Homozygous Mutations in WEE2 Cause Fertilization Failure and Female Infertility

Abstract

Fertilization is a fundamental process of development and is a prerequisite for successful human reproduction. In mice, although several receptor proteins have been shown to play important roles in the process of fertilization, only three genes have been shown to cause fertilization failure and infertility when deleted in vivo. In clinical practice, some infertility case subjects suffer from recurrent failure of in vitro fertilization and intracytoplasmic sperm injection attempts due to fertilization failure, but the genetic basis of fertilization failure in humans remains largely unknown. Wee2 is a key oocyte-specific kinase involved in the control of meiotic arrest in mice, but WEE2 has not been associated with any diseases in humans. In this study, we identified homozygous mutations in WEE2 that are responsible for fertilization failure in humans. All four independent affected individuals had homozygous loss-of-function missense mutations or homozygous frameshift protein-truncating mutations, and the phenotype of fertilization failure was shown to follow a Mendelian recessive inheritance pattern. All four mutations significantly decreased the amount of WEE2 protein in vitro and in affected individuals' oocytes in vivo, and they all led to abnormal serine phosphorylation of WEE2 and reduced tyrosine 15 phosphorylation of Cdc2 in vitro. In addition, injection of WEE2 cRNA into affected individuals' oocytes rescued the fertilization failure phenotype and led to the formation of blastocysts in vitro. This work presents a novel gene responsible for human fertilization failure and has implications for future therapeutic treatments for infertility cases.

Novel mutations in WEE2: Expanding the spectrum of mutations responsible for human fertilization failure

“…The locations and conservation analysis of mutant residues in WEE2. A, Distribution of mutations in WEE2 exons, mutations described in our previous study were marked in purple and novel mutations identified in this study were marked in green，mutations c.220_223 delAAAG and c.1006_1007insTA were both found in this study and our previous study. B, Location of mutations in the WEE2 protein, the green ball indicated novel mutations identified in this study, purple balls indicated mutation described in our previous study, p.E75Vfs*6 and p.H337Yfs*24 were both found in this study and our previous study.…”

“…In the present study, we identified six affected individuals with nine mutations in WEE2 that are responsible for ICSI fertilization failure, among which mutation c.220_223 delAAAG (p.E75Vfs*6) and c.1006_1007insTA (p.H337Yfs*24) have been described in our previous study, the other seven are novel mutations. The function of WEE2 in the individuals from families 3, 4, and 5 was expected to be completely lost because of frameshift and nonsense mutations, and none of the retrieved oocytes from these patients could be fertilized.…”

“…Recently, mutations in a series of genes were found to be responsible for female infertility by us and others. For example, mutations in TUB B8 (MIM: 616768) and PATL2 (MIM: 614661) lead to oocyte maturation arrest, mutations in PADI6 (MIM: 610363) lead to early embryonic arrest, and mutations in TLE6 and WEE2 lead to fertilization failure . All of these results show the role that abnormalities in these genetic factors play in oocyte maturation arrest.…”

“…Target gene sequencing was then used to detect new rare WEE2 variants according to GRCh37. Variants analysis were based on a previously published procedure . For splicing mutation analysis, total RNA was extracted from granulosa cells from the affected individuals.…”

“…In mouse oocytes, downregulation of Wee1b (the mouse homolog of human WEE2) leads to constitutively high MPF (maturation promoting factor) activity, which causes failure of both MII exit and the formation of pronuclei . In our previous report, we found that mutations in WEE2 resulted in failure of MII exit by affecting the phosphorylation status of the downstream molecule Cdc2 . Given the important role of WEE2, we screened for novel WEE2 mutations in a new cohort of patients with fertilization failure.…”