Cellular reproduction defines life, yet our textbook-level understanding of cell division is limited to a small number of model organisms centered around humans. The horizon on cell division variants is expanded here by advancing insights on the fascinating cell division modes found in the Apicomplexa, a key group of protozoan parasites. The Apicomplexa display remarkable variation in offspring number, whether karyokinesis follows each S/M-phase or not, and whether daughter cells bud in the cytoplasm or bud from the cortex. We find that the terminology used to describe the various manifestations of asexual apicomplexan cell division emphasizes either the number of offspring or site of budding, which are not directly comparable features and has led to confusion in the literature. Division modes have been primarily studied in two human pathogenic Apicomplexa, malaria-causing Plasmodium spp. and Toxoplasma gondii, a major cause of opportunistic infections. Plasmodium spp. divide asexually by schizogony, producing multiple daughters per division round through a cortical budding process, though at several life-cycle nuclear amplifications stages, are not followed by karyokinesis. T. gondii divides by endodyogeny producing two internally budding daughters per division round. Here we add to this diversity in replication mechanisms by considering the cattle parasite Babesia bigemina and the pig parasite Cystoisospora suis. B. bigemina produces two daughters per division round by a “binary fission” mechanism whereas C. suis produces daughters through both endodyogeny and multiple internal budding known as endopolygeny. In addition, we provide new data from the causative agent of equine protozoal myeloencephalitis (EPM), Sarcocystis neurona, which also undergoes endopolygeny but differs from C. suis by maintaining a single multiploid nucleus. Overall, we operationally define two principally different division modes: internal budding found in cyst-forming Coccidia (comprising endodyogeny and two forms of endopolygeny) and external budding found in the other parasites studied (comprising the two forms of schizogony, binary fission and multiple fission). Progressive insights into the principles defining the molecular and cellular requirements for internal vs. external budding, as well as variations encountered in sexual stages are discussed. The evolutionary pressures and mechanisms underlying apicomplexan cell division diversification carries relevance across Eukaryota.

细胞繁殖决定了生命，但我们在教科书一级对细胞分裂的理解仅限于少数以人类为中心的模型生物。通过深入了解蚜虫这一重要的原生动物寄生虫群中令人着迷的细胞分裂模式，可以扩大细胞分裂变体的视野。顶叶复合体在后代数量上显示出显着的变化，无论是否每个S / M期都发生了核运动，子细胞是在细胞质中发芽还是从皮层发芽。我们发现，用于描述无性双复合体细胞分裂的各种表现的术语强调了后代的数量或出芽的位点，这不是直接可比的特征，并且导致了文献中的混乱。疟原虫spp。和弓形虫，这是机会性感染的主要原因。 疟原虫spp。按精神分裂症无性分裂，尽管在生命周期的几个核扩增阶段中，核分裂运动并没有通过核皮层萌芽过程在每个分裂轮中产生多个子代。弓形虫通过内生分裂进行​​划分，每个分裂轮产生两个内部萌芽的女儿。在这里，我们通过考虑牛寄生虫来增加复制机制的多样性巴贝斯虫 还有猪的寄生虫 猪孢杆菌。 双歧杆菌 通过“二元裂变”机制每个分区产生两个女儿，而 猪C.通过内生性和多个内部出芽而产生子代，称为内多态。此外，我们提供了来自马原生动物脊髓性脑炎（EPM）病原体的新数据，肉胞藻，它也经历了内多态性，但与 猪C.通过维持单个多倍体核。总的来说，我们在操作上定义了两种主要不同的分裂方式：在形成囊肿的球菌中发现内部发芽（包括内生性和两种形式的内多菌型），在研究的其他寄生虫中发现外部发芽（包括精神分裂，二元裂变和多裂变的两种形式）。 ）。讨论了对定义内部和外部萌芽的分子和细胞要求的原理的渐进见解，以及在性阶段遇到的变异。apicomplexan细胞分裂多样化背后的进化压力和机制在整个真核生物中具有相关性。