The dimeric Golgi protein Gorab binds to Sas6 as a monomer to mediate centriole duplication

Vimentin intermediate filaments provide structural stability to the mammalian Golgi complex

The Golgi complex comprises a connected ribbon of stacked cisternal membranes localized to the perinuclear region in most vertebrate cells. The position and morphology of this organelle depends upon interactions with microtubules and the actin cytoskeleton. In contrast, we know relatively little about the relationship of the Golgi complex with intermediate filaments (IFs). In this study, we show that the Golgi is in close physical proximity to vimentin IFs in cultured mouse and human cells. We also show that the trans-Golgi network coiled-coil protein GORAB can physically associate with vimentin IFs. Loss of vimentin and/or GORAB had a modest effect upon Golgi structure at the steady state. The Golgi underwent more rapid disassembly upon chemical disruption with brefeldin A or nocodazole, and slower reassembly upon drug washout, in vimentin knockout cells. Moreover, loss of vimentin caused reduced Golgi ribbon integrity when cells were cultured on high-stiffness hydrogels, which was exacerbated by loss of GORAB. These results indicate that vimentin IFs contribute to the structural stability of the Golgi complex and suggest a role for GORAB in this process.

The factory, the antenna and the scaffold: the three-way interplay between the Golgi, cilium and extracellular matrix underlying tissue function

The growth and development of healthy tissues is dependent on the construction of a highly specialised extracellular matrix (ECM) to provide support for cell growth and migration and to determine the biomechanical properties of the tissue. These scaffolds are composed of extensively glycosylated proteins which are secreted and assembled into well-ordered structures that can hydrate, mineralise, and store growth factors as required. The proteolytic processing and glycosylation of ECM components is vital to their function. These modifications are under the control of the Golgi apparatus, an intracellular factory hosting spatially organised, protein-modifying enzymes. Regulation also requires a cellular antenna, the cilium, which integrates extracellular growth signals and mechanical cues to inform ECM production. Consequently, mutations in either Golgi or ciliary genes frequently lead to connective tissue disorders. The individual importance of each of these organelles to ECM function is well-studied. However, emerging evidence points towards a more tightly linked system of interdependence between the Golgi, cilium and ECM. This review examines how the interplay between all three compartments underpins healthy tissue. As an example, it will look at several members of the golgin family of Golgi-resident proteins whose loss is detrimental to connective tissue function. This perspective will be important for many future studies looking to dissect the cause and effect of mutations impacting tissue integrity.

Targeting Drosophila Sas6 to mitochondria reveals its high affinity for Gorab

The ability to relocalize proteins to defined subcellular locations presents a powerful tool to examine protein-protein interactions that can overcome a tendency of non-targeted exogenous proteins to form inaccessible aggregates. Here, we show that a 24-amino-acid sequence from the Drosophila proapoptotic protein Hid's tail anchor (HTA) domain can target exogenous proteins to the mitochondria in Drosophila cells. We use this HTA tag to target the Drosophila centriole cartwheel protein Sas6 to the mitochondria, and show that both exogenous and endogenous Gorab can be co-recruited from the Golgi to the new mitochondrial site. This accords with our previous observation that monomeric Drosophila Gorab binds Sas6 to become centriole associated with a 50-fold greater affinity than dimeric Gorab binds Rab6 to become localized at the Golgi. Strikingly, Drosophila Sas6 can bind both Drosophila Gorab and its human GORAB ortholog, whereas human SAS6 is unable to bind either GORAB or Gorab. We discuss these findings in relation to the evolutionary conservation of Gorab and the divergence of Sas6, possibly reflecting known differences in persistence of the cartwheel in the centriole duplication cycle of fly and human cells.

Nine-fold symmetry of centriole: The joint efforts of its core proteins

The centriole is a widely conserved organelle required for the assembly of centrosomes, cilia, and flagella. Its striking feature - the nine-fold symmetrical structure, was discovered over 70 years ago by transmission electron microscopy, and since elaborated mostly by cryo-electron microscopy and super-resolution microscopy. Here, we review the discoveries that led to the current understanding of how the nine-fold symmetrical structure is built. We focus on the recent findings of the centriole structure in high resolution, its assembly pathways, and its nine-fold distributed components. We propose a model that the assembly of the nine-fold symmetrical centriole depends on the concerted efforts of its core proteins.