Kidney filtration of the blood requires specialized cells known as podocytes. Podocyte slit diaphragms (SDs) are intercellular junctions that contribute to size-selective filtration, which excludes larger proteins from the urine. Abnormalities in SDs cause proteinuria and nephrotic syndrome, which refer to the excessive excretion of proteins through urine due to renal defects. Podocytes have been shown to exhibit apicobasal polarity, which can affect fundamental aspects of cell biology, including intercellular junction formation. Indeed, in humans and rodent models, mutations in genes encoding apical polarity proteins cause defects in SD formation and nephrotic syndrome. While previous research suggests key roles for apicobasal polarity in podocytes, there is no evidence that basolateral polarity proteins contribute to SDs. In fact, studies of basolateral polarity proteins in mouse podocytes revealed no obvious functional role, however we speculate this may be due to genetic redundancy in vertebrates. Thus, the role of apicobasal polarity in podocytes remains unclear.
To explore the potential role of basolateral polarity proteins in SD formation, we examined the consequences of disrupting basolateral polarity proteins in Drosophila nephrocytes, which possess SDs remarkably similar in molecular composition and function as those in mammalian podocytes. Using confocal and electron microscopy we characterized SD integrity following loss of basolateral polarity proteins. Our study identified the basolateral polarity proteins Dlg, Scrib, Lgl, and Par-1 as novel regulators of nephrocyte SDs. Loss of basolateral polarity proteins also compromised the central function of nephrocytes—filtration of the fly hemolymph. We also performed genetic interaction studies, which suggest the basolateral polarity proteins work together, in concert with apical polarity proteins, to regulate SDs by promoting normal endocytosis and trafficking of SD proteins.
Given the recognized importance of apical polarity proteins and SD protein trafficking in podocytopathies, our findings connecting basolateral polarity proteins to these processes significantly advance our understanding of podocyte biology.Bachelor of Scienc
