Katsuhiko Shirahige, Miho Ohsugi and colleagues report the largest transcriptome analysis of mouse preimplantation cells to date (Genes Dev. 27, 2736–2748, 2013). The authors synchronized over 140,000 in vitro–fertilized mouse embryos and parthenotes at specific stages—from fertilization to the two-cell stage—and compared their expression changes both to each other and to unfertilized oocytes using RNA sequencing. They identified 5,364 genes expressed in oocytes and early embryos whose expression was not detected in earlier microarray studies. Consistent with previous reports, the authors found extensive changes in gene expression between the one- and two-cell stages but unexpectedly discovered that these changes occurred for noncoding RNAs as well as for mRNAs. Among the new insights uncovered in their analysis is the discovery of fertilization-regulated transcription factors, including five whose expression was not detected in oocytes or parthenotes: Foxd1, Nkx2-5, Sox18, Myod1 and Runx1. The authors suggest that these transcription factors are required for developmental progression, as parthenotes fail to develop past the four-cell stage. The freely available database is likely to be an important resource for future developmental research.