Biology Faculty :: Charles Sullivan
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Charles Sullivan Professor of Biology Ph.D., 1983, University of Maryland, College Park; Postdoctoral Fellow, 1983-1986, University of Virginia; Developmental Biology. Tel: 641-269-3042; FAX: 641-269-4285; Office: AWAY 2009-2010; Email: sullivac@grinnell.edu Cell Biology / Developmental Biology
Members of my laboratory are studying the process of cell differentiation
during embryonic development. The major cells and tissues of all vertebrates,
including humans, develop as a result of chemical interactions between different
tissues. One well-studied example of such interactions is formation of the lens
of the eye. For many years it was believed that a lens was induced to form
because of signals sent by the optic vesicle of the brain. However, recent
experiments on amphibian embryos have shown that the optic vesicle is not
a lens inducer, but that earlier tissue interactions induce a lens. Yet, the lens
must form in conjunction with the optic vesicle because most of the eye tissue
is derived from the optic vesicle.
It is likely that the optic vesicle is not the lens inducer in chicken embryos either. This conclusion is based on the observation that a large region of head ectoderm, including ectoderm far away from the optic vesicle, will differentiate into lenses when grown in tissue culture. We want to determine when lens-forming potential first appears in the ectoderm and how large a region has lens potential. We are also interested in determining why non-lens head ectoderm does not differentiate into lenses in the embryo (this ectoderm produces feathers). We have begun to test the hypothesis that neural crest cells, which migrate through the underlying mesenchyme, are the source of an inhibitory signal. Neural crest cells are present under most of the ectoderm in the head, but are not found under the presumptive lens ectoderm. It is possible that the tight adhesion between lens ectoderm and the optic vesicles prevents neural crest cells from migrating under future lens cells. If this is the case, then the optic vesicle would still have a role in determining where a lens forms during development because the inhibitory signal from neural crest cells would never reach the cells which then differentiate into the lens. The figure below shows the distribution of neural crest cells revealed by immunocytochemistry using the HNK-1 monoclonal antibody. Brown staining of neural crest cells is present under most of the ectoderm in the head, but is not found under the presumptive lens ectoderm (arrows). It is possible that the tight adhesion between lens ectoderm and the optic vesicles (ov) prevents neural crest cells from migrating under future lens cells. If this is the case, then the optic vesicle would still have a role in determining where a lens forms during development because the inhibitory signal from neural crest cells would never reach the lens cells. 
Recent Publications & Presentations
(Undergraduate students in bold)
Courses 2009-2010
Archived Courses Taught by Dr. Sullivan
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