Rab19, a member of the Rab subfamily of small GTPases, is likely a tissue-or cell type-specific protein [4]. It plays crucial roles in multiple biological processes. In primary ciliogenesis, it coordinates cortical remodeling and ciliary membrane growth, which is essential for the formation of primary cilia, sensory organelles important for organ development and homeostasis [1]. It also functions in endolysosomal cargo trafficking [2,3].

In polarized epithelial cells, Rab19-mediated clearing of apical cortical actin is required for ciliogenesis. Loss of the lysosomal membrane-tethering HOPS complex disrupts the targeting of Rab19 to the basal body, impairing actin-clearing and ciliogenesis [2,3]. In non-polarized cell types, loss of Rab19 blocks ciliogenesis even with a docked ciliary vesicle [1]. In Drosophila, loss of Rab19 or its binding partner Atg16 impairs Slit production, affecting the differentiation of pre-enteroendocrine cells and triggering an intestinal inflammatory response, potentially related to inflammatory bowel disease (IBD) [5].

In conclusion, Rab19 is essential for primary ciliogenesis and endolysosomal cargo trafficking. Its loss-of-function in different models reveals its importance in processes related to ciliogenesis and cell differentiation, with implications for diseases like IBD. Studies on Rab19 contribute to understanding the underlying mechanisms of these biological processes and associated diseases.