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: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:We use the continuously replacing dentition of Lake Malawi cichlid fishes to understand de-novo tooth replacement in adult vertebrates. In this system, each tooth is replaced in a one-for-one fashion every ~50 days. Here, we explore the source of epithelial stem cells for tooth replacement.
Project description:Inheritance and plasticity of epigenetic divergence characterise early stages of speciation in an incipient cichlid species of an African crater lake.
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:Throughout the animal kingdom, we know many examples of mating system evolution that exemplify adaptive responses to changes in the environment, yet our understanding of the accompanying neural and molecular mechanisms that give rise to such behavioral changes remains understudied. In the present study we aimed to define the molecular basis of interspecific variation in social organization in Ectodini cichlids from Lake Tanganyika. We selected four closely related species that represent two independent evolutions of monogamy: the polygynous Xenotilapia ochrogenys, the monogamous Xenotilapia flavipinnis, the polygynous Microdontochromis tenuidentata and the monogamous Asprotilapia leptura. Using a single cichlid microarray platform, we conducted a total of 28 direct comparisons for neural gene expression level among males and 26 among females of four species that represent 2 independent evolutions of monogamy. Our results indicate the gene expression profiles display remarkable plasticity across different time scales because we find differences associated with sex, mating system, and lineage.