Project description:Bilaterian animals differ from other metazoans in their apparent bilateral symmetry and the development of a third germ layer. Both might have facilitated the evolution of the diverse and complex bilaterian body plans. The first cnidarian genome sequence revealed that despite their morphological simplicity, this sister group to all bilaterians shares an immense genomic complexity with vertebrates. This suggested that it might have been the complexity of gene regulation which increased during the evolution of bilaterians. We compared the gene regulatory landscape of cnidarians and bilaterians. To this end we generated the first genome-wide prediction of gene regulatory elements and profiled five epigenetic marks in a non-bilaterian animal, the cnidarian Nematostella vectensis. We found that the location of chromatin modifications relative to genes and distal enhancers is conserved among eumetazoans. Surprisingly, the genomic landscape of gene regulatory elements is highly similar between Nematostella and bilaterian model organisms. This suggests that complex regulation of developmental gene expression evolved in eumetazoans without a major increase in complexity in bilaterians. ChIP-seq of p300, RNA Pol2, and five histone modifications in Nematostella vectensis.
Project description:Nematocysts are secretory organelles in cnidarians that play important roles in predation, de-fense, locomotion, and host invasion. However, the extent to which nematocysts contribute to adaptation and the mechanisms underlying nematocyst evolution are unclear. Here, we inves-tigated the role of the nematocyst in cnidarian evolution based on 8 nematocyst proteomes and 110 cnidarian transcriptomes/genomes. We detected extensive species-specific adaptative muta-tions in nematocyst proteins (NEMs) and evidence for decentralized evolution, in which most evolutionary events involved non-core NEMs, reflecting the rapid diversification of NEMs in cnidarians. Moreover, there was a 33–55 million year macroevolutionary lag between nematocyst evolution and the main phases of cnidarian diversification, suggesting that the nematocyst can act as a driving force in evolution. Quantitative analysis revealed an excess of adaptive changes in NEMs and enrichment for positively selected conserved NEMs. Together, these findings suggest that nematocyst may be key to the adaptive success of cnidarians and provide a reference for quantitative analyses of the roles of phenotypic novelties in adaptation.
Project description:Bilaterian animals differ from other metazoans in their apparent bilateral symmetry and the development of a third germ layer. Both might have facilitated the evolution of the diverse and complex bilaterian body plans. The first cnidarian genome sequence revealed that despite their morphological simplicity, this sister group to all bilaterians shares an immense genomic complexity with vertebrates. This suggested that it might have been the complexity of gene regulation which increased during the evolution of bilaterians. We compared the gene regulatory landscape of cnidarians and bilaterians. To this end we generated the first genome-wide prediction of gene regulatory elements and profiled five epigenetic marks in a non-bilaterian animal, the cnidarian Nematostella vectensis. We found that the location of chromatin modifications relative to genes and distal enhancers is conserved among eumetazoans. Surprisingly, the genomic landscape of gene regulatory elements is highly similar between Nematostella and bilaterian model organisms. This suggests that complex regulation of developmental gene expression evolved in eumetazoans without a major increase in complexity in bilaterians.
Project description:The evolution of the first body axis in the animal kingdom and an extensive ability to regenerate makes Hydra, a Cnidarian, an excellent model system to understand the underlying epigenetic mechanisms. We identify that SETD8 is critical for regeneration, and H4K20me1 colocalizes with transcriptional activation machinery locally at the β-catenin bound TCF/LEF binding sites on the promoters of head-associated genes, marking an epigenetic activation node. Contrastingly, a global genome-wide analysis of the H4K20me1 occupancy revealed a negative correlation with transcriptional activation. We propose H4K20me1 as a general repressive histone mark in Cnidaria and describe its dichotomous role in transcriptional regulation in Hydra.
Project description:The evolution of the first body axis in the animal kingdom and an extensive ability to regenerate makes Hydra, a Cnidarian, an excellent model system to understand the underlying epigenetic mechanisms. We identify that SETD8 is critical for regeneration, and H4K20me1 colocalizes with transcriptional activation machinery locally at the β-catenin bound TCF/LEF binding sites on the promoters of head-associated genes, marking an epigenetic activation node. Contrastingly, a global genome-wide analysis of the H4K20me1 occupancy revealed a negative correlation with transcriptional activation. We propose H4K20me1 as a general repressive histone mark in Cnidaria and describe its dichotomous role in transcriptional regulation in Hydra.
Project description:Coding and non-coding mutations in DNA contribute significantly to phenotypic variability during evolution. However, less is known about the role of epigenetics in this process. Although previous studies have identified eye development genes associated with the loss of eyes phenotype in the Pachón blind cave morph of the Mexican tetra Astyanax mexicanus1-6, no inactivating mutations have been found in any of these genes2,3,7-10. Here we show that excess DNA methylation-based epigenetic silencing promotes eye degeneration in blind cave Astyanax mexicanus. By performing parallel analyses in Astyanax mexicanus cave and surface morphs and in the zebrafish Danio rerio, we have discovered that DNA methylation mediates eye-specific gene repression and globally regulates early eye development. The most significantly hypermethylated and down-regulated genes in the cave morph are also linked to human eye disorders, suggesting the function of these genes is conserved across the vertebrates. Our results show that changes in DNA methylation-based gene repression can serve as an important molecular mechanism generating phenotypic diversity during development and evolution.
Project description:Understanding how brains evolved is critical to determine the origin(s) of centralized nervous systems. Brains are patterned along their anteroposterior axis by stripes of gene expression that appear to be conserved, suggesting brains are homologous. However, the striped expression is also part of the deeply conserved anteroposterior axial program. An emerging hypothesis is that similarities in brain patterning are convergent, arising through the repeated co-option of axial programs. To resolve whether shared brain neurogenic programs likely reflect convergence or homology, we investigated the evolution of axial programs in neurogenesis. We show that the bilaterian anteroposterior program patterns the nerve net of the cnidarian Nematostella along the oral-aboral axis arguing that anteroposterior programs regionalized developing nervous systems in the cnidarian-bilaterian common ancestor prior to the emergence of brains. This finding rejects shared patterning as sufficient evidence to support brain homology and provides functional support for the plausibility that axial programs could be co-opted if nervous systems centralized in multiple lineages