The role of acroblast formation duringDrosophilaspermatogenesis

Abstract

Protein 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.

Vps54 regulatesDrosophilaneuromuscular junction development and controls postsynaptic density composition via a Rab7-dependent mechanism

“…Vps54 localizes primarily to the TGN in yeast and in mouse spermatids (Berruti et al, 2010; Conibear and Stevens, 2000). Similar localization patterns have been observed with fluorescently-tagged Scat protein in Drosophila (Fari et al, 2016b). Based on this, we predicted that Scat would localize to the TGN in larval MNs and muscle cells.…”

“…The classic scat 1 allele is a P-element insertion near the 5’ end of the second coding exon of the scat gene (Figure S1) (Castrillon et al, 1993). Protein expression is completely disrupted in scat 1 homozygotes suggesting that it is a null allele (Fari et al, 2016b). We found that the morphology of the NMJ was distinctly different in scat 1 mutants compared to controls (Figure 1A).…”

“…Analysis of Golgi morphology in the symptomatic wobbler mouse reveals significant vacuolization of the Golgi in the soma of MNs (Palmisano et al, 2011). Finally, in Drosophila post-mitotic spermatids, scat 1 mutants have defects in the localization of Golgin245, a conserved golgin associated with the TGN, although the cis- Golgi marker (the golgin GM130) was unaffected (Fari et al, 2016b). Based on this, we cannot rule out that partial Stx16 mislocalization we observed in scat 1 MNs is not due to a more global defect in the integrity of both sides of the Golgi ribbon.…”

“…This is a diagram showing the location of the P-element insertion in the second exon of the scat locus. Using an antibody targeting the N-terminal 200 amino acids of the Scat protein, it has previously been shown that this is a null allele (Fari et al, 2016a). …”

Epithelial-to-mesenchymal transition drives a pro-metastatic Golgi compaction process through scaffolding protein PAQR11

“…During Drosophila spermatogenesis, COG and the Golgi-associated retrograde protein complex promote ribbon formation in the acroblast (41), and COG is essential for tethering activity in the cell-free vesicle tethering assay used here (32), implying that PAQR11 could well be acting as a scaffold in retrograde vesicle tethering, which in turn may be needed for ribbon formation. Additionally, both GRASP55 and GRASP65 are phosphorylated by ERK, a RAS-activated kinase, and mutation of the ERK phosphorylation sites on GRASP55 enhances cisternal stacking, indicating that ERK negatively regulates GRASP55 activity (42).…”