Rab19, a small GTPase of the Rab subfamily, is likely a tissue-or cell type-specific protein [5]. It has been implicated in multiple biological processes. One of its crucial functions is in ciliogenesis, where it coordinates cortical remodeling and membrane growth [1]. In polarized epithelial cells, it is involved in clearing apical cortical actin, which is essential for the cilium to grow from the apically-docked basal body into the extracellular space [2,3]. Additionally, it has roles in endolysosomal cargo trafficking [2,3], and in acrosome biogenesis, where it interacts with WDR38 and GM130 [4].

In loss-of-function studies, Rab19 loss in non-polarized cell types blocks ciliogenesis with a docked ciliary vesicle [1]. In polarized epithelial cells, disruption of the lysosomal membrane-tethering HOPS complex, which affects Rab19 targeting to the basal body, impairs actin-clearing and ciliogenesis, highlighting the importance of Rab19 in this process [2,3]. In Drosophila, loss of Atg16 or its binding partner Rab19 impairs Slit production, affecting enteroendocrine cell differentiation and triggering an intestinal inflammatory response, suggesting a link to inflammatory bowel disease [6].

In conclusion, Rab19 is essential for ciliogenesis, endolysosomal cargo trafficking, and acrosome biogenesis. The gene knockout and conditional knockout models in Drosophila and cell-based studies have revealed its role in processes related to ciliogenesis and cell differentiation, with potential implications for understanding ciliopathies and inflammatory bowel disease.