For a long time, it has been assumed that the only role of sperm at fertilization is to introduce the male genome into the egg. Recently, ideas have emerged that the epigenetic state of the sperm nucleus could influence transcription in the embryo. However, conflicting reports have challenged the existence of epigenetic marks on sperm genes, and there are no functional tests supporting the role of sperm epigenetic marking on embryonic gene expression. Here, we show that sperm is epigenetically programmed to regulate embryonic gene expression. By comparing the development of sperm- and spermatid-derived frog embryos, we show that the programming of sperm for successful development relates to its ability to regulate transcription of a set of developmentally important genes. During spermatid maturation into sperm, these genes lose H3K4me2/3 and retain H3K27me3 marks. Experimental removal of these epigenetic marks at fertilization de-regulates gene expression in the resulting embryos in a paternal chromatin-dependent manner. This demonstrates that epigenetic instructions delivered by the sperm at fertilization are required for correct regulation of gene expression in the future embryos. The epigenetic mechanisms of developmental programming revealed here are likely to relate to the mechanisms involved in transgenerational transmission of acquired traits. Understanding how parental experience can influence development of the progeny has broad potential for improving human health.

Eggs and oocytes have a remarkable ability to induce transcription of sperm after normal fertilization and in somatic nuclei after somatic cell nuclear transfer. This ability of eggs and oocytes is essential for normal development. Nuclear actin and actin-binding proteins have been shown to contribute to transcription, although their mode of action is elusive. Here, we find that Xenopus Wave1, previously characterized as a protein involved in actin cytoskeleton organization, is present in the oocyte nucleus and is required for efficient transcriptional reprogramming. Moreover, Wave1 knockdown in embryos results in abnormal development and defective hox gene activation. Nuclear Wave1 binds by its WHD domain to active transcription components, and this binding contributes to the action of RNA polymerase II. We identify Wave1 as a maternal reprogramming factor that also has a necessary role in gene activation in development.Eggs and oocytes efficiently reprogram transplanted somatic nuclei to an embryonic state (1,2). This reprogramming ability of eggs and oocytes toward somatic nuclei is believed to relate to their natural activity to activate sperm nuclei at fertilization. Reprogramming factors are synthesized and accumulated during egg formation and are especially enriched in the amphibian oocyte nucleus, named the germinal vesicle (GV) (1). GVs also contain necessary factors for embryonic development (3, 4). It is unclear what kinds of GV factors are required for reprogramming and for normal development, and how they contribute to these fundamental processes. To identify such a maternal factor, we have developed a nuclear transfer assay; hundreds of mammalian somatic cell nuclei are injected into the GV of Xenopus oocytes, and these nuclei undergo not only continuous transcription of active genes but also transcriptional reactivation of somatically silenced embryonic genes within 2 days (1). This system thus provides a unique opportunity to identify maternal factors responsible for reprogramming the transcription of somatic nuclei. We tested the involvement of Wave in transcriptional reprogramming. WAVE plays a cytoplasmic role in actin reorganization as a downstream target of RAC (13). Rac1 protein is present in GVs, including in transplanted nuclei ( fig. S2A). To our surprise, Wave1, one isoform of Wave enriched in brain, is also accumulated in the oocyte GV (Fig. 1A). We therefore focused on Wave1 as a candidate reprogramming factor. Little WAVE1 is detected in C2C12 nuclei before nuclear transfer (NT) (green color, fig. S2B). After NT, the accumulation of Wave1 was observed, especially in some somatic nuclei that showed extensive swelling (white arrow, fig. S2B), known to correlate with high transcriptional activity (14). Accordingly, localization of Wave1 and active RNA Pol II phosphorylated at serine 2 was examined. Xenopus laevis Wave1 tagged with a nuclear localization signal (NLS) and hemagglutinin (HA) (HA-NLS-Wave1) was expressed in GVs. A NLS was added to target Wave1 to the nucleus in orde...