Mice deficient in the candidate tumor suppressor gene Hic1 exhibit developmental defects of structures affected in the Miller-Dieker syndrome

The ZBTB family in cardiac development and diseases

ZBTB (zinc finger and BTB domain) proteins are a class of evolutionarily conserved transcriptional factors (TFs) with zinc finger (ZF) and BTB (Broad-complex, Tram-track, and Bric-à-brac) domains. The ZBTB protein family has a wide range of functions in numerous biological processes, including cell cycle regulation, DNA repair, organ development, and haematopoietic stem cell fate determination. The ZBTB proteins regulate gene expression through interactions with transcriptional regulators, influencing processes such as myocardial contractility, inflammation, fibrosis, and cellular metabolism. Given the critical role of the ZBTB family in cardiac biology, the present review endeavours to comprehensively summarize the regulatory roles of seven ZBTB family members (HIC2, BCL6, PLZF, ZBTB17, ZBTB20, ZBTB7a, and ZBTB11) in cardiac development and diseases, along with their potential molecular mechanisms. Elucidating the molecular mechanisms of ZBTB proteins opens avenues for developing targeted therapies for cardiovascular diseases, including hypertrophy, fibrosis, and inflammation. This review provides a comprehensive summary of recent research on the role of ZBTB proteins in regulating cardiac transcription. Particular emphasis is placed on elucidating their functions in both cardiac development and the pathogenesis of cardiac diseases.

Deep clinical and genetic analysis of 17p13.3 region: 38 pediatric patients diagnosed using next-generation sequencing and literature review

BACKGROUND

Chromosome 17p13.3 is a region of genomic instability associated with different neurodevelopmental diseases. The malformation spectrum of 17p13.3 microdeletions ranges from an isolated lissencephaly sequence to Miller-Dieker syndrome, while 17p13.3 microduplications result in autism, learning disabilities, microcephaly and other brain malformations. This study aims to provide a more comprehensive delineation of the clinical and genetic characteristics associated with 17p13.3 alterations.

METHODS

We retrospectively analyzed the next-generation sequencing (NGS) data of more than 40 thousand patients from January 2016 to December 2021 and identified 38 pediatric patients with copy-number variations (CNVs) or single-nucleotide variations (SNVs) in 17p13.3 region. Published patients with CNVs in the 17p13.3 region were also collected and we performed a Chi-square test to compare the phenotype spectrum of microdeletions and microduplications.

RESULTS

Among the 27 CNV patients, 20 patients with microdeletions and 7 patients with microduplications were found. PAFAH1B1 was the most frequently deleted gene and CRK was the most frequently duplicated gene. Affected genes in 11 SNV patients included PAFAH1B1 and PRPF8. Developmental delay was the most common abnormality detected in the 38 patients (29/38, 76.3%). Of note, Case 10 presented omphalocele and Case 23 presented scoliosis, webbed neck and bone cyst, all of which were unusual variant phenotypes in this region. The Chi-square test revealed that epilepsy, lissencephaly and short stature were statistically significant with microdeletions, while behavioral abnormalities and hand and foot abnormalities were significant with microduplications (p < 0.01).

CONCLUSIONS

While PAFAH1B1, YWHAE and CRK are associated with major phenotypes of 17p13.3, RTN4RL1 may be involved in white matter changes and HIC1 might contribute to the occurrence of omphalocele. This study provided a comprehensive understanding of genetic information and phenotype spectrum of the 17p13.3 region.

Ventral body wall closure: Mechanistic insights from mouse models and translation to human pathology

The ventral body wall (VBW) that encloses the thoracic and abdominal cavities arises by extensive cell movements and morphogenetic changes during embryonic development. These morphogenetic processes include embryonic folding generating the primary body wall; the initial ventral cover of the embryo, followed by directed mesodermal cell migrations, contributing to the secondary body wall. Clinical anomalies in VBW development affect approximately 1 in 3000 live births. However, the cell interactions and critical cellular behaviors that control VBW development remain little understood. Here, we describe the embryonic origins of the VBW, the cellular and morphogenetic processes, and key genes, that are essential for VBW development. We also provide a clinical overview of VBW anomalies, together with environmental and genetic influences, and discuss the insight gained from over 70 mouse models that exhibit VBW defects, and their relevance, with respect to human pathology. In doing so we propose a phenotypic framework for researchers in the field which takes into account the clinical picture. We also highlight cases where there is a current paucity of mouse models for particular clinical defects and key gaps in knowledge about embryonic VBW development that need to be addressed to further understand mechanisms of human VBW pathologies.

Research progress on Sirtuins (SIRTs) family modulators

Sirtuins (SIRTs) represent a class of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases that exert a crucial role in cellular signal transduction and various biological processes. The mammalian sirtuins family encompasses SIRT1 to SIRT7, exhibiting therapeutic potential in counteracting cellular aging, modulating metabolism, responding to oxidative stress, inhibiting tumors, and improving cellular microenvironment. These enzymes are intricately linked to the occurrence and treatment of diverse pathological conditions, including cancer, autoimmune diseases, and cardiovascular disorders. Given the significance of histone modification in gene expression and chromatin structure, maintaining the equilibrium of the sirtuins family is imperative for disease prevention and health restoration. Mounting evidence suggests that modulators of SIRTs play a crucial role in treating various diseases and maintaining physiological balance. This review delves into the molecular structure and regulatory functions of the sirtuins family, reviews the classification and historical evolution of SIRTs modulators, offers a systematic overview of existing SIRTs modulation strategies, and elucidates the regulatory mechanisms of SIRTs modulators (agonists and inhibitors) and their clinical applications. The article concludes by summarizing the challenges encountered in SIRTs modulator research and offering insights into future research directions.

Single-cell analysis of mesenchymal cells in permeable neural vasculature reveals novel diverse subpopulations of fibroblasts

BACKGROUND

In the choroid plexus and pituitary gland, vasculature is known to have a permeable, fenestrated phenotype which allows for the free passage of molecules in contrast to the blood brain barrier observed in the rest of the CNS. The endothelium of these compartments, along with secretory, neural-lineage cells (choroid epithelium and pituitary endocrine cells) have been studied in detail, but less attention has been given to the perivascular mesenchymal cells of these compartments.

METHODS

The Hic1CreERT2 Rosa26LSL-TdTomato mouse model was used in conjunction with a PdgfraH2B-EGFP mouse model to examine mesenchymal cells, which can be subdivided into Pdgfra+ fibroblasts and Pdgfra- pericytes within the choroid plexus (CP) and pituitary gland (PG), by histological, immunofluorescence staining and single-cell RNA-sequencing analyses.

RESULTS

We found that both CP and PG possess substantial populations of distinct Hic1+ mesenchymal cells, including an abundance of Pdgfra+ fibroblasts. Within the pituitary, we identified distinct subpopulations of Hic1+ fibroblasts in the glandular anterior pituitary and the neurosecretory posterior pituitary. We also identified multiple distinct markers of CP, PG, and the meningeal mesenchymal compartment, including alkaline phosphatase, indole-n-methyltransferase and CD34.

CONCLUSIONS

Novel, distinct subpopulations of mesenchymal cells can be found in permeable vascular interfaces, including the CP, PG, and meninges, and make distinct contributions to both organs through the production of structural proteins, enzymes, transporters, and trophic molecules.

Molecular and Clinical Spectrum of Primary Hyperparathyroidism

Recent data suggest an increase in the overall incidence of parathyroid disorders, with primary hyperparathyroidism (PHPT) being the most prevalent parathyroid disorder. PHPT is associated with morbidities (fractures, kidney stones, chronic kidney disease) and increased risk of death. The symptoms of PHPT can be nonspecific, potentially delaying the diagnosis. Approximately 15% of patients with PHPT have an underlying heritable form of PHPT that may be associated with extraparathyroidal manifestations, requiring active surveillance for these manifestations as seen in multiple endocrine neoplasia type 1 and 2A. Genetic testing for heritable forms should be offered to patients with multiglandular disease, recurrent PHPT, young onset PHPT (age ≤40 years), and those with a family history of parathyroid tumors. However, the underlying genetic cause for the majority of patients with heritable forms of PHPT remains unknown. Distinction between sporadic and heritable forms of PHPT is useful in surgical planning for parathyroidectomy and has implications for the family. The genes currently known to be associated with heritable forms of PHPT account for approximately half of sporadic parathyroid tumors. But the genetic cause in approximately half of the sporadic parathyroid tumors remains unknown. Furthermore, there is no systemic therapy for parathyroid carcinoma, a rare but potentially fatal cause of PHPT. Improved understanding of the molecular characteristics of parathyroid tumors will allow us to identify biomarkers for diagnosis and novel targets for therapy.

Hic1 identifies a specialized mesenchymal progenitor population in the embryonic limb responsible for bone superstructure formation

The musculoskeletal system relies on the integration of multiple components with diverse physical properties, such as striated muscle, tendon, and bone, that enable locomotion and structural stability. This relies on the emergence of specialized, but poorly characterized, interfaces between these various elements during embryonic development. Within the appendicular skeleton, we show that a subset of mesenchymal progenitors (MPs), identified by Hic1, do not contribute to the primary cartilaginous anlagen but represent the MP population, whose progeny directly contribute to the interfaces that connect bone to tendon (entheses), tendon to muscle (myotendinous junctions), and the associated superstructures. Furthermore, deletion of Hic1 leads to skeletal defects reflective of deficient muscle-bone coupling and, consequently, perturbation of ambulation. Collectively, these findings show that Hic1 identifies a unique MP population that contributes to a secondary wave of bone sculpting critical to skeletal morphogenesis.

Flying under the radar: CDH2 (N-cadherin), an important hub molecule in neurodevelopmental and neurodegenerative diseases

CDH2 belongs to the classic cadherin family of Ca2+-dependent cell adhesion molecules with a meticulously described dual role in cell adhesion and β-catenin signaling. During CNS development, CDH2 is involved in a wide range of processes including maintenance of neuroepithelial integrity, neural tube closure (neurulation), confinement of radial glia progenitor cells (RGPCs) to the ventricular zone and maintaining their proliferation-differentiation balance, postmitotic neural precursor migration, axon guidance, synaptic development and maintenance. In the past few years, direct and indirect evidence linked CDH2 to various neurological diseases, and in this review, we summarize recent developments regarding CDH2 function and its involvement in pathological alterations of the CNS.

Cellular taxonomy of Hic1+ mesenchymal progenitor derivatives in the limb: from embryo to adult

Tissue development and regeneration rely on the cooperation of multiple mesenchymal progenitor (MP) subpopulations. We recently identified Hic1 as a marker of quiescent MPs in multiple adult tissues. Here, we describe the embryonic origin of appendicular Hic1⁺ MPs and demonstrate that they arise in the hypaxial somite, and migrate into the developing limb at embryonic day 11.5, well after limb bud initiation. Time-resolved single-cell-omics analyses coupled with lineage tracing reveal that Hic1⁺ cells generate a unique MP hierarchy, that includes both recently identified adult universal fibroblast populations (Dpt⁺, Pi16⁺ and Dpt⁺ Col15a1⁺) and more specialised mesenchymal derivatives such as, peri and endoneurial cells, pericytes, bone marrow stromal cells, myotenocytes, tenocytes, fascia-resident fibroblasts, with limited contributions to chondrocytes and osteocytes within the skeletal elements. MPs endure within these compartments, continue to express Hic1 and represent a critical reservoir to support post-natal growth and regeneration.

Responsible Genes for Neuronal Migration in the Chromosome 17p13.3: Beyond Pafah1b1(Lis1), Crk and Ywhae(14-3-3ε)

The 17p13.3 chromosome region is often deleted or duplicated in humans, resulting in severe neurodevelopmental disorders such as Miller–Dieker syndrome (MDS) and 17p13.3 duplication syndrome. Lissencephaly can also be caused by gene mutations or deletions of a small piece of the 17p13.3 region, including a single gene or a few genes. PAFAH1B1 gene, coding for LIS1 protein, is a responsible gene for lissencephaly and MDS and regulates neuronal migration by controlling microtubules (MTs) and cargo transport along MTs via dynein. CRK is a downstream regulator of the reelin signaling pathways and regulates neuronal migration. YWHAE, coding for 14-3-3ε, is also responsible for MDS and regulates neuronal migration by binding to LIS1-interacting protein, NDEL1. Although these three proteins are known to be responsible for neuronal migration defects in MDS, there are 23 other genes in the MDS critical region on chromosome 17p13.3, and little is known about their functions in neurodevelopment, especially in neuronal migration. This review will summarize the recent progress on the functions of LIS1, CRK, and 14-3-3ε and describe the recent findings of other molecules in the MDS critical regions in neuronal migration.

New insights into spatio-temporal dynamics of mesenchymal progenitor cell ingress during peri-implant wound healing: Provided by intravital imaging

Surface topography drives the success of orthopedic and dental implants placed in bone, by directing the biology occurring at the tissue-implant interface. Over the last few decades, striking advancements have been made in the development of novel implant surfaces that enhance bone anchorage to their surfaces through contact osteogenesis: the combination of the two phenomena of recruitment and migration of mesenchymal progenitor cells to the implant surface, and their differentiation into bone-forming cells. While the latter is generally understood, the mechanisms and dynamics underlying the migration and recruitment of such progenitor cells into the wound site have garnered little attention. To address this deficit, we surgically inserted metallic implants with two different surface topographies into the skulls of mice, and then employed real-time spatiotemporal microscopic monitoring of the peri-implant tissue healing to track the ingress of cells. Our results show that nano-topographically complex, in comparison to relatively smooth, implant surfaces profoundly affect recruitment of both endothelial cells, which are essential for angiogenesis, and the mesenchymal progenitor cells that give rise to the reparative tissue stroma. The latter appear concomitantly in the wound site with endothelial cells, from the vascularized areas of the periosteum, and demonstrate a proliferative "bloom" that diminishes with time, although some of these cells differentiate into important stromal cells, pericytes and osteocytes, of the reparative wound. In separate experiments we show, using trajectory plots, that the directionality of migration for both endothelial and perivascular cells can be explained by implant surface dependent release of local cytokine gradients from platelets that would become activated on the implant surfaces during initial blood contact. These findings provide new biological insights into the earliest stages of wound healing, and have broad implications in the application of putative nano-topographically complex biomaterials in many tissue types.

HIC1 Represses Atoh1 Transcription and Hair Cell Differentiation in the Cochlea

Across species, expression of the basic helix-loop-helix transcription factor ATOH1 promotes differentiation of cochlear supporting cells to sensory hair cells required for hearing. In mammals, this process is limited to development, whereas nonmammalian vertebrates can also regenerate hair cells after injury. The mechanistic basis for this difference is not fully understood. Hypermethylated in cancer 1 (HIC1) is a transcriptional repressor known to inhibit Atoh1 in the cerebellum. We therefore investigated its potential role in cochlear hair cell differentiation. We find that Hic1 is expressed throughout the postnatal murine cochlear sensory epithelium. In cochlear organoids, Hic1 knockdown induces Atoh1 expression and promotes hair cell differentiation, while Hic1 overexpression hinders differentiation. Wild-type HIC1, but not the DNA-binding mutant C521S, suppresses activity of the Atoh1 autoregulatory enhancer and blocks its responsiveness to β-catenin activation. Our findings reveal the importance of HIC1 repression of Atoh1 in the cochlea, which may be targeted to promote hair cell regeneration.

HIC1 (Hypermethylated in Cancer 1) modulates the contractile activity of prostate stromal fibroblasts and directly regulates CXCL12 expression

HIC1 (Hypermethylated In Cancer 1) a tumor suppressor gene located at 17p13.3, is frequently deleted or epigenetically silenced in many human tumors. HIC1 encodes a transcriptional repressor involved in various aspects of the DNA damage response and in complex regulatory loops with P53 and SIRT1. HIC1 expression in normal prostate tissues has not yet been investigated in detail. Here, we demonstrated by immunohistochemistry that detectable HIC1 expression is restricted to the stroma of both normal and tumor prostate tissues. By RT-qPCR, we showed that HIC1 is poorly expressed in all tested prostate epithelial lineage cell types: primary (PrEC), immortalized (RWPE1) or transformed androgen-dependent (LnCAP) or androgen-independent (PC3 and DU145) prostate epithelial cells. By contrast, HIC1 is strongly expressed in primary PrSMC and immortalized (WMPY-1) prostate myofibroblastic cells. HIC1 depletion in WPMY-1 cells induced decreases in α-SMA expression and contractile capability. In addition to SLUG, we identified stromal cell-derived factor 1/C-X-C motif chemokine 12 (SDF1/CXCL12) as a new HIC1 direct target-gene. Thus, our results identify HIC1 as a tumor suppressor gene which is poorly expressed in the epithelial cells targeted by the tumorigenic process. HIC1 is expressed in stromal myofibroblasts and regulates CXCL12/SDF1 expression, thereby highlighting a complex interplay mediating the tumor promoting activity of the tumor microenvironment. Our studies provide new insights into the role of HIC1 in normal prostatic epithelial-stromal interactions through direct repression of CXCL12 and new mechanistic clues on how its loss of function through promoter hypermethylation during aging could contribute to prostatic tumors.

In vitro modeling for inherited neurological diseases using induced pluripotent stem cells: from 2D to organoid

Stem cells are characterized by self-renewal and by their ability to differentiate into cells of various organs. With massive progress in 2D and 3D cell culture techniques, in vitro generation of various types of such organoids from patient-derived stem cells is now possible. As in vitro differentiation protocols are usually made to resemble human developmental processes, organogenesis of patient-derived stem cells can provide key information regarding a range of developmental diseases. Human stem cell-based in vitro modeling as opposed to using animal models can particularly benefit the evaluation of neurological diseases because of significant differences in structure and developmental processes between the human and the animal brain. This review focuses on stem cell-based in vitro modeling of neurodevelopmental disorders, more specifically, the fundamentals and technical advancements in monolayer neuron and brain organoid cultures. Furthermore, we discuss the drawbacks of the conventional culture method and explore the advanced, cutting edge 3D organoid models for several neurodevelopmental diseases, including genetic diseases such as Down syndrome, Rett syndrome, and Miller-Dieker syndrome, as well as brain malformations like macrocephaly and microcephaly. Finally, we discuss the limitations of the current organoid techniques and some potential solutions that pave the way for accurate modeling of neurological disorders in a dish.

The transcription factor Hypermethylated in Cancer 1 (Hic1) regulates neural crest migration via interaction with Wnt signaling

The transcription factor Hypermethylated in Cancer 1 (HIC1) is associated with both tumorigenesis and the complex human developmental disorder Miller-Dieker Syndrome. While many studies have characterized HIC1 as a tumor suppressor, HIC1 function in development is less understood. Loss-of-function mouse alleles show embryonic lethality accompanied with developmental defects, including craniofacial abnormalities that are reminiscent of human Miller-Dieker Syndrome patients. However, the tissue origin of the defects has not been reported. In this study, we use the power of the Xenopus laevis model system to explore Hic1 function in early development. We show that hic1 mRNA is expressed throughout early Xenopus development and has a spatial distribution within the neural plate border and in migrating neural crest cells in branchial arches. Targeted manipulation of hic1 levels in the dorsal ectoderm that gives rise to neural and neural crest tissues reveals that both overexpression and knockdown of hic1 result in craniofacial defects with malformations of the craniofacial cartilages. Neural crest specification is not affected by altered hic1 levels, but migration of the cranial neural crest is impaired both in vivo and in tissue explants. Mechanistically, we find that Hic1 regulates cadherin expression profiles and canonical Wnt signaling. Taken together, these results identify Hic1 as a novel regulator of the canonical Wnt pathway during neural crest migration.

Development and function of smooth muscle cells is modulated by Hic1 in mouse testis

In mammalian testis, contractile peritubular myoid cells (PMCs) regulate the transport of sperm and luminal fluid, while secreting growth factors and extracellular matrix proteins to support the spermatogonial stem cell niche. However, little is known about the role of testicular smooth muscle cells during postnatal testicular development. Here we report age-dependent expression of hypermethylated in cancer 1 (Hic1; also known as ZBTB29) in testicular smooth muscle cells, including PMCs and vascular smooth muscle cells, in the mouse. Postnatal deletion of Hic1 in smooth muscle cells led to their increased proliferation and resulted in dilatation of seminiferous tubules, with increased numbers of PMCs. These seminiferous tubules contained fewer Sertoli cells and more spermatogonia, and fibronectin was not detected in their basement membrane. The expression levels of genes encoding smooth muscle contractile proteins, Acta2 and Cnn1, were downregulated in the smooth muscle cells lacking Hic1, and the seminiferous tubules appeared to have reduced contractility. These data imply a role for Hic1 in determining the size of seminiferous tubules by regulating postnatal smooth muscle cell proliferation, subsequently affecting spermatogenesis in adulthood.

Mamo decodes hierarchical temporal gradients into terminal neuronal fate

Temporal patterning is a seminal method of expanding neuronal diversity. Here we unravel a mechanism decoding neural stem cell temporal gene expression and transforming it into discrete neuronal fates. This mechanism is characterized by hierarchical gene expression. First, Drosophila neuroblasts express opposing temporal gradients of RNA-binding proteins, Imp and Syp. These proteins promote or inhibit chinmo translation, yielding a descending neuronal gradient. Together, first and second-layer temporal factors define a temporal expression window of BTB-zinc finger nuclear protein, Mamo. The precise temporal induction of Mamo is achieved via both transcriptional and post-transcriptional regulation. Finally, Mamo is essential for the temporally defined, terminal identity of α'/β' mushroom body neurons and identity maintenance. We describe a straightforward paradigm of temporal fate specification where diverse neuronal fates are defined via integrating multiple layers of gene regulation. The neurodevelopmental roles of orthologous/related mammalian genes suggest a fundamental conservation of this mechanism in brain development.

Integrated clinical and omics approach to rare diseases: novel genes and oligogenic inheritance in holoprosencephaly

Holoprosencephaly is a pathology of forebrain development characterized by high phenotypic heterogeneity. The disease presents with various clinical manifestations at the cerebral or facial levels. Several genes have been implicated in holoprosencephaly but its genetic basis remains unclear: different transmission patterns have been described including autosomal dominant, recessive and digenic inheritance. Conventional molecular testing approaches result in a very low diagnostic yield and most cases remain unsolved. In our study, we address the possibility that genetically unsolved cases of holoprosencephaly present an oligogenic origin and result from combined inherited mutations in several genes. Twenty-six unrelated families, for whom no genetic cause of holoprosencephaly could be identified in clinical settings [whole exome sequencing and comparative genomic hybridization (CGH)-array analyses], were reanalysed under the hypothesis of oligogenic inheritance. Standard variant analysis was improved with a gene prioritization strategy based on clinical ontologies and gene co-expression networks. Clinical phenotyping and exploration of cross-species similarities were further performed on a family-by-family basis. Statistical validation was performed on 248 ancestrally similar control trios provided by the Genome of the Netherlands project and on 574 ancestrally matched controls provided by the French Exome Project. Variants of clinical interest were identified in 180 genes significantly associated with key pathways of forebrain development including sonic hedgehog (SHH) and primary cilia. Oligogenic events were observed in 10 families and involved both known and novel holoprosencephaly genes including recurrently mutated FAT1, NDST1, COL2A1 and SCUBE2. The incidence of oligogenic combinations was significantly higher in holoprosencephaly patients compared to two control populations (P < 10-9). We also show that depending on the affected genes, patients present with particular clinical features. This study reports novel disease genes and supports oligogenicity as clinically relevant model in holoprosencephaly. It also highlights key roles of SHH signalling and primary cilia in forebrain development. We hypothesize that distinction between different clinical manifestations of holoprosencephaly lies in the degree of overall functional impact on SHH signalling. Finally, we underline that integrating clinical phenotyping in genetic studies is a powerful tool to specify the clinical relevance of certain mutations.

Biallelic missense variants in ZBTB11 can cause intellectual disability in humans

Exploring genes and pathways underlying intellectual disability (ID) provides insight into brain development and function, clarifying the complex puzzle of how cognition develops. As part of ongoing systematic studies to identify candidate ID genes, linkage analysis and next-generation sequencing revealed Zinc Finger and BTB Domain Containing 11 (ZBTB11) as a novel candidate ID gene. ZBTB11 encodes a little-studied transcription regulator, and the two identified missense variants in this study are predicted to disrupt canonical Zn2+-binding residues of its C2H2 zinc finger domain, leading to possible altered DNA binding. Using HEK293T cells transfected with wild-type and mutant GFP-ZBTB11 constructs, we found the ZBTB11 mutants being excluded from the nucleolus, where the wild-type recombinant protein is predominantly localized. Pathway analysis applied to ChIP-seq data deposited in the ENCODE database supports the localization of ZBTB11 in nucleoli, highlighting associated pathways such as ribosomal RNA synthesis, ribosomal assembly, RNA modification and stress sensing, and provides a direct link between subcellular ZBTB11 location and its function. Furthermore, given the report of prominent brain and spinal cord degeneration in a zebrafish Zbtb11 mutant, we investigated ZBTB11-ortholog knockdown in Drosophila melanogaster brain by targeting RNAi using the UAS/Gal4 system. The observed approximate reduction to a third of the mushroom body size-possibly through neuronal reduction or degeneration-may affect neuronal circuits in the brain that are required for adaptive behavior, specifying the role of this gene in the nervous system. In conclusion, we report two ID families segregating ZBTB11 biallelic mutations disrupting Zn2+-binding motifs and provide functional evidence linking ZBTB11 dysfunction to this phenotype.

HIC1 deletion promotes breast cancer progression by activating tumor cell/fibroblast crosstalk

Breast cancer (BrCa) is the malignant tumor that most seriously threatens female health; however, the molecular mechanism underlying its progression remains unclear. Here, we found that conditional deletion of hypermethylated in cancer 1 (HIC1) in the mouse mammary gland might contribute to premalignant transformation in the early stage of tumor formation. Moreover, the chemokine (C-X-C motif) ligand 14 (CXCL14) secreted by HIC1-deleted BrCa cells bound to its cognate receptor GPR85 on mammary fibroblasts in the microenvironment and was responsible for activating these fibroblasts via the ERK1/2, Akt, and neddylation pathways, whereas the activated fibroblasts promoted BrCa progression via the induction of epithelial-mesenchymal transition (EMT) by the C-C chemokine ligand 17 (CCL17)/CC chemokine receptor 4 (CCR4) axis. Finally, we confirmed that the HIC1-CXCL14-CCL17 loop was associated with the malignant progression of BrCa. Therefore, the crosstalk between HIC1-deleted BrCa cells and mammary fibroblasts might play a critical role in BrCa development. Exploring the progression of BrCa from the perspective of microenvironment will be beneficial for identifying the potential prognostic markers of breast tumor and providing more effective treatment strategies.

Neurodevelopmental Genetic Diseases Associated With Microdeletions and Microduplications of Chromosome 17p13.3

Chromosome 17p13.3 is a region of genomic instability that is linked to different rare neurodevelopmental genetic diseases, depending on whether a deletion or duplication of the region has occurred. Chromosome microdeletions within 17p13.3 can result in either isolated lissencephaly sequence (ILS) or Miller-Dieker syndrome (MDS). Both conditions are associated with a smooth cerebral cortex, or lissencephaly, which leads to developmental delay, intellectual disability, and seizures. However, patients with MDS have larger deletions than patients with ILS, resulting in additional symptoms such as poor muscle tone, congenital anomalies, abnormal spasticity, and craniofacial dysmorphisms. In contrast to microdeletions in 17p13.3, recent studies have attracted considerable attention to a condition known as a 17p13.3 microduplication syndrome. Depending on the genes involved in their microduplication, patients with 17p13.3 microduplication syndrome may be categorized into either class I or class II. Individuals in class I have microduplications of the YWHAE gene encoding 14-3-3ε, as well as other genes in the region. However, the PAFAH1B1 gene encoding LIS1 is never duplicated in these patients. Class I microduplications generally result in learning disabilities, autism, and developmental delays, among other disorders. Individuals in class II always have microduplications of the PAFAH1B1 gene, which may include YWHAE and other genetic microduplications. Class II microduplications generally result in smaller body size, developmental delays, microcephaly, and other brain malformations. Here, we review the phenotypes associated with copy number variations (CNVs) of chromosome 17p13.3 and detail their developmental connection to particular microdeletions or microduplications. We also focus on existing single and double knockout mouse models that have been used to study human phenotypes, since the highly limited number of patients makes a study of these conditions difficult in humans. These models are also crucial for the study of brain development at a mechanistic level since this cannot be accomplished in humans. Finally, we emphasize the usefulness of the CRISPR/Cas9 system and next generation sequencing in the study of neurodevelopmental diseases.

The tumor suppressor Hic1 maintains chromosomal stability independent of Tp53

Hypermethylated-in-Cancer 1 (Hic1) is a tumor suppressor gene frequently inactivated by epigenetic silencing and loss-of-heterozygosity in a broad range of cancers. Loss of HIC1, a sequence-specific zinc finger transcriptional repressor, results in deregulation of genes that promote a malignant phenotype in a lineage-specific manner. In particular, upregulation of the HIC1 target gene SIRT1, a histone deacetylase, can promote tumor growth by inactivating TP53. An alternate line of evidence suggests that HIC1 can promote the repair of DNA double strand breaks through an interaction with MTA1, a component of the nucleosome remodeling and deacetylase (NuRD) complex. Using a conditional knockout mouse model of tumor initiation, we now show that inactivation of Hic1 results in cell cycle arrest, premature senescence, chromosomal instability and spontaneous transformation in vitro. This phenocopies the effects of deleting Brca1, a component of the homologous recombination DNA repair pathway, in mouse embryonic fibroblasts. These effects did not appear to be mediated by deregulation of Hic1 target gene expression or loss of Tp53 function, and rather support a role for Hic1 in maintaining genome integrity during sustained replicative stress. Loss of Hic1 function also cooperated with activation of oncogenic KRas in the adult airway epithelium of mice, resulting in the formation of highly pleomorphic adenocarcinomas with a micropapillary phenotype in vivo. These results suggest that loss of Hic1 expression in the early stages of tumor formation may contribute to malignant transformation through the acquisition of chromosomal instability.

Hypermethylated in cancer 1(HIC1) suppresses non-small cell lung cancer progression by targeting interleukin-6/Stat3 pathway

Non-small cell lung cancer (NSCLC), which accounts for more than 80% of lung cancers, is a leading cause of cancer mortality worldwide. However, the mechanism underlying its progression remains unclear. Here we found that HIC1 promoter was heavily methylated in NSCLC cell lines and tissues contributing to its low expression compared to normal controls. Restoring HIC1 expression inhibited migration, invasion and promoted inducible apoptosis of NSCLC cells. Notably, HIC1 is a tumor suppressor through inhibiting the transcription of IL-6 by sequence-specific binding on its promoter. Restoring IL-6 expression could partially rescue these phenotypes induced by HIC1 in vitro and in vivo. Mechanistic analyses show that autocrine secretion of IL-6 induced by loss of HIC1 activated STAT3 through IL-6/JAK pathway and was associated with NSCLC progression. The HIC1/IL-6 axis may serve as a prognostic biomarker and provide an attractive therapeutic target for NSCLC.

Genomic data illuminates demography, genetic structure and selection of a popular dog breed

BACKGROUND

Genomic methods have proved to be important tools in the analysis of genetic diversity across the range of species and can be used to reveal processes underlying both short- and long-term evolutionary change. This study applied genomic methods to investigate population structure and inbreeding in a common UK dog breed, the Labrador Retriever.

RESULTS

We found substantial within-breed genetic differentiation, which was associated with the role of the dog (i.e. working, pet, show) and also with coat colour (i.e. black, yellow, brown). There was little evidence of geographical differentiation. Highly differentiated genomic regions contained genes and markers associated with skull shape, suggesting that at least some of the differentiation is related to human-imposed selection on this trait. We also found that the total length of homozygous segments (runs of homozygosity, ROHs) was highly correlated with inbreeding coefficient.

CONCLUSIONS

This study demonstrates that high-density genomic data can be used to quantify genetic diversity and to decipher demographic and selection processes. Analysis of genetically differentiated regions in the UK Labrador Retriever population suggests the possibility of human-imposed selection on craniofacial characteristics. The high correlation between estimates of inbreeding from genomic and pedigree data for this breed demonstrates that genomic approaches can be used to quantify inbreeding levels in dogs, which will be particularly useful where pedigree information is missing.

Hypermethylation of the HIC1 promoter and aberrant expression of HIC1/SIRT1 contribute to the development of thyroid papillary carcinoma

Hypermethylation leading to the loss of hypermethylated in cancer-1 (HIC1) gene expression occurs in many different types of human cancer. HIC1 is a transcriptional repressor that directly binds to the promoter region of NAD-dependent deacetylase sirtuin-1 (SIRT1). SIRT1 functions in cell growth, is anti-apoptotic, protect neurons, functions in senescence, and regulates energy restriction. Epigenetic modification and dysregulation affecting the HIC1/SIRT1 axis is potentially important for the development of malignancies. However, the importance of HIC1 expression in the development of papillary thyroid carcinoma, especially in Chinese patients, is uncertain. Therefore, we assessed the level of methylation in the HIC1 promoter and the mRNA and protein expression levels of HIC1 and SIRT1 in human thyroid papillary carcinoma and tumor adjacent control tissues. The demethylation reagent 5-aza-2'-deoxyctidine (5-aza-dc) and an HIC1 overexpression plasmid were used to manipulate the HIC1/SIRT1 pathway, and the effects on cell senescence, apoptosis, and cell cycle progression were assessed. Compared to normal thyroid tissue, thyroid tumors had lower expression of HIC1 and higher SIRT1 expression. The level of HIC1 methylation was also higher in thyroid carcinoma tissues than adjacent tissues. HIC1 expression was closely correlated with patient age and tumor progression. Restoration of HIC1 expression through an overexpression plasmid or 5-aza-dC treatment reduced SIRT1 expression and cell proliferation, and led to senescence, cell cycle arrest, and apoptosis. Aberrant expression of HIC1/SIRT1 and hypermethylation of the HIC1 promoter may be critical for the development and progression of papillary thyroid cancer.

Determinants of orofacial clefting II: Effects of 5-Aza-2'-deoxycytidine on gene methylation during development of the first branchial arch

Defects in development of the secondary palate, which arise from the embryonic first branchial arch (1-BA), can cause cleft palate (CP). Administration of 5-Aza-2'-deoxycytidine (AzaD), a demethylating agent, to pregnant mice on gestational day 9.5 resulted in complete penetrance of CP in fetuses. Several genes critical for normal palatogenesis were found to be upregulated in 1-BA, 12h after AzaD exposure. MethylCap-Seq (MCS) analysis identified several differentially methylated regions (DMRs) in DNA extracted from AzaD-exposed 1-BAs. Hypomethylated DMRs did not correlate with the upregulation of genes in AzaD-exposed 1-BAs. However, most DMRs were associated with endogenous retroviral elements. Expression analyses suggested that interferon signaling was activated in AzaD-exposed 1-BAs. Our data, thus, suggest that a 12-h in utero AzaD exposure demethylates and activates endogenous retroviral elements in the 1-BA, thereby triggering an interferon-mediated response. This may result in the dysregulation of key signaling pathways during palatogenesis, causing CP.

HIC1 controls cellular- and HIV-1- gene transcription via interactions with CTIP2 and HMGA1

Among many cellular transcriptional regulators, Bcl11b/CTIP2 and HGMA1 have been described to control the establishment and the persistence of HIV-1 latency in microglial cells, the main viral reservoir in the brain. In this present work, we identify and characterize a transcription factor i.e. HIC1, which physically interacts with both Bcl11b/CTIP2 and HMGA1 to co-regulate specific subsets of cellular genes and the viral HIV-1 gene. Our results suggest that HIC1 represses Tat dependent HIV-1 transcription. Interestingly, this repression of Tat function is linked to HIC1 K314 acetylation status and to SIRT1 deacetylase activity. Finally, we show that HIC1 interacts and cooperates with HGMA1 to regulate Tat dependent HIV-1 transcription. Our results also suggest that HIC1 repression of Tat function happens in a TAR dependent manner and that this TAR element may serve as HIC1 reservoir at the viral promoter to facilitate HIC1/TAT interaction.

Post-mortem cytogenomic investigations in patients with congenital malformations

Congenital anomalies are the second highest cause of infant deaths, and, in most cases, diagnosis is a challenge. In this study, we characterize patterns of DNA copy number aberrations in different samples of post-mortem tissues from patients with congenital malformations. Twenty-eight patients undergoing autopsy were cytogenomically evaluated using several methods, specifically, Multiplex Ligation-dependent Probe Amplification (MLPA), microsatellite marker analysis with a MiniFiler kit, FISH, a cytogenomic array technique and bidirectional Sanger sequencing, which were performed on samples of different tissues (brain, heart, liver, skin and diaphragm) preserved in RNAlater, in formaldehyde or by paraffin-embedding. The results identified 13 patients with pathogenic copy number variations (CNVs). Of these, eight presented aneuploidies involving chromosomes 13, 18, 21, X and Y (two presented inter- and intra-tissue mosaicism). In addition, other abnormalities were found, including duplication of the TYMS gene (18p11.32); deletion of the CHL1 gene (3p26.3); deletion of the HIC1 gene (17p13.3); and deletion of the TOM1L2 gene (17p11.2). One patient had a pathogenic missense mutation of g.8535C>G (c.746C>G) in exon 7 of the FGFR3 gene consistent with Thanatophoric Dysplasia type I. Cytogenomic techniques were reliable for the analysis of autopsy material and allowed the identification of inter- and intra-tissue mosaicism and a better understanding of the pathogenesis of congenital malformations.

Rotational imaging optical coherence tomography for full-body mouse embryonic imaging

Optical coherence tomography (OCT) has been widely used to study mammalian embryonic development with the advantages of high spatial and temporal resolutions and without the need for any contrast enhancement probes. However, the limited imaging depth of traditional OCT might prohibit visualization of the full embryonic body. To overcome this limitation, we have developed a new methodology to enhance the imaging range of OCT in embryonic day (E) 9.5 and 10.5 mouse embryos using rotational imaging. Rotational imaging OCT (RI-OCT) enables full-body imaging of mouse embryos by performing multiangle imaging. A series of postprocessing procedures was performed on each cross-section image, resulting in the final composited image. The results demonstrate that RI-OCT is able to improve the visualization of internal mouse embryo structures as compared to conventional OCT.

De Novo Assembly of the Donkey White Blood Cell Transcriptome and a Comparative Analysis of Phenotype-Associated Genes between Donkeys and Horses

Prior to the mechanization of agriculture and labor-intensive tasks, humans used donkeys (Equus africanus asinus) for farm work and packing. However, as mechanization increased, donkeys have been increasingly raised for meat, milk, and fur in China. To maintain the development of the donkey industry, breeding programs should focus on traits related to these new uses. Compared to conventional marker-assisted breeding plans, genome- and transcriptome-based selection methods are more efficient and effective. To analyze the coding genes of the donkey genome, we assembled the transcriptome of donkey white blood cells de novo. Using transcriptomic deep-sequencing data, we identified 264,714 distinct donkey unigenes and predicted 38,949 protein fragments. We annotated the donkey unigenes by BLAST searches against the non-redundant (NR) protein database. We also compared the donkey protein sequences with those of the horse (E. caballus) and wild horse (E. przewalskii), and linked the donkey protein fragments with mammalian phenotypes. As the outer ear size of donkeys and horses are obviously different, we compared the outer ear size-associated proteins in donkeys and horses. We identified three ear size-associated proteins, HIC1, PRKRA, and KMT2A, with sequence differences among the donkey, horse, and wild horse loci. Since the donkey genome sequence has not been released, the de novo assembled donkey transcriptome is helpful for preliminary investigations of donkey cultivars and for genetic improvement.

HIC1 Tumor Suppressor Loss Potentiates TLR2/NF-κB Signaling and Promotes Tissue Damage-Associated Tumorigenesis

Hypermethylated in cancer 1 (HIC1) represents a prototypic tumor suppressor gene frequently inactivated by DNA methylation in many types of solid tumors. The gene encodes a sequence-specific transcriptional repressor controlling expression of several genes involved in cell cycle or stress control. In this study, a Hic1 allele was conditionally deleted, using a Cre/loxP system, to identify genes influenced by the loss of Hic1. One of the transcripts upregulated upon Hic1 ablation is the toll-like receptor 2 (TLR2). Tlr2 expression levels increased in Hic1-deficient mouse embryonic fibroblasts (MEF) and cultured intestinal organoids or in human cells upon HIC1 knockdown. In addition, HIC1 associated with the TLR2 gene regulatory elements, as detected by chromatin immunoprecipitation, indicating that Tlr2 indeed represents a direct Hic1 target. The Tlr2 receptor senses "danger" signals of microbial or endogenous origin to trigger multiple signaling pathways, including NF-κB signaling. Interestingly, Hic1 deficiency promoted NF-κB pathway activity not only in cells stimulated with Tlr2 ligand, but also in cells treated with NF-κB activators that stimulate different surface receptors. In the intestine, Hic1 is mainly expressed in differentiated epithelial cells and its ablation leads to increased Tlr2 production. Finally, in a chemical-induced mouse model of carcinogenesis, Hic1 absence resulted in larger Tlr2-positive colonic tumors that showed increased proportion of proliferating cells.

IMPLICATIONS

The tumor-suppressive function of Hic1 in colon is related to its inhibitory action on proproliferative signaling mediated by the Tlr2 receptor present on tumor cells.

HIC2 is a novel dosage-dependent regulator of cardiac development located within the distal 22q11 deletion syndrome region

RATIONALE

22q11 deletion syndrome arises from recombination between low-copy repeats on chromosome 22. Typical deletions result in hemizygosity for TBX1 associated with congenital cardiovascular disease. Deletions distal to the typically deleted region result in a similar cardiac phenotype but lack in extracardiac features of the syndrome, suggesting that a second haploinsufficient gene maps to this interval.

OBJECTIVE

The transcription factor HIC2 is lost in most distal deletions, as well as in a minority of typical deletions. We used mouse models to test the hypothesis that HIC2 hemizygosity causes congenital heart disease.

METHODS AND RESULTS

We created a genetrap mouse allele of Hic2. The genetrap reporter was expressed in the heart throughout the key stages of cardiac morphogenesis. Homozygosity for the genetrap allele was embryonic lethal before embryonic day E10.5, whereas the heterozygous condition exhibited a partially penetrant late lethality. One third of heterozygous embryos had a cardiac phenotype. MRI demonstrated a ventricular septal defect with over-riding aorta. Conditional targeting indicated a requirement for Hic2 within the Nkx2.5+ and Mesp1+ cardiovascular progenitor lineages. Microarray analysis revealed increased expression of Bmp10.

CONCLUSIONS

Our results demonstrate a novel role for Hic2 in cardiac development. Hic2 is the first gene within the distal 22q11 interval to have a demonstrated haploinsufficient cardiac phenotype in mice. Together our data suggest that HIC2 haploinsufficiency likely contributes to the cardiac defects seen in distal 22q11 deletion syndrome.

Ectodermal Wnt signaling regulates abdominal myogenesis during ventral body wall development

Defects of the ventral body wall are prevalent birth anomalies marked by deficiencies in body wall closure, hypoplasia of the abdominal musculature and multiple malformations across a gamut of organs. However, the mechanisms underlying ventral body wall defects remain elusive. Here, we investigated the role of Wnt signaling in ventral body wall development by inactivating Wls or β-catenin in murine abdominal ectoderm. The loss of Wls in the ventral epithelium, which blocks the secretion of Wnt proteins, resulted in dysgenesis of ventral musculature and genito-urinary tract during embryonic development. Molecular analyses revealed that the dermis and myogenic differentiation in the underlying mesenchymal progenitor cells was perturbed by the loss of ectodermal Wls. The activity of the Wnt-Pitx2 axis was impaired in the ventral mesenchyme of the mutant body wall, which partially accounted for the defects in ventral musculature formation. In contrast, epithelial depletion of β-catenin or Wnt5a did not resemble the body wall defects in the ectodermal Wls mutant. These findings indicate that ectodermal Wnt signaling instructs the underlying mesodermal specification and abdominal musculature formation during ventral body wall development, adding evidence to the theory that ectoderm-mesenchyme signaling is a potential unifying mechanism for the origin of ventral body wall defects.

The Reelin receptors ApoER2 and VLDLR are direct target genes of HIC1 (Hypermethylated In Cancer 1)

The tumor suppressor gene HIC1 (Hypermethylated In Cancer 1) is located in 17p13.3 a region frequently hypermethylated or deleted in tumors and in a contiguous-gene syndrome, the Miller-Dieker syndrome which includes classical lissencephaly (smooth brain) and severe developmental defects. HIC1 encodes a transcriptional repressor involved in the regulation of growth control, DNA damage response and cell migration properties. We previously demonstrated that the membrane-associated G-protein-coupled receptors CXCR7, ADRB2 and the tyrosine kinase receptor EphA2 are direct target genes of HIC1. Here we show that ectopic expression of HIC1 in U2OS and MDA-MB-231 cell lines decreases expression of the ApoER2 and VLDLR genes, encoding two canonical tyrosine kinase receptors for Reelin. Conversely, knock-down of endogenous HIC1 in BJ-Tert normal human fibroblasts through RNA interference results in the up-regulation of these two Reelin receptors. Finally, through chromatin immunoprecipitation (ChIP) in BJ-Tert fibroblasts, we demonstrate that HIC1 is a direct transcriptional repressor of ApoER2 and VLDLR. These data provide evidence that HIC1 is a new regulator of the Reelin pathway which is essential for the proper migration of neuronal precursors during the normal development of the cerebral cortex, of Purkinje cells in the cerebellum and of mammary epithelial cells. Deregulation of this pathway through HIC1 inactivation or deletion may contribute to its role in tumor promotion. Moreover, HIC1, through the direct transcriptional repression of ATOH1 and the Reelin receptors ApoER2 and VLDLR, could play an essential role in normal cerebellar development.

The duplication 17p13.3 phenotype: analysis of 21 families delineates developmental, behavioral and brain abnormalities, and rare variant phenotypes

Chromosome 17p13.3 is a gene rich region that when deleted is associated with the well-known Miller-Dieker syndrome. A recently described duplication syndrome involving this region has been associated with intellectual impairment, autism and occasional brain MRI abnormalities. We report 34 additional patients from 21 families to further delineate the clinical, neurological, behavioral, and brain imaging findings. We found a highly diverse phenotype with inter- and intrafamilial variability, especially in cognitive development. The most specific phenotype occurred in individuals with large duplications that include both the YWHAE and LIS1 genes. These patients had a relatively distinct facial phenotype and frequent structural brain abnormalities involving the corpus callosum, cerebellar vermis, and cranial base. Autism spectrum disorders were seen in a third of duplication probands, most commonly in those with duplications of YWHAE and flanking genes such as CRK. The typical neurobehavioral phenotype was usually seen in those with the larger duplications. We did not confirm the association of early overgrowth with involvement of YWHAE and CRK, or growth failure with duplications of LIS1. Older patients were often overweight. Three variant phenotypes included cleft lip/palate (CLP), split hand/foot with long bone deficiency (SHFLD), and a connective tissue phenotype resembling Marfan syndrome. The duplications in patients with clefts appear to disrupt ABR, while the SHFLD phenotype was associated with duplication of BHLHA9 as noted in two recent reports. The connective tissue phenotype did not have a convincing critical region. Our experience with this large cohort expands knowledge of this diverse duplication syndrome.

DNA double-strand breaks lead to activation of hypermethylated in cancer 1 (HIC1) by SUMOylation to regulate DNA repair

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene frequently epigenetically silenced in human cancers. HIC1 encodes a transcriptional repressor involved in the regulation of growth control and DNA damage response. We previously demonstrated that HIC1 can be either acetylated or SUMOylated on lysine 314. This deacetylation/SUMOylation switch is governed by an unusual complex made up of SIRT1 and HDAC4 which deacetylates and thereby favors SUMOylation of HIC1 by a mechanism not yet fully deciphered. This switch regulates the interaction of HIC1 with MTA1, a component of the NuRD complex and potentiates the repressor activity of HIC1. Here, we show that HIC1 silencing in human fibroblasts impacts the repair of DNA double-strand breaks whereas ectopic expression of wild-type HIC1, but not of nonsumoylatable mutants, leads to a reduced number of γH2AX foci induced by etoposide treatment. In this way, we demonstrate that DNA damage leads to (i) an enhanced HDAC4/Ubc9 interaction, (ii) the activation of SIRT1 by SUMOylation (Lys-734), and (iii) the SUMO-dependent recruitment of HDAC4 by SIRT1 which permits the deacetylation/SUMOylation switch of HIC1. Finally, we show that this increase of HIC1 SUMOylation favors the HIC1/MTA1 interaction, thus demonstrating that HIC1 regulates DNA repair in a SUMO-dependent way. Therefore, epigenetic HIC1 inactivation, which is an early step in tumorigenesis, could contribute to the accumulation of DNA mutations through impaired DNA repair and thus favor tumorigenesis.

Deciphering HIC1 control pathways to reveal new avenues in cancer therapeutics

INTRODUCTION

The tumor suppressor gene HIC1 (Hypermethylated in Cancer 1), which encodes a transcriptional repressor with multiple partners and multiple targets, is epigenetically silenced but not mutated in tumors. HIC1 has broad biological roles during normal development and is implicated in many canonical processes of cancer such as control of cell growth, cell survival upon genotoxic stress, cell migration, and motility.

AREAS COVERED

The HIC1 literature herein discussed includes its discovery as a candidate tumor suppressor gene hypermethylated or deleted in many human tumors, animal models establishing it as tumor suppressor gene, its role as a sequence-specific transcriptional repressor recruiting several chromatin regulatory complexes, its cognate target genes, and its functional roles in normal tissues. Finally, this review discusses how its loss of function contributes to the early steps in tumorigenesis.

EXPERT OPINION

Given HIC1's ability to direct repressive complexes to sequence-specific binding sites associated with its target genes, its loss results in specific changes in the transcriptional program of the cell. An understanding of this program through identification of HIC1's target genes and their involvement in feedback loops and cell process regulation will yield the ability to leverage this knowledge for therapeutic translation.

Developmentally programmed 3' CpG island methylation confers tissue- and cell-type-specific transcriptional activation

During development, a small but significant number of CpG islands (CGIs) become methylated. The timing of developmentally programmed CGI methylation and associated mechanisms of transcriptional regulation during cellular differentiation, however, remain poorly characterized. Here, we used genome-wide DNA methylation microarrays to identify epigenetic changes during human embryonic stem cell (hESC) differentiation. We discovered a group of CGIs associated with developmental genes that gain methylation after hESCs differentiate. Conversely, erasure of methylation was observed at the identified CGIs during subsequent reprogramming to induced pluripotent stem cells (iPSCs), further supporting a functional role for the CGI methylation. Both global gene expression profiling and quantitative reverse transcription-PCR (RT-PCR) validation indicated opposing effects of CGI methylation in transcriptional regulation during differentiation, with promoter CGI methylation repressing and 3' CGI methylation activating transcription. By studying diverse human tissues and mouse models, we further confirmed that developmentally programmed 3' CGI methylation confers tissue- and cell-type-specific gene activation in vivo. Importantly, luciferase reporter assays provided evidence that 3' CGI methylation regulates transcriptional activation via a CTCF-dependent enhancer-blocking mechanism. These findings expand the classic view of mammalian CGI methylation as a mechanism for transcriptional silencing and indicate a functional role for 3' CGI methylation in developmental gene regulation.

Cys2His2 zinc finger protein family: classification, functions, and major members

Cys2His2 (C2H2)-type zinc fingers are widespread DNA binding motifs in eukaryotic transcription factors. Zinc fingers are short protein motifs composed of two or three β-layers and one α-helix. Two cysteine and two histidine residues located in certain positions bind zinc to stabilize the structure. Four other amino acid residues localized in specific positions in the N-terminal region of the α-helix participate in DNA binding by interacting with hydrogen donors and acceptors exposed in the DNA major groove. The number of zinc fingers in a single protein can vary over a wide range, thus enabling variability of target DNA sequences. Besides DNA binding, zinc fingers can also provide protein-protein and RNA-protein interactions. For the most part, proteins containing the C2H2-type zinc fingers are trans regulators of gene expression that play an important role in cellular processes such as development, differentiation, and suppression of malignant cell transformation (oncosuppression).

Signification of Hypermethylated in Cancer 1 (HIC1) as Tumor Suppressor Gene in Tumor Progression

Hypermethylated in cancer 1(HIC1) was identified as a strong suppressor gene in chromosome region 17p13.3 telomeric to TP53. This gene encodes a transcriptional repressor and is ubiquitously expressed in normal tissues but downexpressed in different tumor tissues where it is hypermethylated. The hypermethylation of this chromosomal region leads to epigenetic inactivation of HIC1, which would prompt cancer cells to alter survival and signaling pathways or specific transcription factors during the period of tumorigenesis. In vitro, HIC1 function is mainly a sequence-specific transcriptional repressor interacting with a still growing range of histone deacetylase(HDAC)-dependent and HDAC-independent corepressor complexes. Furthermore, a role for HIC1 in tumor development is firmly supported by Hic1 deficient mouse model and two double heterozygote models cooperate with p53 and Ptch1. Notably, our findings suggest that potential factors derived from tumor microenviroment may play a role in modulating HIC1 expression in tumor cells by epigenetic modification, which is responsible for tumor progression. In this review, we will describe genomic and proteinic structure of HIC1, and summary the potential role of HIC1 in human various solid tumors and leukemia, and explore the influence of tumor microenviroment on inducing HIC1 expression in tumor cells.

The BTB-ZF transcription factors

The BTB-ZF (broad-complex, tramtrack and bric-à-brac--zinc finger) proteins are encoded by at least 49 genes in mouse and man and commonly serve as sequence-specific silencers of gene expression. This review will focus on the known physiological functions of mammalian BTB-ZF proteins, which include essential roles in the development of the immune system. We discuss their function in terminally differentiated lymphocytes and the progenitors that give rise to them, their action in hematopoietic malignancy and roles beyond the immune system.

Hypermethylated in cancer 1 (HIC1) recruits polycomb repressive complex 2 (PRC2) to a subset of its target genes through interaction with human polycomb-like (hPCL) proteins

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene epigenetically silenced or deleted in many human cancers. HIC1 is involved in regulatory loops modulating p53- and E2F1-dependent cell survival, growth control, and stress responses. HIC1 is also essential for normal development because Hic1-deficient mice die perinatally and exhibit gross developmental defects throughout the second half of development. HIC1 encodes a transcriptional repressor with five C(2)H(2) zinc fingers mediating sequence-specific DNA binding and two repression domains: an N-terminal BTB/POZ domain and a central region recruiting CtBP and NuRD complexes. By yeast two-hybrid screening, we identified the Polycomb-like protein hPCL3 as a novel co-repressor for HIC1. Using multiple biochemical strategies, we demonstrated that HIC1 interacts with hPCL3 and its paralog PHF1 to form a stable complex with the PRC2 members EZH2, EED, and Suz12. Confirming the implication of HIC1 in Polycomb recruitment, we showed that HIC1 shares some of its target genes with PRC2, including ATOH1. Depletion of HIC1 by siRNA interference leads to a partial displacement of EZH2 from the ATOH1 promoter. Furthermore, in vivo, ATOH1 repression by HIC1 is associated with Polycomb activity during mouse cerebellar development. Thus, our results identify HIC1 as the first transcription factor in mammals able to recruit PRC2 to some target promoters through its interaction with Polycomb-like proteins.