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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.07.029 Byline: Jens H. Fritzenwanker (a), Grigory Genikhovich (a), Yulia Kraus (b), Ulrich Technau (a) Keywords: Nematostella; Cnidaria; Early embryonic development; Embryonic axis; Polarity; Cytoplasmic determinants; Organizer Abstract: We investigated the early development of the sea anemone Nematostella vectensis, an emerging model system of the Cnidaria. Early cleavage stages are characterized by substantial variability from embryo to embryo, yet invariably lead to the formation of a coeloblastula. The coeloblastula undergoes a series of unusual broad invaginations-evaginations which can be blocked by cell cycle inhibitors suggesting a causal link of the invagination cycles to the synchronized cell divisions. Blastula invagination cycles stop as cell divisions become asynchronous. Marking experiments show a clear correspondence of the animal-vegetal axis of the egg to the oral-aboral axis of the embryo. The animal pole gives rise to the concave side of the blastula and later to the blastopore of the gastrula, and hence the oral pole of the future polyp. Asymmetric distribution of granules in the unfertilized egg suggest an animal-vegetal asymmetry in the egg in addition to the localized position of the pronucleus. To determine whether this asymmetry reflects asymmetrically distributed determinants along the animal-vegetal axis, we carried out blastomere isolations and embryonic divisions at various stages. Our data strongly indicate that normal primary polyps develop only if cellular material from the animal hemisphere is included, whereas the vegetal hemisphere alone is incapable to differentiate an oral pole. Molecular marker analysis suggests that also the correct patterning of the aboral pole depends on signals from the oral half. This suggests that in Nematostella embryos the animal hemisphere contains organizing activity to form a normal polyp. Author Affiliation: (a) Sars International Centre for Marine Molecular Biology, University of Bergen, ThormA[cedilla]hlensgt. 55, N-5008 Bergen, Norway (b) Department of Evolutionary Biology, Biological Faculty, Lomonosov Moscow State University, 119992, Moscow, Russia Article History: Received 18 April 2007; Revised 22 July 2007; Accepted 23 July 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.10.028 Byline: Grigory Genikhovich, Ulrich Kurn, Georg Hemmrich, Thomas C.G. Bosch Keywords: Embryo; Subtractive hybridization; Polycomb group genes; Methylation; Interstitial stem cells; Spermatogenesis Abstract: Hydra's remarkable capacity to regenerate, to proliferate asexually by budding, and to form a pattern de novo from aggregates allows studying complex cellular and molecular processes typical for embryonic development. The underlying assumption is that patterning in adult hydra tissue relies on factors and genes which are active also during early embryogenesis. Previously, we reported that in Hydra the timing of expression of conserved regulatory genes, known to be involved in adult patterning, differs greatly in adults and embryos (Frobius, A.C., Genikhovich, G., Kurn, U., Anton-Erxleben, F. and Bosch, T.C.G., 2003. Expression of developmental genes during early embryogenesis of Hydra. Dev. Genes Evol. 213, 445-455). Here, we describe an unbiased screening strategy to identify genes that are relevant to Hydra vulgaris embryogenesis. The approach yielded two sets of differentially expressed genes: one set was expressed exclusively or nearly exclusively in the embryos, while the second set was upregulated in embryos in comparison to adult polyps. Many of the genes identified in hydra embryos had no matches in the database. Among the conserved genes upregulated in embryos is the Hydra orthologue of Embryonic Ectoderm Development (HyEED). The expression pattern of HyEED in developing embryos suggests that interstitial stem cells in Hydra originate in the endoderm. Importantly, the observations uncover previously unknown differences in genes expressed by embryos and polyps and indicate that not only the timing of expression of developmental genes but also the genetic context is different in Hydra embryos compared to adults. Author Affiliation: Zoological Institute, Christian-Albrechts University of Kiel, Am Botanischen Garten 1-9, 24118 Kiel, Germany Article History: Received 13 June 2005; Revised 4 October 2005; Accepted 18 October 2005

A study investigating the types of genes responsible for regeneration and asexual budding in Hydra is presented. Evidence was obtained by embryological research.