Kron S J, Styles C A, Fink G R
Whitehead Institute for Biomedical Research, Cambridge, Massachusetts.
Mol Biol Cell. 1994 Sep;5(9):1003-22. doi: 10.1091/mbc.5.9.1003.
Laboratory strains of Saccharomyces cerevisiae are dimorphic; in response to nitrogen starvation they switch from a yeast form (YF) to a filamentous pseudohyphal (PH) form. Time-lapse video microscopy of dividing cells reveals that YF and PH cells differ in their cell cycles and budding polarity. The YF cell cycle is controlled at the G1/S transition by the cell-size checkpoint Start. YF cells divide asymmetrically, producing small daughters from full-sized mothers. As a result, mothers and daughters bud asynchronously. Mothers bud immediately but daughters grow in G1 until they achieve a critical cell size. By contrast, PH cells divide symmetrically, restricting mitosis until the bud grows to the size of the mother. Thus, mother and daughter bud synchronously in the next cycle, without a G1 delay before Start. YF and PH cells also exhibit distinct bud-site selection patterns. YF cells are bipolar, producing their second and subsequent buds at either pole. PH cells are unipolar, producing their second and subsequent buds only from the end opposite the junction with their mother. We propose that in PH cells a G2 cell-size checkpoint delays mitosis until bud size reaches that of the mother cell. We conclude that yeast and PH forms are distinct cell types each with a unique cell cycle, budding pattern, and cell shape.
酿酒酵母的实验室菌株具有二态性；在氮饥饿条件下，它们会从酵母形态（YF）转变为丝状假菌丝（PH）形态。对分裂细胞进行延时视频显微镜观察发现，YF细胞和PH细胞在细胞周期和出芽极性方面存在差异。YF细胞周期在G1/S转换点受细胞大小检查点Start控制。YF细胞不对称分裂，由全尺寸的母细胞产生小的子细胞。因此，母细胞和子细胞异步出芽。母细胞立即出芽，但子细胞在G1期生长，直到达到临界细胞大小。相比之下，PH细胞对称分裂，将有丝分裂限制到芽生长到母细胞大小为止。因此，母细胞和子细胞在下一个周期同步出芽，在Start之前没有G1期延迟。YF细胞和PH细胞还表现出不同的芽位选择模式。YF细胞是双极的，在两极产生第二个及后续的芽。PH细胞是单极的，仅从与其母细胞连接处相对的一端产生第二个及后续的芽。我们提出，在PH细胞中，一个G2细胞大小检查点会将有丝分裂延迟到芽大小达到母细胞大小。我们得出结论，酵母形态和PH形态是不同的细胞类型，每种类型都有独特的细胞周期、出芽模式和细胞形状。
