Centriole behavior during meiosis in oocytes of the sea urchin Hemicentrotus pulcherrimus.
Ultrastructural changes in the maturing oocyte of the sea urchin Hemicentrotus pulcherrimus were observed, with special reference to the behavior of centrioles and chromosomes, using oocytes that had spontaneously started the maturation division process in vitro after dissection from ovaries. The proportion of oocytes entering the maturation process differed from batch to batch. In those eggs that accomplished the maturation division, it took ~4.5-5 h from the beginning of germinal vesicle breakdown to the formation of a second polar body. Serial sections revealed that a young oocyte before germinal vesicle breakdown had a pair of centrioles with procentrioles, located between the presumed animal pole and the germinal vesicle and accompanied by amorphous aggregates of moderately dense material and dense granules (granular aggregate). Just before germinal vesicle breakdown, a pair of fully grown centrioles located in the granular aggregate, which is present until this stage and then disappears, had already separated from another pair of centrioles. In meiosis I, each division pole had two centrioles, whereas in meiosis II each had only one. The two centrioles in the secondary oocyte separated into single units and formed the mitotic figure of meiosis II. The first polar body had two centrioles and the second had only one. The two centrioles in the first polar body did not form the mitotic figure nor did they separate at the time of meiosis II. These results indicate that, in sea urchins, duplication of the centrioles does not occur during the two successive meiotic divisions and the egg inherits only one centriole from the primary oocyte, confirming the results previously reported for starfish oocytes.
Nakashima
S
S
Institute of Natural Sciences, Nagoya City University, Mizuho-cho, Mizuho-ku, Nagoya 467-8501, Japan.
Kato
K H
KH
D000818:Animals; D002502:Centrioles / Q000502:physiology*; D008540:Meiosis / Q000502:physiology*; D009865:Oocytes / Q000502:physiology* / Q000648:ultrastructure; D012617:Sea Urchins / Q000502:physiology*