No abstract

Eukaryotic cells assemble an actomyosin ring during cytokinesis to function as a force-generating machine to drive membrane invagination, and to counteract the intracellular pressure and the cell surface tension. How the extracellular matrix affects actomyosin ring contraction has not been fully explored. While studying the S. pombe 1,3− β-glucan-synthase mutant cps1-191, which is defective in division septum synthesis and arrests with a stable actomyosin ring and, we found that weakening of the extracellular glycan matrix caused the generated spheroplasts to divide at the non-permissive condition. This non-medial slow division was dependent on a functional actomyosin ring and vesicular trafficking, but independent of normal septum synthesis. Interestingly, the high intracellular turgor pressure appears to play minimal roles in inhibiting ring contraction in the absence of cell wall remodeling in cps1-191 mutants as decreasing the turgor pressure alone did not enable spheroplast division. We propose that during cytokinesis, the extracellular glycan matrix restricts actomyosin ring contraction and membrane ingression, and remodeling of the extracellular components through division septum synthesis relieves the inhibition and facilitates actomyosin ring contraction.

Chronological studies on the respiratory function and membrane components of newborn rat liver mitochondria revealed that perinatal mitochondria retained considerably well-coupled oxidative phosphorylation that functioned in sites II and III prior to site I. The ratio of protein to phospholipid contents (mg/μmol) was low in these mitochondria, in which phospholipids were characterized by their high phosphatidylethanolamine contents (43% of the total phospholipids) and low cardiolipin contents (6% of the total), as compared to those of the adult. The fatty acid composition in major phospholipid species was also different from those of the adult. These characteristics altered with development, and the carbamylphosphate synthetase contents markedly increased from 12 to 20% of the total polypeptides in 10 days postnatal time. From these results structural and functional completion of mitochondria accompaying development is discussed from a mitochondrial biogenesis viewpoint.

Eukaryotic cells assemble an actomyosin ring during cytokinesis to function as a force-generating machine to drive membrane invagination, and to counteract the intracellular pressure and the cell surface tension. It is unclear whether additional factors such as the extracellular matrix (cell wall in yeasts and fungi) affect the actomyosin ring contraction. While studying the fission yeast β-glucan synthase mutant cps1-191, which is defective in division septum synthesis and actomyosin ring contraction, we found that significantly weakening of the extracellular glycan matrix caused the spheroplasts to divide at the non-permissive condition. This division was dependent on a functional actomyosin ring and vesicular trafficking, but independent of normal septum synthesis. cps1-191 cells with weakened extracellular glycan matrix divide non-medially with a much slower ring contraction rate compared to wild type cells under similar conditions, which we term as cytofission.Interestingly, the high turgor pressure appears to play minimal roles in inhibiting ring contraction in cps1-191 mutants as decreasing the turgor pressure alone does not enable cytofission. We propose that during cytokinesis, the extracellular glycan matrix restricts actomyosin ring contraction and membrane ingression, and remodeling of the extracellular components through division septum synthesis relieves the inhibition and facilitates actomyosin ring contraction.