An ancient chordin-like gene in organizer formation of Hydra

Abstract

Signaling centers or organizers play a key role in axial patterning processes in animal embryogenesis. The function of most vertebrate organizers involves the activity of secreted antagonists of bone morphogenetic proteins (BMPs) such as Chordin or Noggin. Although BMP homologs have been isolated from many phyla, the evolutionary origin of the antagonistic BMP/Chordin system in organizer signaling is presently unknown. Here we describe a Chordin-like molecule (HyChdl) from Hydra that inhibits BMP activity in zebrafish embryos and acts in Hydra axis formation when new head organizers are formed during budding and regeneration. hychdl transcripts are also up-regulated in the head regeneration-deficient mutant strain reg-16. Accordingly, HyChdl has a function in organizer formation, but not in head differentiation. Our data indicate that the BMP/Chordin antagonism is a basic property of metazoan signaling centers that was invented in early metazoan evolution to set up axial polarity.axis formation ͉ bone morphogenetic protein/Chordin ͉ Cnidaria ͉ regeneration ͉ signaling L ocalized signaling centers or organizers are widely used for the patterning of embryos or tissues during animal development. In general, organizers are able to generate polarity in surrounding tissue and to induce specific cell fates and cell behavior (1). One of the best-characterized examples is the amphibian embryonic organizer known as the Spemann-Mangold organizer (2). This organizer, localized at the dorsal blastopore lip, is able to induce the formation of a second body axis upon transplantation to the ventral side of a host embryo. The inductive capacity of the organizer is demonstrated by its ability to recruit host tissue into the second axis (3, 4). Functionally equivalent embryonic organizers are found in most vertebrates, including the node in amniotes and the embryonic shield in teleosts (5). The evolutionary origin of the embryonic organizer is unclear at present, but it was proposed that it is a vertebrate-specific invention (6).There is evidence that the embryonic organizer is much older than commonly assumed. In the freshwater polyp Hydra, a member of the Ͼ500-million-year-old phylum Cnidaria, Browne (7) demonstrated the existence of an organizer-like activity already in 1909: Transplantation of a hypostome into the body column of a labeled host led to the formation of a second body axis including hostderived tissue (7,8). The hypostome is the oral end of a cnidarian body axis and corresponds to the blastopore of a gastrula. However, whether the head organizer of Hydra represents the evolutionary origin of the vertebrate embryonic organizer or whether they arose independently is currently not known.On the molecular level, Wnt/␤-catenin signaling and the inhibition of bone morphogenetic protein (BMP) signaling by secreted antagonist such as Chordin and Noggin play a pivotal role in the establishment of the Spemann-Mangold organizer in Xenopus and the shield in zebrafish (4, 9, 10) as well as in the establishment of axial polarity...

Finding partners: How BMPs select their targets

“…1). Ligands and downstream components of the signaling cascade have been found both in Cnidaria (metazoans that include Hydra, the anemone Nematostella, jellyfish, and corals), and also in the sponges, the most ancient metazoan clade (Suga et al, 1999;Hayward et al, 2002;Finnerty et al, 2004;Reinhardt et al, 2004;Rentzsch et al, 2006Rentzsch et al, , 2007Reber-Mü ller et al, 2006;Nichols et al, 2006;Adamska et al, 2007;Zoccola et al, 2009). Thus far, no TGF␤ superfamily signaling components have been reported in taxa "basal to" the sponges, including the single-celled choanoflagellates, fungi, or protozoa (Nichols et al, 2006;King et al, 2008).…”

On growth and form: a Cartesian coordinate system of Wnt and BMP signaling specifies bilaterian body axes

“…In summary, as for the Wnt-Dkk axis, the occurrence of a BMPChordin axis is probably not due to evolutionary convergence, but instead represents an ancient, conserved molecular module for bilaterian secondary axis specification (Martindale, 2005;Gerhart, 2006;Rentzsch et al, 2007;Mizutani and Bier, 2008). The fact that the well-characterized nematode C. elegans apparently does without a BMP system for axial patterning is probably due to a secondary loss of this feature, which would be consistent with the poor conservation of the C. elegans genome (compared with, for example, the genome of the more primitive sea anemone Nematostella) and with C. elegans having lost genes, introns and gene linkages (Putnam et al, 2007).…”

An organizing region in metamorphosing hydrozoan planula larvae - stimulation of axis formation in both larval and in adult tissue

“…Organizing regions during gastrulation have been found in a wide variety of animal species (Lemaire and Kodjabachian 1996;Niehrs 2001Niehrs , 2004Robb and Tam 2004 for review). An organizing centre in the head has been found even earlier in the diploblast freshwater polyp hydra, a lower phylum Cnidaria (Browne 1908, Hobmayer et al 2000, Rentzsch et al 2007). This reference cnidarian species exhibits an organizing center in the hypostome.…”