Hedgehog signaling patterns mesoderm in the sea urchin

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2009.04.018 Byline: Katherine D. Walton (a), Jacob Warner (a), Philip H. Hertzler (b), David R. McClay (a) Keywords: Hedgehog; Patched; Smoothened; Morphogenesis; Endoderm; Mesoderm; Signal transduction Abstract: The Hedgehog (Hh) signaling pathway is essential for patterning many structures in vertebrates including the nervous system, chordamesoderm, limb and endodermal organs. In the sea urchin, a basal deuterostome, Hh signaling is shown to participate in organizing the mesoderm. At gastrulation the Hh ligand is expressed by the endoderm downstream of the Brachyury and FoxA transcription factors in the endomesoderm gene regulatory network. The co-receptors Patched (Ptc) and Smoothened (Smo) are expressed by the neighboring skeletogenic and non-skeletogenic mesoderm. Perturbations of Hh, Ptc and Smo cause embryos to develop with skeletal defects and inappropriate non-skeletogenic mesoderm patterning, although initial specification of mesoderm occurs without detectable abnormalities. Perturbations of the pathway caused late defects in skeletogenesis and in the non-skeletogenic mesoderm, including altered numbers of pigment and blastocoelar cells, randomized left-right asymmetry of coelomic pouches, and disorganized circumesophageal muscle causing an inability to swallow. Together the data support the requirement of Hh signaling in patterning each of the mesoderm subtypes in the sea urchin embryo. Author Affiliation: (a) Department of Biology, Duke University, Box 90338, Durham, NC 27708, USA (b) Department of Biology, Central Michigan University, Mount Pleasant, MI 48859, USA Article History: Received 23 May 2008; Revised 30 March 2009; Accepted 17 April 2009