Breed W G, Simerly C, Navara C S, VandeBerg J L, Schatten G
Department of Anatomy and Histology, University of Adelaide, South Australia.
Dev Biol. 1994 Jul;164(1):230-40. doi: 10.1006/dbio.1994.1194.
The marsupials represent a separate evolutionary lineage from eutherians from which they diverged over 100 million years ago. In order to explore the origin and mode of centrosome inheritance amongst this group of mammals, this study investigates the microtubule organization during fertilization, parthenogenesis, and polyspermy in the didelphid, Monodelphis domestica. Microtubules and DNA were visualized in maturing ovarian oocytes, parthenogenetically activated oocytes, monospermic and polyspermic zygotes, and early embryos. Ovarian oocytes had a central region of yolky cytoplasm that, after fertilization, became polarized; much of the yolk was then extruded into the perivitelline space as an enucleated cytoplasmic mass. Immunofluorescence microscopy, using a monoclonal antibody to beta-tubulin, demonstrated microtubules in the meiotic spindle in unfertilized oocytes, but cytasters were not detected. After fertilization, a cluster of microtubules forming into a sperm aster was evident around the male pronucleus. The sperm aster remained largely restricted to the nonyolky region of the egg cytoplasm, resulting in a cytoplasmic heterogeneity between a microtubule-rich region and one in which microtubules were largely absent. Once the two pronuclei came close together, abundant microtubules were found surrounding both pronuclei. In the early embryo, microtubules were found in the outer cortical region of the blastomeres and, in addition, there was an extensive and elaborate network of microtubules throughout the yolk mass. Disruption of the meiotic spindle microtubules with nocodazole or cold treatment did not result in chromosome dispersion in the cortex and recovery from drug or cold depolymerization demonstrated that microtubules might not be as dynamic as those in eutherian mammals. Taxol stabilization resulted in an increase in cortical microtubules. In this marsupial species, therefore, the centrosome appears to be of paternal origin, and the radiating microtubules that form may well be involved both in bringing the pronuclei together and in the cytoplasmic polarization that results in extrusion of the yolk mass.
有袋类动物代表了一个与有胎盘类动物不同的进化谱系，它们在一亿多年前就分道扬镳了。为了探究这群哺乳动物中心体遗传的起源和方式，本研究调查了袋鼬科动物家短尾负鼠在受精、孤雌生殖和多精受精过程中的微管组织。在成熟的卵巢卵母细胞、孤雌激活的卵母细胞、单精和多精受精卵以及早期胚胎中观察微管和DNA。卵巢卵母细胞有一个富含卵黄的细胞质中心区域，受精后该区域极化；然后大部分卵黄作为无核细胞质团被挤出到卵周隙中。使用抗β-微管蛋白单克隆抗体的免疫荧光显微镜观察显示，未受精卵母细胞的减数分裂纺锤体中有微管，但未检测到星体。受精后，围绕雄原核明显形成了一簇微管，形成精子星体。精子星体在很大程度上局限于卵细胞质的非卵黄区域，导致富含微管的区域和基本没有微管的区域之间存在细胞质异质性。一旦两个原核靠近，在两个原核周围都发现了丰富的微管。在早期胚胎中，微管存在于卵裂球的外周皮质区域，此外，在整个卵黄团中还有广泛而精细的微管网络。用诺考达唑或冷处理破坏减数分裂纺锤体微管不会导致染色体在皮质中分散，从药物或冷解聚中恢复表明微管可能不像有胎盘类哺乳动物中的微管那样具有动态性。紫杉醇稳定化导致皮质微管增加。因此，在这种有袋类物种中，中心体似乎起源于父方，形成的放射状微管很可能既参与将原核聚集在一起，也参与导致卵黄团挤出的细胞质极化。
