Biallelic mutations in ANAPC13 cause female infertility characterized by oocyte maturation arrest both in humans and...

Oocyte maturation arrest is an intractable clinical problem, resulting in recurrent failure of assisted reproductive treatments. The anaphase-promoting complex or cyclosome orchestrates a series of proteolytic events to ensure proper cell cycle progression of mitosis in somatic cell proliferation and meiosis during oocyte maturation. Defects in anaphase-promoting complex or cyclosome subunits, such as ANAPC8 and ANAPC12, have been demonstrated linked to oocyte maturation arrest. However, the roles of other anaphase-promoting complex or cyclosome subunits in oocyte maturation remain unclear.

This study aimed to reveal the causal relationship between ANAPC13 mutations and oocyte maturation arrest, while elucidating the pathogenic mechanism to provide a theoretical basis for clinical diagnosis and treatment.

Patients diagnosed with oocyte maturation arrest by morphologic assessment during assisted reproductive treatments were recruited and underwent whole-exome sequencing. Mutations in ANAPC13 were identified in 3 patients and screened out as the candidate. The recurrent mutation c.6C>A was recapitulated in a knock-in mouse model (Anapc13^M/M mice) to clarify its association with oocyte maturation arrest, with wild-type mice (Anapc13^+/+ mice) serving as controls. Further phenotyping experiments with mouse oocytes, proteomic analysis of human oocytes, and molecular experiments with cell lines and plasmids were conducted to determine the role of ANAPC13 in oocyte maturation. Anapc13 mRNA microinjection was performed as an exploratory rescue treatment.

We identified 2 biallelic ANAPC13 mutations (NM_001242374.1: c.6C>A; p.D2E and c.71T>G; p.L24R) in 3 infertile females with oocyte maturation arrest at metaphase I. Oocytes from the Anapc13^M/M female mice similarly displayed an extremely low proportion of mature oocytes, whether obtained after superovulation (Anapc13^+/+: 96.63% ± 3.40% vs Anapc13^M/M: 1.66% ± 3.34%, P<0.001) or in vitro maturation (Anapc13^+/+: 70.30% ± 1.10% vs Anapc13^M/M: 0.83% ± 1.66%, P<0.001). An in-depth study of oocytes demonstrated that mutant ANAPC13 disrupts the protein composition of oocytes during metaphase I-to-anaphase I transition by impairing anaphase-promoting complex or cyclosome function, without changing the spindle assembly checkpoint dynamics. Furthermore, a molecular mechanistic study revealed that anaphase-promoting complex or cyclosome dysfunction resulted from abnormal subunit interaction. Moreover, Anapc13-mutant oocytes can be partially (49.20% ± 3.60%) rescued to extrude the first polar body by microinjection of Anapc13 mRNA.

Our study demonstrated the critical role of ANAPC13 in human and mouse oocyte maturation, established a causal relationship between ANAPC13 mutations and oocyte maturation arrest, and further provided preliminary evidence that microinjection may serve as a potential treatment for these patients with ANAPC13 mutations.