Abstract
ABSTRACTProtein recycling is important for maintaining homeostasis of the Golgi and its cisternae. The Vps54 (Scat) protein, a subunit of the GARP tethering complex, is a central factor in retrograde transport to the trans-Golgi. We found the scat1 mutant to be male sterile in Drosophila with individualization problems occurring during spermatogenesis. Another typically observed phenotype was the abnormal nuclear structure in elongated mutant cysts. When examining the structure and function of the Golgi, a failure in acrosome formation and endosome-Golgi vesicular transport were found in the scat1 mutant. This acrosome formation defect was due to a fault in the trans-Golgi side of the acroblast ribbon. When testing a mutation in a second retrograde transport protein, Fws, a subunit of the conserved oligomeric Golgi (COG) tethering complex, the acroblast structure, was again disrupted. fwsP caused a similar, albeit milder, acrosome and sperm individualization phenotype as the scat1 mutant. In the case of fwsP the cis side of the acroblast ribbon was dispersed, in-line with the intra-Golgi retrograde function of COG. Our results highlight the importance of an intact acroblast for acrosome formation, nuclear elongation and therefore sperm maturation. Moreover, these results suggest the importance of retrograde tethering complexes in the formation of a functional Golgi ribbon.
Highlights
In most mammalian cell types the Golgi apparatus appears as a ribbon formed from interconnected stacks of cisternae, this arrangement is not universal
The scat1 mutant has a male fertility defect In order to probe the function of vesicle tethering complexes that act at the Golgi during spermatogenesis, we investigated the Vps54 subunit of the Golgi associated retrograde protein (GARP) complex, encoded by the scat gene
We found that the Scat-RFP signal localized close but slightly displaced from dGM130 in all stages of spermatogenesis, suggesting that Scat is localized to the trans side of the Golgi (Fig. 2C-E)
Summary
In most mammalian cell types the Golgi apparatus appears as a ribbon formed from interconnected stacks of cisternae, this arrangement is not universal. In gastric parietal cells the Golgi appears in the form of mini-stacks dispersed throughout the cytoplasm (Gunn et al, 2011) This scattered arrangement is common in most cell types of the fruit fly Drosophila melanogaster (Kondylis and Rabouille, 2009). The Golgi apparatus of developing Drosophila spermatids is in a peri-nuclear location just prior to and during the nuclear elongation phase of spermatogenesis (Kondylis and Rabouille, 2009) This specialized Golgi assemblage, known as the acroblast, is likely to be needed to organize the secretory pathway in this highly polarized cell type of the fruit fly
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