No abstract

The structural and functional unit of the Golgi apparatus is the stack, formed by piled membranous cisternae. Among eukaryotes the number of stacks ranges from one to several copies per cell. When present in multiple copies, the Golgi is observed in two arrangements: stacks either remain separated or link into a centralized structure referred to as the ribbon, after its description by Camillo Golgi. This Golgi architecture is considered to be restricted to vertebrate cells and its biological functions remain unclear. Here we show that the ribbon-like Golgi organization is instead present in the cells of several animals belonging to the cnidarian and bilaterian clades, implying its appearance in their common ancestor. We hypothesize a possible scenario driving this structural innovation. The Golgi Reassembly and Stacking Proteins, GRASPs, are central to the formation of the mammalian Golgi ribbon by mediating stack tethering. To link the stacks, GRASPs must be correctly oriented on Golgi membranes through dual anchoring including myristoylation and interaction with a protein partner of the Golgin class. We propose that the evolution of binding of Golgin-45 to GRASP led to Golgi stack tethering and the appearance of the ribbon-like organization. This hypothesis is supported by AlphaFold2 modelling of Golgin-45/GRASP complexes of animals and their closest unicellular relatives. Early evolution and broad conservation of the ribbon-like Golgi architecture imply its functional importance in animal cellular physiology. We anticipate that our findings will stimulate a wave of new studies on the so far elusive biological roles of this Golgi arrangement.

No abstract