The integrity of the genome transmitted to the next generation intrinsically relies on cells of the germline. Processes that ensure germ cell development, genomic stability and reproductive lifespan are essential for the long-term health and success of a species. We tackle fundamental questions regarding the mammalian germ line and heredity from an RNA perspective. Specifically, our research explores the contribution of PIWI-interacting RNAs (piRNAs) and RNA modification pathways to germ cell development. We also have a keen interest in characterizing spermatogonial stem cell (SSC) populations that underpin male fertility throughout adult life.
The PIWI-piRNA pathway.
In mammals, the acquisition of the germline from the soma provides the germline with an essential challenge, the necessity to erase and reset genomic methylation. De novo genome methylation re-encodes the epigenome, imprinting and transposable element (TE) silencing. In the male germline RNA-directed DNA methylation silences young active TEs. This poorly understood but essential process is central to the immortality of the germline. Upon completion of germline reprogramming with the full erasure of genomic methylation transposons become derepressed. PIWI proteins and their associated small non-coding PIWI-interacting RNAs (piRNAs) neutralize this threat. Firstly, through base complementarity piRNAs guide the PIWI endonuclease MILI to destroy cytoplasmic transposon RNAs. Secondly, antisense TE-derived piRNAs generated from intricate biogenesis pathways act to guide the nuclear PIWI protein MIWI2 to instruct TE DNA methylation by an unknow mechanism. We have made an important contribution to the mechanism of piRNA biogenesis as well as elucidating the functions of the piRNA pathway during adult spermatogenesis. Our future goal is to understand the elusive mechanism by which MIWI2 instructs TE methylation.
The variety and abundance of RNA modifications coupled with the realization of their regulatory importance have given rise to the nascent field of epitranscriptomics. Several stages of both male and female germ cell development are transcriptionally inert and thus rely on post-transcriptional regulation of gene expression. Thus, the study of RNA modification in the germline will likely give profound insights into both processes. My laboratory has longstanding interest in mechanism that direct mRNA degradation. We focus on the function of N6-methyladenosine (m6A) and 3 terminal uridylation mRNA modifications, both of which can promote RNA degradation. We recently showed essential and specific functions for poly(A) tail length and TUT4/7-mediated 3 terminal uridylation in sculpting a functional maternal transcriptome during oocyte growth. We demonstrated that the m6A-reader YTHDF2 regulates transcript dosage during oocyte maturation and is an intrinsic determinant of mammalian oocyte competence as well as early zygotic development. Our future goal is to develop more sensitive sequencing approaches for the measurement of poly(A) tail length and 3 terminal modifications. We also try to understand additional functions for these as well as other modifications in the germline and beyond.
Spermatogonial stem cell populations.
Spermatogonial stem cells (SSCs) maintain spermatogenesis throughout adult life as well as underpin the regenerative capacity of the testis. A small population of undifferentiated spermatogonia have SSC activity. We showed that Miwi2 expression defines a population of transit-amplifying spermatogonia that also retain facultative stem cell function and is essential for the efficient regenerative capacity of the adult testis. We also recently demonstrated that defective germline de novo genome methylation rewires spermatogonial transcriptomes. We are currently using single-cell techniques to define the impact of regeneration and ageing on SSC populations. In addition, we utilize and develop state of the art cellular barcoding techniques to understand the clonality of SSCs and their clonal contribution to spermatogenesis.
- Vasiliauskaitė L, Berrens RV, Ivanova I, Carrieri C, Reik W, Enright AJ, O'Carroll D. Defective germline reprogramming rewires the spermatogonial transcriptome. Nat Struct Mol Biol. 2018 May;25(5):394-404. doi:10.1038/s41594-018-0058-0.
- Ivanova I, Much C, Di Giacomo M, Azzi C, Morgan M, Moreira PN, Monahan J, Carrieri C, Enright AJ, O'Carroll D. The RNA m6A Reader YTHDF2 Is Essential for the Post-transcriptional Regulation of the Maternal Transcriptome and Oocyte Competence. Mol Cell. 2017 Sep 21;67(6):1059-1067.e4. doi:10.1016/j.molcel.2017.08.003.
- Morgan M, Much C, DiGiacomo M, Azzi C, Ivanova I, Vitsios DM, Pistolic J, Collier P, Moreira PN, Benes V, Enright AJ, O'Carroll D. mRNA 3' uridylation and poly(A) tail length sculpt the mammalian maternal transcriptome. Nature. 2017 Aug 9. doi: 10.1038/nature23318.
New and noted
- Prof Kamil Kranc, Barts Cancer Institute, London.
- Dr Anton Enright, EMBL European Bioinformatics Institute, Cambridge
- Dr Vladimir Benes, EMBL, Heidelberg, Germany.
- Dr Tania Auchynnikava, Wellcome Centre for Cell Biology, University of Edinburgh, UK.
- Prof David Tollervey, Wellcome Centre for Cell Biology, University of Edinburgh, UK.
- Prof Robin Alshire, Wellcome Centre for Cell Biology, Unviersity of Edinburgh, UK.
- Prof Juri Rappsilber, Wellcome Centre fro Cell Biology, University of Edinburgh, UK.