Meeting Abstract

S3.3-4  Saturday, Jan. 4 15:00  Ectodermal inputs into patterning skeletogenesis LYONS, Diedre; MCINTYRE, Dan; MCCLAY, David R.*; Duke University; Duke University; Duke University dmcclay@duke.edu

Sea urchin larvae produce a skeleton using a limited number of skeletogenic cells, usually either 32 or 64 cells depending on the species. Each skeletogenic cell is capable of producing any piece of larval skeleton, depending on where that skeletogenic cell finds itself in the blastocoel of the embryo. Information for the pattern that cell produces originates from the ectoderm. Four known signals are produced by the ectoderm: VEGF, FGF, Wnt5 and Wnt3. Each of these signals operates at short range. The production of each of the signals depends upon specification of two bands of ectoderm: the ciliary band which forms at the boundary between the ventral and dorsal ectoderm, and the “border ectoderm” which forms orthogonal to the ciliary band and borders the endoderm. Skeletogenesis is initiated just beneath the site where the ciliary band and border ectoderm intersect. VEGF, FGF and Wnt5 are produced at that intersection. Absence of any one of the signals leads to the absence of, or to an abnormally patterned skeleton. Ectopic expression of VEGF or Wnt5 leads to ectopic production of skeletal elements, in each case, just beneath the cells producing the ectopic signal. Once skeletogenesis is initiated the skeleton grows either in parallel to the ciliary band or border ectoderm, or in the case of two sets of rods, is initiated in one of the two bands and grows perpendicular to the band producing long arms in many species. The sequence of specification is initiated by Nodal signaling to establish the site of the ciliary band, and by endodermal Wnt5 to induce the border ectoderm. The sequence of events from induction of ectodermal territories, to production of ectodermal signals, to the specific responses of the skeletogenic cells will be described based on a large series of perturbations of both transcription factors, and of the signals necessary for patterning the skeletons.