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Suppression of Vps13 adaptor protein mutants reveals a central role for PI4P in regulating prospore membrane extension.

ABSTRACT: Vps13 family proteins are proposed to function in bulk lipid transfer between membranes, but little is known about their regulation. During sporulation of Saccharomyces cerevisiae, Vps13 localizes to the prospore membrane (PSM) via the Spo71-Spo73 adaptor complex. We previously reported that loss of any of these proteins causes PSM extension and subsequent sporulation defects, yet their precise function remains unclear. Here, we performed a genetic screen and identified genes coding for a fragment of phosphatidylinositol (PI) 4-kinase catalytic subunit and PI 4-kinase noncatalytic subunit as multicopy suppressors of spo73Δ. Further genetic and cytological analyses revealed that lowering PI4P levels in the PSM rescues the spo73Δ defects. Furthermore, overexpression of VPS13 and lowering PI4P levels synergistically rescued the defect of a spo71Δ spo73Δ double mutant, suggesting that PI4P might regulate Vps13 function. In addition, we show that an N-terminal fragment of Vps13 has affinity for the endoplasmic reticulum (ER), and ER-plasma membrane (PM) tethers localize along the PSM in a manner dependent on Vps13 and the adaptor complex. These observations suggest that Vps13 and the adaptor complex recruit ER-PM tethers to ER-PSM contact sites. Our analysis revealed that involvement of a phosphoinositide, PI4P, in regulation of Vps13, and also suggest that distinct contact site proteins function cooperatively to promote de novo membrane formation.

SUBMITTER: Nakamura TS

PROVIDER: S-EPMC8372973 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Sporulation of Saccharomyces cerevisiae is a developmental process in which an ascus containing four haploid spores forms from a diploid cell. During this process, newly formed membrane structures called prospore membranes extend along the nuclear envelope and engulf and package daughter nuclei along with cytosol and organelles to form precursors of spores. Proteins involved in prospore membrane extension, Vps13 and Spo71, have recently been reported; however, the overall mechanism of membrane extension remains unclear. Here, we identified Spo73 as an additional factor involved in prospore membrane extension. Analysis of a spo73? mutant revealed that it shows defects similar to those of a spo71? mutant during prospore membrane formation. Spo73 localizes to the prospore membrane, and this localization is independent of Spo71 and Vps13. In contrast, a Spo73 protein carrying mutations in a surface basic patch mislocalizes to the cytoplasm and overexpression of Spo71 can partially rescue localization to the prospore membrane. Similar to spo71? mutants, spo73? mutants display genetic interactions with the mutations in the SMA2 and SPO1 genes involved in prospore membrane bending. Further, our bioinformatic analysis revealed that Spo73 is a dysferlin domain-only protein. Thus, these results suggest that a dysferlin domain-only protein, Spo73, functions with a dual pleckstrin homology domain protein, Spo71, in prospore membrane extension. Analysis of Spo73 will provide insights into the conserved function of dysferlin domains, which is related to dysferlinopathy. IMPORTANCE Prospore membrane formation consists of de novo double-membrane formation, which occurs during the developmental process of sporulation in Saccharomyces cerevisiae. Membranes are formed into their proper size and shape, and thus, prospore membrane formation has been studied as a general model of membrane formation. We identified SPO73, previously shown to be required for spore wall formation, as an additional gene involved in prospore membrane extension. Genetic and cell biological analyses suggested that Spo73 functions on the prospore membrane with other factors in prospore membrane extension, counteracting the bending force of the prospore membrane. Spo73 is the first dysferlin domain-only protein ever analyzed. The dysferlin domain is conserved from yeast to mammals and is found in dysferlin proteins, which are involved in dysferlinopathy, although the precise function of the domain is unknown. Continued analysis of Spo73 will contribute to our understanding of the function of dysferlin domains and dysferlinopathy.

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Suppression of Vps13 adaptor protein mutants reveals a central role for PI4P in regulating prospore membrane extension.

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