A Requirement for Zic2 in the Regulation of Nodal Expression Underlies the Establishment of Left-Sided Identity

ZIC2 and ZIC3 promote SWI/SNF recruitment to safeguard progression towards human primed pluripotency

The primed epiblast acts as a transitional stage between the relatively homogeneous naïve epiblast and the gastrulating embryo. Its formation entails coordinated changes in regulatory circuits driven by transcription factors and epigenetic modifications. Using a multi-omic approach in human embryonic stem cell models across the spectrum of peri-implantation development, we demonstrate that the transcription factors ZIC2 and ZIC3 have overlapping but essential roles in opening primed-specific enhancers. Together, they are essential to facilitate progression to and maintain primed pluripotency. ZIC2/3 accomplish this by recruiting SWI/SNF to chromatin and loss of ZIC2/3 or degradation of SWI/SNF both prevent enhancer activation. Loss of ZIC2/3 also results in transcriptome changes consistent with perturbed Polycomb activity and a shift towards the expression of genes linked to differentiation towards the mesendoderm. Additionally, we find an intriguing dependency on the transcriptional machinery for sustained recruitment of ZIC2/3 over a subset of primed-hESC specific enhancers. Taken together, ZIC2 and ZIC3 regulate highly dynamic lineage-specific enhancers and collectively act as key regulators of human primed pluripotency.

Diverse logics and grammar encode notochord enhancers

The notochord is a defining feature of all chordates. The transcription factors Zic and ETS regulate enhancer activity within the notochord. We conduct high-throughput screens of genomic elements within developing Ciona embryos to understand how Zic and ETS sites encode notochord activity. Our screen discovers an enhancer located near Lama, a gene critical for notochord development. Reversing the orientation of an ETS site within this enhancer abolishes expression, indicating that enhancer grammar is critical for notochord activity. Similarly organized clusters of Zic and ETS sites occur within mouse and human Lama1 introns. Within a Brachyury (Bra) enhancer, FoxA and Bra, in combination with Zic and ETS binding sites, are necessary and sufficient for notochord expression. This binding site logic also occurs within other Ciona and vertebrate Bra enhancers. Collectively, this study uncovers the importance of grammar within notochord enhancers and discovers signatures of enhancer logic and grammar conserved across chordates.

The Role of Sonic Hedgehog in Human Holoprosencephaly and Short-Rib Polydactyly Syndromes

The Hedgehog (HH) signalling pathway is one of the major pathways controlling cell differentiation and proliferation during human development. This pathway is complex, with HH function influenced by inhibitors, promotors, interactions with other signalling pathways, and non-genetic and cellular factors. Many aspects of this pathway are not yet clarified. The main features of Sonic Hedgehog (SHH) signalling are discussed in relation to its function in human development. The possible role of SHH will be considered using examples of holoprosencephaly and short-rib polydactyly (SRP) syndromes. In these syndromes, there is wide variability in phenotype even with the same genetic mutation, so that other factors must influence the outcome. SHH mutations were the first identified genetic causes of holoprosencephaly, but many other genes and environmental factors can cause malformations in the holoprosencephaly spectrum. Many patients with SRP have genetic defects affecting primary cilia, structures found on most mammalian cells which are thought to be necessary for canonical HH signal transduction. Although SHH signalling is affected in both these genetic conditions, there is little overlap in phenotype. Possible explanations will be canvassed, using data from published human and animal studies. Implications for the understanding of SHH signalling in humans will be discussed.

Single-minded 2 is required for left-right asymmetric stomach morphogenesis

The morphogenesis of left-right (LR) asymmetry is a crucial phase of organogenesis. In the digestive tract, the development of anatomical asymmetry is first evident in the leftward curvature of the stomach. To elucidate the molecular events that shape this archetypal laterality, we performed transcriptome analyses of the left versus right sides of the developing stomach in frog embryos. Besides the known LR gene pitx2, the only gene found to be expressed asymmetrically throughout all stages of curvature was single-minded 2 (sim2), a Down Syndrome-related transcription factor and homolog of a Drosophila gene (sim) required for LR asymmetric looping of the fly gut. We demonstrate that sim2 functions downstream of LR patterning cues to regulate key cellular properties and behaviors in the left stomach epithelium that drive asymmetric curvature. Our results reveal unexpected convergent cooption of single-minded genes during the evolution of LR asymmetric morphogenesis, and have implications for dose-dependent roles of laterality factors in non-laterality-related birth defects.

Zic Family Member 2 (ZIC2): a Potential Diagnostic and Prognostic Biomarker for Pan-Cancer

Background: As a transcription factor, Zinc finger protein ZIC2 can interact with various DNAs and proteins. Current studies have shown that ZIC2 plays an oncogene role in various cancers. In this study, we systematically characterize the prevalence and predictive value of ZIC2 expression across multiple cancer types. Methods: We mined several public databases, including Oncomine, the Cancer Genome Atlas (TCGA), cBioPortal, Kaplan-Meier Plotter and PrognoScan to evaluated the differentially expressed ZIC2 between tumor samples and normal control samples in pan-cancner, and then explored the association between ZIC2 expression and patient survival, prognosis and clinicopathologic stage. We also analyzed the relationship between tumor mutation burden (TMB), microsatellite instability (MSI), tumor microenvironment, tumor- and immune-related genes and ZIC2 expression. Finally, we explored the potential signaling pathway mechanism through gene set enrichment analysis (GSEA). Results: ZIC2 expression was higher in most cancer tissues compared with adjacent normal tissues. High ZIC2 expression was associated with worse prognosis and a higher clinicopathologic stage. ZIC2 expression was strongly associated with the TMB, MSI, tumor microenvironment and tumor- and immune-related genes. The GSEA revealed that multiple tumor- and immune-related pathways were differentially enriched in ZIC2 high or low expression phenotype. Conclusion: ZIC2 expression may be a potential prognostic molecular biomarker of poor survival in pan-cancer and may act as an oncogene with a strong effect in the processes of tumorigenesis and progression.

Genome-wide CRISPR screen identifies ZIC2 as an essential gene that controls the cell fate of early mesodermal precursors to human heart progenitors

Cardiac progenitor formation is one of the earliest committed steps of human cardiogenesis and requires the cooperation of multiple gene sets governed by developmental signaling cascades. To determine the key regulators for cardiac progenitor formation, we have developed a two‐stage genome‐wide CRISPR‐knockout screen. We mimicked the progenitor formation process by differentiating human pluripotent stem cells (hPSCs) into cardiomyocytes, monitored by two distinct stage markers of early cardiac mesodermal formation and commitment to a multipotent heart progenitor cell fate: MESP1 and ISL1, respectively. From the screen output, we compiled a list of 15 candidate genes. After validating seven of them, we identified ZIC2 as an essential gene for cardiac progenitor formation. ZIC2 is known as a master regulator of neurogenesis. hPSCs with ZIC2 mutated still express pluripotency markers. However, their ability to differentiate into cardiomyocytes was greatly attenuated. RNA‐Seq profiling of the ZIC2‐mutant cells revealed that the mutants switched their cell fate alternatively to the noncardiac cell lineage. Further, single cell RNA‐seq analysis showed the ZIC2 mutants affected the apelin receptor‐related signaling pathway during mesoderm formation. Our results provide a new link between ZIC2 and human cardiogenesis and document the potential power of a genome‐wide unbiased CRISPR‐knockout screen to identify the key steps in human mesoderm precursor cell‐ and heart progenitor cell‐fate determination during in vitro hPSC cardiogenesis.