The Budding Yeast Amphiphysin Complex Is Required for Contractile Actin Ring (CAR) Assembly and Post-Contraction GEF-Independent Accumulation of Rho1-GTP

Abstract

The late events of the budding yeast cell division cycle, cytokinesis and cell separation, require the assembly of a contractile actomyosin ring (CAR), primary and secondary septum formation followed by enzymatic degradation of the primary septum. Here we present evidence that demonstrates a role for the budding yeast amphiphysin complex, a heterodimer comprising Rvs167 and Rvs161, in CAR assembly and cell separation. The iqg1-1 allele is synthetically lethal with both rvs167 and rvs161 null mutations. We show that both Iqg1 and the amphiphysin complex are required for CAR assembly in early anaphase but cells are able to complete assembly in late anaphase when these activities are, respectively, either compromised or absent. Amphiphysin dependent CAR assembly is dependent upon the Rvs167 SH3 domain, but this function is insufficient to explain the observed synthetic lethality. Dosage suppression of the iqg1-1 allele demonstrates that endocytosis is required for the default cell separation pathway in the absence of CAR contraction but is unlikely to be required to maintain viability. The amphiphysin complex is required for normal, post-mitotic, localization of Chs3 and the Rho1 GEF, Rom2, which are responsible for secondary septum deposition and the accumulation of GTP bound Rho1 at the bud neck. It is concluded that a failure of polarity establishment in the absence of CAR contraction and amphiphysin function leads to loss of viability as a result of the consequent cell separation defect.

An actomyosin clamp assembled by the Amphiphysin-Rho1-Dia/DAAM-Rok pathway reinforces somatic cell membrane folded around spermatid heads

“…Amph-dependent Rho1 and Dia recruitment at the membrane folded around the spermatid heads triggers actin polymerization We found that the N-BAR family protein Amph recruits Rho1 and Dia on the somatic cell membrane during the final stages of spermatid maturation and promotes F-actin assembly at the basket. Rvs 167, the Amph ortholog in yeast, is also suggested to promote Rho1 localization at the membrane furrow during cytokinesis (Cundell and Price, 2014). Some BAR-domain proteins are shown to interact with the Cdc42 and Rac1 families of Rho-GTPases through their SH3 domain and nucleate F-actin assembly through the WASp/WAVE NPFs (Aspenströ m, 2014;Fricke et al, 2009).…”