Assisted Reproduction Unit, Department of Obstetrics and Gynecology, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
Key Laboratory of Reproductive Dysfunction Management of Zhejiang Province, Hangzhou, China.
Hum Reprod. 2022 Jul 30;37(8):1932-1944. doi: 10.1093/humrep/deac120.
What is the genetic basis of female infertility involving abnormal oocyte morphology with the production of a large first polar body (PB1)?
The homozygous missense variant (c.791C>G) and compound missense variants (c.596A>T and c.875C>T) in MOS proto-oncogene, serine/threonine kinase (MOS) (Online Mendelian Inheritance in Man (OMIM) reference: 190060; NM_005372.1) are responsible for abnormal oocyte morphology with the production of a large PB1 to cause infertility in women.
MOS, an oocyte-specific gene, encodes a serine/threonine-protein kinase that directly phosphorylates mitogen-activated protein kinase (MAPK) kinase (MEK) to activate MAPK (also called extracellular-signal-regulated kinase (ERK)) signal cascade in the oocyte. Female mice lacking Mos remained viable, but infertile because of oocyte symmetric division, spontaneous parthenogenetic activation and early embryonic arrest. Recently, two independent studies demonstrated that female infertility with early embryonic arrest and fragmentation can be caused by biallelic mutations in MOS. However, so far, MOS variants have not been associated with the phenotype of large PB1 extrusion in human oocytes to contribute to female infertility.
STUDY DESIGN, SIZE, DURATION: Two independent infertile families characterized by the presence of large PB1 in oocytes were recruited between December 2020 and February 2022.
PARTICIPANTS/MATERIALS, SETTING, METHODS: Genomic DNA was extracted from the peripheral blood samples of the subjects for whole-exome sequencing. Pedigree analysis was validated by Sanger sequencing. Then, the pathogenic effects of the MOS variants on MOS protein properties and ERK1/2 activation were determined in HEK293 cells and mouse oocytes.
We identified three rare missense variants in MOS, including a homozygous missense variant (c.791C>G) from Patient 1 in Family 1 and two compound missense variants (c.596A>T and c.875C>T) from twin sisters in Family 2. The MOS variants followed a recessive inheritance pattern in infertile patients. All three patients displayed a high percentage of large PB1 extrusion in the oocytes. The three MOS variants could not activate MEK1/2 and ERK1/2 in oocytes and HEK293 cells. In addition, when compared with wild-type MOS, the MOS variants decreased the MOS protein level and attenuated the binding capacity with MEK1. Microinjection of wild-type human MOS complementary RNAs (cRNAs) reversed the symmetric division of oocytes after siMos treatment. In contrast, the three MOS variants demonstrated no rescuing ability.
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LIMITATIONS, REASONS FOR CAUTION: Owing to the scarcity of human oocyte samples and the associated ethical restrictions, we could not perform the rescue attempt for the study patients.
Our findings expand the genetic and phenotypic spectrum of MOS variants in causing female infertility. Our study findings facilitate the early genetic diagnosis of abnormal oocyte morphology characterized as large PB1 that eventually causes infertility in women.
STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the National Natural Science Foundation of China (82071640 and 82001633), Natural Science Foundation of Zhejiang Province (LD22C060001), the Key Projects Jointly Constructed by the Ministry and the Province of Zhejiang Medical and Health Science and Technology Project (WKJ-ZJ-2005), China Postdoctoral Science Foundation (2020M682575 and 2021T140198), the Changsha Municipal Natural Science Foundation (kq2007022) and Hunan Provincial Grant for Innovative Province Construction (2019SK4012). None of the authors declare any competing interests.
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导致卵子形态异常并产生大第一极体（PB1）的女性不孕的遗传基础是什么？
MOS 原癌基因丝氨酸/苏氨酸激酶（MOS）中的纯合错义变异（c.791C>G）和复合错义变异（c.596A>T 和 c.875C>T）（在线孟德尔遗传在线数据库（OMIM）参考：190060；NM_005372.1）负责产生大 PB1 的卵子形态异常，导致女性不孕。
MOS 是一种卵母细胞特异性基因，编码一种丝氨酸/苏氨酸蛋白激酶，可直接磷酸化丝裂原活化蛋白激酶（MAPK）激酶（MEK），在卵母细胞中激活 MAPK（也称为细胞外信号调节激酶（ERK））信号级联。缺乏 Mos 的雌性小鼠仍然存活，但由于卵母细胞的对称分裂、自发的孤雌激活和早期胚胎阻滞而不育。最近，两项独立的研究表明，MOS 基因的双等位基因突变可导致女性不孕伴早期胚胎阻滞和碎片化。然而，迄今为止，MOS 变体尚未与人类卵母细胞中 PB1 大量挤出的表型相关，以导致女性不孕。
研究设计、大小、持续时间：2020 年 12 月至 2022 年 2 月期间招募了两个特征为卵母细胞中存在大 PB1 的独立不孕家庭。
参与者/材料、设置、方法：从受试者的外周血样中提取基因组 DNA 进行全外显子组测序。通过 Sanger 测序验证家系分析。然后，在 HEK293 细胞和小鼠卵母细胞中确定 MOS 变体对 MOS 蛋白性质和 ERK1/2 激活的致病作用。
我们在 MOS 中发现了三个罕见的错义变体，包括来自 1 号家庭的患者中的纯合错义变体（c.791C>G）和 2 号家庭的双胞胎姐妹中的两个复合错义变体（c.596A>T 和 c.875C>T）。MOS 变体在不孕患者中遵循隐性遗传模式。所有三名患者的卵母细胞中均显示出大 PB1 挤出的高百分比。这三种 MOS 变体都不能激活 MEK1/2 和 ERK1/2 在卵母细胞和 HEK293 细胞中。此外，与野生型 MOS 相比，MOS 变体降低了 MOS 蛋白水平并减弱了与 MEK1 的结合能力。用野生型人 MOS 互补 RNA（cRNAs）微注射可逆转 siMos 处理后卵母细胞的对称分裂。相比之下，这三种 MOS 变体没有恢复能力。
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局限性、谨慎的原因：由于人类卵母细胞样本稀缺且相关伦理限制，我们无法对研究患者进行挽救尝试。
我们的研究结果扩展了 MOS 变体导致女性不孕的遗传和表型谱。我们的研究结果有助于对特征为大 PB1 的异常卵子形态导致女性不孕的早期遗传诊断。
研究资金/竞争利益：本研究得到了国家自然科学基金（82071640 和 82001633）、浙江省自然科学基金（LD22C060001）、浙江省部共建医学科技项目重点项目（WKJ-ZJ-2005）、中国博士后科学基金（2020M682575 和 2021T140198）、长沙市自然科学基金（kq2007022）和湖南省创新型省份建设项目拨款（2019SK4012）的支持。作者均无任何竞争利益。
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