MC4R mutant mice develop ovarian teratomas

<jats:title>Abstract</jats:title><jats:p>Teratomas in mice, composed of different tissue types, are derived from primordial germ cells (PGCs) in the foetal gonads. The strongest candidate gene in the testicular teratoma locus (<jats:italic>Ter</jats:italic>) responsible for testicular teratoma formation was identified as mutation in <jats:italic>Dnd1, Dnd1R178*</jats:italic>. However, the phenotype of mice with a mutated <jats:italic>Dnd1</jats:italic> gene was germ cell loss. This suggests that other genes are involved in teratoma formation. Testicular teratomas can also be induced experimentally (experimentally testicular teratomas: ETTs) in 129/Sv mice by transplanting E12.5 foetal testes into adult testes. Previously, we mapped the <jats:italic>ett1</jats:italic> locus, which is the locus responsible for ETT formation on chromosome 18. By exome sequence analysis of the 129 and LTXBJ (LT) strains, we identified a missense mutation in the <jats:italic>melanocortin 4 receptor (MC4R)</jats:italic> gene among 8 genes in the <jats:italic>ett1</jats:italic> region. The missense mutation causes a substitution of glycine 25 by serine. Thus, this gene is a candidate for ETT formation. We established the LT-<jats:italic>ett1</jats:italic> congenic strain, which introduced the locus responsible for ETT formation genetically into the genomes of a testicular teratoma non-susceptible strain. In this study, we crossed LT-<jats:italic>ett1</jats:italic> and a previously established LT-<jats:italic>Ter</jats:italic> strain to establish the double congenic strain LT-<jats:italic>Ter</jats:italic>-<jats:italic>ett1</jats:italic>. Also, we established a strain with a point mutation in the <jats:italic>MC4R</jats:italic> gene of the LT strain by genome editing, LT-<jats:italic>MC4R</jats:italic><jats:sup><jats:italic>G25S</jats:italic></jats:sup>. Furthermore, double genetically modified strain LT-<jats:italic>Ter-MC4R</jats:italic><jats:sup>G25S</jats:sup> was established to address the relation between <jats:italic>Ter</jats:italic> and <jats:italic>MC4R</jats:italic>. Surprisingly, highly developed ovarian teratomas (OTs), instead of testicular teratomas, appeared not only in the LT-<jats:italic>Ter-MC4R</jats:italic><jats:sup><jats:italic>G25S</jats:italic></jats:sup> and LT-<jats:italic>MC4R</jats:italic><jats:sup><jats:italic>G25S</jats:italic></jats:sup> strains but also in the LT-<jats:italic>ett1</jats:italic> and LT-<jats:italic>Ter</jats:italic>-<jats:italic>ett1</jats:italic> strains. The incidence of OT formation was high in double genetically modified strains. The results demonstrated that <jats:italic>MC4R</jats:italic> is one of the genes responsible for OT formation. It was suggested that the effect of the missense mutation in <jats:italic>MC4R</jats:italic> on teratoma formation was promoted by abnormal germ cell formation by the mutation in <jats:italic>DND1.</jats:italic></jats:p>