Project description:BackgroundEnhancers play an important role in morphological evolution and speciation by controlling the spatiotemporal expression of genes. Previous efforts to understand the evolution of enhancers in primates have typically studied many enhancers at low resolution, or single enhancers at high resolution. Although comparative genomic studies reveal large-scale turnover of enhancers, a specific understanding of the molecular steps by which mammalian or primate enhancers evolve remains elusive.ResultsWe identified candidate hominoid-specific liver enhancers from H3K27ac ChIP-seq data. After locating orthologs in 11 primates spanning around 40 million years, we synthesized all orthologs as well as computational reconstructions of 9 ancestral sequences for 348 active tiles of 233 putative enhancers. We concurrently tested all sequences for regulatory activity with STARR-seq in HepG2 cells. We observe groups of enhancer tiles with coherent trajectories, most of which can be potentially explained by a single gain or loss-of-activity event per tile. We quantify the correlation between the number of mutations along a branch and the magnitude of change in functional activity. Finally, we identify 84 mutations that correlate with functional changes; these are enriched for cytosine deamination events within CpGs.ConclusionsWe characterized the evolutionary-functional trajectories of hundreds of liver enhancers throughout the primate phylogeny. We observe subsets of regulatory sequences that appear to have gained or lost activity. We use these data to quantify the relationship between sequence and functional divergence, and to identify CpG deamination as a potentially important force in driving changes in enhancer activity during primate evolution.
Project description:STARR-seq assay tiling across putative hominoid-specific enhancers and for orthologs from 11 primates and 9 ancestral reconstructions of each active tile
Project description:Long noncoding RNA sequences evolve relatively rapidly, but it is unclear whether this is due to relaxed constraint or accelerated evolution. Here, we trace the recent evolutionary history of human lncRNAs, using genomes of multiple individuals from all great ape species to map fixed lineage-specific nucleotide variants. We find that the lower conservation of lncRNAs compared to protein coding genes partially arises from lncRNA’s more recent evolutionary origin. We identify more than one hundred lncRNAs that show some evidence of accelerated evolution in at least one primate species, including 17 in human. Several of these display transcriptional regulatory activity in an RNA-specific reporter assay. By experimentally reconstructing the ancestral lncRNA sequence, we find that this activity has been altered by human-specific nucleotide substitutions. Functional analysis of accelerated lncRNAs with specific expression in blood suggests lncRNAs have participated in adaptive regulatory changes in the immune system during recent human evolution. Together our results provide evidence that accelerated evolution of lncRNAs may have contributed, through regulatory changes, to human-specific phenotypes.
Project description:Phenotypic differences between closely related species are thought to arise primarily from changes in gene expression due to mutations in cis-regulatory sequences (enhancers). However, it has remained unclear, how frequently mutations alter enhancer activity or create functional enhancers de novo. Here, we use STARR-seq, a recently developed quantitative enhancer assay, to determine genome-wide enhancer activity profiles for five Drosophila species in the constant trans-regulatory environment of D. melanogaster S2 cells. We find that the function of a large fraction of D. melanogaster enhancers is conserved in their orthologous sequences due to selection and stabilizing turnover of transcription factor motifs. Moreover, hundreds of enhancers have been gained since the D. melanogaster M-bM-^@M-^S D. yakuba split about 11 million years ago without apparent adaptive selection and can contribute to gene expression changes in vivo. Our finding that enhancer activity is often deeply conserved and frequently gained provides important functional insights into regulatory evolution. STARR-seq was performed in S2 cells with paired-end sequencing in two replicates and respective inputs using genomic DNA from different Drosophila species. RNA-seq was performed in a non-stranded manner without replicates for two Drosophila species.
Project description:Many transposable elements (TEs) contain transcription factor binding sites and are implicated as potential regulatory elements. However, TEs are rarely functionally tested for regulatory activity, which in turn limits our understanding of how TE regulatory activity has evolved. We systematically tested the human LTR18A subfamily for regulatory activity using massively parallel reporter assay (MPRA) and found AP-1 and C/EBP-related binding motifs as drivers of enhancer activity. Functional analysis of evolutionarily reconstructed ancestral sequences revealed that LTR18A elements have generally lost regulatory activity over time through sequence changes, with the largest effects occurring due to mutations in the AP-1 and C/EBP motifs. We observed that the two motifs are conserved at higher rates than expected based on neutral evolution. Finally, we identified LTR18A elements as potential enhancers in the human genome, primarily in epithelial cells. Together, our results provide a model for the origin, evolution, and co-option of TE-derived regulatory elements.
Project description:This SuperSeries is composed of the following subset Series: GSE40684: Foxp3 exploits a preexistent enhancer landscape for regulatory T cell lineage specification [ChIP-Seq] GSE40685: Foxp3 exploits a preexistent enhancer landscape for regulatory T cell lineage specification [Expression] Refer to individual Series
Project description:Many endogenous retroviruses (ERVs) in the human genome are primate-specific and contribute novel cis-regulatory elements and transcripts. Classification and annotation of ERVs, which are flanked by long terminal repeats (LTRs) containing sequences that control their transcriptional activity, is important to better understand their evolution and potential roles in the host. Here, we observed that many of the currently annotated LTR subfamilies spreading in the primate lineage have subsets of instances that appear to be misclassified. Focusing on the evolutionary young MER11A/B/C subfamilies, we performed a phylogenetic analysis and relied on cross-species conservation to reveal the presence of 4 phyletic groups, suggesting a new annotation for 412 (19.8%) of the MER11 instances. Next, we showed that the epigenetic heterogeneity observed within the MER11A/B/C subfamilies was better explained in the context of these new phyletic groups. Using a massively parallel reporter assay (MPRA), we also demonstrated the regulatory potential of the four phyletic groups and identified motifs that were associated with their differential activities. The MPRA combined with the use of phyletic groups across primates revealed an apes-specific gain of SOX related motifs through a single-nucleotide deletion. Finally, we applied a similar approach across all 53 simian-specific LTR subfamilies and determined the presence of 75 phyletic groups. We found that 3,807 (30.0%) instances from 26 of these LTR subfamilies changed annotation and could be characterized into one of these novel phyletic groups, many of which with a distinct epigenetic profile. This refined annotation of simian-specific LTRs could improve our understanding of the evolution of ERVs in primate genomes and reveal functional signals that would have been missed otherwise.
Project description:Sequence changes in regulatory regions have often been invoked to explain phenotypic divergence among species, but molecular examples of this have been difficult to obtain.In this study we identified an anthropoid primate-specific sequence element that contributed to the regulatory evolution of the low-density lipoprotein receptor. Using a combination of close and distant species genomic sequence comparisons coupled with in vivo and in vitro studies, we found that a functional cholesterol-sensing sequence motif arose and was fixed within a pre-existing enhancer in the common ancestor of anthropoid primates.Our study demonstrates one molecular mechanism by which ancestral mammalian regulatory elements can evolve to perform new functions in the primate lineage leading to human.
Project description:Transcriptional enhancers are the primary determinants of tissue-specific gene expression and influence a variety of cellular phenotypes. The regulatory components controlling enhancer assembly and turnover during stem cell development remain largely unknown. Here we compared the similarities and differences in enhancer landscape, transcriptional factor (TF) occupancy and transcriptomic changes in human primary fetal and adult hematopoietic stem/progenitor cells (HSPCs) and committed erythroid progenitors. We find that enhancers are modulated dynamically and extensively, and direct lineage and developmental stage-specific transcriptional programs. GATA2-to-GATA1 switch is prevalent within transcriptionally dynamic enhancers and drives enhancer commissioning. Further examination of lineage-specific enhancers identified TFs and their combinatorial patterns with known and unknown roles as putative drivers of enhancer turnover during differentiation. Importantly, by site-directed loss-of-function analysis of individual lineage-selective enhancers within the SLC25A37 super-enhancer using CRISPR/Cas9-mediated genomic editing, we uncover unexpected functional hierarchy of constituent enhancers within the super-enhancer cluster. Despite the indistinguishable chromatin features between the GATA switch enhancers at the GATA2 gene, we reveal through genomic editing the functional diversity of GATA switch enhancers in which enhancers with opposing functions cooperate to coordinate gene expression during development. Thus, genome-wide enhancer profiling coupled with in-depth enhancer editing in situ provide critical insights into the functional hierarchy and complexity of enhancers during stem cell development.