Reproduction Abstracts

In humans, mutation of the ATRX gene leads to improper methylation of repetitive DNA sequences. By performing a meta-analysis on published microarray data across several model species we previously identified ATRX as a potential biomarker of oocyte quality. The aim of the present study was to determine the expression and regulation of ATRX at a protein level, in the bovine cumulus oocyte complex (COC).

ATRX protein was found to be expressed during oogenesis and to be dramatically downregulated during oocyte maturation. We have previously shown that inhibition of progesterone signalling during bovine in vitro oocyte maturation has a detremental affect on subsequent embryonic development. Here we show that this is characterized by to an increase in ATRX expression and a parallel increase in the expression of a known marker of apoptosis (active Caspase-3) during oocyte maturation, in both oocytes and cumulus cells.

Immunohistochemistry studies performed on bovine oocytes at different stages of meiotic maturation showed ATRX to be localized to the chromosomal area of GV oocytes, but undetectable in MII oocytes. Inhibition of progesterone signaling during maturation resulted in the stabilization of ATRX in bovine oocytes, with ATRX remaining localized to the chromosomal area of mature MII oocytes.

In conclusion, ATRX protein expression and localization appears to be progesterone regulated and associated with oocyte quality. However, further work is needed to determine how the regulation of ATRX corresponds to specific epignetic regulations and subsequent developmental competence.