Meeting Abstract
P2.40 Jan. 5 Disheveled is a localized maternal determinant mediating egg polarity and germ layer segregation in the cnidarian, Nematostella vectensis LEE, P.N.**; KUMBUREGAMA, S.; MARTINDALE, M.Q.; WIKRAMANAYAKE, A.H.; Kewalo Marine Lab/PBRC, Honolulu, HI; Univ. of Hawaii, Honolulu; Kewalo Marine Lab/PBRC, Honolulu, HI; Univ. of Hawaii, Honolulu plee@hawaii.edu
In most bilaterians, polarity along the animal-vegetal (AV) axis of the egg specifies either the anterior-posterior or dorsal-ventral axis of the adult through the Wnt/&beta-catenin pathway. In hydrozoan cnidarians, the adult oral-aboral axis is not specified in the egg but is established at the time of first cleavage by the position of the cleavage furrow. The molecular mechanisms involved in axis specification and germ-layer segregation in hydrozoan embryogenesis are not known. We examined for the first time in an anthozoan the developmental and molecular mechanisms directing axis and germ-layer specification in the sea anemone, Nematostella vectensis. Egg separation and sperm localization experiments indicate Nematostella eggs are fertilized at the animal pole at the site of polar body formation. We demonstrate by vital staining that the animal pole of the egg corresponds to the site of first cleavage, the site of gastrulation, and the oral pole of the adult. Embryo separation experiments reveal a determinant localized to the animal pole as early as the 8-cell stage is responsible for differences in fates of cells derived from animal and vegetal regions of the egg. Previous experiments in Nematostella showed the asymmetric nuclear localization of &beta-catenin during early cleavage is the first molecular marker of axial polarity and is responsible for endoderm formation. Here, we identify Disheveled, an upstream component of Wnt/&beta-catenin signaling, as a maternal determinant localized to the animal pole of the Nematostella egg. Using dominant negative approaches we show Disheveled is required for specifying embryonic polarity and endoderm formation by stabilizing &beta-catenin via the canonical Wnt pathway.
