The price of independence: cell separation in fission yeast

Abstract

The ultimate goal of cell division is to give rise to two viable independent daughter cells. A tight spatial and temporal regulation between chromosome segregation and cytokinesis ensures the viability of the daughter cells. Schizosaccharomyces pombe, commonly known as fission yeast, has become a leading model organism for studying essential and conserved mechanisms of the eukaryotic cell division process. Like many other eukaryotic cells it divides by binary fission and the cleavage furrow undergoes ingression due to the contraction of an actomyosin ring. In contrast to mammalian cells, yeasts as cell-walled organisms, also need to form a division septum made of cell wall material to complete the process of cytokinesis. The division septum is deposited behind the constricting ring and it will constitute the new ends of the daughter cells. Cell separation also involves cell wall degradation and this process should be precisely regulated to avoid cell lysis. In this review, we will give a brief overview of the whole cytokinesis process in fission yeast, from the positioning and assembly of the contractile ring to the final step of cell separation, and the problems generated when these processes are not precise.

Overview of fission yeast septation

“…It is possible that the separation machinery, which at least includes the septins, the exocyst, Rho GTPases and glucanases (Fig. ) (reviewed in Martin‐Garcia and Santos, ), is set at the beginning of septation, and if the AR constriction/septation is delayed, separation can no longer take place. The Sep1–Ace2 transcription‐factor cascade regulates the periodic expression of many genes encoding proteins required for AR constriction and for cell separation (Rustici et al ., ; Alonso‐Nuñez et al ., ).…”

The Role of the Cell Integrity Pathway in Septum Assembly in Yeast

“…Cell separation also involves cell wall degradation between the two halves of the division septum that will constitute the new ends of the daughter cells. The overall process has been deeply studied, and there are excellent reviews on cytokinesis [ 10 , 11 , 12 , 13 ], septation [ 14 , 15 ] and cell separation [ 16 ]. In this review, we will first summarise key steps of fission yeast cytokinesis, including ring assembly, constriction and septum formation, before discussing emerging mechanisms that involve the cell integrity pathway (CIP) in the regulation of cytokinesis and their biological implications.…”

The Multiple Functions of Rho GTPases in Fission Yeasts

“…The final and most critical step of cytokinesis is cell separation, which initiates by the activation of the Morphogenesis Orb6 (MOR) pathway upon completing actomyosin ring constriction and septum formation. In fission yeast, the separation machinery includes septin protein complexes (Mid2 and septins Spn1-4), the exocyst, Rho GTPases and the glucanases Eng1 and Agn1 (reviewed in [230]). First, Agn1 digests the cell wall material that surrounds the septum followed by the action of Eng1, which is necessary for the dissolution of the primary septum.…”