Affecting Rhomboid-3 Function Causes a Dilated Heart in Adult Drosophila

Abstract

Drosophila is a well recognized model of several human diseases, and recent investigations have demonstrated that Drosophila can be used as a model of human heart failure. Previously, we described that optical coherence tomography (OCT) can be used to rapidly examine the cardiac function in adult, awake flies. This technique provides images that are similar to echocardiography in humans, and therefore we postulated that this approach could be combined with the vast resources that are available in the fly community to identify new mutants that have abnormal heart function, a hallmark of certain cardiovascular diseases. Using OCT to examine the cardiac function in adult Drosophila from a set of molecularly-defined genomic deficiencies from the DrosDel and Exelixis collections, we identified an abnormally enlarged cardiac chamber in a series of deficiency mutants spanning the rhomboid 3 locus. Rhomboid 3 is a member of a highly conserved family of intramembrane serine proteases and processes Spitz, an epidermal growth factor (EGF)–like ligand. Using multiple approaches based on the examination of deficiency stocks, a series of mutants in the rhomboid-Spitz–EGF receptor pathway, and cardiac-specific transgenic rescue or dominant-negative repression of EGFR, we demonstrate that rhomboid 3 mediated activation of the EGF receptor pathway is necessary for proper adult cardiac function. The importance of EGF receptor signaling in the adult Drosophila heart underscores the concept that evolutionarily conserved signaling mechanisms are required to maintain normal myocardial function. Interestingly, prior work showing the inhibition of ErbB2, a member of the EGF receptor family, in transgenic knock-out mice or individuals that received herceptin chemotherapy is associated with the development of dilated cardiomyopathy. Our results, in conjunction with the demonstration that altered ErbB2 signaling underlies certain forms of mammalian cardiomyopathy, suggest that an evolutionarily conserved signaling mechanism may be necessary to maintain post-developmental cardiac function.

Cardiomyopathy Is Associated with Ribosomal Protein Gene Haplo-Insufficiency inDrosophila melanogaster

“…wy 1 ;+/+;p{tinC-Gal4}/p{tinC-Gal4} stock was provided by Manfred Frasch (Yin and Frasch 1998). wy 1; p{tubP-GAL80 ts }/p{tubP-GAL80 ts };p{tinC-Gal4}/p{tinC-Gal4} stock was created as described (Kim and Wolf 2009;Yu et al 2010). All stocks were maintained on standard media at room temperature.…”

“…In vivo adult Drosophila cardiac function was measured in 7-day-old awake female flies as described (Wolf et al 2006;Kim and Wolf 2009;Kim et al 2010;Yu et al 2010), using an OCT microscopy system (Bioptigen, Inc., Durham, NC).…”

“…OCT allows assessment of in vivo heart function in awake adult Drosophila in a manner similar to that of echocardiography in mammals (Wolf et al 2006;Kim and Wolf 2009;Kim et al 2010;Yu et al 2010). EDD measures the heart chamber in the fully relaxed state, and ESD measures the fully contracted state during each beat.…”

“…Cardiac expression of UASRpS15Aa RNAi using a heart-specific driver tinC-Gal4 (Yin and Frasch 1998;Qian and Bodmer 2009;Yu et al 2010) resulted in very few progeny; however, flies that escaped lethality had severely impaired heart function ( Figure 2B). Ubiquitous expression of UAS-RpS15Aa RNAi by using an actin5C-Gal4 driver resulted in lethality during development.…”

“…We addressed this question using optical coherence tomography (OCT) (Wolf et al 2006;Kim and Wolf 2009;Kim et al 2010;Yu et al 2010) to examine in vivo cardiac size and function in adult Drosophila with ribosomal deficiency. We show that haploinsufficiency of RpS15Aa, a predicted Minute gene, results in characteristic short, slender bristles as well as significant dilation and dysfunction of the Drosophila heart.…”