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| Author(s): |
Isabele Picada Emanuelli
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Pirassununga. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT) |
| Defense date: | 2005-03-18 |
| Examining board members: |
Flavio Vieira Meirelles;
José Buratini Júnior;
Claudia Lima Verde Leal
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| Advisor: | Flavio Vieira Meirelles |
| Abstract | |
About 40% of fertilized bovine oocytes do not complete development during the preimplantation period. It is known that the in vitro embryo production system is influenced by several factors, among them, the morphological quality of cumulus-oocyte complexes (COCs). The present work aimed to study the cumulus-oocyte interaction on the process of programmed cell death in bovine COCs of different morphological classes. The COCs were obtained from bovine ovaries and classified according to the morphology of their cumulus cell layers, as follows: class A, compact and with many layers; class B, compact with few layers; class C, expanded (all classes with homogeneous ooplasm). Before in vitro maturation (IVM), the nuclear maturation in COCs and DNA fragmentation in cumulus cells (CC) were evaluated. After IVM, oocytes and CC were analyzed for nuclear maturation, DNA fragmentation and BCL-2 and BAX transcripts and proteins. The developmental competence and quality of parthenogenetic embryos at the 9th day post-activation were also analyzed. The results showed that the majority of class A immature oocytes were at iGV stage, with minimal or inexistent DNA fragmantation, contrasting with the other classes of oocytes. In immature class B and C oocytes, the fGV stage of nuclear maturation was the most frequent, with increased DNA fragmentation. After IVM, an increase in DNA fragmentation was observed in B and C COCs, mainly in B group. The morphological type of COCs was not related with blastocyst quality, but affected the proportion of embryos capable of overcoming developmental block and reaching the blastocyst stage. BCL-2 protein in CC had the same expression level in all the COCs groups. However, the BCL-2/BAX proteins ratio was higher in A and C groups. COC-B had the highest BAX expression and lower ratio. These data demonstrate that there is a negative correlation between DNA fragmentation in CC and embryo developmental potential in different morphological types of COCs, and that the lower the BCL2/BAX protein ratio the greates the DNA fragmentation in CC, but this relation does not occur with transcripts (AU) | |