Elmod1, or ELMO domain-containing protein 1, functions as a guanine nucleoside triphosphatase activating protein (GAP) for ARF6, a member of the ADP-ribosylation factor (ARF) small GTPase family. ARF family GTPases regulate membrane trafficking and cytoskeletal assembly, and thus Elmod1 is crucial in these cellular processes. Genetic models, such as knockout mouse models, have been valuable in studying its functions [1,4].

In rda/rda mice lacking functional Elmod1, utricle hair cell cuticular plates initially form normally but degenerate after postnatal day 5, with vesicles invading the compromised plate. Hair bundles also show abnormal development, including apical membrane detachment, stereocilia elongation and fusion. The ARF6 GTP/GDP ratio is elevated in rda/rda utricles, indicating that Elmod1-mediated conversion of ARF6 to its GDP-bound form is necessary for hair bundle stabilization [1]. Deletion of Elmod1 in cells leads to decreased ability to form primary cilia, loss of some ciliary proteins, and their accumulation at the Golgi, suggesting a role in ciliogenesis and ciliary protein traffic [2]. A novel mutation in the human Elmod1 gene has been associated with mental retardation and autism spectrum disorder, demonstrating differences in phenotypes between humans and mice with Elmod1 mutations [3].

In conclusion, Elmod1 is essential for the normal development and function of hair cells by stabilizing apical structures, and also plays a role in ciliogenesis and ciliary protein traffic. Mouse models with Elmod1 mutations have provided insights into its functions in these processes and its potential link to human diseases such as mental retardation and autism spectrum disorder.