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The cnidarian freshwater polyp Hydra sp. exhibits an unparalleled regeneration capacity in the animal kingdom. Using an integrative transcriptomic and stable isotope labeling by amino acids in cell culture proteomic/phosphoproteomic approach, we studied stem cell-based regeneration in Hydra polyps. As major contributors to head regeneration, we identified diverse signaling pathways adopted for the regeneration response as well as enriched novel genes. Our global analysis reveals two distinct molecular cascades: an early injury response and a subsequent, signaling driven patterning of the regenerating tissue. A key factor of the initial injury response is a general stabilization of proteins and a net upregulation of transcripts, which is followed by a subsequent activation cascade of signaling molecules including Wnts and transforming growth factor (TGF) beta-related factors. We observed moderate overlap between the factors contributing to proteomic and transcriptomic responses suggesting a decoupled regulation between the transcriptional and translational levels. Our data also indicate that interstitial stem cells and their derivatives (e.g., neurons) have no major role in Hydra head regeneration. Remarkably, we found an enrichment of evolutionarily more recent genes in the early regeneration response, whereas conserved genes are more enriched in the late phase. In addition, genes specific to the early injury response were enriched in transposon insertions. Genetic dynamicity and taxon-specific factors might therefore play a hitherto underestimated role in Hydra regeneration. [ABSTRACT FROM AUTHOR]

Abstract: Wnt genes and β-Catenin signaling are involved in axial patterning processes in vertebrate embryogenesis in setting up the Spemann–Mangold organizer in amphibian embryos. An organizer with a similar function is present in the hypostome of an adult Hydra polyp. Previously, a Hydra ortholog of Wnt3 (HyWnt3), which is expressed in the hypostome, has been described. Here, ten additional Hydra Wnt genes have been identified. Of these, six (HyWnt1, -7, -9/10a, -9/10c, -11, and -16) are expressed in the adult hypostome. And, as is HyWnt3, these six Wnt genes are also expressed when a new head organizer is formed during head regeneration and bud formation. The kinetics of Wnt gene expressions during head regeneration suggests that a cascade of consecutive Wnt activation accompanies regeneration, and HyWnt3 begins this cascade. Recombinant HyWnt3 protein induced body column tissue to undergo head formation. It also increased the head formation capacity in the head regeneration-deficient mutant strain reg-16 to that of wild-type strains. In addition our data reveal striking similarities in the molecular basis of the organizer in Hydra and axis polarization in chordates (e.g. Spemann''s organizer) as well as it''s role in regeneration suggesting a conserved function of Wnt signaling in setting up this ancient metazoan signaling center. [Copyright &y& Elsevier]