Muñoz et al. show that a cell wall polysaccharide promotes fungal cell division by helping to center the contractile ring.
During animal cell division, the contractile ring pinches the cell in two, and then the plasma membrane extends to separate the daughter cells. A fungal cell is encased in a cell wall that complicates the division process. As the contractile ring closes and the plasma membrane expands, an extension of the cell wall called the septum stretches across the cell. When this barrier is complete, the central part of the septum deteriorates and the remaining material forms the new end of each daughter cell. The cell wall and septum contain several polysaccharides known as glucans, including branched β(1,3)glucan (B-BG), which is made by the enzyme Bgs4 and helps the cell maintain its shape and integrity. But the role of B-BG during cell division isn’t clear.
The contractile ring typically forms in the middle of the cell, but in cells lacking Bgs4 it was often off center and at the wrong angle. Moreover, the ring often slid instead of remaining in place until septum synthesis started. This suggests that B-BG helps situate the contractile ring and hold it in position.
B-BG also helps locate and fortify the septum. The structure normally grows perpendicular to the sides of the cell, but when B-BG was lacking it sometimes formed at an oblique angle or appeared wavy. The septum usually advances across the cell at the same time that the contractile ring closes and the cell membrane extends. But if B-BG was missing, the contractile ring and cell membrane were out of sync with septum growth, suggesting that B-BG helps link all three together so that they progress in unison.
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Text by Mitch Leslie
