The FERM protein EPB41L5 regulates actomyosin contractility and focal adhesion formation to maintain the kidney filtration barrier.

Podocytes form the outer part of the glomerular filter, where they have to withstand enormous transcapillary filtration forces driving glomerular filtration. Detachment of podocytes from the glomerular basement membrane precedes most glomerular diseases. However, little is known about the regulation of podocyte adhesion in vivo. Thus, we systematically screened for podocyte-specific focal adhesome (FA) components, using genetic reporter models in combination with iTRAQ-based mass spectrometry. This approach led to the identification of FERM domain protein EPB41L5 as a highly enriched podocyte-specific FA component in vivo. Genetic deletion of Epb41l5 resulted in severe proteinuria, detachment of podocytes, and development of focal segmental glomerulosclerosis. Remarkably, by binding and recruiting the RhoGEF ARGHEF18 to the leading edge, EPB41L5 directly controls actomyosin contractility and subsequent maturation of focal adhesions, cell spreading, and migration. Furthermore, EPB41L5 controls matrix-dependent outside-in signaling by regulating the focal adhesome composition. Thus, by linking extracellular matrix sensing and signaling, focal adhesion maturation, and actomyosin activation EPB41L5 ensures the mechanical stability required for podocytes at the kidney filtration barrier. Finally, a diminution of EPB41L5-dependent signaling programs appears to be a common theme of podocyte disease, and therefore offers unexpected interventional therapeutic strategies to prevent podocyte loss and kidney disease progression.

aPKCλ/ι and aPKCζ contribute to podocyte differentiation and glomerular maturation.

Precise positioning of the highly complex interdigitating podocyte foot processes is critical to form the normal glomerular filtration barrier, but the molecular programs driving this process are unknown. The protein atypical protein kinase C (aPKC)--a component of the Par complex, which localizes to tight junctions and interacts with slit diaphragm proteins--may play a role. Here, we found that the combined deletion of the aPKCλ/ι and aPKCζ isoforms in podocytes associated with incorrectly positioned centrosomes and Golgi apparatus and mislocalized molecules of the slit diaphragm. Furthermore, aPKC-deficient podocytes failed to form the normal network of foot processes, leading to defective glomerular maturation with incomplete capillary formation and mesangiolysis. Our results suggest that aPKC isoforms orchestrate the formation of the podocyte processes essential for normal glomerular development and kidney function. Defective aPKC signaling results in a dramatically simplified glomerular architecture, causing severe proteinuria and perinatal death.

Ephrin/ephrin receptor expression during early stages of mouse inner ear development.

Ephrins and their tyrosine kinase receptors (Ephs) are a highly conserved family of signaling proteins with various functions during embryonic development. Among others, Eph/ephrin signaling is involved in regulating axon guidance, cell migration, and tissue border formation through inducing modifications of the actin cytoskeleton and cell adhesion. During development ephrins and Ephs are expressed in spatially and temporarily regulated patterns in a wide range of tissues. Here, we analyzed the expression of seven members of the Eph and four member of the ephrin family during early stages of mouse inner ear development by whole-mount in situ hybridization. We detected expressions of EphA2, EphA4, EphA7, EphB1, ephrinA4, and ephrinA5 in and around the forming otic placode between embryonic day (E) 8.5 and E10, and report their detailed expression patterns. Our results reveal dynamic expression of several members of the ephrin/Eph family consistent with functions in otic placode development, invagination and neuroblast delamination.