Mechanisms of minor pole-mediated spindle bipolarization in human oocytes.

Spindle bipolarization, the process of a microtubule mass transforming into a bipolar spindle, is a prerequisite for accurate chromosome segregation. In contrast to mitotic cells, the process and mechanism of spindle bipolarization in human oocytes remains unclear. Using high-resolution imaging in more than 1800 human oocytes, we revealed a typical state of multipolar intermediates that form during spindle bipolarization and elucidated the mechanism underlying this process. We found that the minor poles formed in multiple kinetochore clusters contribute to the generation of multipolar intermediates. We further determined the essential roles of HAUS6, KIF11, and KIF18A in spindle bipolarization and identified mutations in these genes in infertile patients characterized by oocyte or embryo defects. These results provide insights into the physiological and pathological mechanisms of spindle bipolarization in human oocytes.

Identification novel mutations and phenotypic spectrum expanding in PATL2 in infertile women with IVF/ICSI failure.

AIM: Abnormalities in oocyte maturation, fertilization, and early embryonic development are major causes of primary infertility in women who are undergoing IVF/ICSI attempts. Although many genetic factors responsible for these abnormal phenotypes have been identified, there are more additional pathogenic genes and variants yet to be discovered. Previous studies confirmed that bi-allelic PATL2 deficiency is an important factor for female infertility. In this study, 935 infertile patients with IVF/ICSI failure were selected for whole-exome sequencing, and 18 probands carrying PATL2 variants with a recessive inheritance pattern were identified. METHODS: We estimated that the prevalence contributed by PATL2 was 1.93% (18/935) in our study cohort. RESULTS: 15 novel variants were found in those families, including c.1093C > T, c.1609dupA, c.1204C > T, c.643dupG, c.877-2A > G, c.1228C > G, c.925G > A, c.958G > A, c.4A > G, c.1258T > C, c.1337G > A, c.1264dupA, c.88G > T, c.1065-2A > G, and c.1271T > C. The amino acids altered by the corresponding variants were highly conserved in mammals, and in silico analysis and 3D molecular modeling suggested that the PATL2 mutants impaired the physiologic function of the resulting proteins. Diverse clinical phenotypes, including oocyte maturation defect, fertilization failure, and early embryonic arrest might result from different variants of PATL2. CONCLUSIONS: These results expand the spectrum of PATL2 variants and provide an important reference for genetic counseling for female infertility, and they increase our understanding of the mechanisms of oocyte maturation arrest caused by PATL2 deficiency.

Bi-allelic missense variants in MEI4 cause preimplantation embryonic arrest and female infertility.

Preimplantation embryonic arrest is an important pathogenesis of female infertility, but little is known about the genetic factors behind this phenotype. MEI4 is an essential protein for DNA double-strand break formation during meiosis, and Mei4 knock-out female mice are viable but sterile, indicating that MEI4 plays a crucial role in reproduction. To date, MEI4 has not been found to be associated with any human reproductive diseases. Here, we identified six compound heterozygous and homozygous MEI4 variants-namely, c.293C > T, p.(Ser98Leu), c.401C > G, p.(Pro134Arg), c.391C > G, p.(Pro131Ala), c.914A > T, p.(Tyr305Phe), c.908C > G, p.(Ala303Gly), and c.899A > T, p.(Gln300Leu)-in four independent families that were responsible for female infertility mainly characterized by preimplantation embryonic arrest. In vitro, we found that these variants reduced the interaction between MEI4 and DNA. In vivo, we generated a knock-in mouse model and demonstrated that female mice were infertile and were characterized by developmental defects during oogenesis. Our findings reveal the important roles of MEI4 in human reproduction and provide a new diagnostic marker for genetic counseling of clinical infertility patients.

Bi-allelic pathogenic variants in PABPC1L cause oocyte maturation arrest and female infertility.

Oocyte maturation arrest is one of the important causes of female infertility, but the genetic factors remain largely unknown. PABPC1L, a predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos prior to zygotic genome activation, plays a key role in translational activation of maternal mRNAs. Here, we identified compound heterozygous and homozygous variants in PABPC1L that are responsible for female infertility mainly characterized by oocyte maturation arrest in five individuals. In vitro studies demonstrated that these variants resulted in truncated proteins, reduced protein abundance, altered cytoplasmic localization, and reduced mRNA translational activation by affecting the binding of PABPC1L to mRNA. In vivo, three strains of Pabpc1l knock-in (KI) female mice were infertile. RNA-sequencing analysis showed abnormal activation of the Mos-MAPK pathway in the zygotes of KI mice. Finally, we activated this pathway in mouse zygotes by injecting human MOS mRNA, and this mimicked the phenotype of KI mice. Our findings reveal the important roles of PABPC1L in human oocyte maturation and add a genetic potential candidate gene to be screened for causes of infertility.