Increasing evidence indicates that metabolic disorders in offspring can result from the father's diet, but the mechanism remains unclear. In a paternal mouse model given a high-fat diet (HFD), we showed that a subset of sperm transfer RNA-derived small RNAs (tsRNAs), mainly from 5' transfer RNA halves and ranging in size from 30 to 34 nucleotides, exhibited changes in expression profiles and RNA modifications. Injection of sperm tsRNA fractions from HFD males into normal zygotes generated metabolic disorders in the F1 offspring and altered gene expression of metabolic pathways in early embryos and islets of F1 offspring, which was unrelated to DNA methylation at CpG-enriched regions. Hence, sperm tsRNAs represent a paternal epigenetic factor that may mediate intergenerational inheritance of diet-induced metabolic disorders.

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.

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Although high-throughput RNA sequencing (RNA-seq) has greatly advanced small non-coding RNA (sncRNA) discovery, the currently widely used complementary DNA library construction protocol generates biased sequencing results. This is partially due to RNA modifications that interfere with adapter ligation and reverse transcription processes, which prevent the detection of sncRNAs bearing these modifications. Here, we present PANDORA-seq (panoramic RNA display by overcoming RNA modification aborted sequencing), employing a combinatorial enzymatic treatment to remove key RNA modifications that block adapter ligation and reverse transcription. PANDORA-seq identified abundant modified sncRNAs-mostly transfer RNA-derived small RNAs (tsRNAs) and ribosomal RNA-derived small RNAs (rsRNAs)-that were previously undetected, exhibiting tissue-specific expression across mouse brain, liver, spleen and sperm, as well as cell-specific expression across embryonic stem cells (ESCs) and HeLa cells. Using PANDORA-seq, we revealed unprecedented landscapes of microRNA, tsRNA and rsRNA dynamics during the generation of induced pluripotent stem cells. Importantly, tsRNAs and rsRNAs that are downregulated during somatic cell reprogramming impact cellular translation in ESCs, suggesting a role in lineage differentiation.RNA modifications, warrant future extensive investigations in different systems.

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Graphical AbstractHighlights d LincGET is asymmetrically expressed in the nucleus of twoto four-cell mouse embryos d LincGET overexpression biases blastomere fate toward inner cell mass (ICM) d LincGET physically binds to CARM1 d LincGET/CARM1 activates ICM-specific genes In BriefAn endogenous retrovirus-associated nuclear long noncoding RNA biases cell fate in mouse two-cell embryos.

During mammalian pre-implantation embryo development, when the first asymmetry emerges and how it develops to direct distinct cell fates remain longstanding questions. Here, by analyzing single-blastomere transcriptome data from mouse and human preimplantation embryos, we revealed that the initial blastomere-toblastomere biases emerge as early as the first embryonic cleavage division, following a binomial distribution pattern. The subsequent zygotic transcriptional activation further elevated overall blastomereto-blastomere biases during the two-to 16-cell embryo stages. The trends of transcriptional asymmetry fell into two distinct patterns: for some genes, the extent of asymmetry was minimized between blastomeres (monostable pattern), whereas other genes, including those known to be lineage specifiers, showed ever-increasing asymmetry between blastomeres (bistable pattern), supposedly controlled by negative or positive feedbacks. Moreover, our analysis supports a scenario in which opposing lineage specifiers within an early blastomere constantly compete with each other based on their relative ratio, forming an inclined 'lineage strength' that pushes the blastomere onto a predisposed, yet flexible, lineage track before morphological distinction.