Stem cells are pivotal for development and tissue homeostasis of multicellular animals, and the quest for a gene toolkit associated with the emergence of stem cells in a common ancestor of all metazoans remains a major challenge for evolutionary biology. We reconstructed the conserved gene repertoire of animal stem cells by transcriptomic profiling of totipotent archeocytes in the demosponge Ephydatia fluviatilis and by tracing shared molecular signatures with flatworm and Hydra stem cells. Phylostratigraphy analyses indicated that most of these stem-cell genes predate animal origin, with only few metazoan innovations, notably including several partners of the Piwi machinery known to promote genome stability. The ancestral stem-cell transcriptome is strikingly poor in transcription factors. Instead, it is rich in RNA regulatory actors, including components of the "germ-line multipotency program" and many RNA-binding proteins known as critical regulators of mammalian embryonic stem cells.Porifera | stem cells | evolution | uPriSCs | RNA binding
Development of gut microflora in abalone Haliotis discus hannai cultured at two abalone farms in Japan was similar: (i) gut microflora of juvenile abalones fed on microalgae matched microflora cultured from seawater; and (ii) gut microflora changed coincident with the abalone switching food sources from microalgae to algal pellets. After abalone reached 4 months of age, the gut microflora was replaced by algal polysaccharide-degrading bacteria, which were almost entirely characterized as facultative anaerobes. Dominant species were alginolytic, non-motile fermenters (NMF) and Vibrio spp. The gut microflora seemed to be stable in abalone older than 1 year, with NMF bacteria dominating. Ninety-six percent of the NMF isolates were identified as Vibrio halioticoli by species-specific identification using the colony hybridization method. These results show that abalone H. discus hannai has a unique developmental process in which gut microflora shifts to alginate-degrading bacteria, especially V. halioticoli .
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