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NUCLEAR AND CYTOPLASMIC INTERRELATIONS IN THE FERTILIZATION OF THE ASTERIAS EGG

1949; Marine Biological Laboratory (MBL); Volume: 96; Issue: 3 Linguagem: Inglês

10.2307/1538362

1939-8697

Robert Chambers, Edward L. Chambers,

Reproductive biology and impacts on aquatic species

Full-sized germinal vesicle oocytes of Asterias forbesii undergo normal maturation in sea water. At 16° C. the first polar bodies are formed in about 80 minutes, and the second, in 108 minutes. The eggs are sperm-fertilizable from the time of germinal vesicle breakdown until some time after elimination of the second polar bodies. Fol (1879, p. 204) indicated that the optimum time for insemination is after germinal vesicle breakdown up to the first polar body formation. In accordance with Fol, the earliest period for the sperm aster to appear was found to be always a few minutes after the formation of the second polar body. A feature to be stressed is the progressive change of the karyocytoplasm induced by the mixing of the contents of the germinal vesicle with the cytoplasm during maturation.Maturation of the karyocytoplasm1. When eggs are inseminated two to three minutes before first polar body formation or later, the time for the sperm aster to appear in the living egg is about 35 minutes at 16° C.When the eggs are inseminated at any time prior to the above, the time taken for the sperm aster to appear is equal to 35 minutes plus the interval between the time of insemination and the time of initiation of the first polar body.Evidently, therefore, the time of appearance of the sperm aster is a function of the maturation of the karyocytoplasm. The maturation begins at the time of germinal vesicle breakdown and reaches completion two to three minutes prior to formation of the first polar body. In a fully mature karyocytoplasm the interval between sperm entry and the appearance of the sperm aster is constant.The egg nucleus2. Sperm-fertilization of whole eggs or of egg-nucleated fragments accelerates the egg nucleus in the formation of its polar bodies. The earlier the insemination the greater is the acceleration.3. The effect of the fertilization process in accelerating polar body formation persists after removal of the sperm pronucleus. This was ascertained by removing the sperm pronucleus, through bisection, at several intervals of time, the earliest being ten minutes after insemination.In other words, once given the impetus the egg nucleus maintains its hastened progress independently of the presence of the sperm pronucleus.The sperm aster4. In eggs bisected while undergoing maturation and then inseminated, the sperm aster appears earlier in the fragment lacking the egg nucleus than in the egg-nucleated fragment.In eggs fertilized while undergoing maturation and then bisected at different times, the sooner the sperm pronucleus has been isolated from the egg nucleus, the earlier the sperm aster appears.In other words, the presence of the egg nucleus has a delaying action on the development of the sperm aster. However, the earlier the egg nucleus has been removed through bisection of the egg, the less is the delaying action.GENERAL CONCLUSIONThere is a close interrelation between (a) the fertilization process,(b) the ripening of the karyocytoplasm, (c) the development of the sperm pronucleus, and (d) the activity of the egg nucleus in forming its polar bodies. The fertilization process, by hastening the maturation of the karyocytoplasm, accelerates the activity of the egg nucleus in forming its polar bodies. On the other hand, the egg nucleus exerts a lag effect on that feature of the maturation of the karyocytoplasm which is concerned with the development of the sperm aster. The net result is the attainment of an adequate spacing between the times of the cytoplasmic streaming activities concerned with polar body formation and those concerned with the development of the sperm aster. This permits normal development of Asterias eggs fertilized at any time during their maturation.