Athula H. Wikramanayake

Ph.D. University of California, Davis, 1993

Assistant Professor, Department of Zoology

Mailing Address:

Department of Zoology, Edmondson 461
University of Hawaii at Manoa
2538 McCarthy Mall
Honolulu, HI 6822

TEL: 808-956-8884

FAX: 808-956-9812

Developmental biology of marine invertebrates/ Evolution of pattern formation

Our laboratory investigates the cellular and molecular mechanisms that establish the animal-vegetal (A/V) axis in animal eggs and the mechanisms by which developmental information along this axis regulates early cell fates. The A/V axis is a cytoplasmic polarity that is maternally established in the egg and is present in most animal eggs. During early embryogenesis maternal determinants asymmetrically distributed along this axis are inherited by cleaving blastomeres and these determinants play critical roles in fate specification of these cells. Despite the presence of the A/V axis in many animal eggs and its importance in early cell fate specification little is known about the mechanisms that specify and pattern this axis. For our studies on A/V axis specification we have used sea urchin embryos as a model system because they are relatively simple and can be manipulated using a combination of experimental embryology coupled with cellular and molecular biology techniques. In addition, sea urchins are echinoderms and since this phylum occupies an evolutionarily important position as basal deuterostomes, studies on A/V axis specification in this group of animals is likely to provide insight into the evolution of bilaterians.

Our current work focuses on the role of the Wnt/beta-catenin signaling pathway in pattern formation along the A/V axis of the sea urchin embryo. Our lab along with David McClay’s lab at Duke University has recently shown that the critical early step in axial patterning in the sea urchin embryo is the activation of beta-catenin signaling by the translocation of this protein into nuclei of vegetal cells. Work on sea urchins as well as work on other deuterostome embryos now suggests that the initial step in axial patterning in this clade of animals is the activation of nuclear beta-catenin signaling. Our current research is focused on investigating how the selective translocation of beta-catenin into vegetal cell nuclei is regulated in the early embryo, identifying target genes of this transcription factor and elucidating the mechanisms by which nuclear beta-catenin target genes mediate cell fates along the A/V axis.

Recent work on deuterostome embryos has raised the possibility that the Wnt/beta-catenin pathway may play a fundamental role in A/V axis patterning in protostome embryos as well. We are pursuing this idea by extending our studies to include protostome species with eggs that have an A/V axis. These studies will initially focus on local species of mollusks, annelids and marine arthropods (crustaceans). We have also started some preliminary studies on early embryogenesis in the anthozoan cnidarian Nematostella vectensis to examine the role of Wnt/beta-catenin signaling in the evolution of endoderm and gastrulation. This sea anemone is a useful model system for studying early embryonic development in diploblasts because they can be easily maintained in the laboratory and can be conditioned to consistently produce gametes. The long-term goals of these studies are to gain insight into the role of the Wnt/beta-catenin pathway in the evolution of pattern formation in metazoan embryos.

Representative publications

Wikramanayake, A.H., Peterson, R., Chen, J., Huang, L., McClay, D.R. and Klein, W.H. (2001). Wnt8 mediates endomesoderm specification in the sea urchin embryo. (Submitted).

Huang, L., Li, X., El-Hodiri, H., Dayal, S., Wikramanayake, A.H., and Klein, W.H.

Involvement of Lef/Tcf in establishing cell types along the animal-vegetal axis of sea urchins. Dev. Genes. Evol. 210, 73-81, 2000.

Wessel, G.M. and A.H. Wikramanayake. (1999). How to grow a gut: Ontogeny of the endoderm in the sea urchin embryo. BioEssays, 21, 459-471.

Wikramanayake, A.H., Huang, L.and W.H. Klein. (1998). b-catenin is essential for patterning the maternally specified animal-vegetal axis in the sea urchin embryo. Proc. Natl. Acad. Sci. USA 95, 9343-9348.

Wikramanayake, A.H. and W.H. Klein. (1998). Otx, b-catenin and specification of ectodermal cell fates in the sea urchin embryo. In: Cell Lineage and Fate Determination, S.A. Moody, ed., Academic Press.

Wikramanayake, A.H., and W.H. Klein. (1997). Multiple signaling events pattern ectoderm and polarize the oral-aboral axis in the sea urchin embryo. Development 124, 13-20.

Wikramanayake, A.H., Brandhorst, B., and W.H. Klein. (1995). Autonomous and non-autonomous differentiation of ectoderm in different sea urchin species. Development 121, 1497-1505.

Wikramanayake, A.H., and W.H. Clark, Jr. (1994). Two extracellular matrices from oocytes of the marine shrimp Sicyonia ingentis that independently mediate primary or secondary sperm binding. Dev. Growth Differ. 36, 86-101.

Clark, W.H., Jr., Griffin, F.J., and A.H. Wikramanayake. (1994). Pre-fusion events of sperm-oocyte interaction in the marine shrimp, Sicyonia ingentis. Sem. Dev. Biol. 5, 225-231.

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