Tumor necrosis factor-α gene expression in mouse oocytes and follicular cells

Abstract

Ovarian cells that transcribe and translate the gene for tumor necrosis factor alpha (TNFα) were identified in the adult cyclic mouse by using in situ hybridization and immunocytochemistry. TNFα mRNA was observed in >97% and protein was contained in ~53% of the oocytes of healthy follicles with two or more layers of granulosa cells, but neither was detectable in oocytes of primordial follicles and follicles with a single layer of granulosa cells. In early atretic follicles, only 13% contained TNFα protein and 40% contained TNFα mRNA. In late stages of atresia, intense immunoreactive TNFα was observed in all of the oocytes, but TNFα mRNA was present in only 13%. In ~85% of follicles, theca and/or granulosa cells exhibited TNFα mRNA hybridization signals. Macrophage-like cells within the interstitium were positive for TNFα mRNA and protein. In corpora lutea, luteal cells and macrophage-like cells contained TNFα message, while only the latter lineage contained immunoreactive TNFα. Hybridization signals and immunoreactivity were more intense in older corpora lutea than in corpora lutea of the present cycle. Northern blot analysis revealed a 2.2-kb TNFα mRNA in the ovary that was unchanged relative to 28S rRNA (constitutive RNA) during the cycle. Similarly, TNFα hybridization signals and immunoreactivity did not appear to change throughout the cycle. These results indicate that TNFα gene transcription in the oocyte coincides with the synthesis of immunoreactive TNFα and that these complex biochemical processes occur at distinct steps of follicular development in the mouse. The formation of the second layer of granulosa cells is coupled with the initial phase of TNFα gene transcription in the oocyte since TNFα mRNA and protein appear at this stage. Our findings also suggest that TNFα may be involved in various phases of follicular development, atresia, and luteal function in the mouse.