Athula H. Wikramanayake
Ph.D. University of California, Davis, 1993
Associate Professor, Department of Zoology
University of Hawaii at Manoa
2538 McCarthy Mall
Honolulu, HI 6822
phone: 808-956-8884
fax: 808-956-9812
athula@hawaii.edu

http://www.bio.miami.edu/Fac/Athula.html

Developmental biology of marine invertebrates/ Evolution of pattern formation
The broad interest of our laboratory is to understand how an embryo develops from a fertilized egg. In particular, we are interested in understanding the mechanisms by which maternally loaded developmental information is partitioned in a reproducible manner in the early embryo to initiate pattern formation. In addition, we are interested in understanding how these mechanisms are modified during evolution to produce morphological diversity.

Currently we use two model systems in our research, sea urchins and sea anemones. We have used sea urchin embryos for many years to study the mechanisms that initiate pattern formation along the maternally specified animal-vegetal (A/V) axis. 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. We and others recently showed that the Wnt/beta-catenin signaling pathway is selectively activated in vegetal cells of early sea urchin embryos. Signaling by this pathway plays a critical role in the initial specification of the A/V axis and also in its subsequent patterning. Our research is now focused on understanding how this pathway is activated in vegetal cells, and how signaling by downstream target genes of this pathway regulates the segregation of the primary germ layers.

More recently, in collaboration with Dr. Mark Martindale's laboratory at the Kewalo Marine Laboratory we have begun to use the starlet sea anemone Nematostella vectensis, as a model system for studying endomesoderm specification. Recent studies with invertebrates and vertebrates have suggested that endoderm and mesoderm are initially specified as a bipotential anlage called the endomesoderm. This bipotential layer is subsequently segregated into endoderm and mesoderm. Studies have also shown that the genes regulating endomesoderm specification are also conserved between invertebrates and vertebrates. We have recently shown that the diploblast N. vectensis has a functional endomesoderm making it an ideal model system for studying the origin of this bipotential germ layer. This animal is also an ideal model system for studying the evolution of the third germ layer, mesoderm, during bilaterian evolution. Additionally, since cnidarian eggs do not have an A/V axis, N. vectensis embryos provide a useful system to begin to understand how this critical polarity was established during bilaterian evolution.

Our studies combine classical embryological techniques with modern methods in molecular and cellular biology. We use a variety of molecular techniques including southern and northern analysis, PCR cloning, RT-PCR, in situ hybridization and carry out functional studies using RNA overexpression techniques or using morpholino anti-sense oligonucleotides. We also use a variety of methods to detect protein-protein interactions including co-immunolocalization, immunoprecipitation and yeast two-hybrid analysis. Additionally we use a number of microscopic techniques to analyze embryos in our studies including confocal and differential interference contrast microscopy.

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Publications

Research papers

1. Wikramanayake, A.H., Uhlinger, K.R., Griffin, F.J., and W.H. Clark, Jr.
(1992). Sperm of the shrimp Sicyonia ingentis undergo a bi-phasic
capacitation accompanied by morphological changes. Dev. Growth
Differ. 34, 347-355.

2. 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.

3. Gan, L., Mao, C., Wikramanayake, A.H., Angerer, L., Angerer, R., and W. H.
Klein. (1995). An orthodenticle-related gene from Strongylocentrotus
purpuratus. Dev. Biol. 167, 517-528.

4. 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.

5. Mao, C.A*, Wikramanayake, A.H.*, Gan, L., Chuang, C-k, Summers, R.G., and W.H. Klein. (1996). Redirecting sea urchin cell fate by overexpressing an orthodenticle-related protein, SpOtx. Development 122, 1489-1498.
* Denotes equal contribution by these authors.

6. Chuang, C.K., Wikramanayake, A.H., Mao, C-A., Li, X., and W.H. Klein. (1996). Transient appearance of Strongylocentrotus purpuratus Otx in micromere nuclei: Cytoplasmic retention of SpOtx possibly mediated through an a-actinin interaction. Dev. Genet. 19, 231-237.

7. Wang, W., Wikramanayake, A.H., Gonzalez-Rimbau, M., Vlahou, A., Flytzanis, C.N., and W.H. Klein. (1996). Very early and transient vegetal plate expression of SpKrox1, a Kruppel/Krox gene from Strongylocentrotus purpuratus. Mechan.
Dev. 60, 185-195.

8. 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.

9. Ramachandran, R.K., Wikramanayake, A.H., Uzman, J.A., Govindarajan, V. and C.R. Tomlinson. (1997). Disruption of gastrulation and oral-aboral ectoderm differentiation in the Lytechinus pictus embryo by a dominant/negative PDGF
receptor. Development 124, 2355-2364.

10. 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.

13. Li, X., Wikramanayake, A.H., and W.H. Klein. (1999). Requirement of SpOtx in cell fate decisions in the sea urchin embryo and possible role as a mediator of b-catenin signaling. Dev. Biol. 212, 425-439.

12. Huang, L., Li, X., El-Hodiri, H., Dayal, S.,Wikramanayake, A.H., and W.H. Klein. (1999). Involvement of Lef/Tcf in establishing cell types along the animal-vegetal axis of sea urchins. Dev. Genes. Evol. 210, 73-81.

13. Moore, J.C., Sumeral, J.L., Schnackenberg, B.J., Nichols, J.A., Wikramanayake, A.H., Wessel, G.M. and Marzluff, W.F. (2002). Cyclin D and cdk4 are required for normal development beyond the blastula stage in sea urchin embryos. Mol. Cell. Biol. 22, 4863-75

14. Pillai, M.C. Vines, C.A. Wikramanayake, A.H. and G. N. Cherr. (2003) Polycyclic aromatic hydrocarbons disrupt axial development in sea urchin embryos via a beta-catenin dependent pathway Toxicology 186, 93-108

15. Wikramanayake, A.H., Hong, M., Lee, P.N., Pang, K., Byrum, C.A., Bince, J.M., Xu, R. and M.Q. Martindale. (2003). An ancient role for nuclear beta-catenin in the evolution of axial polarity and germ layer segregation. Nature 426, 446-450

16. Weitzel, H. E., Illies, M. R., Byrum, C. A., Xu, R., Wikramanayake, A. H.,
and Ettensohn, C. A. Differential stability of beta-catenin along the animal-vegetal axis of the sea urchin embryo mediated by Dishevelled. Development 131, 2947-2956

17. Wikramanayake, A.H., Peterson, R., Huang, L., Chen, J., Bince, J.M., McClay, D.R., and W.H. Klein. (2004) Nuclear beta-catenin-dependent Wnt8 signaling in vegetal cells of the early sea urchin embryo regulates gastrulation and differentiation of endoderm and mesodermal cell lineages. Genesis 39, 194-205

18. Minokawa, T., Wikramanayake, A.H. and E.H. Davidson. (2005) cis- Regulatory inputs of the wnt8 gene in the sea urchin endomesoderm network. Dev. Biol. (Published online: doi:10.1016/j.ydbio.2005.09.047)

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Reviews and book chapters

1. 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.

2. Klein, W.H., and A.H. Wikramanayake. (1996). The sea urchin Spec/LpS1
proteins. In: Guidebook to the Calcium-Binding Proteins, M.R. Celio, ed.,
Oxford University Press.

3. Klein, W.H., Mao, C.A., Gan, L., Chuang, C.K., and A.H. Wikramanayake. (1997). Manipulating cell fates in the sea urchin embryo. Invert. Reprod. Dev. 31, 21-29

4. 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.

5. 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.

6. Byrum, C.A. and Wikramanayake, A.H. (2003). Autonomous cell specification: An overview Encyclopedia of Life Sciences, Nature Publishing Group, http://www.els.net

7. Sweet, H., Amemiya, S., Ransick, A., Minokawa, T., McClay, D., Wikramanayake, A., Kuraishi, R., Nishida, H., and Henry, J. (2004). "Blastomere isolation and transplantation" In: Methods in Cell Biology, Vol. 74;

8. Developmental Biology of sea urchins, ascidians, and other invertebrate deuterostomes: Experimental approaches. C.A. Ettensohn, G. Wessel, G. Wray. Eds. Academic Press/Elsevier Science.

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