Using a semi-quantitative, single-cell sensitive RT-PCR method, we studied the expression of oogenesis specific genes (Nobox, Oct4, Bmp15, Gdf9, Oogenesin1 and Oogenesin2) in single oocytes collected from primordial, primary, secondary, preantral and antral follicles during natural and gonadotropin-induced mouse follicular development. We compared the number of transcripts of these genes, showing that they are differentially expressed, both in natural conditions and under gonadotropin-induction throughout the assessed developmental stages. Our data show a clear increase in the number of transcripts between the primordial until the preantral stages, with the exception of the Oogenesin1 transcripts under gonadotropin-induction. The number of transcripts starts decreasing at the antral stage and proceeds until the metaphase II stage, with values very similar to those obtained for the primordial oocytes in both analyzed conditions. Under exogenous gonadotropin-induction, oocyte recruitment to ovulation at the preantral stage is marked by an increase in Nobox and Oogenesin2 gene expression that is concomitant with a decrease in Oogenesin1 gene expression. Oocytes that are able to proceed into whole embryo development show a tight regulation of Nobox and Oct4 expression at the antral stage. A parallel immunocytochemical study at the protein level corroborates these findings. Mol. Reprod. Dev. 76: 994–1003, 2009. © 2009 Wiley-Liss, Inc.