Project description:East African cichlid fishes have radiated in an explosive fashion. The (epi)genetic basis for the abundant phenotypic diversity of these fishes remains largely unknown. As transposable elements (TEs) contribute extensively to genome evolution, we reasoned that TEs may have fuelled cichlid radiations. While TE-derived genetic and epigenetic variability has been associated with phenotypic traits, TE expression and epigenetic silencing remain unexplored in cichlids. Here, we profiled TE expression in African cichlids, and describe dynamic expression patterns during embryogenesis and according to sex. Most TE silencing factors are conserved and expressed in cichlids. We describe an expansion of two truncated Piwil1 genes in Lake Malawi/Nyasa cichlids, encoding a Piwi domain with catalytic potential. To further dissect epigenetic silencing of TEs, we focused on small RNA-driven epigenetic silencing. We detect a small RNA population in gonads consistent with an active Piwi-interacting RNA (piRNA) pathway targeting TEs. We uncover fluid genomic origins of piRNAs in closely related cichlid species. This, along with signatures of positive selection in piRNA pathway factors, points towards fast co-evolution of TEs and the piRNA pathway. Our study is the first step to understand the contribution of ongoing TE-host arms races to the cichlid radiations in Africa.
Project description:East African cichlid fishes have diversified in an explosive fashion, but the (epi)genetic basis of the phenotypic diversity of these fishes remains largely unknown. Although transposable elements (TEs) have been associated with phenotypic variation in cichlids, little is known about their transcriptional activity and epigenetic silencing. Here, we describe dynamic patterns of TE expression in African cichlid gonads and during early development. Orthology inference revealed an expansion of piwil1 genes in Lake Malawi cichlids, likely driven by PiggyBac TEs. The expanded piwil1 copies have signatures of positive selection and retain amino acid residues essential for catalytic activity. Furthermore, the gonads of African cichlids express a Piwi-interacting RNA (piRNA) pathway that target TEs. We define the genomic sites of piRNA production in African cichlids and find divergence in closely related species, in line with fast evolution of piRNA-producing loci. Our findings suggest dynamic co-evolution of TEs and host silencing pathways in the African cichlid radiations. We propose that this co-evolution has contributed to cichlid genomic diversity.
Project description:East African cichlid fishes have diversified in an explosive fashion, but the (epi)genetic basis of the phenotypic diversity of these fishes remains largely unknown. Although transposable elements (TEs) have been associated with phenotypic variation in cichlids, little is known about their transcriptional activity and epigenetic silencing. Here, we describe dynamic patterns of TE expression in African cichlid gonads and during early development. Orthology inference revealed an expansion of piwil1 genes in Lake Malawi cichlids, likely driven by PiggyBac TEs. The expanded piwil1 copies have signatures of positive selection and retain amino acid residues essential for catalytic activity. Furthermore, the gonads of African cichlids express a Piwi-interacting RNA (piRNA) pathway that target TEs. We define the genomic sites of piRNA production in African cichlids and find divergence in closely related species, in line with fast evolution of piRNA-producing loci. Our findings suggest dynamic co-evolution of TEs and host silencing pathways in the African cichlid radiations. We propose that this co-evolution has contributed to cichlid genomic diversity.
Project description:Adaptations relating to how nutrients are acquired and processed play a central role in the colonization of novel ecological niches and, therefore, in organismal diversification. While the evolution of feeding structures has been studied extensively in this context, the nature of dietary adaptations in the digestive tract remains largely unexplored. Here, we investigate the cellular and molecular basis of dietary adaptations in the massive radiation of cichlid fishes in Lake Tanganyika using comprehensive single-cell transcriptomic data derived from the intestines of 25 African cichlid species with distinct habitats and diets. We show that, at the cellular level, dietary adaptations are primarily driven by anterior enterocytes, and that both the abundance and gene expression profiles of these cells have evolved in response to dietary specializations. These dietary adaptations in enterocytes are driven by rapidly evolving cell population-specific genes, suggesting that alterations in gene regulatory programmes and cell-state specification promote ecological diversification.
Project description:Adaptations relating to how nutrients are acquired and processed play a central role in the colonization of novel ecological niches and, therefore, in organismal diversification. While the evolution of feeding structures has been studied extensively in this context, the nature of dietary adaptations in the digestive tract remains largely unexplored. Here, we investigate the cellular and molecular basis of dietary adaptations in the massive radiation of cichlid fishes in Lake Tanganyika using comprehensive single-cell transcriptomic data derived from the intestines of 25 African cichlid species with distinct habitats and diets. We show that, at the cellular level, dietary adaptations are primarily driven by anterior enterocytes, and that both the abundance and gene expression profiles of these cells have evolved in response to dietary specializations. These dietary adaptations in enterocytes are driven by rapidly evolving cell population-specific genes, suggesting that alterations in gene regulatory programmes and cell-state specification promote ecological diversification.
Project description:Whole-genome methylomes and total transcriptomes for muscle and liver tissues of Lake Malawi cichlid species characterised in the context of phenotypic diversification.
Project description:We have investigated whether we can understand the speciation of the cichlid fishes using proteogenomic approach. We have deposited both the RNA-Seq data and Mass Spectra data here. Details of methods carried out can be found in the Methods Section of the paper.
Project description:Polymorphisms have fascinated biologists for a long time, but their genetic underpinnings often remain elusive. Here, we aim to uncover the genetic basis of the gold/dark polymorphism that is eponymous of Midas cichlid fish (Amphilophus spp.) adaptive radiations in Nicaraguan crater lakes. While most Midas cichlids are of the melanic "dark morph", about 10% of individuals lose their melanic pigmentation during their ontogeny and transition into a conspicuous "gold morph". Using a new haplotype-resolved long-read assembly we discover an 8.2 kb, transposon-derived inverted repeat in an intron of an undescribed gene, which we term goldentouch in reference to the Greek myth of King Midas. The gene goldentouch is differentially expressed between morphs, presumably due to structural implications of inverted repeats in both DNA and/or RNA (cruciform and hairpin formation). The near-perfect association of the insertion with the phenotype across independent populations suggests that it likely underlies this trans-specific, stable polymorphism.
Project description:We examined the methylation state of upstream intergenic regions associated with two aromatase genes (cyp19a1A and cyp19a1B) in P. pulcher, a cichlid fish with pH-based sex and male morph determination. Methylation levels in fry head and trunk and adult brain and gonad samples were assessed with a bisulfite amplicon sequencing assay and sequence data was processed through two pipelines to determine % methylation of individual CpG sites and abundance of specific patterns of methylated and unmethylated CpGs (i.e., epialleles).