Mutations in TUBB8 and Human Oocyte Meiotic Arrest

A heterozygous SPRY4 variant identified in female infertility characterized by reduced oocyte potential and early embryonic arrest

STUDY QUESTION

Can novel genetic factors contributing to early embryonic arrest in infertile patients be identified, along with the underlying mechanisms of the pathogenic variant?

SUMMARY ANSWER

We identified a heterozygous variant in the SPRY4 (sprouty RTK signaling antagonist 4) in infertile patients and conducted in vitro and in vivo studies to investigate the effects of the variant/deletion, highlighting its critical role in female reproductive health.

WHAT IS KNOWN ALREADY

SPRY4 acts as a negative regulator of receptor tyrosine kinases (RTKs) and functions as a tumor suppressor. Its abnormal expression can lead to recurrent miscarriage by affecting trophoblast function. In mice, Spry4 knockout (KO) leads to craniofacial anomalies and growth defects. A human study links the SPRY4 variant to a male patient with isolated hypogonadotropic hypogonadism (IHH), hypothetically impacting gonadotropin-releasing hormone (GnRH) neurons, and causing reproductive dysfunctions. SPRY4 is thus potentially integral in regulating endocrine homeostasis and reproductive function. To date, no study has reported SPRY4 variants associated with female fertility, and a causal relationship has not been established with functional evidence.

STUDY DESIGN, SIZE, DURATION

Whole-exome sequencing (WES) was performed in 392 infertile women who suffered from primary infertility of unknown reason, and the heterozygous SPRY4 variant were identified in one independent family. The infertile patients presenting were recruited from July 2017 to November 2023.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women diagnosed with primary infertility were recruited from the Reproduction Center of Zhongshan Hospital, Fudan University. Genomic DNA was extracted from peripheral blood for WES analysis. The SPRY4 variant were identified through WES, in silico analysis, and variant screening. All variants were confirmed by Sanger sequencing. The effects of the variants were investigated in human embryonic kidney (HEK) 293T (HEK293T) cells via western blotting, and in mouse oocytes and embryos through complementary RNA (cRNA) injection, RNA sequencing, fluorescence, absorbance, and RT-qPCR assays. Gene function was further examined in Spry4 KO mice via histology, western blotting, ELISA, and RT-qPCR assays.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified a missense heterozygous pathogenic variant in SPRY4 (GRCh38, GenBank: NM_030964.5, c.157C>T p.(Arg53Trp), rs200531302) that reduces SPRY4 protein levels in HEK293T cells and disrupts the redox system and mitochondrial function in mouse oocyte, and perturbs developmental potential in mouse embryos. These phenotypes could be partially reversed by the exogenous addition of Nrf1 cRNA. Additionally, Spry4-/- mice exhibit ovarian oxidative stress and decreased ovarian function.

LIMITATIONS, REASONS FOR CAUTION

Due to the limited WES data and population, we identified only one family with a SPRY4 mutation. The deeper mechanism and therapeutic strategy should be further investigated through mutant mice and recovery experiment.

WIDER IMPLICATIONS OF THE FINDINGS

Our study has identified a pathogenic variant in SPRY4 associated with early embryonic arrest in humans. These findings enhance our understanding of the role of SPRY4 in early embryonic development and present a new genetic marker for female infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China (82071643 and 82171655) and Natural Science Foundation of Shanghai (22ZR1456200). None of the authors have any competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Unraveling the mysteries of early embryonic arrest: genetic factors and molecular mechanisms

Early embryonic arrest (EEA) is a critical impediment in assisted reproductive technology (ART), affecting 40% of infertile patients by halting the development of early embryos from the zygote to blastocyst stage, resulting in a lack of viable embryos for successful pregnancy. Despite its prevalence, the molecular mechanism underlying EEA remains elusive. This review synthesizes the latest research on the genetic and molecular factors contributing to EEA, with a focus on maternal, paternal, and embryonic factors. Maternal factors such as irregularities in follicular development and endometrial environment, along with mutations in genes like NLRP5, PADI6, KPNA7, IGF2, and TUBB8, have been implicated in EEA. Specifically, PATL2 mutations are hypothesized to disrupt the maternal-zygotic transition, impairing embryo development. Paternal contributions to EEA are linked to chromosomal variations, epigenetic modifications, and mutations in genes such as CFAP69, ACTL7A, and M1AP, which interfere with sperm development and lead to infertility. Aneuploidy may disrupt spindle assembly checkpoints and pathways including Wnt, MAPK, and Hippo signaling, thereby contributing to EEA. Additionally, key genes involved in embryonic genome activation-such as ZSCAN4, DUXB, DUXA, NANOGNB, DPPA4, GATA6, ARGFX, RBP7, and KLF5-alongside functional disruptions in epigenetic modifications, mitochondrial DNA, and small non-coding RNAs, play critical roles in the onset of EEA. This review provides a comprehensive understanding of the genetic and molecular underpinnings of EEA, offering a theoretical foundation for the diagnosis and potential therapeutic strategies aimed at improving pregnancy outcomes.

Advances in the genetic etiology of female infertility

Human reproduction is a complex process involving gamete maturation, fertilization, embryo cleavage and development, blastocyst formation, implantation, and live birth. If any of these processes are abnormal or arrest, reproductive failure will occur. Infertility is a state of reproductive dysfunction caused by various factors. Advances in molecular genetics, including cell and molecular genetics, and high-throughput sequencing technologies, have found that genetic factors are important causes of infertility. Genetic variants have been identified in infertile women or men and can cause gamete maturation arrest, poor quality gametes, fertilization failure, and embryonic developmental arrest during assisted reproduction technology (ART), and thus reduce the clinical success rates of ART. This article reviews clinical studies on repeated in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) failures caused by ovarian dysfunction, oocyte maturation defects, oocyte abnormalities, fertilization disorders, and preimplantation embryonic development arrest due to female genetic etiology, the accumulation of pathogenic genes and gene pathogenic loci, and the functional mechanism and clinical significance of pathogenic genes in gametogenesis and early embryonic development.

Identification of a novel splicing variant of thyroid hormone receptor interaction protein 13 (TRIP13) in female infertility characterized by oocyte maturation arrest

PURPOSE

As a cause of primary female infertility, oocyte maturation arrest (OMA) is characterized by failure to obtain mature oocytes due to abnormal meiosis. We aimed to identify pathogenic variants in two sisters with OMA phenotype from a non-consanguineous family.

METHODS

Whole-exome sequencing and Sanger sequencing were conducted to identify and validate the disease-causing gene variant. Additionally, we performed a minigene assay, quantitative reverse transcription PCR, and Western blotting to assess the effects of the variant.

RESULTS

We identified a novel homozygous splicing variant (c.1021-11T>C) in TRIP13, which followed a recessive inheritance pattern. Minigene assay showed that the variant could disrupt the integrity of TRIP13 mRNA, as evidenced by the production of an alternative transcript with intron10 intermediate retention of 79 bp. Compared to normal controls, the expression of TRIP13 mRNA and abundance of TRIP13 protein were also significantly decreased in Epstein-Barr virus-immortalized lymphoblastoid cells derived from affected individuals.

CONCLUSION

Our findings confirm the contribution of genetic factors to OMA and expand the mutation spectrum of TRIP13 in female infertility.

TUBB4B is essential for the cytoskeletal architecture of cochlear supporting cells and motile cilia development

Microtubules are essential for various cellular processes. The functional diversity of microtubules is attributed to the incorporation of various α- and β-tubulin isotypes encoded by different genes. In this work, we investigated the functional role of β4B-tubulin isotype (TUBB4B) in hearing and vision as mutations in TUBB4B are associated with sensorineural disease. Using a Tubb4b knockout mouse model, our findings demonstrate that TUBB4B is essential for hearing. Mice lacking TUBB4B are profoundly deaf due to defects in the inner and middle ear. Specifically, in the inner ear, the absence of TUBB4B lead to disorganized and reduced densities of microtubules in pillar cells, suggesting a critical role for TUBB4B in providing mechanical support for auditory transmission. In the middle ear, Tubb4b-/- mice exhibit motile cilia defects in epithelial cells, leading to the development of otitis media. However, Tubb4b deletion does not affect photoreceptor function or cause retinal degeneration. Intriguingly, β6-tubulin levels increase in retinas lacking β4B-tubulin isotype, suggesting a functional compensation mechanism. Our findings illustrate the essential roles of TUBB4B in hearing but not in vision in mice, highlighting the distinct functions of tubulin isotypes in different sensory systems.

Variants in NLRP2 and ZFP36L2, non-core components of the human subcortical maternal complex, cause female infertility with embryonic development arrest

The subcortical maternal complex (SCMC), which is vital in oocyte maturation and embryogenesis, consists of core proteins (NLRP5, TLE6, OOEP), non-core proteins (PADI6, KHDC3L, NLRP2, NLRP7), and other unknown proteins that are encoded by maternal effect genes. Some variants of SCMC genes have been linked to female infertility characterized by embryonic development arrest. However, so far, the candidate non-core SCMC components associated with embryonic development need further exploration and the pathogenic variants that have been identified are still limited. In this study, we discovered two novel variants [p.(Ala131Val) and p.(Met326Val)] of NLRP2 in patients with primary infertility displaying embryonic development arrest from large families. In vitro studies using 293T cells and mouse oocytes, respectively, showed that these variants significantly decreased protein expression and caused the phenotype of embryonic development arrest. Additionally, we combined the 'DevOmics' database with the whole exome sequence data of our cohort and screened out a new candidate non-core SCMC gene ZFP36L2. Its variants [p.(Ala241Pro) and p.(Pro291dup)] were found to be responsible for embryonic development arrest. Co-immunoprecipitation experiments in 293T cells, used to demonstrate the interaction between proteins, verified that ZFP36L2 is one of the human SCMC components, and microinjection of ZFP36L2 complementary RNA variants into mouse oocytes affected embryonic development. Furthermore, the ZFP36L2 variants were associated with disrupted stability of its target mRNAs, which resulted in aberrant H3K4me3 and H3K9me3 levels. These disruptions decreased oocyte quality and further developmental potential. Overall, this is the first report of ZFP36L2 as a non-core component of the human SCMC and we found four novel pathogenic variants in the NLRP2 and ZFP36L2 genes in 4 of 161 patients that caused human embryonic development arrest. These findings contribute to the genetic diagnosis of female infertility and provide new insights into the physiological function of SCMC in female reproduction.

TUBB4B is essential for the expansion of differentiating spermatogonia

Microtubules, polymers of αβ-tubulin heterodimers, are essential for various cellular processes. The incorporation of different tubulin isotypes, each encoded by distinct genes, is proposed to contribute to the functional diversity observed in microtubules. However, the functional roles of each tubulin isotype are not completely understood. In this study, we investigated the role of the β4B-tubulin isotype (Tubb4b) in spermatogenesis, utilizing a Tubb4b knockout mouse model. We showed that β4B-tubulin is expressed in the germ cells throughout spermatogenesis. β4B-tubulin was localized to cytoplasmic microtubules, mitotic spindles, manchette, and axonemes of sperm flagella. We found that the absence of β4B-tubulin resulted in male infertility and failure to produce sperm cells. Our findings demonstrate that a lack of β4B-tubulin leads to defects in the initial stages of spermatogenesis. Specifically, β4B-tubulin is needed for the expansion of differentiating spermatogonia, which is essential for the subsequent progression of spermatogenesis.

Evolutionarily new genes in humans with disease phenotypes reveal functional enrichment patterns shaped by adaptive innovation and sexual selection

New genes (or young genes) are genetic novelties pivotal in mammalian evolution. However, their phenotypic impacts and evolutionary patterns over time remain elusive in humans due to the technical and ethical complexities of functional studies. Integrating gene age dating with Mendelian disease phenotyping, our research shows a gradual rise in disease gene proportion as gene age increases. Logistic regression modeling indicates that this increase in older genes may be related to their longer sequence lengths and higher burdens of deleterious de novo germline variants (DNVs). We also find a steady integration of new genes with biomedical phenotypes into the human genome over macroevolutionary timescales (~0.07% per million years). Despite this stable pace, we observe distinct patterns in phenotypic enrichment, pleiotropy, and selective pressures across gene ages. Notably, young genes show significant enrichment in diseases related to the male reproductive system, indicating strong sexual selection. Young genes also exhibit disease-related functions in tissues and systems potentially linked to human phenotypic innovations, such as increased brain size, musculoskeletal phenotypes, and color vision. We further reveal a logistic growth pattern of pleiotropy over evolutionary time, indicating a diminishing marginal growth of new functions for older genes due to intensifying selective constraints over time. We propose a "pleiotropy-barrier" model that delineates higher potentials for phenotypic innovation in young genes compared to older genes, a process that is subject to natural selection. Our study demonstrates that evolutionarily new genes are critical in influencing human reproductive evolution and adaptive phenotypic innovations driven by sexual and natural selection, with low pleiotropy as a selective advantage.

A novel heterozygous missense variant of PANX1 causes human oocyte death and female infertility

Pannexin1 (PANX1) is a highly glycosylated membrane channel-forming protein, which has been found to implicate in multiple physiological and pathophysiological functions. Variants in the PANX1 gene have been reported to be associated with oocyte death and recurrent in vitro fertilization failure. In this study, we identified a novel heterozygous PANX1 variant (NM_015368.4 c.410 C > T (p.Ser137Leu)) associated with the phenotype of oocyte death in a non-consanguineous family, followed by an autosomal dominant (AD) mode. We explored the molecular mechanism of the novel variant and the variant c.976_978del (p.Asn326del) that we reported previously. Both of the variants altered the PANX1 glycosylation pattern in cultured cells, led to aberrant PANX1 channel activation, affected ATP release and membrane electrophysiological properties, which resulted in mouse and human oocyte death in vitro. For the first time, we presented the direct evidence of the effect of the PANX1 variants on human oocyte development. Our findings expand the variant spectrum of PANX1 genes associated with oocyte death and provide new support for the genetic diagnosis of female infertility.

Biallelic variants in α-tubulin isotypes cause female infertility characterised as recurrent preimplantation embryo arrest

BACKGROUND

Recurrent preimplantation embryo developmental arrest (RPEA) is the most common phenotype in assisted reproductive technology treatment failure associated with identified genetic abnormalities. Currently known maternal genetic variants explain only a limited number of cases. Variants of the β-tubulin subunit gene, TUBB8, cause oocyte meiotic arrest and RPEA through a broad spectrum of spindle defects. In contrast, α-tubulin subunit genes are poorly studied in the context of preimplantation embryonic development.

METHODS

Whole exome sequencing was performed on the PREA cohort. Functional characterisations of the identified candidate disease-causing variants were validated using Sanger sequencing, bioinformatics, in vitro functional analyses and single-cell RNA-sequencing of arrested embryos.

RESULTS

Four homozygous variants were identified in the PREA cohort: two of TUBA1C (p.Gln358Ter and p.Asp444Metfs*42) and two of TUBA4A (p.Arg339Cys and p.Tyr440Ter). These variants cause varying degrees of spindle assembly defects. Additionally, we characterised changes in the human arrested embryo transcriptome carrying TUBA4A variants, with a particular focus on spindle organisation, chromosome segregation and mRNA decay.

CONCLUSION

Our findings identified TUBA1C as a novel genetic marker and expanded the genetic and phenotypic spectrum of TUBA4A in female infertility and RPEA, which altogether highlighted the importance of α-tubulin isotypes in preimplantation embryonic development.

Evaluation of an Updated Gene Panel as a Diagnostic Tool for Both Male and Female Infertility

In recent years, an increasing number of genes associated with male and female infertility have been identified. The genetics of infertility is no longer limited to the analysis of karyotypes or specific genes, and it is now possible to analyse several dozen infertility genes simultaneously. Here, we present the diagnostic activity over the past two years including 140 patients (63 women and 77 men). Targeted sequencing revealed causative variants in 17 patients, representing an overall diagnostic rate of 12.1%, with prevalence rates in females and males of 11% and 13%, respectively. The gene-disease relationship (GDR) was re-evaluated for genes due to the addition of new patients and/or variants in the actual study. Five genes changed categories: two female genes (MEIOB and TBPL2) moved from limited to moderate; two male genes (SOHLH1 and GALNTL5) moved from no evidence to strong and from limited to moderate; and SEPTIN12, which was unable to classify male infertility, was reclassified as limited. Many infertility genes have yet to be identified. With the increasing integration of genetics in reproductive medicine, the scope of intervention extends to include other family members, in addition to individual patients or couples. Genetic counselling consultations and appropriate staffing will need to be established in fertility centres. Trial registration number: Not applicable.

Genetic factors of oocyte maturation arrest: an important cause for recurrent IVF/ICSI failures

Oocyte maturation arrest (OMA) is a common phenotype observed in IVF/ICSI cycles, characterized by the production of immature oocytes which lead to infertility. Previous studies have demonstrated that genetic factors play an important role in OMA, but the genetic mechanisms underlying a group of patients remain to be elucidated. In the recent issue of Journal of Assisted Reproduction and Genetics, Hu et al. and Wan et al. identified novel PATL2 or ZFP36L2 variants in OMA patients, respectively. By conducting in vitro experiments, they demonstrated the destructive effect of the variants on protein function. These findings expand the mutational spectrum of PATL2 and ZFP36L2, and provide precise reference for genetic counseling of OMA patients.

AlphaFold2-guided engineering of split-GFP technology enables labeling of endogenous tubulins across species while preserving function

Dynamic properties are essential for microtubule (MT) physiology. Current techniques for in vivo imaging of MTs present intrinsic limitations in elucidating the isotype-specific nuances of tubulins, which contribute to their versatile functions. Harnessing the power of the AlphaFold2 pipeline, we engineered a strategy for the minimally invasive fluorescence labeling of endogenous tubulin isotypes or those harboring missense mutations. We demonstrated that a specifically designed 16-amino acid linker, coupled with sfGFP11 from the split-sfGFP system and integration into the H1-S2 loop of tubulin, facilitated tubulin labeling without compromising MT dynamics, embryonic development, or ciliogenesis in Caenorhabditis elegans. Extending this technique to human cells and murine oocytes, we visualized MTs with the minimal background fluorescence and a pathogenic tubulin isoform with fidelity. The utility of our approach across biological contexts and species set an additional paradigm for studying tubulin dynamics and functional specificity, with implications for understanding tubulin-related diseases known as tubulinopathies.

Identification of novel compound heterozygous ZFP36L2 variants implicated in oocyte maturation defects and female infertility

PURPOSE

To explore the pathogenesis of oocyte maturation defects.

METHODS

Whole exome sequencing was conducted to identify potential variants, which were then confirmed within the pedigree through Sanger sequencing. The functional characterization of the identified variants responsible for the disease, including their subcellular localization, protein levels, and interactions with other proteins, was verified through transient transfection in HeLa cells in vitro. Additionally, we employed real-time RT-PCR and single-cell RNA sequencing to examine the impact of ZFP36L2 pathogenic variants on mRNA metabolism in both HeLa cells and mouse or human oocytes.

RESULTS

A novel compound heterozygous variant in ZFP36L2 (c.186T > G, p.His62Gln and c.869 C > T, p.Pro290Leu) was discovered in a patient with oocyte maturation defects. Our findings indicate that these variants lead to compromised binding capacity of the ZFP36L2-CONT6L complex and impaired mRNA degradation in HeLa cells and mouse oocytes. Furthermore, we characterized the changes in the human oocyte transcriptome associated with ZFP36L2 variants, with a particular emphasis on cell division, mitochondrial function, and ribosome metabolism.

CONCLUSIONS

This study broadens the mutation spectrum of ZFP36L2 and constitutes the first report of human oocyte transcriptome alterations linked to ZFP36L2 variants. In conjunction with existing knowledge of ZFP36L2, our research lays the groundwork for genetic counseling aimed at addressing female infertility.

Novel PATL2 variants cause female infertility with oocyte maturation defect

PURPOSE

Oocyte maturation defect (OOMD) is a rare cause of in vitro fertilization failure characterized by the production of immature oocytes. Compound heterozygous or homozygous PATL2 mutations have been associated with oocyte arrest at the germinal vesicle (GV), metaphase I (MI), and metaphase II (MII) stages, as well as morphological changes.

METHODS

In this study, we recruited three OOMD cases and conducted a comprehensive multiplatform laboratory investigation.

RESULTS

Whole exome sequence (WES) revealed four diagnostic variants in PATL2, nonsense mutation c.709C > T (p.R237*) and frameshift mutation c.1486_1487delinsT (p.A496Sfs*4) were novel mutations that have not been reported previously. Furthermore, the pathogenicity of these variants was predicted using in silico analysis, which indicated detrimental effects. Molecular dynamic analysis suggested that the A496S variant disrupted the hydrophobic segment, leading to structural changes that affected the overall protein folding and stability. Additionally, biochemical and molecular experiments were conducted on cells transfected with wild-type (WT) or mutant PATL2 (p.R237* and p.A496Sfs*4) plasmid vectors.

CONCLUSIONS

The results demonstrated that PATL2A496Sfs*4 and PATL2R237* had impacts on protein size and expression level. Interestingly, expression levels of specific genes involved in oocyte maturation and early embryonic development were found to be simultaneously deregulated. The findings in our study expand the variation spectrum of the PATL2 gene, provide solid evidence for counseling on future pregnancies in affected families, strongly support the application of in the diagnosis of OOMD, and contribute to the understanding of PATL2 function.

Genomic aspects in reproductive medicine

Infertility is a complex disease characterized by extreme genetic heterogeneity, compounded by various environmental factors. While there are exceptions, individual genetic and genomic variations related to infertility are typically rare, often family-specific, and may serve as susceptibility factors rather than direct causes of the disease. Consequently, identifying the cause of infertility and developing prevention and treatment strategies based on these factors remain challenging tasks, even in the modern genomic era. In this review, we first examine the genetic and genomic variations associated with infertility, and subsequently summarize the concepts and methods of preimplantation genetic testing in light of advances in genome analysis technology.

Conserved genes regulating human sex differentiation, gametogenesis and fertilization

The study of the functional genome in mice and humans has been instrumental for describing the conserved molecular mechanisms regulating human reproductive biology, and for defining the etiologies of monogenic fertility disorders. Infertility is a reproductive disorder that includes various conditions affecting a couple's ability to achieve a healthy pregnancy. Recent advances in next-generation sequencing and CRISPR/Cas-mediated genome editing technologies have facilitated the identification and characterization of genes and mechanisms that, if affected, lead to infertility. We report established genes that regulate conserved functions in fundamental reproductive processes (e.g., sex determination, gametogenesis, and fertilization). We only cover genes the deletion of which yields comparable fertility phenotypes in both rodents and humans. In the case of newly-discovered genes, we report the studies demonstrating shared cellular and fertility phenotypes resulting from loss-of-function mutations in both species. Finally, we introduce new model systems for the study of human reproductive biology and highlight the importance of studying human consanguineous populations to discover novel monogenic causes of infertility. The rapid and continuous screening and identification of putative genetic defects coupled with an efficient functional characterization in animal models can reveal novel mechanisms of gene function in human reproductive tissues.

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.

Early embryonic failure caused by a novel mutation in the TUBB8 gene: A case report

BACKGROUND

This study aimed to explore the relationship between gene mutations and early embryonic development arrest and to provide more possibilities for the diagnosis and treatment of repeated implantation failure.

CASE SUMMARY

Here, we collected and described the clinical data of a patient with early embryonic development stagnation after repeated in vitro fertilization attempts for primary infertility at the Department Reproductive Center of Zaozhuang Maternal and Child Healthcare Hospital. We also detected the whole-exon gene of the patient's spouse and parents, and conducted bioinformatics analysis to determine the pathogenesis of the gene.

CONCLUSION

A novel mutant of the TUBB8 gene [c.602G>T(p.C201F)] was identified, and this mutant provided new data on the genotype-phenotype relationships of related diseases.

Mouse KL2 is a unique MTSE involved in chromosome-based spindle organization and regulated by multiple kinases during female meiosis

Microtubule-severing enzymes (MTSEs) play important roles in mitosis and meiosis of the primitive organisms. However, no studies have assessed their roles in mammalian meiosis of females, whose abnormality accounts for over 80% of the cases of gamete-originated human reproductive disease. In the current study, we reported that katanin-like 2 (KL2) was the only MTSE concentrating at chromosomes. Furthermore, the knockdown of KL2 significantly reduced chromosome-based increase in the microtubule (MT) polymer, increased aberrant kinetochore-MT (K-MT) attachment, delayed meiosis, and severely affected normal fertility. Importantly, we demonstrated that the inhibition of aurora B, a key kinase for correcting aberrant K-MT attachment, eliminated KL2 from chromosomes completely. KL2 also interacted with phosphorylated eukaryotic elongation factor-2 kinase; they competed for chromosome binding. We also observed that the phosphorylated KL2 was localized at spindle poles, and that KL2 phosphorylation was regulated by extracellular signal-regulated kinase 1/2. In summary, our study reveals a novel function of MTSEs in mammalian female meiosis and demonstrates that multiple kinases coordinate to regulate the levels of KL2 at chromosomes.

Live birth derived from a markedly large polar body oocyte: a rare case report

Oocytes with excessively large first polar bodies (PB1) often occur in assisted reproductive procedures. Many times these oocytes are discarded without insemination and, as a result, the application of this portion of oocytes has scarcely been reported to date. Few studies have examined large PB1 oocytes in infertile women and have virtually entirely studied genetic variations for large PB1 oocyte abnormalities. Here, we describe an unusual case of a live birth from a remarkably large PB1 oocyte in a frozen embryo transfer (FET) cycle. This is the first instance of a successful live birth resulting from a PB1 oocyte with an extremely large polar body measuring 80 μM × 40 μM in size. The large PB1 oocyte was performed by an early rescue intracytoplasmic sperm injection (r-ICSI) and was formed into a blastocyst on day 5. Following FET, a healthy boy baby weighing 3100 g was finally delivered by caesarean section at 37 weeks and 5 days after conception. Additionally, there were no complications throughout the antenatal period or the perinatal phase of this following full-term delivery. In this study, it is revealed for the first time that a huge PB1 oocyte can be fertilized, resulting in the growth of a blastocyst, a subsequent pregnancy, and a live birth. This new information prompts us to reconsider the use of large PB1 oocytes. More insightful talks should be given attention to prevent the waste of embryos because not all oocytes with aberrant morphology are unavailable.

A case report of a family with developmental arrest of human prokaryotic stage zygote

To study the genetic variation leading to the arrest phenotype of pronuclear (PN) zygotes. We recruited a family characterized by recurrent PN arrest during in vitro fertilization (IVF) and intracytoplasmic sperm injection cycles (ICSI) and performed whole-exome sequencing for 2 individuals. The transcriptome profiles of PN-arrest zygotes were assessed by single-cell RNA sequencing analysis. The variants were then validated by PCR amplification and Sanger sequencing in the affected individuals and other family members. A family characterized by recurrent PN arrest during IVF and ICSI cycles were enrolled after giving written informed consent. Peripheral blood samples were taken for DNA extraction. Three PN-arrest zygotes from patient III-3 were used for single-cell RNA-seq as described. This phenotype was reproduced after multiple cycles of egg retrieval and after trying different fertilization methods and multiple ovulation regimens. The mutant genes of whole exon sequencing were screened and verified. The missense variant c. C1630T (p.R544W) in RGS12 was responsible for a phenotype characterized by paternal transmission. RGS12 controls Ca2+ oscillation, which is required for oocyte activation after fertilization. Single-cell transcriptome profiling of PN-arrest zygotes revealed defective established translation, RNA processing and cell cycle, which explained the failure of complete oocyte activation. Furthermore, we identified proximal genes involved in Ca2+ oscillation-cytostatic factor-anaphase-promoting complex (Ca2+ oscillation-CSF-APC) signaling, including upregulated CaMKII, ORAI1, CDC20, and CDH1 and downregulated EMI1 and BUB3. The findings indicate abnormal spontaneous Ca2+ oscillations leading to oocytes with prolonged low CSF level and high APC level, which resulted in defective nuclear envelope breakdown and DNA replication. We have identified an RGS12 variant as the potential cause of female infertility characterized by arrest at the PN stage during multiple IVF and ICSI.

Mitochondrial deoxyguanosine kinase is required for female fertility in mice

Mitochondrial homeostasis plays a pivotal role in oocyte maturation and embryonic development. Deoxyguanosine kinase (DGUOK) is a nucleoside kinase that salvages purine nucleosides in mitochondria and is critical for mitochondrial DNA replication and homeostasis in non-proliferating cells. Dguok loss-of-function mutations and deletions lead to hepatocerebral mitochondrial DNA deletion syndrome. However, its potential role in reproduction remains largely unknown. In this study, we find that Dguok knockout results in female infertility. Mechanistically, DGUOK deficiency hinders ovarian development and oocyte maturation. Moreover, DGUOK deficiency in oocytes causes a significant reduction in mitochondrial DNA copy number and abnormal mitochondrial dynamics and impairs germinal vesicle breakdown. Only few DGUOK-deficient oocytes can extrude their first polar body during in vitro maturation, and these oocytes exhibit irregular chromosome arrangements and different spindle lengths. In addition, DGUOK deficiency elevates reactive oxygen species levels and accelerates oocyte apoptosis. Our findings reveal novel physiological roles for the mitochondrial nucleoside salvage pathway in oocyte maturation and implicate DGUOK as a potential marker for the diagnosis of female infertility.

Oocyte in-vitro maturation primed with letrozole-HCG versus FSH-HCG in women with oocyte maturation abnormalities: a retrospective study

RESEARCH QUESTION

Are there differences between in-vitro maturation (IVM) primed with letrozole-human chorionic gonadotrophin (HCG) and IVM primed with FSH-HCG in women with oocyte maturation abnormalities (OMAs), defined as at least two failed IVF cycles where immature oocytes were retrieved?

DESIGN

This retrospective study was conducted at a private fertility clinic from January 2009 to April 2023. The final analysis included 75 women in Group 1 (IVM primed with FSH-HCG) and 52 women in Group 2 (IVM primed with letrozole-HCG).

RESULTS

A significantly higher median number of oocytes was obtained in Group 1 compared with Group 2 {9 [interquartile range (IQR) 1-5] versus 5 (IQR 1-18); P < 0.001}. However, no differences in oocyte maturation stage at collection were found between the groups (P > 0.05). At the end of IVM, Group 1 had 73/666 mature oocytes and Group 2 had 106/322 mature oocytes, and the median metaphase II oocyte rate per patient was higher in Group 2 [33.3% (IQR 66.7-100.0%) versus 0.0% (IQR 0.0-22.2%); P < 0.001]. Moreover, Group 2 demonstrated a higher median fertilization rate [66.7% (IQR 50.0-100.0%) versus 50.0% (IQR 0.0-66.7%); P = 0.027]. Group 2 had a higher proportion of Grade 2 embryos (58.5% versus 6.3%), and Group 1 had a higher proportion of Grade 3 embryos (93.8% vs 24.4%; P < 0.001). Notably, all pregnancies obtained in the study were in Group 2 (5 versus 0; P = 0.042).

CONCLUSIONS

IVM primed with letrozole-HCG in women with prior failed IVF cycles due to OMAs may result in mature oocytes, clinical pregnancies and live births. The effectiveness of letrozole priming for the subtypes of OMAs needs further investigation, with studies including greater numbers of cases.

Predicting Infertility: How Genetic Variants in Oocyte Spindle Genes Affect Egg Quality

Successful reproduction relies on the union of a single chromosomally normal egg and sperm. Chromosomally normal eggs develop from precursor cells, called oocytes, that have undergone accurate chromosome segregation. The process of chromosome segregation is governed by the oocyte spindle, a unique cytoskeletal machine that splits chromatin content of the meiotically dividing oocyte. The oocyte spindle develops and functions in an idiosyncratic process, which is vulnerable to genetic variation in spindle-associated proteins. Human genetic variants in several spindle-associated proteins are associated with poor clinical fertility outcomes, suggesting that heritable etiologies for oocyte dysfunction leading to infertility exist and that the spindle is a crux for female fertility. This chapter examines the mammalian oocyte spindle through the lens of human genetic variation, covering the genes TUBB8, TACC3, CEP120, AURKA, AURKC, AURKB, BUB1B, and CDC20. Specifically, it explores how patient-identified variants perturb spindle development and function, and it links these molecular changes in the oocyte to their cognate clinical consequences, such as oocyte maturation arrest, elevated egg aneuploidy, primary ovarian insufficiency, and recurrent pregnancy loss. This discussion demonstrates that small genetic errors in oocyte meiosis can result in remarkably far-ranging embryonic consequences, and thus reveals the importance of the oocyte's fine machinery in sustaining life.

NLRP14 deficiency causes female infertility with oocyte maturation defects and early embryonic arrest by impairing cytoplasmic UHRF1 abundance

Oocyte maturation is vital to attain full competence required for fertilization and embryogenesis. NLRP14 is preferentially expressed in mammalian oocytes and early embryos. Yet, the role and molecular mechanism of NLRP14 in oocyte maturation and early embryogenesis are poorly understood, and whether NLRP14 deficiency accounts for human infertility is unknown. Here, we found that maternal loss of Nlrp14 resulted in sterility with oocyte maturation defects and early embryonic arrest (EEA). Nlrp14 ablation compromised oocyte competence due to impaired cytoplasmic and nuclear maturation. Importantly, we revealed that NLRP14 maintained cytoplasmic UHRF1 abundance by protecting it from proteasome-dependent degradation and anchoring it from nuclear translocation in the oocyte. Furthermore, we identified compound heterozygous NLRP14 variants in women affected by infertility with EEA, which interrupted the NLRP14-UHRF1 interaction and decreased UHRF1 levels. Our data demonstrate NLRP14 as a cytoplasm-specific regulator of UHRF1 during oocyte maturation, providing insights into genetic diagnosis for female infertility.

Evaluative effectiveness of follicular output rate, ovarian sensitivity index, and ovarian response prediction index for the ovarian reserve and response of low-prognosis patients according to the POSEIDON criteria: a retrospective study

The aim was to explore the implications of follicular output rate (FORT), ovarian sensitivity index (OSI), ovarian response prediction index (ORPI), and follicle-to-oocyte index (FOI) in low-prognosis patients defined by POSEIDON criteria. In total, 4030 fresh in vitro fertilization (IVF) cycles from January 2013 to October 2021 were included in this retrospective cohort analysis and were categorized into four groups based on the POSEIDON criteria. The FORT between Groups 1 and 2 (0.61 ± 0.34 vs. 0.65 ± 0.35, P = 0.081) and Groups 3 and 4 (1.08 ± 0.82 vs. 1.09 ± 0.94, P = 0.899) were similar. The OSI in the order from the highest to the lowest were 3.01 ± 1.46 in Group 1, 2.28 ± 1.09 in Group 2, 1.54 ± 1.04 in Group 3, and 1.34 ± 0.96 in Group 4 (P < 0.001). The trend in the ORPI values was consistent with that in the OSI. FORT, OSI, ORPI, and FOI complemented each other and offered excellent effectiveness in reflecting ovarian reserve and response, but they were not good predictors of clinical pregnancy rate (CPR) from IVF.

Identification of nonfunctional PABPC1L causing oocyte maturation abnormalities and early embryonic arrest in female primary infertility

Oocyte maturation arrest, fertilization failure, and early embryonic arrest are important causes of female infertility, whereas the genetic events that contribute to these processes are largely unknown. Loss-of-function of PABPC1L in mice has been suggested to cause female infertility involved in the absence of mature oocytes or embryos in vivo or in vitro. However, the role of PABPC1L in human female reproduction remains largely elusive. In this study, we identified a homozygous missense mutation (c.536G>A, p.R179Q) and a compound heterozygous mutation (c.793C>T, p.R265W; c.1201C>T, p.Q401*) in PABPC1L in two unrelated infertile females characterized by recurrent oocyte maturation abnormalities and early embryonic arrest. These variants resulted in nonfunctional PABPC1L protein and were associated with impaired chromatin configuration and transcriptional silencing in GV oocytes. Moreover, the binding capacity of mutant PABPC1L to mRNAs related to oocyte maturation and early embryonic development was decreased significantly. Our findings revealed novel PABPC1L mutations causing oocyte maturation abnormalities and early embryonic arrest, confirming the essential role of PABPC1L in human female fertility.

Novel variants in TUBB8 gene cause multiple phenotypic abnormalities in human oocytes and early embryos

BACKGROUND

The genotype-phenotype relationships between TUBB8 variants and female infertility are difficult to clearly define due to the complex inheritance patterns and the highly heterogeneous phenotypes. This study aims to identify novel TUBB8 variants and relevant phenotypes in more infertile females.

METHODS

A total of 35 females with primary infertility were recruited from two reproductive centers and investigated for identifying variants in TUBB8. Pedigree analysis, in-silico analysis and molecular remodeling were performed to assess their clinical significance. The effects of the variants on human oocytes and embryos as well as HeLa cells were analyzed by morphological observations, immunostaining and Western blot.

RESULTS

We totally identified five novel variants (p.G13R, p.Y50C, p.T136I, p.F265V and p.T366A) and five previously reported variants (p.I4L, p.L42V, p.Q134*, p.V255M and p.V349I) in TUBB8 from 9 unrelated females with primary infertility. These variants were rare and highly conserved among different species, and were inherited in autosomal dominant/recessive patterns, or occurred de novo. In vitro functional assays in HeLa cells revealed that exogenous expression of mutant TUBB8 proteins caused different degrees of microtubule structural disruption. The existence of these pathogenic TUBB8 variants finally induced oocyte maturation arrest or morphological abnormalities, fertilization failure, cleavage failure, embryonic development defects and implantation failure in the affected females.

CONCLUSION

These findings enriched the variant spectrum of TUBB8 gene and could contribute to optimize genetic counselling and clinical management of females with primary infertility.

Nuclear-cytoplasmic asynchrony in oocyte maturation caused by TUBB8 variants via impairing microtubule function: a novel pathogenic mechanism

BACKGROUND

TUBB8, a crucial gene encoding microtubule protein, plays a pivotal role in cellular processes. Deleterious TUBB8 variants have been shown to significantly hinder oocyte maturation. In this study, we conducted an in vitro investigation using TUBB8 mutant mouse oocytes to elucidate the pathogenic mechanisms of TUBB8 variants in oocyte nuclear and cytoplasmic maturation.

METHODS

A mutant model was successfully established in mouse oocytes via microinjection to further investigate the effects of four novel discovered TUBB8 mutations on the nuclear and cytoplasmic maturation of mouse oocytes. Immunofluorescence and confocal microscopy were performed to observe the cortical polarity and spindle and of mutant oocytes. Active mitochondrial staining was performed to analyze mitochondrial distribution patterns. Endoplasmic reticulum and Ca2+ staining were conducted to assess ER distribution and cytoplasmic calcium ion concentration in oocytes.

RESULTS

In mouse oocytes, TUBB8 variants (p.A313V, p.C239W, p.R251Q, and p.G96R) resulted in a reduction of the first polar body extrusion rate, disruption of spindle assembly, and abnormal chromosome distribution. Additionally, these variants induced oocyte organelle abnormalities, including anomalies in mitochondrial redistribution and endoplasmic reticulum stress compared to the wild-type.

CONCLUSION

Deleterious TUBB8 variants could disrupt microtubule function, affecting critical processes such as spindle assembly, chromosome distribution, and organelle rearrangement during oocyte meiosis. These disruptions culminate in compromised nuclear-cytoplasmic maturation, consequently giving rise to oocyte maturation defects.

Evolutionarily new genes in humans with disease phenotypes reveal functional enrichment patterns shaped by adaptive innovation and sexual selection

New genes (or young genes) are structural novelties pivotal in mammalian evolution. Their phenotypic impact on humans, however, remains elusive due to the technical and ethical complexities in functional studies. Through combining gene age dating with Mendelian disease phenotyping, our research reveals that new genes associated with disease phenotypes steadily integrate into the human genome at a rate of ~ 0.07% every million years over macroevolutionary timescales. Despite this stable pace, we observe distinct patterns in phenotypic enrichment, pleiotropy, and selective pressures between young and old genes. Notably, young genes show significant enrichment in the male reproductive system, indicating strong sexual selection. Young genes also exhibit functions in tissues and systems potentially linked to human phenotypic innovations, such as increased brain size, bipedal locomotion, and color vision. Our findings further reveal increasing levels of pleiotropy over evolutionary time, which accompanies stronger selective constraints. We propose a "pleiotropy-barrier" model that delineates different potentials for phenotypic innovation between young and older genes subject to natural selection. Our study demonstrates that evolutionary new genes are critical in influencing human reproductive evolution and adaptive phenotypic innovations driven by sexual and natural selection, with low pleiotropy as a selective advantage.

Homozygous variants in CDC23 cause female infertility characterized by oocyte maturation defects

Oocyte maturation defects are major phenotypes resulting in female infertility. Although many genetic factors have been found to be responsible for these phenotypes, the underlying pathogenic genes and variants remain to be identified. The anaphase promoting complex or cyclosome (APC/C) is known to be essential in the metaphase-to-anaphase transition. In this study, we identified two homozygous missense variants (c.986A > G, p.Y329C and c.988C > T, p.R330C) in CDC23 that are responsible for female infertility characterized by oocyte maturation defects in three infertile individuals. CDC23 (cell division cycle 23) is one of the core subunits of the APC/C. In vitro experiments showed that the variant c.986A > G (p.Y329C) led to a decrease in CDC23 protein level and the variant c.988C > T (p.R330C) changed the localization of CDC23 in HeLa cells and mouse oocytes. In vivo studies showed that Cdc23Y329C/Y329C mice successfully mimicked the patients' phenotype by causing low expression of CDC23 and APC4 and the accumulation of securin and cyclin B1 in oocytes. AZ3146 treatment was able to rescue the phenotype. Taken together, our findings reveal the important roles of CDC23 in human oocyte maturation and provide a new genetic marker for female infertility.

TUBB8 mutations as a cause of oocyte maturation abnormalities: presentation of oocyte and embryo profiles and novel mutations

RESEARCH QUESTION

What are the embryonic profiles and oocyte maturation dynamics in patients with tubulin beta eight class VIII (TUBB8) mutations leading to oocyte maturation abnormalities (OMAS), and are pregnancies possible in this population?

DESIGN

A prospective cohort study was undertaken in a private fertility clinic between January 2019 and December 2022. Whole-exome genomic studies (WES) were performed to detect mutation types. In-vitro maturation (IVM) was compared in 18 subjects: nine with TUBB8 mutations, and nine without TUBB8 mutations to act as the control group. The distributions of oocyte maturation and embryonic development profiles were recorded. IVF and IVM outcomes of the 18 cases were evaluated. The primary outcomes were the embryonic profiles and maturation dynamics of oocytes derived from IVF or IVM in women as related to TUBB8 mutations.

RESULTS

Mutations were detected in 52 of 89 (58.4%) women who underwent WES analysis. Twelve TUBB8 mutations were detected in nine women (10.1%) with OMAS. Seven novel TUBB8 mutations were noted. Two pregnancies were obtained in women with c.535 G>A TUBB8 mutations. When comparing IVM outcomes between women with and without TUBB8 mutations, there were no differences in oocyte, embryo or pregnancy parameters (P>0.05 in all cases).

CONCLUSIONS

It is clear that further TUBB8 mutations which cause oocyte or embryonic arrest will be detected in future. Although biochemical or ectopic pregnancies may be possible in some of these women, no live births or ongoing pregnancies have been reported to date.

Phenotypic variability in two female siblings with oocyte maturation arrest due to a TUBB8 variant

Tubulin beta-8 (TUBB8) is expressed exclusively in the oocyte and early embryo, encoding a beta-tubulin polypeptide that participates in the assembly of microtubules. TUBB8 was first attributed to being responsible for oocyte MI arrest. Further studies have demonstrated that patients with different pathogenic variants have variable phenotypes. We report a TUBB8 variant (c.10 A > C) in two siblings who presented different clinical features of primary infertility. The younger sister showed severe oocyte maturation arrest with abnormal morphology, whereas a few mature oocytes and zygotes could be retrieved from the older sister, but no embryo was available for transfer. This variant was previously reported without in vitro functional assays. In the present study, RT‒qPCR and western blot analyses revealed that c.10 A > C reduces TUBB8 mRNA and protein levels; however, immunofluorescence demonstrated that this variant does not change the localization of the protein. These findings confirm the pathogenicity of the c.10 A > C variant and support the relationship between the variant and phenotype in the patients.

Ectopic expression of human TUBB8 leads to increased aneuploidy in mouse oocytes

Aneuploidy seriously compromises female fertility and increases incidence of birth defects. Rates of aneuploidy in human eggs from even young women are significantly higher than those in other mammals. However, intrinsic genetic factors underlying this high incidence of aneuploidy in human eggs remain largely unknown. Here, we found that ectopic expression of human TUBB8 in mouse oocytes increases rates of aneuploidy by causing kinetochore-microtubule (K-MT) attachment defects. Stretched bivalents in mouse oocytes expressing TUBB8 are under less tension, resulting in continuous phosphorylation status of HEC1 by AURKB/C at late metaphase I that impairs the established correct K-MT attachments. This reduced tension in stretched bivalents likely correlates with decreased recruitment of KIF11 on meiotic spindles. We also found that ectopic expression of TUBB8 without its C-terminal tail decreases aneuploidy rates by reducing erroneous K-MT attachments. Importantly, variants in the C-terminal tail of TUBB8 were identified in patients with recurrent miscarriages. Ectopic expression of an identified TUBB8 variant in mouse oocytes also compromises K-MT attachments and increases aneuploidy rates. In conclusion, our study provides novel understanding for physiological mechanisms of aneuploidy in human eggs as well as for pathophysiological mechanisms involved in recurrent miscarriages.

Evaluation of TUBB8 gene alterations in infertile women with oocyte maturation and cleavage arrest referred to Royan Institute

RESEARCH QUESTION

Are TUBB8 gene variations present in Iranian infertile women with oocyte maturation arrest or embryo cleavage arrest?

DESIGN

TUBB8 gene variations were investigated by polymerase chain reaction sequencing on blood samples from 16 women with oocyte maturation arrest and 12 women with cleavage arrest, collectively referred to as the experimental cohort, as well as 56 fertile women as the control group. The Exome Sequencing Project and dbSNP databases and the Genome Aggregation Database were used to search the frequency of corresponding variants. PolyPhen and SIFT were used to conduct in-silico analysis of gene variations and Align-GVGD was used to predict the effect of missense variants on proteins. The homology modelling and structure evaluation of variations was also checked.

RESULTS

Two likely pathogenic variants [c.713C>T (p.Thr238Met), c.1054G>T (p.Ala352Ser)] were identified in patients with oocyte maturation arrest and one likely pathogenic variant [c.G763A, (p.Val255Met)] was identified in a patient with cleavage arrest. These changes were absent in controls.

CONCLUSIONS

Three deleterious variants in TUBB8 related to oocyte maturation arrest or cleavage arrest and infertility were identified. TUBB8 variant screening for patients with oocyte maturation and cleavage arrest is recommended.

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.

Advances in the study of genetic factors and clinical interventions for fertilization failure

Fertilization failure refers to the failure in the pronucleus formation, evaluating 16-18 h post in vitro fertilization or intracytoplasmic sperm injection. It can be caused by sperm, oocytes, and sperm-oocyte interaction and lead to great financial and physical stress to the patients. Recent advancements in genetics, molecular biology, and clinical-assisted reproductive technology have greatly enhanced research into the causes and treatment of fertilization failure. Here, we review the causes that have been reported to lead to fertilization failure in fertilization processes, including the sperm acrosome reaction, penetration of the cumulus and zona pellucida, recognition and fusion of the sperm and oocyte membranes, oocyte activation, and pronucleus formation. Additionally, we summarize the progress of corresponding treatment methods of fertilization failure. This review will provide the latest research advances in the genetic aspects of fertilization failure and will benefit both researchers and clinical practitioners in reproduction and genetics.

Integrated regulation of tubulin tyrosination and microtubule stability by human α-tubulin isotypes

Tubulin isotypes are critical for the functions of cellular microtubules, which exhibit different stability and harbor various post-translational modifications. However, how tubulin isotypes determine the activities of regulators for microtubule stability and modifications remains unknown. Here, we show that human α4A-tubulin, a conserved genetically detyrosinated α-tubulin isotype, is a poor substrate for enzymatic tyrosination. To examine the stability of microtubules reconstituted with defined tubulin compositions, we develop a strategy to site-specifically label recombinant human tubulin for single-molecule TIRF microscopy-based in vitro assays. The incorporation of α4A-tubulin into the microtubule lattice stabilizes the polymers from passive and MCAK-stimulated depolymerization. Further characterization reveals that the compositions of α-tubulin isotypes and tyrosination/detyrosination states allow graded control for the microtubule binding and the depolymerization activities of MCAK. Together, our results uncover the tubulin isotype-dependent enzyme activity for an integrated regulation of α-tubulin tyrosination/detyrosination states and microtubule stability, two well-correlated features of cellular microtubules.

Assessing the influence of distinct culture media on human pre-implantation development using single-embryo transcriptomics

The use of assisted reproductive technologies is consistently rising across the world. However, making an informed choice on which embryo culture medium should be preferred to ensure satisfactory pregnancy rates and the health of future children critically lacks scientific background. In particular, embryos within their first days of development are highly sensitive to their micro-environment, and it is unknown how their transcriptome adapts to different embryo culture compositions. Here, we determined the impact of culture media composition on gene expression in human pre-implantation embryos. By employing single-embryo RNA-sequencing after 2 or 5 days of the post-fertilization culture in different commercially available media (Ferticult, Global, and SSM), we revealed medium-specific differences in gene expression changes. Embryos cultured pre-compaction until day 2 in Ferticult or Global media notably displayed 266 differentially expressed genes, which were related to essential developmental pathways. Herein, 19 of them could have a key role in early development, based on their previously described dynamic expression changes across development. When embryos were cultured after day 2 in the same media considered more suitable because of its amino acid enrichment, 18 differentially expressed genes thought to be involved in the transition from early to later embryonic stages were identified. Overall, the differences were reduced at the blastocyst stage, highlighting the ability of embryos conceived in a suboptimal in vitro culture medium to mitigate the transcriptomic profile acquired under different pre-compaction environments.

Biallelic variants in MAD2L1BP (p31comet) cause female infertility characterized by oocyte maturation arrest

Human oocyte maturation arrest represents one of the severe conditions for female patients with primary infertility. However, the genetic factors underlying this human disease remain largely unknown. The spindle assembly checkpoint (SAC) is an intricate surveillance mechanism that ensures accurate segregation of chromosomes throughout cell cycles. Once the kinetochores of chromosomes are correctly attached to bipolar spindles and the SAC is satisfied, the MAD2L1BP, best known as p31comet, binds mitosis arrest deficient 2 (MAD2) and recruits the AAA+-ATPase TRIP13 to disassemble the mitotic checkpoint complex (MCC), leading to the cell-cycle progression. In this study, by whole-exome sequencing (WES), we identified homozygous and compound heterozygous MAD2L1BP variants in three families with female patients diagnosed with primary infertility owing to oocyte metaphase I (MI) arrest. Functional studies revealed that the protein variants resulting from the C-terminal truncation of MAD2L1BP lost their binding ability to MAD2. cRNA microinjection of full-length or truncated MAD2L1BP uncovered their discordant roles in driving the extrusion of polar body 1 (PB1) in mouse oocytes. Furthermore, the patient's oocytes carrying the mutated MAD2L1BP resumed polar body extrusion (PBE) when rescued by microinjection of full-length MAD2L1BP cRNAs. Together, our studies identified and characterized novel biallelic variants in MAD2L1BP responsible for human oocyte maturation arrest at MI, and thus prompted new therapeutic avenues for curing female primary infertility.

Embryonic arrest: causes and implications

PURPOSE OF REVIEW

Embryonic arrest is a key determinant of the number of euploid blastocysts obtained after IVF. Here, we review factors that are implicated in the developmental arrest of preimplantation embryos and their relevance for assisted reproduction outcomes.

RECENT FINDINGS

Among the treatment options available to infertile women, IVF is the one associated with most favorable outcomes. The cumulative pregnancy rates in women undergoing IVF are determined by aneuploidy rate (age), ovarian response to stimulation (ovarian reserve), and the rate of embryo developmental arrest. Mutations in maternal effect genes, especially those encoding for subcortical maternal complex, have been implicated in human embryo developmental arrest. In addition, perturbation of biological processes, such as mitochondrial unfolded protein response and long noncoding RNA regulatory pathways, may play a role. However, how each of these factors contributes to embryos' arrest in different cohorts and age groups has not been determined.

SUMMARY

Arrest of human embryos during preimplantation development is a common occurrence and is partly responsible for the limited number of euploid blastocysts obtained in assisted reproduction cycles. Although genetic and metabolic causes have been implicated, the mechanisms responsible for human embryo developmental arrest remain poorly characterized.

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.

Understanding the genetics of human infertility

Reproduction involves a wide range of biological processes, including organ formation and development, neuroendocrine regulation, hormone production, and meiosis and mitosis. Infertility, the failure of reproduction, has become a major issue for human reproductive health and affects up to one in seven couples worldwide. Here, we review various aspects of human infertility, including etiology, mechanisms, and treatments, with a particular emphasis on genetics. We focus on gamete production and gamete quality, which is the core of successful reproduction. We also discuss future research opportunities and challenges to further expand our understanding of human infertility and improve patient care by providing precision diagnosis and personalized treatments.

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.

Large-scale analysis of de novo mutations identifies risk genes for female infertility characterized by oocyte and early embryo defects

BACKGROUND

Oocyte maturation arrest and early embryonic arrest are important reproductive phenotypes resulting in female infertility and cause the recurrent failure of assisted reproductive technology (ART). However, the genetic etiologies of these female infertility-related phenotypes are poorly understood. Previous studies have mainly focused on inherited mutations based on large pedigrees or consanguineous patients. However, the role of de novo mutations (DNMs) in these phenotypes remains to be elucidated.

RESULTS

To decipher the role of DNMs in ART failure and female infertility with oocyte and embryo defects, we explore the landscape of DNMs in 473 infertile parent-child trios and identify a set of 481 confident DNMs distributed in 474 genes. Gene ontology analysis reveals that the identified genes with DNMs are enriched in signaling pathways associated with female reproductive processes such as meiosis, embryonic development, and reproductive structure development. We perform functional assays on the effects of DNMs in a representative gene Tubulin Alpha 4a (TUBA4A), which shows the most significant enrichment of DNMs in the infertile parent-child trios. DNMs in TUBA4A disrupt the normal assembly of the microtubule network in HeLa cells, and microinjection of DNM TUBA4A cRNAs causes abnormalities in mouse oocyte maturation or embryo development, suggesting the pathogenic role of these DNMs in TUBA4A.

CONCLUSIONS

Our findings suggest novel genetic insights that DNMs contribute to female infertility with oocyte and embryo defects. This study also provides potential genetic markers and facilitates the genetic diagnosis of recurrent ART failure and female infertility.

A novel compound heterozygous mutation in TUBB8 causing early embryonic developmental arrest

PURPOSE

Mutations in the β-tubulin isotype, TUBB8, can cause female infertility. Although several mutations of TUBB8 have been reported, the full spectrum for guiding genetics counseling still needs to be further explored. Here, we sought to identify novel variants in TUBB8 and their phenotypic effects on microtubule network structure in vitro.

METHODS

Whole-exome sequence analysis was performed in two families with infertility to detect pathogenic variants, with validation by Sanger sequencing. All gene variants and protein structures were predicted in silico. Cells were transfected with wild-type and mutants, and immunofluorescence analysis was performed to visualize microtubule network changes.

RESULTS

We detected a novel compound heterozygous mutation, c.915_916delCC (p.Arg306Serfs*21) and c.82C > T (p.His28Tyr), and a benign heterozygous variant c.1286C > T (p.Thr429Met) in TUBB8 in the two families. Female patients with p.Arg306Serfs*21 and p.His28Tyr were infertile with early embryonic developmental arrest. The female patient with p.Thr429Met gave birth to a healthy baby in the second in vitro fertilization frozen embryo transfer cycle. The p.Arg306Serfs*21 mutation was predicted to cause large structural alteration in the TUBB8 protein and was confirmed to produce a truncated and trace protein by western blot analysis. Immunofluorescence analysis of transfected HeLa cells showed that p.Arg306Serfs*21 significantly disrupted microtubule structure.

CONCLUSIONS

Our findings expand the known mutational spectrum of TUBB8 associated with early embryonic developmental arrest and female infertility.

Identification of TUBB8 Variants in 5 Primary Infertile Women with Multiple Phenotypes in Oocytes and Early Embryos

Tubulin beta 8 class VIII (TUBB8) is a β-tubulin isotype that is specifically expressed in human oocytes and early embryos. It has been identified as a disease-causing gene in primary female infertility by affecting oocyte maturation arrest. This study investigated the genetic cause of female infertility in five patients from four families. Five women with primary infertility were recruited. Medical-exome sequencing and Sanger sequencing were performed on the patients, and their family members to identify candidate genes that explained infertility. Additionally, the morphology of oocytes and zygotes from the patients and controls were assessed. We observed recurrent oocytes MI arrest, oocytes abnormal fertilization, uncleaved embryos, and embryo transfer failure in the patients. Heterozygous missense variants in TUBB8, c.538G > A (p.V180M), c.527C > G (p.S176W), c.124C > G (p.L42V), and c.628A > C (p.I210L), were verified in four unrelated families. This study expanded the mutational spectrum of TUBB8 by identifying three novel heterozygous missense variants. Screening for TUBB8 mutation demonstrated the diagnostic utility of female infertility.

Insights on the Role of α- and β-Tubulin Isotypes in Early Brain Development

Tubulins are the highly conserved subunit of microtubules which involve in various fundamental functions including brain development. Microtubules help in neuronal proliferation, migration, differentiation, cargo transport along the axons, synapse formation, and many more. Tubulin gene family consisting of multiple isotypes, their differential expression and varied post translational modifications create a whole new level of complexity and diversity in accomplishing manifold neuronal functions. The studies on the relation between tubulin genes and brain development opened a new avenue to understand the role of each tubulin isotype in neurodevelopment. Mutations in tubulin genes are reported to cause brain development defects especially cortical malformations, referred as tubulinopathies. There is an increased need to understand the molecular correlation between various tubulin mutations and the associated brain pathology. Recently, mutations in tubulin isotypes (TUBA1A, TUBB, TUBB1, TUBB2A, TUBB2B, TUBB3, and TUBG1) have been linked to cause various neurodevelopmental defects like lissencephaly, microcephaly, cortical dysplasia, polymicrogyria, schizencephaly, subcortical band heterotopia, periventricular heterotopia, corpus callosum agenesis, and cerebellar hypoplasia. This review summarizes on the microtubule dynamics, their role in neurodevelopment, tubulin isotypes, post translational modifications, and the role of tubulin mutations in causing specific neurodevelopmental defects. A comprehensive list containing all the reported tubulin pathogenic variants associated with brain developmental defects has been prepared to give a bird's eye view on the broad range of tubulin functions.

Graphene-Related Nanomaterials for Biomedical Applications

This paper builds on the context and recent progress on the control, reproducibility, and limitations of using graphene and graphene-related materials (GRMs) in biomedical applications. The review describes the human hazard assessment of GRMs in in vitro and in vivo studies, highlights the composition-structure-activity relationships that cause toxicity for these substances, and identifies the key parameters that determine the activation of their biological effects. GRMs are designed to offer the advantage of facilitating unique biomedical applications that impact different techniques in medicine, especially in neuroscience. Due to the increasing utilization of GRMs, there is a need to comprehensively assess the potential impact of these materials on human health. Various outcomes associated with GRMs, including biocompatibility, biodegradability, beneficial effects on cell proliferation, differentiation rates, apoptosis, necrosis, autophagy, oxidative stress, physical destruction, DNA damage, and inflammatory responses, have led to an increasing interest in these regenerative nanostructured materials. Considering the existence of graphene-related nanomaterials with different physicochemical properties, the materials are expected to exhibit unique modes of interactions with biomolecules, cells, and tissues depending on their size, chemical composition, and hydrophil-to-hydrophobe ratio. Understanding such interactions is crucial from two perspectives, namely, from the perspectives of their toxicity and biological uses. The main aim of this study is to assess and tune the diverse properties that must be considered when planning biomedical applications. These properties include flexibility, transparency, surface chemistry (hydrophil-hydrophobe ratio), thermoelectrical conductibility, loading and release capacity, and biocompatibility.