Mutations in CCNB3 affect its location thus causing a multiplicity of phenotypes in human oocytes maturation by aberrant CDK1 activity and APC/C activity at different stages.

BACKGROUND: Oocyte maturation arrest results in female infertility and the genetic etiology of this phenotype remains largely unknown. Previous studies have proven that cyclins play a significant role in the cell cycle both in meiosis and mitosis. Cyclin B3 (CCNB3) is one of the members of the cyclin family and its function in human oocyte maturation is poorly understood. METHODS: 118 infertile patients were recruited and WES was performed for 68 independent females that experienced oocyte maturation arrest. Four mutations in CCNB3 were found and effects of these mutations were validated by Sanger sequencing and in vitro functional analyses. RESULTS: We found these mutations altered the location of cyclin B3 which affected the function of cyclin dependent kinase 1 (CDK1) and led to mouse oocyte arrested at germinal vesicle (GV) stage. And then, low CDK1 activity influenced the degradation of cadherin 1 (CDH1) and the accumulation of cell division cycle 20 (CDC20) which are two types of anaphase-promoting complex/cyclosome (APC/C) activators and act in different stages of the cell cycle. Finally, APC/C activity was downregulated due to insufficient CDC20 level and resulted in oocyte metaphase I (MI) arrest. Moreover, we also found that the addition of PP1 inhibitor Okadic acid and CDK1 inhibitor Roscovitine at corresponding stages during oocyte in vitro maturation (IVM) significantly improved the maturation rates in CCNB3 mutant cRNAs injected oocytes. The above experiments were performed in mouse oocytes. CONCLUSION: Here, we report five independent patients in which mutations in CCNB3 may be the cause of oocyte maturation arrest. Our findings shed lights on the critical role of CCNB3 in human oocyte maturation.

NLRP7 participates in the human subcortical maternal complex and its variants cause female infertility characterized by early embryo arrest.

Successful human reproduction requires normal oocyte maturation, fertilization, and early embryo development. Early embryo arrest is a common phenomenon leading to female infertility, but the genetic basis is largely unknown. NLR family pyrin domain-containing 7 (NLRP7) is a member of the NLRP subfamily. Previous studies have shown that variants of NLRP7 are one of the crucial causes of female recurrent hydatidiform mole, but whether NLRP7 variants can directly affect early embryo development is unclear. We performed whole-exome sequencing in patients who experienced early embryo arrest, and five heterozygous variants (c.251G > A, c.1258G > A, c.1441G > A, c. 2227G > A, c.2323C > T) of NLRP7 were identified in affected individuals. Plasmids of NLRP7 and subcortical maternal complex components were overexpressed in 293 T cells, and Co-IP experiments showed that NLRP7 interacted with NLRP5, TLE6, PADI6, NLRP2, KHDC3L, OOEP, and ZBED3. Injecting complementary RNAs in mouse oocytes and early embryos showed that NLRP7 variants influenced the oocyte quality and some of the variants significantly affected early embryo development. These findings contribute to our understanding of the role of NLRP7 in human early embryo development and provide a new genetic marker for clinical early embryo arrest patients. KEY MESSAGES: Five heterozygous variants of NLRP7 (c.1441G > A; 2227G > A; c.251G > A; c.1258G > A; c.2323C > T) were identified in five infertile patients who experienced early embryo arrest. NLRP7 is a component of human subcortical maternal complex. NLRP7 variants lead to poor quality of oocytes and early embryo development arrest. This study provides a new genetic marker for clinical early embryo arrest patients.