SHMT2 is essential for mammalian preimplantation embryonic development through de novo biosynthesis of nucleotide metabolites

Assisted reproductive technology (ART) is used widely and efficiently to treat infertility. During the ART procedure, one of the main factors affecting the success rate is abnormal development of preimplantation embryos. The establishment and maintenance of developmental competence are precisely regulated at different levels, while minor errors at early stages may result in adverse outcomes, including developmental arrest and implantation failure. As one of the major inputs, the regulatory mechanisms of metabolites in embryonic development are less known. In this study, we investigated the functional relevance of the metabolic enzyme serine hydroxymethyltransferase 2 (SHMT2) and deoxyribonucleotide (dNTP) metabolites in mouse preimplantation embryonic development. By using a well-characterized SHMT2 inhibitor, SHMT-IN-2, we effectively inhibited the catalytic activity of the SHMT2 enzyme, which led to developmental arrest at the pronuclear stage of the embryo. A low-input liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and applied for detecting dNTP content in embryos. We found that SHMT2 inhibition led to an insufficient dTTP supply and replication stress during the first mitotic cleavage, thereby causing failure of pronuclear fusion and developmental arrest. Our findings demonstrate a specific mechanism where, apart from building blocks of DNA, the availability of dNTPs contributes to the control of mouse preimplantation embryonic development.