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Analysis of two distinct functions of the Roundabout 2 receptor during
Drosophila cardiac assembly

Judith J. Canabal Alvear
B.S., Universidad de Puerto Rico, Rio Piedras - 2008

Thesis Advisors: Sunita G. Kramer Ph.D
Graduate Program in Cell & Developmental Biology

RWJMS Research Tower
Room V-10

Thursday, July 17, 2014
10:00 a.m.


Biological tubes are required for the development of complex organisms given that they distribute molecules to important tissues. In this study, we investigate two unknown functions for the receptor Roundabout2 (Robo2) during Drosophila dorsal vessel (DV) assembly. Two steps are required for DV formation. First, cardioblasts (CBs) migrate toward the dorsal midline of the embryo and second, the CBs undergo cell shape changes to form a tube. The two rows of CBs are flanked by two rows of pericardial cells (PCs). CBs express Robo1, while PCs express Robo1 and Robo2. Accompanying the cardiac cells is the dorsal ectoderm (DE), which localizes above the CBs. During cardiac cell migration, Robo2 protein is basally localized to the DE cells, which come into contact with the migrating CBs. Loss of robo2 results in slower CB migration, while overexpression of robo2 causes mis-regulation of Robo2 protein and an arrest in migration. I also found preliminary evidence that ectodermally expressed Robo2 may also play a role in regulating CB cell differentiation. During CB lumen formation, we uncovered a non-cell autonomous role for Robo2 in the PCs that requires the extracellular IG1 and IG2 domains of Robo2. In robo2 LOF embryos, we observe defects in lumen formation. Furthermore, expression of robo2 at low levels in the CBs results in a lumen-less phenotype, while expression of Robo2 at high levels in the CBs produces a phenotype where the CBs do not make attachment domains rendering a lumen-less structure. In conclusion, we have found that Robo2s function during Drosophila cardiac development is complex and involves two a two-part system to promote cardiac cell de-adhesion during migration and to promote CB-CB attraction during lumen formation.

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