Project description:DNA methylation (5mC) is an epigenetic mark that plays a critical role in defining cell fate. Following fertilisation, DNA methylation inherited from gametes must be reprogrammed to establish totipotency and enable the parental-to-zygotic transition. To accomplish this, non-mammalian vertebrates such as zebrafish and medaka subtly reprogram maternal 5mC profiles while maintaining high methylation levels throughout embryogenesis. In contrast, eutherian mammals such as mouse and human undergo global 5mC erasure in both embryonic and extraembryonic lineages. However, while embryonic 5mC is rapidly re-established to high levels upon implantation, the trophectoderm, which gives rise to the placenta, displays sustained and conserved DNA hypomethylation, suggesting that this drastic 5mC erasure may be functionally linked to complex placentation in mammals. To clarify whether extensive post-fertilisation 5mC erasure co-evolved with placentation, we explored embryonic methylome dynamics in another lineage of placental mammals, the marsupials. To address this, we produced detailed DNA methylation maps of embryonic development for an Australian marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata), using enzymatic-methyl sequencing (Vaisvila et al Genome Res 2021).
Project description:DNA methylation (5mC) is an epigenetic mark that plays a critical role in defining cell fate. Following fertilisation, DNA methylation inherited from gametes must be reprogrammed to establish totipotency and enable the parental-to-zygotic transition. To accomplish this, non-mammalian vertebrates such as zebrafish and medaka subtly reprogram maternal 5mC profiles while maintaining high methylation levels throughout embryogenesis. In contrast, eutherian mammals such as mouse and human undergo global 5mC erasure in both embryonic and extraembryonic lineages. However, while embryonic 5mC is rapidly re-established to high levels upon implantation, the trophectoderm, which gives rise to the placenta, displays sustained and conserved DNA hypomethylation, suggesting that this drastic 5mC erasure may be functionally linked to complex placentation in mammals. To clarify whether extensive post-fertilisation 5mC erasure co-evolved with placentation, we explored embryonic methylome dynamics in another lineage of placental mammals, the marsupials. To address this, we produced single-cell DNA methylation maps of the bilaminar blastocyst for an Australian marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata).
Project description:The six-layered neocortex is exclusively present in mammals and mediates sensory-motor and higher-order functions. Key differences in this structure and its connections exist between the main mammalian groups: eutherians and marsupials, however, the molecular changes that underlie these known morphological differences remain unknown. This question is particularly difficult to address because small and transient changes in gene expression during development may be crucial to brain formation, which would not be detectable in adult transcriptomic analyses. To address this question of the developmental origin of changes in the evolution of the mammalian neocortex, we performed transcriptomic analysis on the marsupial fat-tailed dunnart (Sminthopsis crassicaudata) at postnatal ages P12 and P20 corresponding to the generation of infragranular (layers 5/6) and supragranular (layers 2/3) neurons, respectively. We assembled a de novo transcriptome of the neocortex of fat-tailed dunnarts using RNA-seq data from all samples, then differential gene expression analysis performed across the two ages. Additional cross-species analysis was performed against existing mouse neocortical datasets in the NCBI Sequence Read Archive at equivalent developmental ages embryonic (E) day 12.5 (SRR1509162, SRR1509163, SRR1509164) and E16 (SRR5755669, SRR5755670, SRR5755671, SRR5755672). We identified 12,632 protein-coding transcripts orthologous to mouse RNA reference sequences (Refseq) in the dunnart neocortical transciptome. The results also revealed divergences in gene sets known to be enriched in different neuronal populations, revealing a more advanced stage of maturation in the marsupial neocortex at the period of infragranular birth compared to the eutherian mouse.
