Genes preferentially expressed in bovine oocytes revealed by subtractive and suppressive hybridization

To isolate bovine oocyte marker genes, we performed suppressive and subtractive hybridization between oocytes and somatic tissues (i.e., intestine, lung, muscle, and cumulus cells). The subtracted library was characterized by sequencing 185 random clone inserts, representing 146 nonredundant genes. After Blast analysis within GenBank, 64% could be identified, 21% were homologous to unannotated expressed sequence tag (EST) or genomic sequences, and 15% were novel. Of 768 clone inserts submitted for differential screening by macroarray hybridization, 83% displayed a fourfold overexpression in the oocyte. The 40 most preferential nonredundant ESTs were submitted to GenBank analysis. Several well-known oocyte-specific genes were represented, including growth differentiation factor 9, bone morphogenetic protein 15, or the zona pellucida glycoprotein genes. Other ESTs were not identified. We investigated the expression profile of several candidates in the oocyte and a panel of gonadal and somatic tissues by reverse transcription-polymerase chain reaction. B-cell translocation gene 4, cullin 1, MCF.2 transforming sequence, a locus similar to snail soma ferritin, and three unidentified genes were, indeed, preferentially expressed in the oocyte, even though most were also highly expressed in testis. The transcripts were degraded throughout preimplantation development and were not compensated for by embryonic transcription after the morula stage. These profiles suggest a role in gametogenesis, fertilization, or early embryonic development.