In the present study, correlations between the oocyte messenger RNA (mRNA) stockpile of Cyclin B, insulin-like growth factor I (IGF-I), insulin-like growth factor (IGF-II), insulin-like growth factor receptor Ib (IGFR Ib), and p53 transcripts and the developmental competence of the oocyte were studied. For this purpose, post-ovulatory ageing was used as a tool to generate oocytes of varying developmental competence. Mature female rainbow trout were held at 12 degrees C and periodically checked for ovulation. Oocytes were collected from each female at ovulation and 5, 14, 21 days later. For each collected egg batch, the abundance of several mRNAs in the oocyte was analyzed by real-time PCR and embryo development was monitored after fertilization. Egg quality was estimated not only through embryonic survival but also by studying the occurrence of specific morphological abnormalities. The present study showed that oocyte post-ovulatory ageing was associated with variations of the relative abundance of several studied transcripts within the oocyte. In addition, the abundance of specific mRNAs could be correlated with either the embryonic survival or the occurrence of malformations. Thus, the abundance of IGFR Ib and Cyclin B transcripts in the oocyte was correlated with the occurrence of morphological abnormalities observed at yolk-sac resorption (negatively for IGFR Ib and positively for Cyclin B), while the maternal stockpile of IGF-I, IGF-II, and IGFR Ib mRNAs was positively correlated with embryonic survival.
Copyright 2004 Wiley-Liss, Inc.