The Dysferlin Domain-Only Protein, Spo73, Is Required for Prospore Membrane Extension in Saccharomyces cerevisiae

Abstract

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.

Dynamic localization of a yeast development–specific PP1 complex during prospore membrane formation is dependent on multiple localization signals and complex formation

“…Prospore membrane closure is partially defective in spo73 ∆, spo71 ∆, and vps13 ∆ cells; in contrast, prospore membrane closure is normal in gip1 ∆ cells ( Park and Neiman, 2012 ). While nuclear capture by the prospore membrane is partially defective in spo73 ∆, spo71 ∆, and vps13 ∆ cells ( Okumura et al , 2016 ), our observations showed that nuclear capture is normal in gip1 ∆ cells.…”

“…However, phenotypes of these mutants are distinct in some regards. While intraluminal vesicles are observed between inner and outer leaflets of the prospore membrane in spo73 ∆, spo71 ∆, and vps13 ∆ cells ( Park and Neiman, 2012 ; Park et al , 2013 ; Okumura et al , 2016 ), no such structures were observed in gip1 ∆ cells ( Tachikawa et al , 2001 ). Prospore membrane closure is partially defective in spo73 ∆, spo71 ∆, and vps13 ∆ cells; in contrast, prospore membrane closure is normal in gip1 ∆ cells ( Park and Neiman, 2012 ).…”

“…Prospore membranes in gip1 ∆ mutants appeared smaller than those in wild-type cells ( Figure 1 A). To quantify the difference in prospore membrane size, Htb2 tagged with mCherry was used as a nuclear marker ( Okumura et al , 2016 ) to identify postmeiotic cells and the perimeter lengths of prospore membranes were measured ( Figure 1 B). The results indicate that prospore membranes in gip1 ∆ mutant cells are smaller than those in wild-type cells ( Figure 1 C), with most of the prospore membranes successfully capturing nuclei (>90%).…”

“…These sporulation-specific septin structures are required for prospore membrane extension, at least in some strains ( Heasley and McMurray, 2016 ). Extension of the prospore membrane requires VPS13 , SPO71 , and SPO73 ( Park and Neiman, 2012 ; Parodi et al , 2012 , 2015 ; Okumura et al , 2016 ). Loss of any of these genes causes prospore membrane growth to stop at the small round stage.…”

“…Loss of any of these genes causes prospore membrane growth to stop at the small round stage. Spo71 recruits Vps13 to the prospore membrane and also interacts with Spo73 ( Park et al , 2013 ; Okumura et al , 2016 ). Although the precise mechanisms by which these proteins work are still unknown, the proteins are thought to form a complex on the prospore membrane and to facilitate membrane extension.…”