Eukaryotes have evolved towards one of two extremes along a spectrum of strategies for remodelling the nuclear envelope during cell division: disassembling the nuclear envelope in an open mitosis or constructing an intranuclear spindle in a closed mitosis^1,2. Both classes of mitotic remodelling involve key differences in the core division machinery but the evolutionary reasons for adopting a specific mechanism are unclear. Here we use an integrated comparative genomics and ultrastructural imaging approach to investigate mitotic strategies in Ichthyosporea, close relatives of animals and fungi. We show that species in this clade have diverged towards either a fungal-like closed mitosis or an animal-like open mitosis, probably to support distinct multinucleated or uninucleated states. Our results indicate that multinucleated life cycles favour the evolution of closed mitosis.

真核生物在细胞分裂过程中沿着一系列重塑核膜的策略朝着两个极端之一进化：在开放有丝分裂中拆卸核膜或在闭合有丝分裂中构建核内纺锤体 ^1,2 。这两类有丝分裂重塑都涉及核心分裂机制的关键差异，但采用特定机制的进化原因尚不清楚。在这里，我们使用集成的比较基因组学和超微结构成像方法来研究鱼孢子虫（动物和真菌的近亲）的有丝分裂策略。我们表明，该进化枝中的物种已分化为类似真菌的封闭有丝分裂或类似动物的开放有丝分裂，可能是为了支持不同的多核或单核状态。我们的结果表明，多核生命周期有利于封闭有丝分裂的进化。