral defense, transposon silencing to the establishment of heterochromatin domains. The Argonaute family is defined by the presence of both the Paz and Piwi domains. Paz domains bind to the 3’ end of small RNAs, whereas the Piwi domain adopts a classical RNase H fold with many Argonaute proteins being active small-RNA guided Slicer endonucleases. In mammals two subclades of Argonaute proteins exist, the Ago and Piwi sub-families.
MicroRNAs (miRNAs) and short-interfering RNAs (siRNA) are small non-coding RNA molecules that are potent negative regulators of gene expression. MiRNA/siRNA-mediated gene silencing is executed by the multi-protein RNA-induced silencing complex (RISC). At the core of RISC is an Ago protein that binds a small-RNA and executes their function. Our current RISC interests now focus on the physiological importance of Ago2 post-translational regulation in vivo.
Piwi proteins bind a class of small non-coding RNAs known as Piwi-interacting RNAs (piRNAs) that are believed to act as guides for targeting of the respective ribonuclear particles. In the mammalian male germline, the members of the Piwi subclade of the Argonaute family, Mili and Miwi2, are essential for de novo DNA methylation of transposons and spermatogenesis. We currently address several basic questions on the intrinsic mechanism and function of mammalian Piwi proteins in and beyond transposon silencing.
Selected publications
The endonuclease activity of Mili fuels piRNA amplification that silences LINE1 elements.
De Fazio, S., Bartonicek, N., Di Giacomo, M., Abreu-Goodger, C., Sankar, A., Funaya, C., Antony, C., Moreira, P.N., Enright, A.J. & O'Carroll, D.
Nature. 2011 Oct 23. doi: 10.1038/nature10547.
The miR-144/451eGFP allele, a novel tool for resolving the erythroid potential of hematopoietic precursors.
Rasmussen, K.D. & O'Carroll, D.
Blood. 2011 Jul 25.
Conserved vertebrate mir-451 provides a platform for Dicer-independent, Ago2-mediated microRNA biogenesis.
Yang, J.S., Maurin, T., Robine, N., Rasmussen, K.D., Jeffrey, K.L., Chandwani, R., Papapetrou, E.P., Sadelain, M., O'Carroll, D. & Lai, E.C.
Proc Natl Acad Sci U S A. 2010 Aug 24;107(34):15163-8. Epub 2010 Aug 10.
The miR-144/451 locus is required for erythroid homeostasis.
Rasmussen, K.D., Simmini, S., Abreu-Goodger, C., Bartonicek, N., Di Giacomo, M., Bilbao-Cortes, D., Horos, R., Von Lindern, M., Enright, A.J. & O'Carroll, D.
J Exp Med. 2010 May 31.
A Slicer-independent role for Argonaute 2 in hematopoiesis and the microRNA pathway.
O'Carroll, D., Mecklenbrauker, I., Das, P.P., Santana, A., Koenig, U., Enright, A.J., Miska, E.A. & Tarakhovsky, A.
Genes Dev. 2007 Aug 15;21(16):1999-2004. Epub 2007 Jul 12.
Future projects and goals
- Determine the in vivo significance of post-translational modifications of Ago2.
- Understand the mechanism of Miwi2 and Mili in the process of epigenetic transposon silencing
- Explore the function of Miwi2 and Mili during spermatogenesis beyond transposon silencing.