Stander Symposium abstract book - University of Dayton

9:00 AM to 10:30 AM
The Role of Hemocytes in Shell Formation in the Eastern Oyster, Crassostrea virginica
Presenter(s): Cristina R Prall
Advisor(s): Karolyn M Hansen
Biology - Independent Research
The Eastern oyster, Crassostrea virginica, produces a tough, fracture-resistant protective composite shell that is composed of calcite (a polymorph
of calcium carbonate) as well as organic material (proteins, glycoproteins). Scientists have examined the shell formation process in molluscs for
many decades and have proposed two models for the shell formation process. The matrix-mediated model focuses on the role of proteins as nucleation
sites for calcite crystal formation while the hemocyte-mediated model proposes the role of oyster blood cells for transport of calcite nuclei to
the shell formation front. Specifically, the hemocyte-mediated model proposes that the hemocytes of C. virginica contain calcium carbonate crystals
that are transported through the tissues and deposited at the shell formation front. These nuclei then grow and coalesce to form the typical
layered organic-mineral shell structure. This study focused on determining if hemocytes were capable of producing mineral structure when cultured
outside the organism. Hemocytes were collected from notched oysters and cultured for up to ninety six hours ex vivo in order to determine if
crystal formation occurred. Microscopic analysis (scanning electron microscopy, SEM) of the hemocyte samples revealed crystal structures within
and around cells cultured on glass substrates. The process of shell formation is very complex and probably involves both the matrix-mediated
and hemocyte-mediated model for movement of both organic and mineral resources to the shell formation front. While elucidation of the basic
biological process of shell formation is of great interest, there is potential for use of hemocyte crystal deposition for development of biomedical
implant coatings. The biocompatible oyster-derived material may function as a better interface for integration of tissue with metallic implants.
Using Drosophila eye mutants to model defects in Microphthalmia or Anophthalmia
Presenter(s): Katelin E Hanes, Shilpi Verghese
Advisor(s): Madhuri Kango-Singh
Biology - Honors Thesis
Micropthalmia and anophthalmia are congenital birth defects, which result in severe growth defects in eyes resulting in small eyes or visual field.
However, if these defects occur due to defective differentiation of cells under the regulation of eye-specific genes, or due to defects in the regulation
of genes responsible for growth of the eye primordium and the production of uncommitted progenitor cells remains unknown. Drosophila
melanogaster is a well-established model to study human diseases as genes involved in eye development exhibit structural and functional similarities
from flies to humans. Eye development involves (a) growth of the eye field, and (b) the differentiation of the different cell types. Several
genetic pathways, and signaling from Decapentaplagic (Dpp) and Hedgehog (Hh) is absolutely essential for the differentiation of photoreceptor
cells in a field controlled by Eyeless (Ey). These pathways are conserved between flies and humans as are pathways regulating organ size. Our goal
is to test if the Hippo pathway plays a role in the determination of final eye size. The Hippo pathway is responsible for generation of uncommitted
precursor cells for organ development and size determination. Our objective is to test if changes in levels of Hippo signaling alter the phenotype of
fly mutants that cause a reduction in eye size. Our initial data identified sine-oculis (so), a retinal determination gene, as a quantifiable model for
our studies. However, soD is a dominant negative allele, therefore, we developed the tools to test the effect of Hippo signaling on a strong hypomorph
of so [so1]. These studies will shed light on the role of uncommitted precursor cells in determining the size of the eye field, and contribute
to our understanding of early eye development.
Visualizing Evolution through Differences in Gene Expression
Presenter(s): David J Tacy
Advisor(s): Thomas M Williams
Biology - Honors Thesis
Variations in when and where genes are expressed (that is where they make a protein) are suspected to be a major source for organismal evolution.
Identifying which genes have undergone expression changes is a necessary prerequisite to understand how expression patterns evolve.
Pigmentation trait differences between Drosophila fruit fly species remain a leading model to identify gene expression changes underlying trait
evolution. This is due to the fact that many of the genes required to make pigments and those that specify where pigments are produced have
been identified in the genetic model organism species Drosophila melanogaster. Two important regulators of pigmentation are the tandem du-
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