Assembly and composition of the cECM is critical for heart physiology

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Title: Assembly and composition of the cECM is critical for heart physiology
Authors: Lammers, Kay
Thesis advisor: Prof. Dr. Achim Paululat
Thesis referee: Prof. Dr. Jürgen Heinisch
Abstract: The present study focuses on the cardiac function of Drosophila melanogaster. Drosophila heart parameters are evolutionarily conserved, making Drosophila a useful human heart disease model. This model enables the in vivo investigation of physiological and genetic methods. This thesis is subdivided into four parts: parts 1-3 comprise the introductions of three publications, and part 4 presents unpublished data. The first publication is about the heart physiology of Drosophila. It explains how intracardiac valve cells work and proves their participation in blood flow directionality. A databased model shows the orientation of myofibrils within the valve cell. The myofibrils allow the valve cells to oscillate between a roundish and elongated cell shape. A toll-GFP enhancer line was shown to mediate strong reporter gene activity in the intracardiac valve of third instar larvae, pupae and adults. Transmission electron microscopy (TEM) analyses and immunohistochemical studies showed the differentiation of larval valve cells for the first time. The second publication focuses on the cardiac extracellular matrix (ECM), which contains two unique proteins - Lonely heart (Loh) and Pericardin (Prc). The study demonstrated that Loh is crucial for Prc recruitment to the developing matrix. Loh is anchored to the ECM by its thrombospondin type 1 repeat (TSR1-1) with its embedded putative glycosaminoglycan (GAG)-binding side. The N-terminus of Loh is proposed to face the plasma membrane. Prc is presumably recruited by two Loh TSR1 domains (TSR1-2 and TSR1-4). Nearly all Drosophila tissues, except salivary glands, create Prc networks through ectopic Loh expression. The study also found that the amount of Prc and Loh in the cardiac ECM influences heart function. The third publication investigated a set of neuropeptides and their ability to modulate cardiac function in third instar larvae. The results showed that 11 of the 19 tested peptides significantly affected the heart function in semi-intact larvae. Furthermore, the peptides’ in vivo relevance was tested through the knockdown of chronotropic peptide precursors. The study found that a RNAi mediated knockdown of all respective peptide precursors affected the heart rate. By combining semi-intact heart preparations and in vivo analyses, we identified several heartbeat-modulatory peptides in Drosophila. The unpublished data introduces a new software program called HIRO. It is written in Java, platform-independent and can easily detect the heart rhythm. Only mild anaesthesia and basic equipment are needed to record the Drosophila heartbeat. HIRO was used to show the influence of the RNAi-mediated downregulation of critical ECM proteins in Drosophila third instar larvae. The screen revealed Myospheroid and Laminin A as promising candidates that can significantly affect the heart parameters. HIRO is optimised for future applications and can be used as a high-throughput screening software with a simple setup. Taken together, this thesis provides new insights into the physiology and function of the Drosophila heart. The developed software HIRO comes with a user-friendly interface and a step-by-step introduction to easily conduct heart parameter measurements. HIRO will help to expand our knowledge of the fundamental processes in the model organism Drosophila melanogaster.
Subject Keywords: Drosophila; Java; ECM; Heart; Heart beat; Valve cells
Issue Date: 12-Apr-2022
Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB05 - E-Dissertationen

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