学术报告
题目：Minotaur is critical for primary piRNA biogenesis
报告人：Yang Yu, Ph.D
Cold Spring Harbor Laboratory
时间：2013年7月11日 (周四) 14:00PM‐15:30PM
地点：生命科学学院411会议室
Piwi proteins and their associated small RNAs are essential for fertility in animals. This is due, in part, to their roles in guarding germ cell genomes against the activity of mobile genetic elements. piRNA populations direct Piwi proteins to silence transposon targets and form a molecular code that discriminates transposons. Information carried by piRNAs is encoded within genomic loci, termed piRNA clusters. These give rise to primary transcripts that are processed into piRNAs. Despite the biological importance of this pathway, neither the characteristics nor the mechanisms are well understood. We searched an EMS-mutant collection annotated for fertility phenotypes for genes involved in the piRNA pathway. Twenty-seven homozygous-sterile strains showed transposon-silencing defects. One of these, which strongly impacted primary piRNA biogenesis, harbored a causal mutation in CG5508, a member of the Drosophila glycerol-3-phosphate O-acetyltransferase (GPAT) family. Although these enzymes catalyze the first acylation step on the path to the production of phosphatidic acid (PA), a mutant form of CG5508, which lacks the GPAT active site, still functions in piRNA biogenesis. We have named this new biogenesis factor Minotaur.
Using secondary structure prediction algorithms, we uncovered a simple winged-helix motif located at C-terminus of Minotaur that might provide nucleic acid binding capacity. Indeed, Minotaur can be specifically cross-linked to piRNA precursors in vivo by PAR-CLIP. Importantly, such interaction is dependent on the presence of the predicted RNA binding motif. Interestingly, Zucchini, a single-strand specific endonuclease, co-localizes with Minotaur on the outer membrane of mitochondria. Consistent with its proposed role in generating 5` ends of piRNAs, Zucchini also binds to piRNA precursors. Specifically, Zucchini binds to the regions that are largely overlapping with Minotaur binding sites. Strikingly, both binding sites are concentrated around the residues that are destined for piRNA 5` ends. In Minotaur mutant ovaries, the interactions between Zucchini and piRNA precursors are greatly diminished. Since loss of either gene leads to the accumulation of piRNA primary transcripts, we concluded that Minotaur might be required for either the recruitment of piRNA precursors to Zucchini and/or the endonuclease activity of Zucchini in vivo to produce 5` ends of piRNAs.
欢迎各位老师和同学积极参加！