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Ultrastructure of canine oocytes during in vivo maturation
Author(s) -
de Lesegno Christine Viaris,
Reynaud Karine,
Pechoux Christine,
Thoumire Sandra,
ChastantMaillard Sylvie
Publication year - 2008
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.20763
Subject(s) - ovulation , oocyte , biology , nucleolus , ultrastructure , in vivo , medicine , andrology , endocrinology , ovariectomized rat , cytoplasm , microbiology and biotechnology , anatomy , estrogen , genetics , hormone , embryo
The aim of the present study was to describe the canine oocyte ultrastructural modifications during in vivo maturation, with precise reference to the timing of the LH surge and of ovulation. Twenty‐five bitches were ovariectomized at specific stages between the onset of proestrus and the fifth day post‐ovulation: 65 oocytes were observed by transmission electron microscopy (TEM), either before the LH surge (n = 10), between the LH surge and ovulation (n = 12) or after ovulation (n = 43). Prior to the LH surge, the oocyte nucleus had already begun its displacement to the vicinity of the oolemma and reticulated nucleoli were infrequent. The cytoplasm showed signs of immaturity (few organelles preferentially located in the cortical zone, “mitochondrial cloud”, scarce cortical granules). The LH surge was immediately followed by cumulus expansion but the ovulation occurred 2 days later. Retraction of the transzonal projections and the meiotic resumption occurred after another 3 days (5 days after the LH peak). The ovulation was then followed by gradual cytoplasmic modifications. Nucleoli re‐assumed a reticulated aspect around 24 hr post‐ovulation. From 48 hr post‐ovulation mitochondria and SER were very numerous and evenly distributed. In conclusion canine oocyte maturation began prior to the LH surge and no cytoplasmic or nuclear modifications followed immediately the LH surge and ovulation. This study suggests that two distinct signals are needed for the final in vivo maturation: one prior to the LH surge (to induce maturation) and another one, around 3 days post‐ovulation (to induce meiotic resumption). Mol. Reprod. Dev. 75: 115–125, 2008. © 2007 Wiley‐Liss, Inc.