Localisation of a tagged insect Piwi protein to perinuclear cytoplasmic granules in insect cell cultures. These are putative piRNA biogenesis sites, similar to the nuage in germ cells.
The Pillai group seeks to understand the molecular mechanisms involved in piRNA biogenesis and its function in protecting the genome from instability.
Previous and current research
Past invasion events from mobile genetic elements have left eukaryotic genomes littered with repeats and other transposon sequences. Much of these are inactive fossils, but some could still get activated and cause genome instability, despite being silenced in the germlines. This silencing is mediated, in animal germ cells, by a specialised class of ~30 nt small non-coding RNAs called piwi-interacting RNAs (piRNAs). They constitute an epigenetic component of the genome defense mechanism. In mammals, they are believed to recruit DNA methyltransferases to transposon sequences. In Drosophila, maternally produced piRNAs are deposited in the egg and they contribute to protection from new transposons brought in by the paternal genome.
Our lab is interested in understanding the molecular mechanisms involved in piRNA biogenesis and function, both in mammals and in Drosophila. A striking feature of piRNAs is their clustered genomic origins: it is believed that a long single-stranded transcript arising from a cluster is processed into thousands of piRNAs. This mechanism and the factors involved are still unknown, so we have taken a biochemical approach to identify them in mice. We identified the Tudor domain-containing protein 1 (Tdrd1), which recognises symmetrical dimethyl arginine modification marks on Piwi proteins, and the putative helicase Mov10l, which is an essential piRNA biogenesis factor. In all these studies, we have used a variety of techniques such as protein biochemistry, cellular imaging, small RNA bioinformatics, and mouse mutants. We also collaborate with structural biologists to obtain atomic resolution images of the identified pathway components: we recently unveiled the structure of the recognition pattern between the 2’-O-methyl mark on piRNAs and the PAZ domain of a Piwi protein.
Future projects and goals
We will continue to analyse additional factors identified in our complex purifications. We aim to understand what features define genomic regions as piRNA clusters, and whether there is a link between transcription from the clusters and piRNA biogenesis. Via live cell imaging techniques we want to study assemblies of small RNPs in vivo and define the contribution of the individual constituents of the complex to this process. We will intensify the collaborations on structural biology of Piwi complexes, adding another dimension to our understanding of germline small RNAs.
Recently highlighted research
Xiol J, Spinelli P, Laussmann MA, Homolka D, Yang Z, Cora E, Couté Y, Conn S, Kadlec J, Sachidanandam R, Kaksonen M, Cusack S, Ephrussi A, Pillai RS (2014)
RNA Clamping by Vasa Assembles a piRNA Amplifier Complex on Transposon Transcripts
Cell 157(7):1698-1711. doi:10.1016/j.cell.2014.05.018
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