Formation of the vitelline envelope precedes the active uptake of vitellogenin during oocyte development in the rainbow trout,Oncorhynchus mykiss |
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Authors: | Sven Johan Hyllner Christer Silvers Carl Haux |
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Abstract: | In order to study the initial formation of the vitelline envelope and the appearance of vitellogenin in oocytes of rainbow trout, females were sampled monthly from 19 to 5 mo before ovulation. lmmunohistochemistry revealed that the formation of the vitelline envelope starts when the oocytes reach a diameter of about 450 μm. Oocytes of this size were first found in females sampled a year before ovulation at the time when plasma levels of estradiol-17β increased from 0.2 to 0.6 ng/ml. An antiserum directed against vitellogenin crossreacted with small vesicles (around 2 μm) present just inside the oolemma, when the oocytes reached a diameter of 600 μm. This was interpreted as an active uptake of vitellogenin. Oocytes of this size were first found in females sampled 9 mo before ovulation at the time when estradiol 17β levels increased from 0.6 to 1.0 ng/ml and the gonadal somatic index was doubled. Oocytes with a diameter of 600 μm had an immunoreactive vitelline envelope with a thickness of about 3 μm. It is apparent that the initial formation of the vitelline envelope starts before the active uptake of vitellogenin and that the low previtellogenic plasma levels of estradiol-17β observed in females are of physiological significance. © 1994 Wiley-Liss, Inc. |
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Keywords: | Fish Oogenesis Chorion Zona radiata Estradiol-17β |
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