Three-dimensional architecture of pericardial nephrocytes in Drosophila melanogaster revealed by FIB/SEM tomography

Abstract

Nephrocytes are similar in structure to podocytes and play a role in the isolation of toxic substances from hemolymph in insects. Drosophila melanogaster nephrocytes have recently been used to study podocyte function and disease. However, the threedimensional ultrastructure of nephrocytes is not clearly understood because their surrounding basement membrane makes it difficult to observe using conventional scanning electron microscopy. We reconstructed the three-dimensional ultrastructure of Drosophila pericardial nephrocytes using serial focused-ion beam/scanning electron microscopy (FIB/SEM) images. The basal surfaces were occupied by foot processes and slit-like spaces between them. The slit-like spaces corresponded to the podocyte filtration slits and were formed by longitudinal infolding/invagination of the basal plasma membrane. The basal surface between the slit-like spaces became the foot processes, which ran almost linearly, and had a Bwashboard-like^appearance. Both ends of the foot processes were usually anastomosed to neighboring foot processes and thus free ends were rarely observed. We demonstrated that FIB/SEM is a powerful tool to better understand the three-dimensional architecture of nephrocytes.

Nephrocytes are part of the spectrum of filtration epithelial diversity

“…Drosophila nephrocytes exhibited a washboard-like pattern, as previously reported (Fig. 3a, d) (Kawasaki et al 2019), while decapod nephrocytes exhibited an interdigitating pattern, which could be intercellular (ICI) or autocellular (ACI) interdigitating pattern (Fig. 3b, c).…”

“…Therefore, nephrocytes are not involved in the production of primary urine, but they serve to separate toxic molecules, such as heavy metals, from the hemolymph by endocytosis (Crossley 1984). Moreover, the formation of foot processes differs significantly between Drosophila nephrocytes and eucoelomate podocytes (Kawasaki et al 2019). As mentioned above, the podocyte foot processes are formed by protrusion and are interdigitated between adjacent podocytes, and thus, the podocyte slit diaphragm is an intercellular junction ( Fig.…”

Adipose Triglyceride Lipase protects the endocytosis of renal cells on a high fat diet inDrosophila

“…To determine the ultrastructural changes associated with HFD compromised endocytosis, we used correlative light electron microscopy (CLEM) with Airyscan confocal microscopy and serial blockface scanning electron microscopy (SBF SEM). The plasma membrane of nephrocytes is organised into a dense undulating network of slit diaphragms and lacunae [31,32,38]. These ultrastructural features of the plasma membrane network are visible with serial blockface scanning electron microscopy (SBF SEM) in both STD and HFD nephrocytes ( Fig 3A ).…”

Three-dimensional imaging of podocyte ultrastructure using FE-SEM and FIB-SEM tomography

“…FIB-SEM tomography is also suitable for 3D structural visualization of other cells that are entirely surrounded by the extracellular matrix. For example, mesangial cells and nephrocytes-one of the podocyte-related cells found in arthropods-includingDrosophila melanogaster (Ichimura and Sakai 2017;Kawasaki et al 2019). Although FIB-SEM tomography is a powerful tool for precisely analyzing the 3D ultrastructure of podocytes, this method has several technical disadvantages.…”

“…This is not possible with conventional FE-SEM. Our research group analyzed the 3D ultrastructure of podocytes in health, disease and development by utilizing FE-SEM and FIB-SEM tomography Ichimura et al 2019;Ichimura et al 2015;Ichimura and Sakai 2017;Kawasaki et al 2019).…”