Chromosoma

Infertility affects up to 12% of couples globally, with genetic factors contributing to nearly half of the cases. Advances in genomic technologies have led to the discovery of genes like Bend2, which plays a crucial role in gametogenesis. In the testis, Bend2 expresses two protein isoforms: full-length and a smaller one. Ablation of both proteins results in an arrested spermatogenesis. Because the Bend2 locus is on the X chromosome, and the Bend2-/y mutants are sterile, BEND2s role in oogenesis remained elusive. In this study, we employed a novel Bend2 mutation that blocks the expression of the full-length BEND2 protein but allows the expression of the smaller BEND2 isoform. Interestingly, this mutation does not confer male sterility and mildly affects spermatogenesis. Thus, it allowed us to study the role of BEND2 in oogenesis. Our findings demonstrate that full-length BEND2 is dispensable for male fertility, and its ablation leads to a reduced establishment of the ovarian reserve. These results reveal a critical role for full-length BEND2 in oogenesis and provide insights into the mechanisms underlying the establishment of the ovarian reserve. Furthermore, these findings hold relevance for the diagnostic landscape of human infertility.

Hybrid zones are "natural laboratories" for studying speciation. In the common shrew Sorex araneus, the hybrid zone between extremely divergent in karyotypes the Moscow and Seliger chromosomal races is unique, because complex heterozygotes (interracial hybrids) form the longest meiotic configuration consisting of 11 chromosomes with monobrachial homology (undecavalent or chain-of-eleven - CXI). Different studies suggested that such a multivalent would negatively affect meiotic progression and, in general, would significantly reduce fertility. In this work, using immunocytochemical and electron microscopy methods, we investigated chromosome synapsis, recombination, and meiotic silencing in pachytene spermatocytes carrying undecavalent. Despite some abnormalities detected in spermatocytes, such as single associations of chromosomes, stretched centromeres in the multivalent, shifted recombinational peak towards distal parts of chromosomal arms of superchain, heterozygous shrews were able to form a large number of morphologically normal and active spermatozoa. Possible low stringency of pachytene checkpoints, proper segregation of homologous chromosomes, and the ability of hybrids to form mature germ cells imply rapid evolutionary fixation and circulation of Rb chromosomes within shrew populations, leading to a variety of chromosomal races.

In meiotic prophase I, hundreds of double-strand breaks (DSBs) are formed throughout the genome. A majority of these breaks are repaired as non-crossovers (NCOs), while a minor subset are repaired as crossovers (CO). COs are essential for the faithful segregation of homologous chromsomes at the end of prophase I and errors in CO designation can result in aneuploidy, germ cell death, birth defects, or infertility. These errors are more evident in female meiosis compared to males and suggests that the events of meiotic prophase I are sexually dimorphic with respect to CO formation, placement, resolution, and/or surveillance. Here, we demonstrate a critical role for Cyclin N-Terminal Domain Containing 1 (CNTD1) protein in ensuring appropriate CO frequency and distribution across the genome during meiosis in females. We find that CNTD1 localizes with the heterodimer, MutL{gamma}, which marks the majority of CO that emerge in pachynema of prophase I, implicating CNTD1 in late-stage CO designation and/or maturation. Accordingly, loss of Cntd1 in oocytes results in failure to load MutL{gamma} and thus results in a catastrophic loss of chiasmata and sterility. Further investigation yielded a distinct phenotype in which the primordial follicles that form upon dictyate arrest are steadily lost from birth onwards, a temporal loss of follicles that is different to that seen in other CO mutants. We find that this follicle loss in Cntd1 mutants is dependent on the checkpoint kinase CHK2. Thus, in females, loss of Cntd1 appears to result in phenotypes that are temporally disconnected from early and late CO mutants such as MutS{gamma} and MutL{gamma}, which show early prophase I disruption and ablation of ovary structure, and no prophase I disruption and an appearance of wildtype ovaries, respectively. These data suggest novel dual roles for CNTD1 in CO designation and faithful progression of oocytes into dictyate arrest at late pachynema, the latter being critical for establishing the ovarian reserve in female mice.

Chromosome segregation requires that centromeres properly attach to spindle microtubules. This is an essential step towards the accuracy of cell division and therefore must be precisely regulated in both mitosis and meiosis. One of the main centromeric regulatory signaling pathways is the Haspin-H3T3ph-chromosomal passenger complex (CPC) cascade, which is responsible for the recruitment of the CPC to the centromeres. In mitosis, Haspin kinase phosphorylates H3 at threonine 3 (H3T3ph), the essential histone mark that recruits the CPC whose catalytic component is Aurora B kinase. To date, no data has yet been presented about the action of the centromeric Haspin-H3T3ph-CPC pathway in mammalian male meiosis. We have analyzed the consequences of Haspin chemical inhibition in cultured spermatocytes using LDN-192960. Our in vitro studies suggest that Haspin kinase activity is required for proper chromosome congression during both meiotic divisions and for the recruitment of phosphorylated Aurora B at meiotic centromeres. These results have been confirmed by the characterization of the meiotic phenotype of the genetic mouse model Haspin-/-, which displays similar defects. In addition, our work demonstrates that the absence of H3T3ph histone mark does not alter SGO2 localization to meiotic centromeres. These results add new and relevant information regarding the regulation of centromere function during meiosis.

In eutherian mammals, hundreds of programmed DNA double-strand breaks (DSBs) are generated at the onset of meiosis. The DNA damage response is then triggered. Although the dynamics of this response is well studied in eutherian mammals, recent findings have revealed different patterns of DNA damage signaling and repair in marsupial mammals. To better characterize these differences, here we analyzed synapsis and the chromosomal distribution of meiotic DSBs markers in three different marsupial species (Thylamys elegans, Dromiciops gliorides, and Macropus eugenii) that represent South American and Australian Orders. Our results revealed inter-specific differences in the chromosomal distribution of DNA damage and repair proteins, which were associated with differing synapsis patterns. In the American species T. elegans and D. gliroides, synapsis progressed exclusively from the chromosomal ends towards interstitial regions. This was accompanied by sparse H2AX phosphorylation, mainly accumulating at chromosomal ends, which appeared conspicuously polarized in a bouquet configuration at early stages of prophase I. Accordingly, RAD51 and RPA were mainly localized at chromosomal ends throughout prophaseI in both American marsupials, likely resulting in reduced recombination rates at interstitial positions. In sharp contrast, synapsis initiated at both interstitial and distal chromosomal regions in the Australian representative M. eugenii, {gamma}H2AX had a broad nuclear distribution, and RAD51 and RPA foci displayed an even chromosomal distribution. Given the basal evolutionary position of T. elegans, it is likely that the meiotic features reported in this species represent an ancestral pattern in marsupials and that a shift in the meiotic program occurred after the split of D. gliroides and the Australian marsupial clade. Our results open intriguing questions about the regulation and homeostasis of meiotic DSBs in marsupials. The low recombination rates observed at the interstitial chromosomal regions in American marsupials can result in the formation of large linkage groups, thus having an impact in the evolution of their genomes.

The kinesin family member 18A (KIF18A) is an essential regulator of microtubule dynamics and chromosome alignment during mitosis. Functional dependency on KIF18A varies by cell type and genetic context but the heritable factors that influence this dependency remain unknown. To address this, we took advantage of the variable penetrance observed in different mouse strain backgrounds to screen for loci that modulate germ cell depletion in the absence of KIF18A. We found a significant association at a Chr5 locus where anaphase promoting complex subunits 5 (Anapc5) and 7 (Anapc7) were the top candidate genes. We found that both genes were differentially expressed in a sensitive strain background when compared to resistant strain background at key timepoints in gonadal development. We also identified a novel retroviral insertion in Anapc7 that may in part explain the observed expression differences. In cell line models, we found that depletion of KIF18A induced mitotic arrest, which was partially rescued by co-depletion of ANAPC7 (APC7) and exacerbated by co-depletion of ANAPC5 (APC5). These findings suggest that differential expression and activity of Anapc5 and Anapc7 may influence sensitivity to KIF18A depletion in germ cells and CIN cells, with potential implications for optimizing antineoplastic therapies.

Meiosis in male Sciara is unique with a single centrosome. A monopolar spindle forms in meiosis I, but a bipolar spindle forms in meiosis II. The imprinted paternal chromosomes are eliminated in meiosis I; there is non-disjunction of the X in meiosis II. Despite differences in spindle construction and chromosome behavior, both meiotic divisions are asymmetric, producing a cell and a small bud. Observations of live spermatocytes made with the LC-PolScope, differential interference contrast optics and fluorescence revealed maternal and paternal chromosome sets on the monopolar spindle in meiosis I and formation of an asymmetric monastral bipolar spindle in meiosis II where all chromosomes except the X congress to the metaphase plate. The X remains near the centrosome after meiosis I and stays with it as the spindle forms in meiosis II. Electron microscopy revealed amorphous material between the X and the centrosome. Immunofluorescence with an antibody against the checkpoint protein Mad2 stains the centromeres of the maternal X dyad in late meiosis I and in meiosis II where it fails to congress to the metaphase plate. Mad2 is also present throughout the paternal chromosomes destined for elimination in meiosis I, suggesting a possible role in chromosome imprinting. If Mad2 on the X dyad mediates a spindle checkpoint in meiosis II, it may delay metaphase to facilitate formation of the second half spindle through a non-centrosomal mechanism.

Non-obstructive azoospermia (NOA) is the absence of sperm in the ejaculate due to spermatogenic failure. Fifty percent of NOA cases are unexplained but may arise from unidentified genetic mutations. Variants in TEX11 have been identified in men with NOA; and Tex11 knockout in mice causes NOA. Here we attempt to validate three TEX11 variants discovered in NOA patients by knocking them into the orthologous region of the mouse genome using CRISPR/Cas9 gene editing. Compared to wild type (144.2 {+/-} 9.87 mg; 1.7 {+/-} 0.5 million sperm/cauda epididymis 4.8 {+/-} 1.3 pups/breeding), Tex11D mice (frameshift mutation) had reduced testis weight (28.33 {+/-} 1.16 mg); no sperm in the epididymis; and were infertile with a maturation arrest testicular phenotype. We did not observe any spermatogenesis or fertility defects Tex11A mice (missense mutation). Tex11L mice had reduced testis weight (87.5 {+/-} 14.79 mg) and epididymal sperm counts (0.33{+/-}0.13 million/cauda epididymis) but an incompletely penetrant infertility phenotype (5.4 {+/-} 1.13 pups/breeding) with one third of mice being infertile. Infertile Tex11L mice also had a distinct epididymal phenotype with reduced sperm density in the caput and no sperm in the cauda, which was filled with amorphous material.

In most mammals, the cell cycle kinase; cyclin-dependent kinase 2 (CDK2) is expressed as two major isoforms due to the inclusion or exclusion of an alternatively spliced exon. The shorter CDK2 isoform: CDK2S, is expressed constitutively during the cell cycle and can be detected in many different tissue types. In contrast, the longer isoform: CDK2L, shows preferential expression in meiotically dividing cells of the germ cells and upon S-phase entry during mitotic cell division. Both CDK2L and CDK2S form heteromeric complexes with cyclins A2 and E1 in vitro. However, complexes comprised of each isoform differ considerably in their kinase activity towards known CDK substrates. It is currently unknown whether the long and short isoforms of CDK2 play functionally different roles in vivo during either mitotic and meiotic divisions as conventional knockout methodology leads to the loss of both isoforms. In this study, we find that both CDK2L and CDK2S are sufficient to support both mitotic and meiotic division when expressed in the absence of the other. This data contributes to the explanation of the apparent tolerance of the evolutionary loss of CDK2L expression in humans.

The histone variant H2AX phosphorylated on serine 139, named {gamma}-H2AX, is a canonical DNA double-strand breaks marker. During mammalian meiotic prophase I, {gamma}-H2AX participates in meiotic recombination, meiotic sex chromosome inactivation and meiotic silencing of unsynapsed chromatin. In this study, we have analyzed the distribution of {gamma}-H2AX during male mouse meiosis by immunofluorescence on spread and squashed spermatocytes. We have found that {gamma}-H2AX locates at the inner kinetochore plate of meiotic kinetochores in both meiotic divisions. Therefore our results, for the first time, uncover a novel role for {gamma}-H2AX at mammalian meiotic kinetochores.

Little is currently known about the rates at which non-allelic homologous recombination (NAHR) occurs. However, most current research suggests that NAHR is rare. Previous work by Small, et al (1998), examined an inversion polymorphism on the long arm of the X-chromosome, involving two genes (FLNA and EMD), and determined the frequency of the two gene arrangements in a group of European individuals. Here we quantify the rate at which the causal NAHR, in inverted repeats flanking the FLNA and EMD genes, occurs in meiosis using digital PCR of sperm samples, with male cheek cells as controls. NAHR was documented in all samples, including the cheek cell samples at a mean recombination rate of 1.8%, indicating that NAHR occurs much more frequently than initially believed, and appears to be occurring in mitosis. The increase in NAHR frequency in spermatogenesis is not significant leaving in question NAHR occurrence in meiosis. This study reveals a more accurate way to quantitate NAHR, serving as an important first step in better understanding various NAHR-associated diseases. Author SummaryWe sought to more accurately quantitate and characterize NAHR at a site at the end of the long arm of the X chromosome that contains a set of inverted repeats flanking two genes, filamin and emerin. We determined that NAHR is happening far more frequently than previously thought, and in this case unequally, depending on the direction of the inversion. We speculate on the possibility of local adaptation playing a role in this. These high-resolution results were obtained by modifying a previously published assay which can be easily adapted to other inversions. This could be especially helpful in studying those NAHR inversions related to disease.

Meiotic recombination plays an important role in ensuring proper chromosome segregation during meiosis I through the creation of chiasmata that connect homologous chromosomes. Recombination plays an additional role in evolution by creating new allelic combinations. Organisms display species-specific crossover patterns, but how these patterns are established is poorly understood. Drosophila mauritana displays a differing recombination pattern compared to Drosophila melanogaster, with D. mauritiana experiencing a reduced centromere effect, the suppression of recombination emanating from the centromeres. To evaluate the contribution of the synaptonemal complex (SC) C(3)G protein to these recombination rate differences, the D. melanogaster allele was replaced with D. mauritiana c(3)G coding sequence. We found that the D. mauritiana C(3)G could interact with the D. melanogaster SC machinery to build full length tripartite SC and chromosomes segregated accurately, indicating sufficient crossovers were generated. However, the placement of crossovers was altered, displaying an increase in frequency of the centromere-proximal euchromatin indicating a decrease in the centromere effect similar to that observed in D. mauritiana. Recovery of chromatids with more than one crossover was also increased, likely due to the larger chromosome span now available for crossovers. As replacement of a single gene mediated a strong shift of one species crossover pattern towards another species, it indicates a small number of discrete factors may have major influence on species-specific crossover patterning. Additionally, it demonstrates the SC, a structure known to be required for crossover formation in many species, is likely one of these discrete factors. Lay AbstractMeiotic crossovers are important for ensuring proper chromosome segregation and generating genetic diversity. Different species display unique crossover patterns but the mechanisms that establish these patterns are poorly understood. The synaptonemal complex (SC) is built between meiotic chromosomes and promotes crossover formation. Replacement of the SC gene c(3)G in the fruit fly Drosophila melanogaster with Drosophila mauritiana c(3)G resulted in full-length SC assembly and proper chromosome segregation, but the D. melanogaster crossover pattern was shifted to appear more similar to D. mauritiana. This demonstrates that crossover patterning can be largely influenced by minor changes in the makeup of the SC.

Break-induced DNA replication (BIR) have been detected not only in the genome of rare disease patients but also in cancer cells, however, the mechanisms of BIR formation havent been explained in details. In the late G2 phase-like mouse oocytes, we found DNA double-strand breaks (DSBs) could induce Rad51 dependent small-scale DNA replication. In addition, we also found the DSBs could be amplified in mouse oocytes, and the amplification could be inhibited by Rad51 inhibitor IBR2 and DNA replication inhibitor ddATP. Lastly, we found the DSB repair was relatively inefficiency in hybrid mouse oocytes compared with that of the purebred mouse oocytes. We found DSBs could induce BIR more easier in hybrid mouse oocytes, indicating the DNA repair in oocytes could be affected by the sequence differences between homologous chromatids. In summary, our results indicated that the condensed chromatin configuration in late G2 phase and the sequence similarity between broken DNA and template DNA are causing factors of BIR in mammalian genome, and the DNA damage could be amplified in late G2 phase cells.

RPA is a heterotrimeric ssDNA binding protein that is highly conserved across all eukaryotes. Arabidopsis (Arabidopsis thaliana) has five RPA1 paralogs divided into three groups (A, B, C) each with unique functions in DNA replication and repair. The group C paralogs (RPA1C and RPA1E in Arabidopsis) function specifically in DNA-damage repair and carry a C-terminal extension unique to group-C paralogs. This C-terminal extension contains a zinc finger motif (ZFM) that is highly conserved and is therefore predicted to be critical to the functionality of the paralogs during DNA damage repair. To address this, we employed a CRISPR-Cas9 strategy to specifically remove the ZFM from RPA1C or RPA1E while leaving the genes otherwise intact (termed C-ZFKO and E-ZFKO). C-ZFKO and E-ZFKO lines were challenged with DNA damaging agents, and their susceptibility was compared to both WT (Col-0) lines and to previously characterized T-DNA null mutants (rpa1c and rpa1e). To address the role of the respective ZFMs in homologous recombination pathways (HRR), we employed a GUS-reporter system to compare WT lines to C-ZFKO and E-ZFKO lines. We find here that C-ZFKO and E-ZFKO lines displayed hypersensitivity to DNA damaging agents at a level comparable to previously characterized T-DNA null mutants (rpa1c and rpa1e). When studying the rate of HRR, both C-ZFKO and rpa1c showed a drastic reduction in single-strand annealing (SSA) while E-ZFKO and rpa1e had a more modest, but still significant decrease. All mutant lines had a comparable decrease in synthesis-dependent strand annealing (SDSA) compared to WT. Thus, we show here that the respective RPA1C and RPA1E-encoded ZFM is crucial for the ability of each paralog to function during DNA damage repair.

Pairings between heterologous chromosomes in meiosis can lead to nondisjunction and the production of aneuploid gametes. To minimize these aberrant outcomes, organisms have evolved mechanisms to disrupt such improper pairings prior to orientation and segregation. In the male fruit fly, Drosophila melanogaster, bivalents segregate to distinct nuclear domains in prophase I, and it has been proposed that the formation of these distinct territories may play a role in disrupting interactions between limited homologies on heterologous chromosomes. To test this, we used fluorescent in situ hybridization to examine pairing between the X chromosome and Dp(1;3) chromosomes in which a segment of the X had been transposed to chromosome 3. We found that 120kb of homology was sufficient to insure nearly complete pairing but was not sufficient to direct merotelic segregation of the paired elements, suggesting that such pairings were being disrupted. We compared the perdurance of X / Dp(1;3) pairings to that of X / Dp(1;Y) pairings (in which homologs are paired),and found that heterologous pairings were disrupted at a higher frequency at the S2b stage of prophase I, the stage at which territory formation is initiated. Our results support the model that movement of bivalents into distinct domains in prophase I provides a mechanism to disrupt pairings between limited regions of homology, and thus may be one means of preventing improper segregation of heterologs in this organism.

Chromosome condensation plays a pivotal role during faithful chromosome segregation, hence understanding the factors that drive condensation is crucial to get mechanistic insight into chromosome segregation. Previously we showed that in budding yeast, the absence of the non-essential kinetochore proteins affects chromatin-condensin association in meiosis but not in mitosis. A differential organization of the kinetochores, that we and others observed earlier during mitosis and meiosis may contribute to the meiotic-specific role. Here, with our in-depth investigation using in vivo chromosome condensation assays in cells sans a non-essential kinetochore protein, Ctf19, we establish that these proteins have roles in achieving a higher meiotic condensation without influencing much of the mitotic condensation. We further observed an accumulation of the polo-like kinase Cdc5 owing to its higher protein stability in ctf19{Delta} meiotic cells. High Cdc5 activity causes hyper-phosphorylation of the condensin resulting in its reduced stability and concomitant decreased association with the chromatin. Overall, our findings highlight the role of Ctf19 in promoting meiotic chromosome condensation by influencing the activity of Cdc5 and thereby affecting the stability and association of condensin with the chromatin.

AbstractIn most mammals the major site of sex hormone-binding globulin (SHBG) synthesis is the liver wherefrom it is secreted into the bloodstream and is the primary determinant of sex steroid access to target tissues. The minor site of SHBG synthesis is the testis and in lower mammals testicular SHBG has long been known to be synthesized and secreted by Sertoli cells. However, human testicular SHBG is expressed in developing germ cells from an upstream alternative promoter (altP-SHBG). Transcripts arising from this region comprise an alternative first exon (1A) with the resultant protein confined to the acrosomal compartment of the mature spermatozoa. I have dissected the regulatory components of the alternative SHBG promoter and identified motifs that are required for optimal transcriptional activity from this region. Transcriptional activity is driven by two CACCC elements that appear to be functionally redundant. The transcription factor KLF4 interacts with promoter the region spanning these elements in vivo. Knockdown of Klf4 results in decreased altP-SHBG activity, while Klf4 overexpression relieves the effects of knockdown. Based on their shared patterns of expression in vivo, I conclude that KLF4 is a transcriptional regulator of SHBG in male germ cells.

The utility of Active Genetic (AG) gene conversion systems in rats and mice holds great promise for facilitating the production of complex strains harboring multiple humanizing genes. The practical application of such systems requires the identification of a robust, reusable, and highly efficient system. By characterizing twenty-eight different promoter and target site pairs we aimed to define the parameters needed to establish an efficient conversion system in male and female rats and mice. Using three specific meiosis prophase I active promoters to drive Cas9 expression. We studied several variables, including the number of Cas9 target sites, the distance between target sites, the cis versus trans configuration in linked pairs, and the effect of Cas9 copy number. In the rat, three of twelve tested configurations provided efficient AG gene conversion in the 22% - 67% range, and four others catalyzed AG in the 0.7-1% range. The rat Ddx4 (Vasa) promoter provides higher AG efficiency than the Sycp1 promoter. In mice, ten of sixteen tested configurations, using the Sycp1 and pSycp1 promoters, provided efficiency in the 0.3% - 3.2% range. In rats, Cas9 expression levels are remarkably well correlated with AG gene conversion efficiency. The rat cis rCyp3A1/rCyp3A2 locus was the most successful configuration, with gene conversion efficiencies of 0.7%-67%. This target site has a special property; the two Cas9 target sites are nearly perfectly homologous in the 100 bases around the gRNA target site. Our findings identify key parameters that improve AG efficiency, including the use of two Cas9 target sites, and efficient promoters that drive high levels of Cas9 expression that are correctly timed during gamete development. These findings also uncover the unexpected benefit of high homology at paired gRNA target sites to promote efficiency. We provide new data to guide future efforts to develop yet further improved AG systems.

Eukaryotic meiosis is a specialized cell cycle involving two successive nuclear divisions that lead to the formation of haploid gametes. The phosphatase Cdc14 plays an essential role in meiosis as revealed in studies of the yeast Saccharomyces cerevisiae. Cdc14 is stored in the nucleolus, a sub-nuclear domain containing the ribosomal DNA, and its release is regulated by two distinct pathways, one acting in early anaphase I of meiosis and a second at the exit from meiosis II. The early anaphase release is thought to be important for disjunction of the ribosomal DNA, disassembly of the anaphase I spindle, spindle pole re-duplication and the counteraction of CDK, all of which are required for progression into meiosis II. The release of Cdc14 from its nucleolar binding partner Net1 is stimulated by phosphorylation of cyclin-dependent kinase sites in Net1, but the importance of that phospho-regulation in meiosis is not well understood. We induced net1-6cdk mutant cells to enter meiosis and examined the localization of Cdc14 and various indicators of meiotic progression. The net1-6cdk mutations inhibit, but dont fully prevent Cdc14 release, and they almost completely prevent disjunction of the ribosomal DNA during meiosis I. Failure to disjoin the ribosomal DNA is lethal in mitosis, and we expected the same to be true in meiosis. However, the cells were able to complete meiosis II, yielding the expected four meiotic products as viable spores. Therefore, all ribosomal DNA disjunction required for meiosis can occur in meiosis II. We discuss the implications of these findings for our understanding of meiotic chromosome segregation.

Zona pellucida (ZP) plays a vital role in reproductive processes including oogenesis, fertilization and preimplantation development of embryo. The ZP of humans is composed of four glycoproteins (ZP1-ZP4), same as rats ZP. Our previous research reported a first case of human infertility due to ZP1 mutation, but the mechanism was unclear. Here we developed a genome editing in vivo rat model and a co-transfected in vitro cell model to investigate the pathogenic effect. In rat homozygous for the homologous mutation, ZP were absent in all of collected eggs. Further the growing and fully grown oocytes in the mutant ovaries completely lack a ZP but with detectable intracellular ZP1 protein. After mating with male rats, none of the mutant female rats got pregnant. Moreover, the co-transfected cell experiments and the ovarian experiments showed that the truncated ZP1 sequestered intracellularly ZP3 and ZP4 to impede their release outside, resulting in an intracellular accumulation of ZP1, ZP3 and ZP4, leading to absence of ZP in mutant oocytes. Our results clearly establish the causal role of ZP1 mutation on ZP defects and female infertility.\n\nSummary statementRat model mirrored completely the phenotypes observed in humans, infertility and abnormal eggs that lack a zona pellucida, through the negative effects of ZP1 mutation.