Senior Honors Projects, 2010-current

Date of Award

Fall 2012

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

Susan R. Halsell

Alexandra Bannigan

Kimberly Slekar

Abstract

In the United States, three out of every 100 babies are born with a major type of birth defect. Human birth defects can be acquired during morphogenetic processes such as neurulation. A prominent morphogenetic process in the Drosophila model system is head involution. During head involution, embryonic epidermis moves anterior ward and simultaneously mouth structures move inward through a series of tucking, folding and migrations. These complex intracellular and intercellular shape changes are driven by RhoA signal transduction and may act on the actomyosin cytoskeleton. RhoA signal transduction is highly conserved, therefore Drosophila melanogaster is an effective model organism to study. Drosophila RhoA mutant alleles are embryonic lethal, failing in head involution; the resulting embryos lack cuticle at the anterior dorsal region and exhibit a “hole in the head” phenotype. I have studied the effect of RhoA on head involution in living Drosophila embryos by expression of an actin-binding Green Fluorescent Protein (GFP)-moesin fusion protein (SGMCA) followed by time-lapse confocal microscopy. First, wild type embryos were analyzed to determine the features of wild type head involution. Next, two null RhoA alleles, RhoAE3.10 and RhoAJ3.8 were analyzed. Homozygous RhoA embryos were derived from a RhoA/CyO, twi-GFP; SGMCA stock. The presence of the twi-GFP insert on the CyO balancer results in a characteristic high expression of GFP. Since homozygous RhoA embryos lack the CyO balancer, they do not express twi-GFP. Thus RhoA homozygotes can be unambiguously identified. Analysis of the time-lapse videos revealed that head involution dorsal ridge formation in RhoA mutants appears grossly normal. On the other hand the procephalon and clypeolabrum fail to drop and retract caudally as the dorsal fold moves anteriorward. The movement of the dorsal fold continues on the ventral side but is impeded by the dorsal side. Thus, the dorsal anterior side of the embryo is not encapsulated by cuticle secreting epidermis. This is consistent with the “hole in the head” phenotype observed in the embryonic cuticle.

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