Project description:We study the genomic and developmental basis of the mammalian gliding membrane, or patagium, an adaptative trait that has repeatedly evolved in different lineages, including in closely related marsupial species. Through comparative genomic analysis of fifteen new marsupial genomes, both from gliding and non-gliding species, we find that the Emx2 locus experienced lineage-specific patterns of accelerated cis-regulatory evolution in gliding species. We confirm our finding via epigenomics, transcriptomics, and in vivo marsupial transgenics.
Project description:Evidence from a few genes of diverse species suggests that marsupial X-chromosome inactivation (XCI) is characterized by exclusive, but leaky, inactivation of the paternally derived X chromosome. To comprehensively study the mechanism of marsupial XCI, we profiled parent-of-origin-specific-allele expression, DNA methylation, and histone modifications in opossum fetal brain and extra-embryonic membranes. The majority (152/176) of X-linked genes exhibited paternally imprinted expression with nearly 100% maternal allele expression, whereas 24 loci (14%) escaped inactivation showing varying levels of biallelic expression. In addition to regulation by the non-coding RSX transcript, strong depletion of H3K27me3 at escaper gene loci indicates that histone states also influence opossum XCI. Notably, the opossum does not show an association between X-linked gene expression and promoter DNA methylation. Our study provides the first comprehensive catalogue of parent-of-origin expression status for X-linked genes in a marsupial and sheds light on the regulation and evolution of imprinted XCI in mammals. Profiling of four histone modifications in embryonic day 13 opossum (Monodelphis domestica) fetal brain by Illumina ChIP-seq
Project description:Marsupials and placental mammals exhibit significant differences in reproductive and life history strategies. Marsupials are born highly underdeveloped after an extremely short period of gestation, leading to prioritization of the development of structures critical for post-birth survival in the pouch. Critically, they must undergo accelerated development of the oro-facial region compared to placentals. Previously we described the accelerated development of the oro-facial region in the carnivorous Australian marsupial, the fat-tailed dunnart Sminthopsis crassicaudata that has one of the shortest gestations of any mammal. By combining genome comparisons of the mouse and dunnart with functional data for the enhancer-associated chromatin modifications, H3K4me3 and H3K27ac, we investigated divergence of craniofacial regulatory landscapes between these species. While genes involved in regulating facial development were largely conserved in mouse and dunnart, the regulatory landscape varied significantly. Additionally, a subset of dunnart-specific enhancers were associated with genes highly expressed only in dunnart relating to cranial neural crest proliferation, embryonic myogenesis and epidermis development. Comparative RNA-seq analyses of facial tissue revealed dunnart-specific expression of genes involved in the development of the mechanosensory system. Accelerated development of the dunnart sensory system likely relates to the sensory cues received by the nasal-oral region during the postnatal journey to the pouch. Together these data suggest that accelerated development in the dunnart can be driven by dunnart-specific enhancer activity. Our study highlights the power of marsupial-placental comparative genomics for understanding the role of enhancers in driving temporal shifts in development.