Paneva, A. | Search bioRxiv

bioRxiv2025

Mammalian RAVE couples V-ATPase assembly to organelle acidification and function

Acidification of lysosomes, endosomes, and the Golgi underpins organelle-specific functions within the endomembrane system. This process is driven by vacuolar-type H-ATPases (V-ATPases), which reversibly assemble from peripheral V and membrane-integral V domains to regulate organelle pH. In yeast, V-V assembly at the vacuole is mediated by the RAVE complex, but V-ATPase assembly in mammalian cells remains less well understood. Here, we systematically define physiological roles of mammalian RAVE. Under basal conditions, mRAVE broadly promotes V-ATPase assembly and organelle acidification. Upon mTORC1 inactivation, mRAVE is recruited to lysosomes and required for the resulting increase in V-ATPase assembly and catabolic activity. Loss of mRAVE disrupts organelle acidification, leading to suppression of lysosomal catabolism, accumulation of dysfunctional lysosomes and compensatory lysosomal exocytosis. Restoring lysosomal pH rescues basal function in mRAVE-deficient cells but not the mTORC1-regulated increase in catabolic activity. Thus, mRAVE is an essential V-ATPase assembly factor that couples acidification to organelle function and nutrient signaling.

cell biology↗

bioRxiv2025

Inverted Assembly of the Lens Within Ocular Organoids Reveals Alternate Paths to Ocular Morphogenesis

The eye is a complex organ composed of two main structures - the retina and the lens. It forms by the invagination of the lens forming head surface ectoderm embedding into the forming optic cup. This "outside-in" mode of morphogenesis ensures that the light focusing lens is positioned centrally inside of the eye in the highly constrained environment of the developing embryo. Advances in stem cell biology in the last decade introduced organoids as model to study organogenesis under normal and diseased conditions. However, even though strikingly similar at some points, it remained elusive to which extend the generation of individual structural features in organoids recapitulates in vivo organogenesis. Here we describe the generation of fish ocular organoids composed of both, lens and retina, using pluripotent embryonic cells from medaka (Oryzias latipes). Formation of the organoid lens followed the key molecular features of the process in vivo, including the establishment of lens progenitor cells and their subsequent differentiation into lens fiber cells. In a process dependent on the coordinated activity of BMP and FGF signaling, lens formation in ocular organoids was marked by the expression of key genes implicated in organismal lens development. Despite adhering to the basic molecular machinery of lens formation in vivo, the morphogenesis into a spherical lens followed an "inside-out" mode. Lens progenitor cells were initially established and differentiated into a spherical lens directly inside of the retina. Subsequent displacement of the lens from the center of the organoid towards its surface ultimately led to the formation of a cup-like shaped retina with a centrally positioned lens. Our study highlights that the self-organization of the organoid can favor routes that were not selected for in the developing embryo. Those routes can lead to an alternative, though highly similar outcome with the respect to achieving specific structural features in an unconstrained, embryo-free environment.

developmental biology↗