Identifying new human oocyte marker genes: a microarray approach

Abstract

The efficacy of classical IVF techniques is still impaired by poor implantation and pregnancy rates after embryo transfer. This is mainly due to a lack of reliable criteria for the selection of embryos with sufficient development potential. Several studies have provided evidence that some gene expression levels could be used as objective markers of oocyte and embryo competence and capacity to sustain a successful pregnancy. These analyses usually use reverse transcription-polymerase chain reaction to look at small sets of pre-selected genes. However, microarray approaches allow the identification of a wider range of cellular marker genes which could include additional and perhaps more suitable genes that could serve as embryo selection markers. Microarray screenings of around 30,000 genes on U133P Affymetrix gene chips made it possible to establish the expression profile of these genes as well as other related genes in human oocytes and cumulus cells. This study identifies new potential regulators and marker genes such as BARD1, RBL2, RBBP7, BUB3 or BUB1B, which are involved in oocyte maturation.

Figure 1. Marker genes up or down-regulated in cumulus cells and oocytes

Histogram representation of the fold increase in the signal between cumulus cell and oocyte average signals for nine genes (cumulus versus oocyte in grey bars and oocyte versus cumulus in white bars). Probe set values are from table 1.

Figure 2. Hierarchical clustering of 46 genes signal values across cumulus cell and oocyte samples

Signal values were floored (minimal signal value = 2), log transformed and mean centered. Average linkage with un-centered correlation was evaluated using the Cluster software (Eisen et al. 1998). On the right side, genes are clustered by their preferential expression in the four samples. Red and green mark over- and under-expression, respectively and black colour represents mean values. GV = germinal vesicle; M = metaphase.

Figure 3. New marker genes involved in oocyte maturation

Factors identified in this study with restricted expression in immature germinal vesicle (GV) and metaphase I (MI) oocytes, in unfertilized metaphase II (MII) oocytes and in cumulus cells. Factors in darker shade are shared by MI and MII oocytes.