Golgi compartmentation and identity

Abstract

Recent work supports the idea that cisternae of the Golgi apparatus can be assigned to three classes, which correspond to discrete stages of cisternal maturation. Each stage has a unique pattern of membrane traffic. At the first stage, cisternae form in association with the ER at multifunctional membrane assembly stations. At the second stage, cisternae synthesize carbohydrates while exchanging material via COPI vesicles. At the third stage, cisternae of the trans-Golgi network segregate into domains and produce transport carriers with the aid of specific lipids and the actin cytoskeleton. These processes are coordinated by cascades of Rab and Arf/Arl GTPases.

Small GTPase Rab2B and Its Specific Binding Protein Golgi-associated Rab2B Interactor-like 4 (GARI-L4) Regulate Golgi Morphology

“…Because functional ablation of certain Rab isoforms either by knockdown or overexpression of their dominant negative mutants has been found to induce fragmentation of the Golgi in mammalian cells (10 -17), Rab proteins are generally thought to be key regulators of Golgi morphology in mammalian cells (5)(6)(7)(8)(9). However, the functional relationships among these presumed Golgi morphology-regulating Rabs or the involvement of additional Rab isoforms in the Golgi morphology of mammalian cells had never been investigated.…”

“…Thus, the proper functions of Rab small GTPases are thought to be important for maintenance of organelle identity and morphology (3,4). A representative example is the role of Rab proteins in the morphology and functions of the Golgi, which is closely connected to the endoplasmic reticulum and trans-Golgi network via membrane trafficking (5)(6)(7)(8)(9). A number of mammalian Rab isoforms have been reported to be present in the Golgi, including Rab1 in the cis-Golgi, Rab33B in the medial Golgi, and Rab6 in the trans-Golgi, and functional ablation of certain Golgi-resident Rabs, e.g.…”

“…More specifically, GCC185 contains multiple Rab-binding sites and interacts with different Rabs, including with Rab1 (cis-Golgi), Rab33B (medial Golgi), and Rab6 (transGolgi) (24), and that may contribute to the stacking of the Golgi cisternae. Although it is now widely believed that functions of Rab small GTPases are indispensable for the compacted Golgi morphology of mammalian cells (5)(6)(7)(8)(9), several important questions regarding the functional diversity and redundancy of Rab small GTPases in the Golgi remain unanswered, e.g. how many of the ϳ60 mammalian Rab isoforms are involved in Golgi iden-tity/morphology, and is there any functional redundancy of the Rabs (e.g.…”

Inactive rhomboid proteins: New mechanisms with implications in health and disease

“…This is significant because the retrograde machinery is crucial to maintain homeostasis of the secretory pathway, returning escaped ER-resident proteins from the cis-Golgi [33]. COPI vesicles also ensure spatial fidelity of Golgi-resident proteins, against a flux of anterograde movement [34].…”

The Golgi apparatus: insights from filamentous fungi

“…), which justifies using it to refer to individual Golgi units of any morphology, in agreement with the terminology used by (Bourett et al 2007) for the fungal Golgi and not just to the flattened saccules present normally in higher eukaryotes. Cisternae making up the Golgi apparatus can be classified according to various interdependent characteristics, such as their content in enzymes that glycosylate biosynthetic cargo (Farquhar 1985, Graham andEmr 1991) or in proteins that regulate membrane identity (Munro 2005), their lipid composition that defines the physical properties of the bilayer (Holthuis and Menon, 2014), as well as the membrane-traffic pathways operating to and from them (Papanikou and Glick 2014). Post-translational modification-mediating enzymes and lipids form gradients through different classes of cisternae, from where cargo is considered to pass in an ordered way, such that the Golgi appears as a polarized organelle.…”