Ferree Patrick M, McDonald Kent, Fasulo Barbara, Sullivan William
Department of Molecular, Cellular and Developmental Biology, University of California, Santa Cruz, 95064, USA.
Curr Biol. 2006 Apr 18;16(8):801-7. doi: 10.1016/j.cub.2006.03.066.
A longstanding enigma has been the origin of maternal centrosomes that facilitate parthenogenetic development in Hymenopteran insects. In young embryos, hundreds of microtubule-organizing centers (MTOCs) are assembled completely from maternal components. Two of these MTOCs join the female pronucleus to set up the first mitotic spindle in unfertilized embryos and drive their development. These MTOCs appear to be canonical centrosomes because they contain gamma-tubulin, CP190, and centrioles and they undergo duplication. Here, we present evidence that these centrosomes originate from accessory nuclei (AN), organelles derived from the oocyte nuclear envelope. In the parasitic wasps Nasonia vitripennis and Muscidifurax uniraptor, the position and number of AN in mature oocytes correspond to the position and number of maternal centrosomes in early embryos. These AN also contain high concentrations of gamma-tubulin. In the honeybee, Apis mellifera, distinct gamma-tubulin foci are present in each AN. Additionally, the Hymenopteran homolog of the Drosophila centrosomal protein Dgrip84 localizes on the outer surfaces of AN. These organelles disintegrate in the late oocyte, leaving behind small gamma-tubulin foci, which likely seed the formation of maternal centrosomes. Accessory nuclei, therefore, may have played a significant role in the evolution of haplodiploidy in Hymenopteran insects.
一个长期存在的谜团是膜翅目昆虫中促进孤雌生殖发育的母源中心体的起源。在年轻胚胎中，数百个微管组织中心（MTOC）完全由母源成分组装而成。其中两个MTOC与雌性原核结合，在未受精胚胎中建立第一个有丝分裂纺锤体并驱动其发育。这些MTOC似乎是典型的中心体，因为它们含有γ-微管蛋白、CP190和中心粒，并且会进行复制。在这里，我们提供证据表明这些中心体起源于辅助核（AN），即源自卵母细胞核膜的细胞器。在寄生蜂丽蝇蛹集金小蜂和单头突粪金小蜂中，成熟卵母细胞中AN的位置和数量与早期胚胎中母源中心体的位置和数量相对应。这些AN还含有高浓度的γ-微管蛋白。在蜜蜂中华蜜蜂中，每个AN中都存在明显的γ-微管蛋白聚集点。此外，果蝇中心体蛋白Dgrip84的膜翅目同源物定位于AN的外表面。这些细胞器在卵母细胞后期解体，留下小的γ-微管蛋白聚集点，这可能为母源中心体的形成提供了种子。因此，辅助核可能在膜翅目昆虫单倍二倍体的进化中发挥了重要作用。
