Essential roles of Gli3 and sonic hedgehog in pattern formation and developmental anomalies caused by their dysfunction

A novel GLI3 frameshift mutation in a Chinese pedigree with polydactyly: A case report

Background

GLI3 gene mutations can result in various forms of polysyndactyly, such as Greig cephalopolysyndactyly syndrome (GCPS, MIM: #175700), Pallister-Hall syndrome (PHS, MIM: #146510), and isolated polydactyly (IPD, MIM: #174200, #174700). Reports on IPD-associated GLI3 mutations are rare. In this study, a novel GLI3 mutation was identified in a Chinese family with IPD.

Results

We report a family with six members affected by IPD. The family members demonstrated several special phenotypes, including sex differences, abnormal finger joint development, and different polydactyly types. We identified a novel frameshift variant in the GLI3 gene (NM_000168.6: c.1820_1821del, NP_000159.3: p.Tyr607Cysfs*9) by whole-exome sequencing. Further analysis suggested that this mutation was the cause of polydactyly in this family.

Conclusions

The discovery of this novel frameshift variant in our study further solidifies the relationship between IPD and GLI3 and expands the previously established spectrum of GLI3 mutations and associated phenotypes.

A reversible state of hypometabolism in a human cellular model of sporadic Parkinson's disease

Sporadic Parkinson's Disease (sPD) is a progressive neurodegenerative disorder caused by multiple genetic and environmental factors. Mitochondrial dysfunction is one contributing factor, but its role at different stages of disease progression is not fully understood. Here, we showed that neural precursor cells and dopaminergic neurons derived from induced pluripotent stem cells (hiPSCs) from sPD patients exhibited a hypometabolism. Further analysis based on transcriptomics, proteomics, and metabolomics identified the citric acid cycle, specifically the α-ketoglutarate dehydrogenase complex (OGDHC), as bottleneck in sPD metabolism. A follow-up study of the patients approximately 10 years after initial biopsy demonstrated a correlation between OGDHC activity in our cellular model and the disease progression. In addition, the alterations in cellular metabolism observed in our cellular model were restored by interfering with the enhanced SHH signal transduction in sPD. Thus, inhibiting overactive SHH signaling may have potential as neuroprotective therapy during early stages of sPD.

A novel variant of GLI3, p.Asp1514Thrfs*5, is identified in a Chinese family affected by polydactyly

Background

Polydactyly is a common congenital malformation characterized by the presence of supernumerary fingers or toes. In this case study, we sought to identify the causative pathogenic factor in a family from a northern region of China affected by non‐syndromic postaxial polydactyly (PAP).

Methods

After recruiting a three‐generation family with PAP, whole‐exome sequencing was performed to identify the causative variant. In silico analysis and Sanger sequencing were used to validate the variant.

Results

We identified a novel heterozygous frameshift variant (NM_000168.6:c.4540delG, p.Asp1514Thrfs*5) in the transcriptional activator (TA1) domain of the GLI3 gene.

Conclusion

The novel frameshift variant identified in this study further confirms the relationship between non‐syndromic PAP and GLI3 and extends the previously established mutational and phenotypic spectra of GLI3.

Androgen/Wnt/β-catenin signal axis augments cell proliferation of the mouse erectile tissue, corpus cavernosum

The murine penile erectile tissues including corpus cavernosum (CC) are composed of blood vessels, smooth muscle, and connective tissue, showing marked sexual differences. It has been known that the androgens are required for sexually dimorphic organogenesis. It is however unknown about the features of androgen signaling during mouse CC development. It is also unclear how androgen-driven downstream factors are involved such processes. In the current study, we analyzed the onset of sexually dimorphic CC formation based on histological analyses, the dynamics of androgen receptor (AR) expression, and regulation of cell proliferation. Of note, we identified Dickkopf-related protein 2 (Dkk2), an inhibitor of β-catenin signaling, was predominantly expressed in female CC compared with male. Furthermore, administration of androgens resulted in activation of β-catenin signaling. We have found the Sox9 gene, one of the essential markers for chondrocyte, was specifically expressed in the developing CC. Hence, we utilized CC-specific, Sox9 ^CreERT2 , β-catenin conditional mutant mice. Such mutant mice showed defective cell proliferation. Furthermore, introduction of activated form of β-catenin mutation (gain of function mutation for Wnt/β-catenin signaling) in CC induced augmented cell proliferation. Altogether, we revealed androgen-Wnt/β-catenin signal dependent cell proliferation was essential for sexually dimorphic CC formation. These findings open new avenues for understanding developmental mechanisms of androgen-dependent cell proliferation during sexual differentiation.

A Novel Frameshift Mutation of GLI3 Causes Isolated Postaxial Polydactyly

BACKGROUND

GLI3 encodes a transcription factor in the sonic hedgehog signaling pathway, which is essential in regulating the human limb bud development, especially on the anteroposterior axis. Mutations in GLI3 have been confirmed to be associated with various human congenital malformations, including Greig cephalopolysyndactyly syndrome, Pallister-Hall syndrome, and isolated polydactyly. A robust gene-phenotype relationship between GLI3 and Greig cephalopolysyndactyly syndrome and Pallister-Hall syndrome has been well elucidated, and less is known about GLI3 mutation-caused isolated polydactyly. This study intended to perform a mutation analysis of GLl3 in a family with isolated polydactyly.

METHODS

A 3-generation Chinese family with 19 members was recruited in this study, of which the proband and her mother were affected with polydactyly. The whole-exon sequencing was performed to find mutations, and Sanger sequencing was performed to validate the mutations.

RESULTS

We found a novel heterozygous frameshift mutation of GLI3 (c.1180C > TT, p.P394fs18x) in the proband of a Chinese family with isolated postaxial polydactyly. No mutation was detected in the proband's father or another 2 patients with sporadic preaxial polydactyly.

CONCLUSIONS

By systematically reviewing the gene-phenotype relationship, we found that GLI3 p.P394fs18x mutation might be specific for isolated postaxial polydactyly.

Novel GLI3 variant causes Greig cephalopolysyndactyly syndrome in three generations of a Lithuanian family

Background

Preaxial polydactyly type IV, also referred as polysyndactyly, has been described in a few syndromes. We present three generations of a family with preaxial polydactyly type IV and other clinical features of Greig cephalopolysyndactyly syndrome (GCPS).

Methods and results

Sequencing analysis of the GLI3 coding region identified a novel donor splice site variant NC_000007.14(NM_000168.6):c.473+3A>T in the proband and the same pathogenic variant was subsequently identified in other affected family members. Functional analysis based on Sanger sequencing of the proband's complementary DNA (cDNA) sample revealed that the splice site variant c.473+3A>T disrupts the original donor splice site, thus leading to exon 4 skipping. Based on further in silico analysis, this pathogenic splice site variant consequently results in a truncated protein NP_000159.3:p.(His123Argfs*57), which lacks almost all functionally important domains. Therefore, functional cDNA analysis confirmed that the haploinsufficiency of the GLI3 is the cause of GCPS in the affected family members.

Conclusion

Despite the evidence provided, pathogenic variants in the GLI3 do not always definitely correlate with syndromic or nonsyndromic clinical phenotypes associated with this gene. For this reason, further transcriptomic and proteomic evaluation could be suggested.

Novel GLI3 variant causing overlapped Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS) phenotype with agenesis of gallbladder and pancreas

Background

A proper balance between the activator and the repressor form of GLI3, a zinc-finger transcription factor downstream of hedgehog signaling, is essential for proper development of various organs during development. Mutations in different domains of the GLI3 gene underlie several congenital diseases including Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS).

Case presentation

Here, we describe the case of an overlapped phenotype of these syndromes with agenesis of the gallbladder and the pancreas, bearing a c.2155 C > T novel likely pathogenic variant of GLI3 gene by missense point mutation causing p.P719S at the proteolytic cleavage site.

Conclusions

Although agenesis of the gallbladder and the pancreas is uncommon in GLI3 morphopathy, a slight difference in the gradient or the balance between activator and repressor in this case may hinder sophisticated spatial and sequential hedgehog signaling that is essential for proper development of gallbladder and pancreas from endodermal buds.

GLI3 mutations in syndromic and non-syndromic polydactyly in two Indian families

The GLI3 protein is a zinc finger transcription factor, expressed early in development. The GLI3 gene exhibits allelic heterogeneity as mutations in this gene are associated with several developmental syndromic and non-syndromic polydactyly. The present study reports two cases: first, a familial case of Greig Cephalopolysyndactyly Syndrome (GCPS); the second is a sporadic case with both postaxial polydactyly (PAP) type A and B. Resequencing of GLI3 gene reveals a previously reported nonsense truncation mutation g.42007251G > A (p.R792X; rs121917714) in the GCPS family and a novel single nucleotide insertion g.42004239_42004240insA (p.E1478X) in the sporadic case of postaxial polydactyly (PAP). Both nonsense truncation mutations; p.R792X (GCPS) and p.E1478X (PAP) introduce a premature stop codon leading to loss of C-terminal domains.

A novel GLI3 mutation affecting the zinc finger domain leads to preaxial-postaxial polydactyly-syndactyly complex

BACKGROUND

Polydactyly is a highly common congenital limb defect. Extra digits may appear as an isolated anomaly or as a part of a syndrome. Mutations in GLI3 have been shown to cause Greig cephalopolysyndactyly, Pallister-Hall syndrome and non-syndromic polydactyly. Genotype-phenotype correlation studies of GLI3 mutations suggest a model by which mutations in the zinc-finger domain (ZFD) of GLI3 likely lead to syndromic polydactyly. Here we describe a rare case of autosomal dominant heterozygous missense mutation in the ZFD of GLI3 leading to a variable polydactyly-syndactyly complex.

CASE PRESENTATION

A large Jewish Moroccan family presented with apparently autosomal dominant heredity of bilateral thumb polydactyly in hands and feet combined with post-axial polydactyly type B or type A. Syndactyly was evident in most patients' hands and feet. Apart from head circumference beyond 90th percentile in some of the affected individuals, none had craniofacial dysmorphism. A novel GLI3 c.1802A > G (p.His601Arg) mutation was found in all affected individuals.

CONCLUSION

We demonstrate that a mutation in the ZFD domain of GLI3 leads to phenotypic variability, including an isolated limb phenotype. Thus, the variability in phenotypes caused by mutations in this master developmental regulator is more profound than has been previously suggested.

CSN-mediated deneddylation differentially modulates Ci(155) proteolysis to promote Hedgehog signalling responses

The Hedgehog (Hh) morphogen directs distinct cell responses according to its distinct signalling levels. Hh signalling stabilizes transcription factor cubitus interruptus (Ci) by prohibiting SCF^Slimb-dependent ubiquitylation and proteolysis of Ci. How graded Hh signalling confers differential SCF^Slimb-mediated Ci proteolysis in responding cells remains unclear. Here, we show that in COP9 signalosome (CSN) mutants, in which deneddylation of SCF^Slimb is inactivated, Ci is destabilized in low-to-intermediate Hh signalling cells. As a consequence, expression of the low-threshold Hh target gene dpp is disrupted, highlighting the critical role of CSN deneddylation on low-to-intermediate Hh signalling response. The status of Ci phosphorylation and the level of E1 ubiquitin-activating enzyme are tightly coupled to this CSN regulation. We propose that the affinity of substrate–E3 interaction, ligase activity and E1 activity are three major determinants for substrate ubiquitylation and thereby substrate degradation in vivo.

Hedgehog signalling gradients are required for proper wing formation in Drosophila, and Hedgehog is known to regulate the cubitus interruptus transcription factor. Here, the authors show that the COP9 signalosome has a critical role in translating a Hedgehog gradient into a cubitus interruptus gradient.

Ontogenetic expression of sonic hedgehog in the chicken subpallium

Sonic hedgehog (SHH) is a secreted signaling factor that is implicated in the molecular patterning of the central nervous system (CNS), somites, and limbs in vertebrates. SHH has a crucial role in the generation of ventral cell types along the entire rostrocaudal axis of the neural tube. It is secreted early in development by the axial mesoderm (prechordal plate and notochord) and the overlying ventral neural tube. Recent studies clarified the impact of SHH signaling mechanisms on dorsoventral patterning of the spinal cord, but the corresponding phenomena in the rostral forebrain are slightly different and more complex. This notably involves separate Shh expression in the preoptic part of the forebrain alar plate, as well as in the hypothalamic floor and basal plates. The present work includes a detailed spatiotemporal description of the singular alar Shh expression pattern in the rostral preoptic forebrain of chick embryos, comparing it with FoxG1, Dlx5, Nkx2.1, and Nkx2.2 mRNA expression at diverse stages of development. As a result of this mapping, we report a subdivision of the preoptic region in dorsal and ventral zones; only the dorsal part shows Shh expression. The positive area impinges as well upon a median septocommissural preoptic domain. Our study strongly suggests tangential migration of Shh-positive cells from the preoptic region into other subpallial domains, particularly into the pallidal mantle and the intermediate septum.

The Hedgehog transcription factor Gli3 modulates angiogenesis

RATIONALE

The Gli transcription factors are mediators of Hedgehog (Hh) signaling and have been shown to play critical roles during embryogenesis. Previously, we have demonstrated that the Hh pathway is reactivated by ischemia in adult mammals, and that this pathway can be stimulated for therapeutic benefit; however, the specific roles of the Gli transcription factors during ischemia-induced Hh signaling have not been elucidated.

OBJECTIVE

To investigate the role of Gli3 in ischemic tissue repair.

METHODS AND RESULTS

Gli3-haploinsufficient (Gli3(+/-)) mice and their wild-type littermates were physiologically similar in the absence of ischemia; however, histological assessments of capillary density and echocardiographic measurements of left ventricular ejection fractions were reduced in Gli3(+/-) mice compared to wild-type mice after surgically induced myocardial infarction, and fibrosis was increased. Gli3-deficient mice also displayed reduced capillary density after induction of hindlimb ischemia and an impaired angiogenic response to vascular endothelial growth factor in the corneal angiogenesis model. In endothelial cells, adenovirus-mediated overexpression of Gli3 promoted migration (modified Boyden chamber), small interfering RNA-mediated downregulation of Gli3 delayed tube formation (Matrigel), and Western analyses identified increases in Akt phosphorylation, extracellular signal-regulated kinase (ERK)1/2 activation, and c-Fos expression; however, promoter-reporter assays indicated that Gli3 overexpression does not modulate Gli-dependent transcription. Furthermore, the induction of endothelial cell migration by Gli3 was dependent on Akt and ERK1/2 activation.

CONCLUSIONS

Collectively, these observations indicate that Gli3 contributes to vessel growth under both ischemic and nonischemic conditions and provide the first evidence that Gli3 regulates angiogenesis and endothelial cell activity in adult mammals.

Shadows of complexity: what biological networks reveal about epistasis and pleiotropy

Pleiotropy, in which one mutation causes multiple phenotypes, has traditionally been seen as a deviation from the conventional observation in which one gene affects one phenotype. Epistasis, or gene-gene interaction, has also been treated as an exception to the Mendelian one gene-one phenotype paradigm. This simplified perspective belies the pervasive complexity of biology and hinders progress toward a deeper understanding of biological systems. We assert that epistasis and pleiotropy are not isolated occurrences, but ubiquitous and inherent properties of biomolecular networks. These phenomena should not be treated as exceptions, but rather as fundamental components of genetic analyses. A systems level understanding of epistasis and pleiotropy is, therefore, critical to furthering our understanding of human genetics and its contribution to common human disease. Finally, graph theory offers an intuitive and powerful set of tools with which to study the network bases of these important genetic phenomena.

Mutations in BMP4 cause eye, brain, and digit developmental anomalies: overlap between the BMP4 and hedgehog signaling pathways

Developmental ocular malformations, including anophthalmia-microphthalmia (AM), are heterogeneous disorders with frequent sporadic or non-Mendelian inheritance. Recurrent interstitial deletions of 14q22-q23 have been associated with AM, sometimes with poly/syndactyly and hypopituitarism. We identify two further cases of AM (one with associated pituitary anomalies) with a 14q22-q23 deletion. Using a positional candidate gene approach, we analyzed the BMP4 (Bone Morphogenetic Protein-4) gene and identified a frameshift mutation (c.226del2, p.S76fs104X) that segregated with AM, retinal dystrophy, myopia, brain anomalies, and polydactyly in a family and a nonconservative missense mutation (c.278A-->G, p.E93G) in a highly conserved base in another family. MR imaging and tractography in the c.226del2 proband revealed a primary brain developmental disorder affecting thalamostriatal and callosal pathways, also present in the affected grandmother. Using in situ hybridization in human embryos, we demonstrate expression of BMP4 in optic vesicle, developing retina and lens, pituitary region, and digits strongly supporting BMP4 as a causative gene for AM, pituitary, and poly/syndactyly. Because BMP4 interacts with HH signaling genes in animals, we evaluated gene expression in human embryos and demonstrate cotemporal and cospatial expression of BMP4 and HH signaling genes. We also identified four cases, some of whom had retinal dystrophy, with "low-penetrant" mutations in both BMP4 and HH signaling genes: SHH (Sonic Hedgehog) or PTCH1 (Patched). We propose that BMP4 is a major gene for AM and/or retinal dystrophy and brain anomalies and may be a candidate gene for myopia and poly/syndactyly. Our finding of low-penetrant variants in BMP4 and HH signaling partners is suggestive of an interaction between the two pathways in humans.

Perturbation of retinoic acid (RA)-mediated limb development suggests a role for diminished RA signaling in the teratogenesis of ethanol

BACKGROUND

A proposed mechanism for ethanol teratogenicity entails ethanol-mediated reductions in retinoic acid (RA). This premise was investigated utilizing a mouse model, with limb reduction defects as the teratogenic end point.

METHODS

Ethanol, Disulfiram, or BMS-189453 was administered to C57BL/6J mice on the 9(th) day of pregnancy. Forelimb morphology was assessed on gestation day 18 using Alcian blue and Alizarin red staining. Nile blue sulfate or LysoTracker Red (LTR) vital staining identified cell death in the limb bud. The ability of RA to prevent ethanol-induced cell death was assessed by coadministration followed by laser scanning confocal microscopic examination of LTR-staining. In situ hybridization and qPCR were used to examine gene expression in treated limb buds.

RESULTS

Ethanol, Disulfiram, and BMS-189453 resulted in postaxial ectrodactyly, intermediate ectrodactyly, and other digital defects. Excessive Nile blue sulfate staining was evident in the presumptive AER following each of the three exposures. Ethanol-induced LTR staining was prevented by RA supplementation. Both in situ hybridization and qPCR illustrated decreases in Shh and Tbx5 in ethanol-exposed embryos as compared to control.

CONCLUSIONS

Contrary to studies of prolonged RA deficiency, acute exposure to functional antagonists of RA results in limb defects that are morphologically similar to those caused by ethanol. The rescue of ethanol-induced cell death by RA and similar changes in Shh transcription further suggest that RA contributes to ethanol-induced limb dysmorphology. Moreover, the repression of key mediators of limb development soon after ethanol exposure adds to the existing knowledge of the pathogenic effects of ethanol.

Emerging roles for zic genes in early development

Members of the Zic family of zinc finger transcription factors play critical roles in a variety of developmental processes. They are involved in development of neural tissues and the neural crest, in left-right axis patterning, in somite development, and in formation of the cerebellum. In addition to their roles in cell-fate specification, zic genes also promote cell proliferation. Further, they are expressed in postmitotic cells of the cerebellum and in retinal ganglion cells. Efforts to determine the role of individual zic genes within an array of developmental and cellular processes are complicated by overlapping patterns of zic gene expression and strong sequence conservation within this gene family. Nevertheless, substantial progress has been made. This review summarizes our knowledge of the molecular events that govern the activities of zic family members, including emerging relationships between upstream signaling pathways and zic genes. In addition, advancements in our understanding of the molecular events downstream of Zic transcription factors are reviewed. Despite significant progress, however, much remains to be learned regarding the mechanisms through which zic genes exert their function in a variety of different contexts.