Identification of oocyte-expressed genes abundant in fetal ovary Yao et al 2004 .
The bovine oocyte microarray was used to identify genes highly expressed in fetal ovary (an enriched source of oocytes) relative to adult spleen and liver tissues. The goal of this experiment was to validate utility of the cDNA microarray and to identify additional oocyte-expressed genes abundant in fetal ovary relative to somatic tissues. Microarray experiments with fetal ovary vs. spleen revealed 24 clones with >2-fold higher expression in fetal ovary (P < 0.05). Likewise, microarray experiments comparing fetal ovary and liver RNA revealed 98 clones with >2-fold higher expression in fetal ovary (P < 0.05). Overall, 11 clones were found to be in common between the lists of genes expressed at higher levels (>2-fold) in fetal ovary than in either spleen or liver. These 11 clones were retrieved from the original source plates and subjected to DNA sequencing. Sequence analysis revealed that these 11 clones represent 7 different genes. Two clones encode for JY-1, a known bovine oocyte-specific gene (Yao J, Huang R, Kobayashi Y, Bettegowda A, Coussens PM, Ireland JJ, and Smith GW. Identification and characterization of expression of JY-1: a novel oocyte specific gene in cattle. Biol Reprod 68: 112, 2003.). Eight of the remaining nine clones encode for five previously identified genes (ribosomal protein L7a, dynein light chain, Doc2 , calmodulin, leucine-rich protein). The final clone encodes for a completely novel transcript (Table 3). Since a heterogeneous tissue source including both oocytes and somatic cells (fetal ovary) was used as an enriched source of bovine oocytes for microarray analysis, expression of above-described genes in isolated bovine oocytes (from adult ovaries) was confirmed by real-time RT-PCR analysis (Fig. 3).