Essential Role of Mg2+ for Mouse Preimplantation Embryo Development Revealed by TRPM7 Chanzyme Deficient Gametes

TRPM7 (transient receptor potential cation channel subfamily M member 7) is a chanzyme with channel and kinase domains essential for embryo development. Using gamete-specific Trpm7-null lines, we report that TRPM7-mediated Mg2+ influx is indispensable for reaching the blastocyst stage. TRPM7 was expressed dynamically from gametes to blastocysts, displaying stage-specific and distinct localizations on the plasma membrane, cytoplasm, and nucleus, and undergoes cleavage that produces C- terminal kinase fragments. TRPM7 underpinned Mg2+ homeostasis throughout this time, and excess Mg2+ but not Zn2+ or Ca2+ overcame the arrest of Trpm7-null embryos; expressing Trpm7 mRNA restored development, but mutant versions failed or were less effective. Transcriptomic analyses of embryos lacking Trpm7 revealed an abundance of oxidative stress-pathway genes, confirmed by mitochondrial dysfunction, and a reduction of transcription factor networks essential for proliferation; Mg2+ supplementation corrected these defects. Hence, TRPM7 underpins Mg2+ homeostasis in preimplantation embryos, prevents oxidative stress, and promotes gene expression patterns necessary for developmental progression and cell lineage specification. RNAseq was performed in control or Trpm7 knockout metaphase II eggs, 1-cell, 2-cell, 4-cell, and 8-cell embryos, morulas, and blastocysts, as well as embryos cultured for 24 or 48 hours from the 2-cell stage in the presence of 10 mM MgSO4.