Characterization of Two Gonadal Genes, zar1 and wt1b, in Hermaphroditic Fish Asian Seabass (Lates calcarifer)

Zygote arrest-1 (Zar1) and Wilms' tumor 1 (Wt1) play an important role in oogenesis, with the latter also involved in testicular development and gender differentiation. Here, Lczar1 and Lcwt1b were identified in Asian seabass (Lates calcarifer), a hermaphrodite fish, as the valuable model for studying sex differentiation. The cloned cDNA fragments of Lczar1 were 1192 bp, encoding 336 amino acids, and contained a zinc-binding domain, while those of Lcwt1b cDNA were 1521 bp, encoding a peptide of 423 amino acids with a Zn finger domain belonging to Wt1b family. RT-qPCR analysis showed that Lczar1 mRNA was exclusively expressed in the ovary, while Lcwt1b mRNA was majorly expressed in the gonads in a higher amount in the testis than in the ovary. In situ hybridization results showed that Lczar1 mRNA was mainly concentrated in oogonia and oocytes at early stages in the ovary, but were undetectable in the testis. Lcwt1b mRNA was localized not only in gonadal somatic cells (the testis and ovary), but also in female and male germ cells in the early developmental stages, such as those of previtellogenic oocytes, spermatogonia, spermatocytes and spermatids. These results indicated that Lczar1 and Lcwt1b possibly play roles in gonadal development. Therefore, the findings of this study will provide a basis for clarifying the mechanism of Lczar1 and Lcwt1b in regulating germ cell development and the sex reversal of Asian seabass and even other hermaphroditic species.

Revisiting ZAR proteins: the understudied regulator of female fertility and beyond

Putative RNA-binding proteins (RBPs), zygote arrested-1 (ZAR1), and ZAR2 (also known as ZAR1L), have been identified as maternal factors that mainly function in oogenesis and embryogenesis. Despite divergence in their spatio-temporal expression among species, the CxxC structure of the C-terminus of ZAR proteins is highly conserved and is reported to be the functional domain for the activity of the RBPs of ZAR proteins. In oocytes from Xenopus laevis and zebrafish, ZAR proteins have been reported to bind to maternal transcripts and inhibit translation in immature growing oocytes, whereas in fully grown mouse oocytes, they promote the translation during meiotic maturation. Thus, ZAR1 and ZAR2 may be required for the maternal-to-zygotic transition by stabilizing the maternal transcriptome in oocytes with partial functional redundancy. In addition, recent studies have suggested non-ovarian expression and function of ZAR proteins, particularly their involvement in tumorigenesis. ZAR proteins are potentially associated with tumor suppressors and can serve as epigenetically inactivated cancer biomarkers. In this review, studies on Zar1/2 are systematically summarized, and some issues that require discussion and further investigation are introduced as perspectives.

The ZAR1 protein in cancer; from epigenetic silencing to functional characterisation and epigenetic therapy of tumour suppressors

ZAR1, zygote arrest 1, is a zinc finger protein (C-terminus), which was initially identified in mouse oocytes. Later it was found that its expression is present in various human tissues e.g. lung and kidney. Interestingly, it was observed that in various tumour types the ZAR1 transcript is missing due to hypermethylation of its CpG island promoter, but not ZAR2. Since methylation of the ZAR1 promoter is described as a frequent event in tumourigenesis, ZAR1 could serve as a useful diagnostic marker in cancer screens. ZAR1 was described as a useful prognostic/diagnostic cancer marker for lung cancer, kidney cancer, melanoma and possibly liver carcinoma. Furthermore, ZAR1 was reactivated as a tumour suppressor by epigenetic therapy using CRISPR-dCas9 method. This method holds the potential to precisely target not only ZAR1 and reactivate tumour suppressors in a tailored cancer therapy. ZAR1 is highly conserved amongst vertebrates, especially its zinc finger, which is the relevant domain for its protein and RNA binding ability. ZAR1 is implicated in various cellular mechanisms including regulation of oocyte/embryo development, cell cycle control and mRNA binding, though little was known about the underlying mechanisms. ZAR1 was reported to regulate and activate translation through the binding to TCS translation control sequences in the 3'UTRs of its target mRNA the kinase WEE1. ZAR1 has a tumour suppressing function by inhibiting cell cycle progression. Here we review the current literature on ZAR1 focusing on structural, functional and epigenetic aspects. Characterising the cellular mechanisms that regulate the signalling pathways ZAR1 is involved in, could lead to a deeper understanding of tumour development and, furthermore, to new strategies in cancer treatment.

Variation Screening of Zygote Arrest 1(ZAR1) in Women with Recurrent Zygote Arrest During IVF/ICSI Programs

Human zygote arrest during in vitro culture is rare and the etiology is unclear. The oocyte-specific gene Zar1 plays an essential role in oocyte-embryo transition, and most embryos from Zar1 knockout female mice arrest at the one-cell stage. This study investigates whether maternal ZAR1 gene variations play a role in human zygote arrest. Sequence analysis of ZAR1 was conducted for 47 women with recurrent uncleaved zygotes in in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles (≥ 70% zygotes uncleaved in at least 2 cycles), 93 women from IVF/ICSI cycles with normal uncleaved rate and live birth (control subset I) and 188 women with spontaneous pregnancy and live birth (control subset II). One novel synonymous variation (c.516C>T) and one novel intron variation (c.964-55A>T) of ZAR1 were identified in the zygote arrest group but not in any of the 188 controls. However, the bioinformatics analysis revealed that neither of the mutations in ZAR1 has effect on ZAR1 protein function. Compared with control subset I, the allele frequencies of rare SNPs rs117545505 and rs17609740 were significantly different in patients with zygote arrest (P = 0.047, OR = 3.66). Allele frequencies of these two SNPs were also significantly different between the case group and control subset II (P = 0.024, OR = 3.28). In conclusion, two SNPs in ZAR1 are associated with human zygote arrest, although additional proof is needed for validation.

Epigenetic therapy of novel tumour suppressor ZAR1 and its cancer biomarker function

Background

Cancer still is one of the leading causes of death and its death toll is predicted to rise further. We identified earlier the potential tumour suppressor zygote arrest 1 (ZAR1) to play a role in lung carcinogenesis through its epigenetic inactivation.

Results

We are the first to report that ZAR1 is epigenetically inactivated not only in lung cancer but also across cancer types, and ZAR1 methylation occurs across its complete CpG island. ZAR1 hypermethylation significantly correlates with its expression reduction in cancers. We are also the first to report that ZAR1 methylation and expression reduction are of clinical importance as a prognostic marker for lung cancer and kidney cancer. We further established that the carboxy (C)-terminally present zinc-finger of ZAR1 is relevant for its tumour suppression function and its protein partner binding associated with the mRNA/ribosomal network. Global gene expression profiling supported ZAR1's role in cell cycle arrest and p53 signalling pathway, and we could show that ZAR1 growth suppression was in part p53 dependent. Using the CRISPR-dCas9 tools, we were able to prove that epigenetic editing and reactivation of ZAR1 is possible in cancer cell lines.

Conclusion

ZAR1 is a novel cancer biomarker for lung and kidney, which is epigenetically silenced in various cancers by DNA hypermethylation. ZAR1 exerts its tumour suppressive function in part through p53 and through its zinc-finger domain. Epigenetic therapy can reactivate the ZAR1 tumour suppressor in cancer.

ZAR1 knockdown promotes the differentiation of human neuroblastoma cells by suppression of MYCN expression

Although DNA hypermethylation at non-promoter region of the Zygote arrest 1 (ZAR1) gene has been observed in many types of tumor, including neuroblastoma (NB), the role of this gene in tumor development and/or progression is unclear. One reason is that knowledge about the function of ZAR1 protein is limited. Although it has been reported that ZAR1 plays a crucial role in early embryogenesis and may act as a transcriptional repressor for some transcripts, the detailed mechanism is still elusive. In the present study, we analyzed public data of NB patients and found that higher expression levels of ZAR1 were significantly associated with a shorter survival period. Consistent with this result, ZAR1-depleted NB cells showed well-differentiated phenotypes with elongated neurites and upregulated expression of TRKA and RET, which are markers for differentiated NB. Moreover, the expression level of MYCN protein was markedly suppressed in ZAR1-depleted NB cells. MYCN-depleted cells showed similar phenotypes to ZAR1-depleted cells. The present findings indicate that ZAR1 has oncogenic effects in NB by suppressing cell differentiation via regulation of MYCN expression.

ZAR1 is a novel epigenetically inactivated tumour suppressor in lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths with 1.8 million new cases each year and poor 5-year prognosis. Promoter hypermethylation of tumour suppressors leads to their inactivation and thereby can promote cancer development and progression.

RESULTS

In this study, we analysed ZAR1 (zygote arrest 1), which has been said to be a maternal-effect gene and its expression mostly limited to certain reproductive tissues. Our study shows that ZAR1 is expressed in normal lung but inactivated by promoter methylation in lung cancer. ZAR1 is hypermethylated in primary lung cancer samples (22% small cell lung carcinoma (SCLC) and 76% non-small cell lung carcinoma (NSCLC), p < 0.001) vs. normal control lung tissue (11%). In lung cancer cell lines, ZAR1 was significantly methylated in 75% of SCLC and 83% of NSCLC vs. normal tissue (p < 0.005/0.05). In matching tumours and control tissues, we observed that NSCLC primary tumour samples exhibited a tumour-specific promoter methylation of ZAR1 in comparison to the normal control lung tissue. Demethylation treatment of various lung cancer cell lines reversed ZAR1 promoter hypermethylation and subsequently re-established ZAR1 expression. In addition, we could show the growth inhibitory potential of ZAR1 in lung cancer cell lines and cancer cell lines. Exogenous expression of ZAR1 not only inhibited colony formation but also blocked cell cycle progression of cancer cell lines.

CONCLUSIONS

Our study shows for the first time the lung tumour-specific epigenetic inactivation of ZAR1 due to DNA methylation of its CpG island promoter. Furthermore, ZAR1 was characterised by the ability to block tumour growth through the inhibition of cell cycle progression in cancer cell lines. We propose that ZAR1 could serve as an epigenetically inactivated biomarker in lung cancer.

Evaluation of ZAR1 and SFRP4 methylation status as potentials biomarkers for diagnosis in cervical cancer: exploratory study phase I

CONTEXT

Aberrant hypermethylation of promoter region of tumor suppressor genes could be used as cancer biomarkers.

OBJECTIVE

To test methylation status of ZAR1 and SFRP4 promoter regions as potentials biomarkers for diagnosis of preneoplastic and neoplastic lesions of cervix.

MATERIALS AND METHODS

Cytobrush samples were evaluated by Methylation specific PCR (MSP) and quantitative MSP (qMSP).

RESULTS

ZAR1 and SFRP4 methylation frequency increased as the grade of lesion increased and the differences between normal and cervical cancer (CC) are statistically significant (p < 0.0001). qMSP showed higher ZAR1 and SFRP4 methylation levels in cancer than normal epithelia (p < 0.001) and preneoplastics lesions (p < 0.01).

DISCUSSION

qMSP quantify methylation levels and have high sensitivity and specificity.

CONCLUSION

ZAR1 and SFRP4 qMSP could be used as potential biomarker for CC diagnosis.

Identification of frequent differentially methylated region in sporadic bladder cancers

INTRODUCTION

Aberrant methylation levels in the cytosine-phosphate-guanine island (CpGi) region from exon 1 to intron 1 of the zygote arrest 1 (ZAR1) gene have been reported in several types of human cancers, including melanoma, brain tumor, and hepatocellular carcinoma. In the present study, methylation levels at the CpGi of ZAR1 exon 1/intron 1 in bladder cancer specimens were analyzed using mass spectrometry.

MATERIALS AND METHODS

Genomic DNA was extracted from 20 sporadic bladder cancers, and the methylation levels at ZAR1 CpGi were quantitatively examined by the MassARRAY EpiTYPER method.

RESULT

The methylation levels at specific CpG sites of the ZAR1 CpGi were significantly lower in high-grade bladder cancers than in low-grade tumors.

CONCLUSIONS

The results of the present study indicated a decreased methylation level at CpG sites of ZAR1 exon 1/intron 1. CpGi could serve as a biomarker for invasive bladder cancer.

Genome-wide screening of aberrant DNA methylation which associated with gene expression in mouse skin cancers

Epigenetic alteration of genomic DNA is a common and key process in carcinogenesis. There is considerable evidence indicating that some of the somatic alterations occurring during carcinogenesis in humans also involve the same processes as those observed in mice. Therefore, we analyzed mouse skin cancer tissues induced by the 2-stage carcinogenesis model to identify skin tumor-specific differentially methylated regions (ST-DMRs) during the multistep carcinogenesis process. We have previously identified ST-DMRs using the restriction landmark genomic scanning (RLGS) technique and reported that some of the mouse ST-DMRs were also epigenetically modified in human cancers, such as melanoma, neuroblastoma, and brain tumor. These results encouraged us to pursue global methylation screening in mouse skin carcinogenesis. Using the methylated DNA immunoprecipitation (MeDIP) method combined with the NimbleGen promoter plus CpG island (CpGi) array, we identified 615 ST-DMRs. In combination with global gene expression analysis, 91 of these ST-DMRs were shown to be located on or around the genes differentially expressed between normal skin and tumor tissues, including a candidate human tumor suppressor gene Tfap2e. As observed in human colorectal cancers, Tfap2e was methylated at a CpGi located in intron 3 and downregulated in skin tumors. Our results identified aberrant methylated regions that were associated with gene expression regulation during carcinogenesis, which may indicate critical genetic regions also involved in human carcinogenesis. © 2013 Wiley Periodicals, Inc.

Non-promoter DNA hypermethylation of Zygote Arrest 1 (ZAR1) in neuroblastomas

BACKGROUND

The comprehensive methylation analysis of tumor-specific differently methylated regions in malignant melanomas and brain tumors has led to the identification of non-promoter hypermethylation of zygote arrest 1 (ZAR1). To search the non-promoter ZAR1 hypermethylation in neuroblastomas, we analyzed the levels of the methylation and transcript expression of ZAR1.

METHODS

The MassARRAY® EpiTYPER (Sequenom Inc., San Diego, CA, USA) system was optimized to determine the quantitative methylation levels of ZAR1 for 12 neuroblastoma cell lines, 23 neuroblastoma samples and four adrenal samples. ZAR1 expression levels were evaluated through a quantitative, real-time reverse transcription-polymerase chain reaction. The quantitative methylation levels of ZAR1 were subjected to correlation studies with the established markers of progressive disease and outcome.

RESULTS

Strikingly, the hypermethylation of ZAR1 regions and ZAR1 expression levels was observed in the neuroblastoma cell lines and neuroblastoma samples, compared to the adrenal samples. Somatic changes in ZAR1 methylation and ZAR1 expression were found in all three neuroblastoma patients. In the ZAR1 regions, poor-outcome tumors that were MYCN-amplified and/or Stage 3 or 4 and/or the age at diagnosis was≥18months, and/or showed an unfavorable histology were frequently hypermethylated.

CONCLUSION

Our results indicate that the hypermethylation of ZAR1 regions is extremely frequent in neuroblastomas and correlates with established markers of progressive disease and outcome.

Xenopus laevis zygote arrest 2 (zar2) encodes a zinc finger RNA-binding protein that binds to the translational control sequence in the maternal Wee1 mRNA and regulates translation

Zygote arrest (Zar) proteins are crucial for early embryonic development, but their molecular mechanism of action is unknown. The Translational Control Sequence (TCS) in the 3' untranslated region (UTR) of the maternal mRNA, Wee1, mediates translational repression in immature Xenopus oocytes and translational activation in mature oocytes, but the protein that binds to the TCS and mediates translational control is not known. Here we show that Xenopus laevis Zar2 (encoded by zar2) binds to the TCS in maternal Wee1 mRNA and represses translation in immature oocytes. Using yeast 3 hybrid assays and electrophoretic mobility shift assays, Zar2 was shown to bind specifically to the TCS in the Wee1 3'UTR. RNA binding required the presence of Zn(2+) and conserved cysteines in the C-terminal domain, suggesting that Zar2 contains a zinc finger. Consistent with regulating maternal mRNAs, Zar2 was present throughout oogenesis, and endogenous Zar2 co-immunoprecipitated endogenous Wee1 mRNA from immature oocytes, demonstrating the physiological significance of the protein-RNA interaction. Interestingly, Zar2 levels decreased during oocyte maturation. Dual luciferase reporter tethered assays showed that Zar2 repressed translation in immature oocytes. Translational repression was relieved during oocyte maturation and this coincided with degradation of Zar2 during maturation. This is the first report of a molecular function of zygote arrest proteins. These data show that Zar2 contains a zinc finger and is a trans-acting factor for the TCS in maternal mRNAs in immature Xenopus oocytes.