Resumen de The role of alternative splicing during mammalian pre-implantation development
The transition from maternal to embryonic control is a crucial time in an organism’s life cycle, with an overhaul of the epigenetic marks, targeted mRNA degradation and the initiation of transcription. In this thesis, we provide the first detailed analysis of the splicing changes that occur during the first few days of a growing mammalian embryo.
Using RNA-Seq from human, mouse and cow from multiple time points representing the transition from the oocyte to blastocyst, we identified thousands of exon-skipping events with dynamic temporal regulation, most of which change at the stage of genome activation. Particularly, we found many changes that led to disruptive or non-canonical isoforms, generally through temporary skipping of constitutive exons. These exon-skipping events were in genes enriched for DNA damage responses in the three species, which may explain reports that particular DNA repair pathways are weaker around genome activation. Analysis of RNA binding protein knockdowns led us to discover a core set of proteins that may be responsible for the inclusion of the skipped exons (including Snrpb and Snrpd2). Microinjection of Snrpb/d2 mRNA into mouse zygotes reduced the levels of temporary exon skipping at genome activation, leading to an increase in the levels of etoposide-induced DNA damage response. This suggests that the low levels of maternal Snrpb/d2 may be responsible for a reduced splicing-mediated in DNA repair at genome activation.
In addition, we document the extent of alternative splicing conservation among human, cow and mouse early embryogenesis, showing that exons with conserved developmental regulation are enriched in core developmental pathways, such as the Wnt pathway, Hippo signalling and chromatin modifications. Finally, we report a set of "pan-pluripotent" exons whose regulation is shared among all pre-implantation stages as well as pluripotent cell types, and is distinct from that of differentiated cell and tissue types.
