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Genes Preferentially Expressed in Bovine Oocytes Revealed by Subtractive and Suppressive Hybridization Pennetier S, et al .
In order to isolate bovine oocyte marker genes, we performed suppressive subtraction 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 non redundant genes. After blast analysis within Genbank, 64% could be identified, while 21% were homologous to unannotated EST or genomic sequences, and 15% were novel. Out of 768 clone inserts submitted to differential screening by macroarray hybridization, 83% displayed a fourfold overexpression in the oocyte. The 40 most preferential non redundant EST 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 EST were not identified. We investigated the expression profile of several candidates in the oocyte and a panel of gonadic and somatic tissues by RT-PCR. B-cell translocation gene 4, cullin 1, MCF.2 transforming sequence, a locus similar to snail soma ferritin and 3 unidentified genes were indeed preferentially expressed in the oocyte, even though most were also highly expressed in testis. . Expression profiles of BTG4, CUL1, MCF2, and EST 5B4, 6D3, 8D7, 8B9 and 7F3 were analysed in oocyte and preimplantation embryos by RT-PCR. All were strongly detected in immature, in vitro matured oocytes and zygotes. 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.
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