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: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. 132 single embryo samples.
Project description:Background: The development of planarians is unique among Spiralians. Instead of the stereotypical spiral cleavage, planarians exhibit a disperse cleavage. There is no apparent gastrulation, and the morphogenesis of the yolk-feeding embryo remains a mystery. In this study, we examine the subcellular localization of βcatenin-1 and the transcriptomic profile during the early embryonic development of Schmidtea polychroa to shed light on these early events. Results: We find that the first nuclearization of βcatenin-1 occurs in yolk cells surrounding the embryonic syncytium. By 24 hours post deposition, βcatenin-1 starts to be nuclearized in blastomeres, coinciding with the activation of signaling and cell motility genes. During morphogenesis of the yolk-feeding embryo, βcatenin-1 is first nuclearized at one pole (gut and pharynx progenitors) and in epidermal progenitors, and afterwards in the embryonic pharynx. At this stage, genes involved in a first morphogenetic event are turned on. Following the yolk ingestion by the embryo, a dramatic transcriptomic shift occurs that coincides with the activation of genes related to cell proliferation. Finally, between 5-7 days post deposition βcatenin-1 is massively nuclearized, and genes involved in the morphogenesis and patterning of the adult tissues get activated. Conclusions: Our findings provide new insights into the early developmental events of Schmidtea polychroa, including cleavage, the involvement of βcatenin-1 in the formation of the embryonic tissues and the morphogenesis of two distinct body plans. These findings are significant to understand the evolution of the peculiar mode of planarian development.