Mitosis, not just open or closed


During cell division, eukaryotic cells must faithfully pass on their genetic material to the next generation during mitosis. It has long been known that lower eukaryotes and higher eukaryotes achieve this in strikingly different ways. Higher eukaryotes undergo an open mitosis in which the nuclear envelope is completely disassembled at the G2/M transition and is not reassembled until after DNA segregation in telophase/G1. In contrast, many lower eukaryotes undergo a closed mitosis in which the nuclear envelope remains intact and mitosis occurs within the nucleus. However, classifying mitosis as being either open or closed has its limitations. Many early studies using phase and electron microscopy indicated that fungi have evolved variations in how the mitotic segregation of the DNA and the nuclear envelope is achieved (1, 2, 16, 38). For example, even in organisms which break down their nuclear envelope during mitosis, the phase during mitosis when the nuclear envelope breaks down can vary between organisms (16). Many of these early studies are described in an extensive and excellent review by Heath (16), which summarized the different morphological characteristics of many fungi and other lower eukaryotes during mitosis. More recently, the availability of fungal genome sequences combined with molecular genetics and live cell imaging has shed light on the mechanisms regulating such variant mitoses. Here we review recent advances in our understanding of fungal mitosis and discuss how the biology of different organisms and cell types may have necessitated variant mitoses.

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