The Fission Yeast Synaptobrevin Ortholog Syb1 Plays an Important Role in Forespore Membrane Formation and Spore Maturation

Abstract

Synaptobrevin, also called vesicle-associated membrane protein (VAMP), is a component of the plasma membrane N-methylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, which plays a key role in intracellular membrane fusion. Previous studies have revealed that, similar to synaptobrevin in other organisms, the fission yeast synaptobrevin ortholog Syb1 associates with post-Golgi secretory vesicles and is essential for cytokinesis and cell elongation. Here, we report that Syb1 has a role in sporulation. After nitrogen starvation, green fluorescent protein (GFP)-Syb1 is found in intracellular dots. As meiosis proceeds, GFP-Syb1 accumulates around the nucleus and then localizes at the forespore membrane (FSM). We isolated a syb-S1 mutant, which exhibits a defect in sporulation. In syb1-S1 mutants, the FSM begins to form but fails to develop a normal morphology. Electron microscopy shows that an abnormal spore wall is often formed in syb1-S1 mutant spores. Although most syb1-S1 mutant spores are germinated, they are less tolerant to ethanol than wild-type spores. The syb1-S1 allele carries a missense mutation, resulting in replacement of a conserved cysteine residue adjacent to the transmembrane domain, which reduces the stability and abundance of the Syb1 protein. Taken together, these results indicate that Syb1 plays an important role in both FSM assembly and spore wall formation. Members of the soluble N-methylmaleimide-sensitive factor attachment protein receptor (SNARE) family contribute to transport specificity by regulating interactions between membrane vesicles and their appropriate target membranes (1). SNARE proteins exist as complementary sets of v-SNAREs, found on vesicle membranes, and t-SNAREs, found on target membranes. Recent classification, however, takes into account the structural features of SNARE proteins, subdividing them into RSNAREs and Q-SNAREs (2).There are approximately 40 SNAREs in an animal cell, and each associates with a particular organelle in the biosyntheticsecretory or endocytic pathway (3). A v-SNARE is a single polypeptide chain, whereas a t-SNARE complex is composed of two or three proteins. The v-SNAREs and t-SNAREs have characteristic helical domains, and when a v-SNARE interacts with a t-SNARE, the helical domains of one wrap around the helical domains of the other to form a stable four-helix bundle. The resulting trans-SNARE complex locks the two membranes together.SNAREs have been well characterized in neurons, where they mediate the docking and fusion of synaptic vesicles at the nerve terminal's plasma membrane (PM) during the process of neurotransmitter release. The SNARE complex responsible for docking synaptic vesicles at the PM of nerve terminals consists of three proteins. The transmembrane proteins v-SNARE synaptobrevin (also called vesicle-associated membrane protein [VAMP]) and t-SNARE syntaxin each contribute one ␣-helix to the complex (4, 5), whereas the peripheral membrane protein t-SNARE SNAP-25 contributes two ␣-helices to the four-helix bun...

The fission yeast spore is coated by a proteinaceous surface layer comprising mainly Isp3

“…Time-lapse observation was performed as previously described ( Nakamura et al. , 2008 ; Yamaoka et al. , 2013 ).…”

Sporulation: A response to starvation in the fission yeast Schizosaccharomyces pombe

“…The interaction of SNAREs serves as a driving force for fusion between vesicles and membranes through the formation of a tetrapeptide helical bundle via the interaction of cytoplasmic domains (Holz & Zimmerberg, 2019 ). During FSM formation of S. pombe , FSM expansion is performed by fusing vesicles with the vesicle SNARE (v‐SNARE) Syb1, an ortholog of synaptobrevin, with the target SNARE (t‐SNARE) complex comprising the syntaxin ortholog Psy1 and the SNAP‐25 ortholog Section 9 (Maeda et al, 2009 ; Nakamura et al, 2005 ; Shimoda, 2004 ; Ucisik‐Akkaya et al, 2014 ; Yamaoka et al, 2013 ) (Figure 2b ). Psy1 resides in the plasma membrane during vegetative growth and is recruited to the FSM precursor after meiosis I (Kashiwazaki et al, 2011 ; Maeda et al, 2009 ; Nakase et al, 2009 ; Shimoda, 2004 ).…”

“…Psy1 resides in the plasma membrane during vegetative growth and is recruited to the FSM precursor after meiosis I (Kashiwazaki et al, 2011 ; Maeda et al, 2009 ; Nakase et al, 2009 ; Shimoda, 2004 ). The psy1 + gene was originally identified as a suppressor of spore defects in a spo3 mutant (Maeda et al, 2009 ; Nakamura et al, 2001 ; Yamaoka et al, 2013 ). Spo3 is an FSM‐integrated meiosis‐specific coiled‐coil transmembrane protein that mediates membrane fusion during postmeiotic FSM expansion (Maeda et al, 2009 ; Nakamura et al, 2008 ).…”