ELMOD1 Stimulates ARF6-GTP Hydrolysis to Stabilize Apical Structures in Developing Vestibular Hair Cells

Abstract

Sensory hair cells require control of physical properties of their apical plasma membranes for normal development and function. Members of the ADP-ribosylation factor (ARF) small GTPase family regulate membrane trafficking and cytoskeletal assembly in many cells. We identified ELMO domain-containing protein 1 (ELMOD1), a guanine nucleoside triphosphatase activating protein (GAP) for ARF6, as the most highly enriched ARF regulator in hair cells. To characterize ELMOD1 control of trafficking, we analyzed mice of both sexes from a strain lacking functional ELMOD1 [roundabout ()]. In mice, cuticular plates of utricle hair cells initially formed normally, then degenerated after postnatal day 5; large numbers of vesicles invaded the compromised cuticular plate. Hair bundles initially developed normally, but the cell's apical membrane lifted away from the cuticular plate, and stereocilia elongated and fused. Membrane trafficking in type I hair cells, measured by FM1-43 dye labeling, was altered in mice. Consistent with the proposed GAP role for ELMOD1, the ARF6 GTP/GDP ratio was significantly elevated in utricles compared with controls, and the level of ARF6-GTP was correlated with the severity of the phenotype. These results suggest that conversion of ARF6 to its GDP-bound form is necessary for final stabilization of the hair bundle. Assembly of the mechanically sensitive hair bundle of sensory hair cells requires growth and reorganization of apical actin and membrane structures. Hair bundles and apical membranes in mice with mutations in the gene degenerate after formation, suggesting that the ELMOD1 protein stabilizes these structures. We show that ELMOD1 is a GTPase-activating protein in hair cells for the small GTP-binding protein ARF6, known to participate in actin assembly and membrane trafficking. We propose that conversion of ARF6 into the GDP-bound form in the apical domain of hair cells is essential for stabilizing apical actin structures like the hair bundle and ensuring that the apical membrane forms appropriately around the stereocilia.

The ARF GAPs ELMOD1 and ELMOD3 act at the Golgi and cilia to regulate ciliogenesis and ciliary protein traffic

“…1B,D). The overlap between localizations of ELMOD1 and ELMOD3 in mouse retinal cells is consistent with previously reported localizations of ELMOD1 in hair cells at the cell apex (Krey et al, 2018) and ELMOD3 in stereocilia and kinocilia in the organ of Corti and inner ear (Jaworek et al, 2013). The localizations of ELMOD3 are also quite similar to what we reported earlier for ELMOD2 in mouse retina (Turn et al, 2021).…”

The ARF GAPs ELMOD1 and ELMOD3 act at the Golgi and Cilia to Regulate Ciliogenesis and Ciliary Protein Traffic

“…1B,D). The overlap in locations between ELMOD1 and ELMOD3 in mouse retinal cells is consistent with previously reported localizations of ELMOD1 in hair cells at the cell apex (40) and ELMOD3 in stereocilia and kinocilia in the organ of Corti and inner ear (39). The localizations of ELMOD3 are also quite similar to what we reported earlier for ELMOD2 in mouse retina (35).…”

Elevated expression of the adhesion GPCR ADGRL4/ELTD1 promotes endothelial sprouting angiogenesis without activating canonical GPCR signalling

“…Although ADGRL4/ELTD1 lacks a PDZ motif, interestingly its overexpression induced the expression of another ELMO protein family member, ELMOD1 . ELMOD1 is a GTPase-activating protein, activates the GTP-binding protein ARF6 to regulate actin assembly and membrane trafficking 40 . In endothelial cells, ARF6 is known to regulate angiogenesis, and does so by modulating the trafficking and recycling of VEGFR2 from the cell surface, ensuring adequate VEGFR2 expression 41 , 42 .…”