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.
Highlights
Cytokinesis is the final stage in the mitotic cell division process whereby cell separation is effected to generate two daughter cells
RVS16713Myc rescued all phenotypes associated with an rvs167 null mutation; synthetic lethality with iqg1-1 on methionine deficient media, salt sensitivity and actin cytoskeleton polarity (Fig. S1A, B and C)
It was concluded from these data that loss of amphiphysin function in a strain where Iqg1 function was compromised resulted in a failure of cytokinesis and cell separation
Summary
Cytokinesis is the final stage in the mitotic cell division process whereby cell separation is effected to generate two daughter cells. In yeast and animal cells this requires the assembly of a contractile actin ring (CAR) that initiates membrane ingression followed by membrane scission [1]. These events are necessarily coupled to the completion of mitosis and contraction initiates immediately after mitotic spindle breakdown [2]. Septation requires the activity of two chitin synthases, Chs and Chs, governing the synthesis of the primary and secondary septa respectively [6]. Following successful construction of the primary and the flanking secondary septa the primary septum is removed by the activity of chitinase to allow the completion of cell separation [8]
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