Familial primary ovarian insufficiency associated with a SYCE1 point mutation: Defective meiosis elucidated in humanized mice

ObjectiveTo investigate if nonsense mutation SYCE1 c.613CT -found in women with familial primary ovarian insufficiency (POI)- is actually responsible for infertility, and to elucidate the involved molecular mechanisms. DesignAs most fundamental mammalian oogenesis events occur during the embryonic phase, thus hindering the study of POIs etiology/pathogeny in infertile women, we have used CRISPR/Cas9 technology to generate a mouse model line with an equivalent genome alteration (humanized mice). SettingAcademic research laboratories. InterventionsWe present the characterization of the biallelic mutant mice phenotype, compared to wild type and monoallelic littermates. AnimalsStudies were conducted employing the generated humanized mice. All studies were performed for both genders, except otherwise stated. Main outcome measuresreproductive capability by fertility tests; gonadal histological analysis; evaluation of chromosome synapsis and synaptonemal complex (SC) assembly by immunolocalizations; protein studies by Western blotting; transcript quantification by RT-qPCR. ResultsThe studied mutation proved to be the actual cause of the infertile phenotype, both in female and male mice homozygous for the change, confirming infertility of genetic origin with a recessive mode of inheritance. The mechanisms that lead to infertility are related to chromosome synapsis defects; no putative truncated SYCE1 protein was observed, and Syce1 transcript was hardly detected in biallelic mutants. ConclusionsWe present for the first time the generation of humanized mice to study the actual consequences of a SC component mutation found in women with familial POI. By this approach we could confirm the suspected etiology, and shed light on the underlying molecular mechanism.