W. M. Keck Science Department, Claremont McKenna, Pitzer and Scripps Colleges, Claremont, CA 91711, USA.
Biol Lett. 2020 May;16(5):20200137. doi: 10.1098/rsbl.2020.0137. Epub 2020 May 13.
Egg development is a defining process of reproduction in higher eukaryotes. In the fruit fly, , this process begins with four mitotic divisions starting from a single germ cell, producing a cyst of 16 cystocytes; one of these cells will become the oocyte and the others supporting nurse cells. These mitotic divisions are exceptional because cytokinesis is incomplete, resulting in the formation of cytoplasmic bridges known as ring canals that interconnect the cystocytes. This organization allows all cystocytes to divide synchronously during each mitotic round, resulting in a final, power-of-2 number of germ cells. Given that numerous insects obey this power-of-2 rule, we investigated if strict cell doubling is a universal, underlying cause. Using confocal microscopy, we found striking departures from this paradigm in three different power-of-2 insects belonging to the Apocrita suborder (ants, bees and wasps). In these insects, the earliest-formed cystocytes cease to divide during the latter mitotic cycles while their descendants undergo further division, thereby producing a 'radial' direction of division activity. Such cystocyte division patterns that depart from strict cell doubling may be 'fine-tuned' in order to maintain a final, power-of-2 germ cell number.
卵子发生是高等真核生物繁殖的一个决定性过程。在果蝇中，这个过程从一个单一的生殖细胞开始，经历四次有丝分裂，产生一个由 16 个细胞组成的胞囊；其中一个细胞将成为卵母细胞，其余的则成为支持细胞。这些有丝分裂是特殊的，因为胞质分裂不完全，导致形成了称为环道的细胞质桥，将胞囊细胞连接起来。这种组织使所有的胞囊细胞在每次有丝分裂过程中都能同步分裂，最终产生 2 的幂次方数量的生殖细胞。鉴于许多昆虫都遵循这个 2 的幂次方规则，我们研究了严格的细胞倍增是否是一个普遍的、潜在的原因。使用共聚焦显微镜，我们在三个属于 Apocrita 亚目的不同 2 的幂次方昆虫（蚂蚁、蜜蜂和黄蜂）中发现了明显偏离这一模式的现象。在这些昆虫中，最早形成的胞囊细胞在后期的有丝分裂周期中停止分裂，而它们的后代则进一步分裂，从而产生了“放射状”的分裂活动方向。这种偏离严格细胞倍增的胞囊细胞分裂模式可能是为了维持最终的 2 的幂次方生殖细胞数量而“微调”的。
