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Polycomb genes expression and histone H3 lysine 27 tri-methylation changes during bovine preimplantation development

P Ross, Animal Science, Michigan State University, 48824, United States
N Ragina, Animal Science, Michigan State University, 48824, United States
R Rodriguez, Animal Science, Michigan State University, 48824, United States
A Iager, Animal Science, Michigan State University, 48824, United States
K Siripattarapravat, Animal Science, Michigan State University, East Lansing, United States
N Lopez-Corrales, Department of Agriculture, Public University of Navarra, Pamplona, Spain
J Cibelli, Animal Science - Physiology, Michigan State University, East Lansing, United States

Correspondence: Jose Cibelli, Email: cibelli{at}msu.edu

Abstract

Tri-methylation of Histone H3 at lysine 27 (H3K27me3) is established by polycomb group genes and is associated with stable and heritable gene silencing. The aim of this study was to characterize the expression of polycomb genes and the dynamics of H3K27me3 during bovine oocyte maturation and preimplantation development. Oocytes and in vitro produced embryos were collected at different stages of development. Polycomb genes expression was analyzed by real-time quantitative RT-PCR and immunofluorescence. Global H3K27me3 levels were determined by semiquantitative immunofluorescence. Transcripts for EZH2, EED and SUZ12 were detected at all stages analyzed, with EZH2 levels being highest of the three at early stages of development. By the time the embryo reached the blastocyst stage the level of PcG gene mRNA levels significantly increased. Immunofluorescence staining indicated nuclear expression of EZH2 at all stages while nuclear localized EED and SUZ12 were only evident at morula and blastocyst stages. Semiquantitative analysis of H3K27me3 levels showed that nuclear fluorescence intensity was highest in immature oocytes, steadily decreased after fertilization to reach a nadir at the 8-cell stage, and then increased at the blastocyst stage. These results suggest that the absence of polycomb repressive complex 2 proteins localized to the nucleus of early embryos could be responsible for the gradual decrease in H3K27me3 during early preimplantation development.