Project description:Limno-terrestrial tardigrades enter a state called anhydrobiosis when exposed to desiccation, and acquire tolerance against various extreme environments. The anhydrobiotic tardigrade Hypsibius dujardini, is a non-pigmented tardigrade easy to culture and RNAi method have been established, therefore making it a model tardigrade for tardigrade molecular research. Previous genome assemblies of this tardigrade had increased size due to heterozygosity. Here, we have sequenced the genome of H. dujardini using single individual Illumina DNA-Seq data and PacBio long read data, and employed a heterozygosity aware assembly method to assemble a near-complete high quality genome. In order to annotate the genome with gene predictions, we conducted RNA-Sequencing of various stages of developmental, juvenile, adult, and anhydrobiotic stage H. dujardini and Ramazzottius varieornatus, a tardigrade capable of rapid anhydrobiosis entry, and used these data for gene prediction with BRAKER v1.9 or differential gene expression analysis of the active and anhydrobiotic stages.
Project description:Classical embryological studies revealed that during mid-embryogenesis vertebrates show similar morphologies. This âphylotypic stageâ has recently received support from transcriptome analyses, which have also detected similar stages in nematodes and arthropods. A conserved stage in these three phyla has led us to ask if all animals pass through a universal definitive stage as a consequence of ancestral constraints on animal development. Previous work has suggested that HOX genes may comprise such a âzootypicâ stage, however this hypothetical stage has hitherto resisted systematic analysis. We have examined the embryonic development of ten different animals each of a fundamentally different phylum, including a segmented worm, a flatworm, a roundworm, a water bear, a fruitfly, a sea urchin, a zebrafish, a sea anemone, a sponge, and a comb jelly. For each species, we collected the embryonic transcriptomes at ~100 different developmental stages and analyzed their gene expression profiles. We found dynamic gene expression across all of the species that is structured in a stage like manner. Strikingly, we found that animal embryology contains two dominant modules of zygotic expression in terms of their protein domain composition: one involving proliferation, and a second involving differentiation. The switch between these two modules involves induction of the zootype; which in addition to homeobox containing genes, also involves Wnt and Notch signaling as well as forkhead domain transcription factors. Our results provide a systematic characterization of animal universality and identify the points of embryological constraints and flexibility. 126 single embryo samples.
Project description:Classical embryological studies revealed that during mid-embryogenesis vertebrates show similar morphologies. This “phylotypic stage” has recently received support from transcriptome analyses, which have also detected similar stages in nematodes and arthropods. A conserved stage in these three phyla has led us to ask if all animals pass through a universal definitive stage as a consequence of ancestral constraints on animal development. Previous work has suggested that HOX genes may comprise such a ‘zootypic’ stage, however this hypothetical stage has hitherto resisted systematic analysis. We have examined the embryonic development of ten different animals each of a fundamentally different phylum, including a segmented worm, a flatworm, a roundworm, a water bear, a fruitfly, a sea urchin, a zebrafish, a sea anemone, a sponge, and a comb jelly. For each species, we collected the embryonic transcriptomes at ~100 different developmental stages and analyzed their gene expression profiles. We found dynamic gene expression across all of the species that is structured in a stage like manner. Strikingly, we found that animal embryology contains two dominant modules of zygotic expression in terms of their protein domain composition: one involving proliferation, and a second involving differentiation. The switch between these two modules involves induction of the zootype; which in addition to homeobox containing genes, also involves Wnt and Notch signaling as well as forkhead domain transcription factors. Our results provide a systematic characterization of animal universality and identify the points of embryological constraints and flexibility.
Project description:Tardigrades are ubiquitous microscopic animals that play an important role in the study of metazoan phylogeny. Most terrestrial tardigrades can withstand extreme environments by entering an ametabolic desiccated state termed anhydrobiosis. Due to their small size and the non-axenic nature of laboratory cultures, molecular studies of tardigrades are prone to contamination. To minimize the possibility of microbial contaminations and to obtain high-quality genomic information, we have developed an ultra-low input library sequencing protocol to enable the genome sequencing of a single tardigrade Hypsibius dujardini individual. Here, we describe the details of our sequencing data and the ultra-low input library preparation methodologies.
Project description:Tardigrada, a phylum of meiofaunal organisms, have been at the center of discussions of the evolution of Metazoa, the biology of survival in extreme environments, and the role of horizontal gene transfer in animal evolution. Tardigrada are placed as sisters to Arthropoda and Onychophora (velvet worms) in the superphylum Panarthropoda by morphological analyses, but many molecular phylogenies fail to recover this relationship. This tension between molecular and morphological understanding may be very revealing of the mode and patterns of evolution of major groups. Limnoterrestrial tardigrades display extreme cryptobiotic abilities, including anhydrobiosis and cryobiosis, as do bdelloid rotifers, nematodes, and other animals of the water film. These extremophile behaviors challenge understanding of normal, aqueous physiology: how does a multicellular organism avoid lethal cellular collapse in the absence of liquid water? Meiofaunal species have been reported to have elevated levels of horizontal gene transfer (HGT) events, but how important this is in evolution, and particularly in the evolution of extremophile physiology, is unclear. To address these questions, we resequenced and reassembled the genome of H. dujardini, a limnoterrestrial tardigrade that can undergo anhydrobiosis only after extensive pre-exposure to drying conditions, and compared it to the genome of R. varieornatus, a related species with tolerance to rapid desiccation. The 2 species had contrasting gene expression responses to anhydrobiosis, with major transcriptional change in H. dujardini but limited regulation in R. varieornatus. We identified few horizontally transferred genes, but some of these were shown to be involved in entry into anhydrobiosis. Whole-genome molecular phylogenies supported a Tardigrada+Nematoda relationship over Tardigrada+Arthropoda, but rare genomic changes tended to support Tardigrada+Arthropoda.