Differentiation and function of intracardiac valve cells

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Haemolymph flow in the Drosophila heart is controlled by intracardiac valves. The valve separates the posterior heart chamber from the anterior aorta and constitutes a simple gate-like structure in the larvae. The intracardiac valve is formed by only two individual cells, both of which display a unique histology with giant vesicular-like compartments, which we called valvosomes. Valvosomes are a characteristic feature of larval and adult Drosophila cardiac valves and are not formed in any other cardiomyocyte. In this project, we have two overarching goals. On the one hand, we want to analyse how exactly, on the molecular and cellular level, recycling endosomes, which are essential for the formation of valvosomes, are recruited towards valvosomes. Rab11 is the focus of interest here, as we identified Rab11-REs as essential for valvosome formation in the first application period. Our second goal is to analyze the importance of the cardiac valve cells for the pumping function of the heart. Here we study mutants with missing or defective cardiac valves and measure haemolymph flow with life markers in living animals. We consider the cardiac valve cells in flies as an evolutionary novelty, in which ancestral, fundamental endosomal pathways were modified to meet specific histological and physiological requirements. The canonical pathway for recycling proteins (RE pathway) is being "hijacked" in valve cells to generate a new and unique organelle, the valvosome. We will learn from our studies how histological and, eventually, anatomical novelties are generated during evolution by utilizing modules from an existing "construction kit".