Summary The discovery of RNAs (e.g. mRNAs, non-coding RNAs) in sperm has opened the possibility that sperm may function in delivering additional paternal information aside from solely providing the DNA1. Increasing evidence now suggests that sperm small non-coding RNAs (sncRNAs) can mediate intergenerational transmission of paternally acquired phenotypes, including mental stress2, 3 and metabolic disorders4–6. How sperm sncRNAs encode paternal information remains unclear, but the mechanism may involve RNA modifications. Here we show that deletion of a mouse tRNA methyltransferase, DNMT2, abolished sperm sncRNA-mediated transmission of high-fat diet (HFD)-induced metabolic disorders to offspring. Dnmt2 deletion prevented the elevation of RNA modifications (m5C, m2G) in sperm 30–40nt RNA fractions that are induced by HFD. Also, Dnmt2 deletion altered the sperm small RNA expression profile, including levels of tRNA-derived small RNAs (tsRNAs) and rRNA-derived small RNAs (rsRNA-28S), which might be essential in composing a sperm RNA ‘coding signature’ that is needed for paternal epigenetic memory. Finally, we show that Dnmt2-mediated m5C contributes to the secondary structure and biological properties of sncRNAs, implicating sperm RNA modifications as an additional layer of paternal hereditary information.

SUMMARY We have identified a subcortical maternal complex (SCMC) that assembles during oocyte growth and is essential for zygotes to progress beyond the first embryonic cell divisions. At least four maternally encoded proteins contribute to this MDa complex: FLOPED, MATER and TLE6 interact with each other while Filia binds independently to MATER. Although the transcripts encoding these proteins are degraded during meiotic maturation and ovulation, the SCMC proteins persist in the early embryo. The SCMC, located in the subcortex of eggs, is excluded from regions of cell-cell contact in the cleavage-stage embryo and segregates to the outer cells of the morulae and blastocyst. Flopedtm/tm and/or Matertm/tm eggs lack the SCMC, but can be fertilized. However, these embryos do not progress beyond cleavage stage development and female mice are sterile. The proteins are conserved in humans and similar maternal effect mutations may result in recurrent embryonic loss.

The hiatus between oocyte and embryonic gene transcription dictates a role for stored maternal factors in early mammalian development. Encoded by maternal-effect genes, these factors accumulate during oogenesis and enable the activation of the embryonic genome, the subsequent cleavage stages of embryogenesis and the initial establishment of embryonic cell lineages. Recent studies in mice have yielded new findings on the role of maternally provided proteins and multi-component complexes in preimplantation development. Nevertheless, significant gaps remain in our mechanistic understanding of the networks that regulate early mammalian embryogenesis, which provide an impetus and opportunities for future investigations.

No abstract

Supplementary data are available at Bioinformatics online.

Prior to activation of the embryonic genome, the initiating events of mammalian development are under maternal control and include fertilization, the block to polyspermy and processing sperm DNA. Following gamete union, the transcriptionally inert sperm DNA is repackaged into the male pronucleus which fuses with the female pronucleus to form a 1-cell zygote. Embryonic transcription begins during the maternal to zygotic transfer of control in directing development. This transition occurs at species-specific times after one or several rounds of blastomere cleavage and is essential for normal development. However, even after activation of the embryonic genome, successful development relies on stored maternal components without which embryos fail to progress beyond initial cell divisions. Better understanding of the molecular basis of maternal to zygotic transition including fertilization, the activation of the embryonic genome and cleavage-stage development will provide insight into early human development that should translate into clinical applications for regenerative medicine and assisted reproductive technologies.

Initial cell lineages that presage the inner cell mass and extra-embryonic trophectoderm are established when eight blastomeres compact to form polarized morulae in preimplantation mouse development. FILIA has been identified as a binding partner to MATER (maternal antigen that embryos require; also known as NLRP5), which is encoded by a maternal effect gene. Products of each gene are detected in growing oocytes and, although transcripts are degraded before fertilization, the cognate proteins persist in early blastocysts. The two proteins co-localize to the cytocortex of ovulated eggs, where the stability of FILIA is dependent on the presence of MATER. After fertilization, FILIA-MATER complexes become asymmetrically restricted in the apical cytocortex of twocell embryos due to their absence in regions of cell-cell contact. This asymmetry is reversible upon disaggregation of blastomeres of the two-and four-cell embryo. Each protein persists in cells of the preimplantation embryo, but the continuous cell-cell contact of 'inner' cells of the morulae seemingly precludes formation of the subcortical FILIA-MATER complex and results in cell populations that are marked by its presence ('outer') or absence ('inner'). Thus, the FILIA-MATER complex provides a molecular marker of embryonic cell lineages, but it remains to be determined if the molecular asymmetry established after the first cell division plays a role in cell fate determinations in the early mouse embryo. If so, the plasticity of the FILIA-MATER complex localization may reflect the regulative nature of preimplantation mouse development.

Ischemic heart disease is a leading cause of death in human population and protection of myocardial infarction (MI) associated with ischemia-reperfusion (I/R) remains a challenge. MG53 is an essential component of the cell membrane repair machinery that protects injury to the myocardium. We investigated the therapeutic value for using the recombinant human MG53 (rhMG53) protein for treatment of MI. Using Langendorff perfusion of isolated mouse heart, we found that I/R caused injury to cardiomyocytes and release of endogenous MG53 into the extracellular solution. rhMG53 protein applied to the perfusion solution concentrated at injury sites on cardiomyocytes to facilitate cardioprotection. With rodent models of I/R-induced MI, we established the in vivo dosing range for rhMG53 in cardioprotection. Using a porcine model of angioplasty-induced MI, the cardioprotective effect of rhMG53 was evaluated. Intravenous administration of rhMG53, either prior to or post ischemia, reduced infarct size and troponin I release in the porcine model when examined at 24 hours post reperfusion. Echocardiogram and histological analyses revealed that the protective effects for rhMG53 observed following acute MI led to long-term improvement in cardiac structure and function in the porcine model when examined at 4 weeks post operation. Our study supports the concept that rhMG53 could have potential therapeutic value for treatment of MI in human patients with ischemic heart diseases.