Identification of NKL, a novel Gli-Kruppel zinc-finger protein that promotes neuronal differentiation

Postnatal zinc deficiency due to giardiasis disrupts hippocampal and cerebellar development

BACKGROUND

Giardiasis and zinc deficiency have been identified as serious health problems worldwide. Although Zn depletion is known to occur in giardiasis, no work has investigated whether changes occur in brain structures.

METHODS

Three groups of gerbils were used: control (1), orogastrically inoculated on day 3 after birth with trophozoites of two isolates of Giardia intestinalis (HGINV/WB) group (2 and 3). Estimates were made at five ages covering: establishment of infection, Giardia population growth, natural parasite clearance and a post-infection age. QuantiChrome zinc assay kit, cresyl violet staining and TUNEL technique were used.

RESULTS

A significant decrease (p<0.01) in tissue zinc was observed and persisted after infection. Cytoarchitectural changes were observed in 75% of gerbils in the HGINV or WB groups. Ectopic pyramidal neurons were found in the cornus ammonis (CA1-CA3). At 60 and 90 days of age loss of lamination was clearly visible in CA1. In the dentate gyrus (DG), thinning of the dorsal lamina and abnormal thickening of the ventral lamina were observed from 30 days of age. In the cerebellum, we found an increase (p<0.01) in the thickness of the external granular layer (EGL) at 14 days of age that persisted until day 21 (C 3 ± 0.3 μm; HGINV 37 ± 5 μm; WB 28 ± 3 μm); Purkinje cell population estimation showed a significant decrease; a large number of apoptotic somas were observed scattered in the molecular layer; in 60 and 90 days old gerbils we found granular cell heterotopia and Purkinje cell ectopia. The pattern of apoptosis was different in the cerebellum and hippocampus of parasitized gerbils.

CONCLUSION

The morphological changes found suggest that neuronal migration is affected by zinc depletion caused by giardiasis in early postnatal life; for the first time, the link between giardiasis-zinc depletion and damaged brain structures is shown. This damage may explain the psychomotor/cognitive delay associated with giardiasis. These findings are alarming. Alterations in zinc metabolism and signalling are known to be involved in many brain disorders, including autism.

Identification of molecular signatures and pathways involved in Rett syndrome using a multi-omics approach

BACKGROUND

Rett syndrome (RTT) is a neurodevelopmental disorder mainly caused by mutations in the methyl-CpG-binding protein 2 gene (MECP2). MeCP2 is a multi-functional protein involved in many cellular processes, but the mechanisms by which its dysfunction causes disease are not fully understood. The duplication of the MECP2 gene causes a distinct disorder called MECP2 duplication syndrome (MDS), highlighting the importance of tightly regulating its dosage for proper cellular function. Additionally, some patients with mutations in genes other than MECP2 exhibit phenotypic similarities with RTT, indicating that these genes may also play a role in similar cellular functions. The purpose of this study was to characterise the molecular alterations in patients with RTT in order to identify potential biomarkers or therapeutic targets for this disorder.

METHODS

We used a combination of transcriptomics (RNAseq) and proteomics (TMT mass spectrometry) to characterise the expression patterns in fibroblast cell lines from 22 patients with RTT and detected mutation in MECP2, 15 patients with MDS, 12 patients with RTT-like phenotypes and 13 healthy controls. Transcriptomics and proteomics data were used to identify differentially expressed genes at both RNA and protein levels, which were further inspected via enrichment and upstream regulator analyses and compared to find shared features in patients with RTT.

RESULTS

We identified molecular alterations in cellular functions and pathways that may contribute to the disease phenotype in patients with RTT, such as deregulated cytoskeletal components, vesicular transport elements, ribosomal subunits and mRNA processing machinery. We also compared RTT expression profiles with those of MDS seeking changes in opposite directions that could lead to the identification of MeCP2 direct targets. Some of the deregulated transcripts and proteins were consistently affected in patients with RTT-like phenotypes, revealing potentially relevant molecular processes in patients with overlapping traits and different genetic aetiology.

CONCLUSIONS

The integration of data in a multi-omics analysis has helped to interpret the molecular consequences of MECP2 dysfunction, contributing to the characterisation of the molecular landscape in patients with RTT. The comparison with MDS provides knowledge of MeCP2 direct targets, whilst the correlation with RTT-like phenotypes highlights processes potentially contributing to the pathomechanism leading these disorders.

Juvenile hormone upregulates sugarbabe for vitellogenesis and egg development in the migratory locust Locusta migratoria

Sugarbabe is a C₂ H₂ zinc-finger transcription factor that is sensitive to sugar and essential for lipid biosynthesis in larvae of Drosophila melanogaster. However, the role of Sugarbabe in adult insect development remains unexplored. Vitellogenesis is a nutrient-dependent process that is promoted by juvenile hormone (JH) in many insect species. Here, we cloned an ortholog gene of D. melanogaster Sugarbabe (DmSug) in the migratory locust Locusta migratoria. The locust Sugarbabe (LmSug) has five C₂ H₂ zinc-finger motifs similar to DmSug. LmSug was expressed at a low level in adult female locusts raised under poor nutrient conditions. JH treatment increased the expression level of LmSug. Knockdown of the JH receptor gene Met caused a reduction of LmSug expression. Depletion of the LmSug transcript level caused a significant reduction in vitellogenin expression in the fat body, resulting in impaired oocyte development and ovary growth. The results suggest that LmSug is expressed in response to JH, and plays an essential role in female insect reproduction.

Comprehensive Transcriptome Profiling of Cryptic CBFA2T3-GLIS2 Fusion-Positive AML Defines Novel Therapeutic Options: A COG and TARGET Pediatric AML Study

PURPOSE

A cryptic inv(16)(p13.3q24.3) encoding the CBFA2T3-GLIS2 fusion is associated with poor outcome in infants with acute megakaryocytic leukemia. We aimed to broaden our understanding of the pathogenesis of this fusion through transcriptome profiling.

EXPERIMENTAL DESIGN

Available RNA from children and young adults with de novo acute myeloid leukemia (AML; N = 1,049) underwent transcriptome sequencing (mRNA and miRNA). Transcriptome profiles for those with the CBFA2T3-GLIS2 fusion (N = 24) and without (N = 1,025) were contrasted to define fusion-specific miRNAs, genes, and pathways. Clinical annotations defined distinct fusion-associated disease characteristics and outcomes.

RESULTS

The CBFA2T3-GLIS2 fusion was restricted to infants <3 years old (P < 0.001), and the presence of this fusion was highly associated with adverse outcome (P < 0.001) across all morphologic classifications. Further, there was a striking paucity of recurrent cooperating mutations, and transduction of cord blood stem cells with this fusion was sufficient for malignant transformation. CBFA2T3-GLIS2 positive cases displayed marked upregulation of genes with cell membrane/extracellular matrix localization potential, including NCAM1 and GABRE. Additionally, miRNA profiling revealed significant overexpression of mature miR-224 and miR-452, which are intronic miRNAs transcribed from the GABRE locus. Gene-set enrichment identified dysregulated Hippo, TGFβ, and hedgehog signaling, as well as NCAM1 (CD56) interaction pathways. Therapeutic targeting of fusion-positive leukemic cells with CD56-directed antibody-drug conjugate caused significant cytotoxicity in leukemic blasts.

CONCLUSIONS

The CBFA2T3-GLIS2 fusion defines a highly refractory entity limited to infants that appears to be sufficient for malignant transformation. Transcriptome profiling elucidated several highly targetable genes and pathways, including the identification of CD56, providing a highly plausible target for therapeutic intervention.

Emerging Roles of GLI-Similar Krüppel-like Zinc Finger Transcription Factors in Leukemia and Other Cancers

GLI-similar 1-3 (GLIS1-3), a subfamily of Krüppel-like zinc finger transcription factors, function as key regulators of several biological processes important to oncogenesis, including control of cell proliferation, differentiation, self-renewal, and epithelial-mesenchymal transition. This review provides a short overview of the critical roles genetic changes in GLIS1-3 play in the development of several malignancies. This includes intrachromosomal translocations involving GLIS2 and ETO2/CBFA2T3 in the development of pediatric non-Down's syndrome (DS), acute megakaryoblastic leukemia (AMKL), a malignancy with poor prognosis, and an association of interchromosomal translocations between GLIS3, GLIS1, and PAX8, and between GLIS3 and CLPTM1L with hyalinizing trabecular tumors (HTTs) and fibrolamellar hepatocellular carcinoma (FHCC), respectively. Targeting upstream signaling pathways that regulate GLIS signaling may offer new therapeutic strategies in the management of cancer.

The changing scenario of non-Down syndrome acute megakaryoblastic leukemia in children

Pediatric non-Down-syndrome acute megakaryoblastic leukemia (non-DS-AMKL) is a heterogeneous subtype of leukemia that has historically been associated with poor prognosis. Until the advent of large-scale genomic sequencing, the management of patients with non-DS-AMKL was very difficult due to the absence of reliable biological prognostic markers. The sequencing of large cohort of pediatric non-DS-AMKL samples led to the discovery of novel genetic aberrations, including high-frequency fusions, such as CBFA2T3-GLIS2 and NUP98-KDM5 A, as well as less frequent aberrations, such as HOX rearrangements. These new insights into the genetic landscape of pediatric non-DS-AMKL has allowed refining the risk-group stratification, leading to important changes in the prognostic scenario of these patients. This review summarizes the most important molecular pathogenic mechanisms of pediatric non-DS-AMKL. A critical discussion on how novel genetic abnormalities have refined the risk profile assessment and changed the management of these patients in clinical practice is also provided.

CBFA2T3-GLIS2-positive acute myeloid leukaemia. A peculiar paediatric entity

The scenario of paediatric acute myeloid leukaemia (AML), particularly non‐Down syndrome acute megakaryoblastic leukaemia (non‐DS‐AMKL), has been recently revolutionized by the advent of large‐scale, genomic sequencing technologies. In this changing landscape, a significantly relevant discovery has been represented by the identification of the CBFA2T3‐GLIS2 fusion gene, which is the result of a cryptic inversion of chromosome 16. It is the most frequent chimeric oncogene identified to date in non‐DS‐AMKL, although it seems not to be exclusively restricted to the French‐American‐British M7 subgroup. The CBFA2T3‐GLIS2 fusion gene characterizes a subtype of leukaemia that is specific to paediatrics, having never been identified in adults. It characterizes an extremely aggressive leukaemia, as the presence of this fusion is associated with a grim outcome in almost all of the case series reported, with overall survival rates ranging between 15% and 30%. Although the molecular basis that underlies this leukaemia subtype is still far from being completely elucidated, unique functional properties induced by CBFA2T3‐GLIS2 in the leukaemogenesis driving process have been recently identified. We here review the peculiarities of CBFA2T3‐GLIS2‐positive AML, describing its intriguing clinical and biological behaviour and providing some challenging targeting opportunities.

GLIS1-3 transcription factors: critical roles in the regulation of multiple physiological processes and diseases

Krüppel-like zinc finger proteins form one of the largest families of transcription factors. They function as key regulators of embryonic development and a wide range of other physiological processes, and are implicated in a variety of pathologies. GLI-similar 1-3 (GLIS1-3) constitute a subfamily of Krüppel-like zinc finger proteins that act either as activators or repressors of gene transcription. GLIS3 plays a critical role in the regulation of multiple biological processes and is a key regulator of pancreatic β cell generation and maturation, insulin gene expression, thyroid hormone biosynthesis, spermatogenesis, and the maintenance of normal kidney functions. Loss of GLIS3 function in humans and mice leads to the development of several pathologies, including neonatal diabetes and congenital hypothyroidism, polycystic kidney disease, and infertility. Single nucleotide polymorphisms in GLIS3 genes have been associated with increased risk of several diseases, including type 1 and type 2 diabetes, glaucoma, and neurological disorders. GLIS2 plays a critical role in the kidney and GLIS2 dysfunction leads to nephronophthisis, an end-stage, cystic renal disease. In addition, GLIS1-3 have regulatory functions in several stem/progenitor cell populations. GLIS1 and GLIS3 greatly enhance reprogramming efficiency of somatic cells into induced embryonic stem cells, while GLIS2 inhibits reprogramming. Recent studies have obtained substantial mechanistic insights into several physiological processes regulated by GLIS2 and GLIS3, while a little is still known about the physiological functions of GLIS1. The localization of some GLIS proteins to the primary cilium suggests that their activity may be regulated by a downstream primary cilium-associated signaling pathway. Insights into the upstream GLIS signaling pathway may provide opportunities for the development of new therapeutic strategies for diabetes, hypothyroidism, and other diseases.

Extended clinical features associated with novel Glis3 mutation: a case report

BACKGROUND

Mutations in the GLI-similar 3 (GLIS3) gene encoding the transcription factor GLIS3 are a rare cause of neonatal diabetes and congenital hypothyroidism with 12 reported patients to date. Additional features, previously described, include congenital glaucoma, hepatic fibrosis, polycystic kidneys, developmental delay, facial dysmorphism, osteopenia, sensorineural deafness, choanal atresia, craniosynostosis and pancreatic exocrine insufficiency.

CASE PRESENTATION

We report a new case for consanguineous parents with homozygous novel mutation in GLIS3 gene who presented with neonatal diabetes mellitus, severe resistant congenital hypothyroidism, cholestatic liver disease, bilateral congenital glaucoma and facial dysmorphism. There were associated abnormalities in the external genitalia in form of bifid scrotum, bilateral undescended testicles, microphallus and scrotal hypospadias which might be a coincidental finding.

CONCLUSIONS

We suggest that infants with neonatal diabetes associated with dysmorphism should be screened for GLIS3 gene mutations.

An in vivo screen to identify candidate neurogenic genes in the developing Xenopus visual system

Neurogenesis in the brain of Xenopus laevis continues throughout larval stages of development. We developed a 2-tier screen to identify candidate genes controlling neurogenesis in Xenopus optic tectum in vivo. First, microarray and NanoString analyses were used to identify candidate genes that were differentially expressed in Sox2-expressing neural progenitor cells or their neuronal progeny. Then an in vivo, time-lapse imaging-based screen was used to test whether morpholinos against 34 candidate genes altered neural progenitor cell proliferation or neuronal differentiation over 3 days in the optic tectum of intact Xenopus tadpoles. We co-electroporated antisense morpholino oligonucleotides against each of the candidate genes with a plasmid that drives GFP expression in Sox2-expressing neural progenitor cells and quantified the effects of morpholinos on neurogenesis. Of the 34 morpholinos tested, 24 altered neural progenitor cell proliferation or neuronal differentiation. The candidates which were tagged as differentially expressed and validated by the in vivo imaging screen include: actn1, arl9, eif3a, elk4, ephb1, fmr1-a, fxr1-1, fbxw7, fgf2, gstp1, hat1, hspa5, lsm6, mecp2, mmp9, and prkaca. Several of these candidates, including fgf2 and elk4, have known or proposed neurogenic functions, thereby validating our strategy to identify candidates. Genes with no previously demonstrated neurogenic functions, gstp1, hspa5 and lsm6, were identified from the morpholino experiments, suggesting that our screen successfully revealed unknown candidates. Genes that are associated with human disease, such as such as mecp2 and fmr1-a, were identified by our screen, providing the groundwork for using Xenopus as an experimental system to probe conserved disease mechanisms. Together the data identify candidate neurogenic regulatory genes and demonstrate that Xenopus is an effective experimental animal to identify and characterize genes that regulate neural progenitor cell proliferation and differentiation in vivo.

An Inv(16)(p13.3q24.3)-encoded CBFA2T3-GLIS2 fusion protein defines an aggressive subtype of pediatric acute megakaryoblastic leukemia

To define the mutation spectrum in non-Down syndrome acute megakaryoblastic leukemia (non-DS-AMKL), we performed transcriptome sequencing on diagnostic blasts from 14 pediatric patients and validated our findings in a recurrency/validation cohort consisting of 34 pediatric and 28 adult AMKL samples. Our analysis identified a cryptic chromosome 16 inversion (inv(16)(p13.3q24.3)) in 27% of pediatric cases, which encodes a CBFA2T3-GLIS2 fusion protein. Expression of CBFA2T3-GLIS2 in Drosophila and murine hematopoietic cells induced bone morphogenic protein (BMP) signaling and resulted in a marked increase in the self-renewal capacity of hematopoietic progenitors. These data suggest that expression of CBFA2T3-GLIS2 directly contributes to leukemogenesis.

Gli-similar proteins: their mechanisms of action, physiological functions, and roles in disease

Gli-similar (Glis) 1-3 proteins constitute a subfamily of Krüppel-like zinc-finger proteins that are closely related to members of the Gli family. Glis proteins have been implicated in several pathologies, including cystic kidney disease, diabetes, hypothyroidism, fibrosis, osteoporosis, psoriasis, and cancer. In humans, a mutation in the Glis2 gene has been linked to the development of nephronophthisis (NPHP), a recessive cystic kidney disease, while mutations in Glis3 lead to an extended multisystem phenotype that includes the development of neonatal diabetes, polycystic kidneys, congenital hypothyroidism, and facial dysmorphism. Glis3 has also been identified as a risk locus for type-1 and type-2 diabetes and additional studies have revealed a role for Glis3 in pancreatic endocrine development, β-cell maintenance, and insulin regulation. Similar to Gli1-3, Glis2 and 3 have been reported to localize to the primary cilium. These studies appear to suggest that Glis proteins are part of a primary cilium-associated signaling pathway(s). It has been hypothesized that Glis proteins are activated through posttranslational modifications and subsequently translocate to the nucleus where they regulate transcription by interacting with Glis-binding sites in the promoter regions of target genes. This chapter summarizes the current state of knowledge regarding mechanisms of action of the Glis family of proteins, their physiological functions, as well as their roles in disease.

Increased hedgehog signaling in postnatal kidney results in aberrant activation of nephron developmental programs

Hedgehog (Hh) is a core signaling pathway implicated in fundamental processes during embryonic kidney development. We previously found that loss-of-function mutations in the transcription factor GLIS2, a putative vertebrate ortholog of Drosophila Ci, cause nephronophthisis type 7 in humans and mice. Kidney tubular cells in Glis2-knockout mice acquire mesenchymal phenotype, but the cellular mechanisms of this transition are unknown. Here, we demonstrate that Glis2 is a functional component of Hh signaling and is necessary to suppress this pathway in the postnatal kidney. In the epithelial compartment, Glis2 opposes Gli1 activity by binding cis-acting regulatory sequences in the 5' flanking regions of Snai1 and Wnt4, thereby inhibiting de-differentiation of tubular cells. We conclude that Glis2 is necessary to inhibit Hh signaling and to maintain the mature tubular epithelial phenotype in the adult kidney. This is the first description of a molecular mechanism that links the Hh signaling pathway to cystic kidney diseases and can open new avenues for the treatment of diverse ciliopathies.

Identification of nuclear localization, DNA binding, and transactivating mechanisms of Kruppel-like zinc finger protein Gli-similar 2 (Glis2)

Gli-similar 1-3 (Glis1-3) constitute a subfamily of Krüppel-like zinc finger (ZF) transcription factors that are closely related to the Gli protein family. Mutations in GLIS2 are linked to nephronophthisis, a chronic kidney disease characterized by renal fibrosis and atrophy in children and young adults. Currently, very little information exists about the mechanism of action of Glis2, its target genes, or the signaling pathways that regulate its activity. In this study, we show that a region within ZF3 is required for the nuclear localization of Glis2. Analysis of Glis2 DNA binding demonstrated that Glis2 binds effectively to the consensus Glis binding sequence (GlisBS) (G/C)TGGGGGGT(A/C). Although Glis2 was unable to induce transactivation of a GlisBS-dependent reporter, it effectively inhibited the GlisBS-mediated transactivation by Gli1. Mutations that disrupt the tetrahedral configuration of each ZF within Glis2 abolished Glis2 binding to GlisBS and also abrogated its inhibition of Gli1-mediated transactivation. In contrast, Glis2 was able to activate the murine insulin-2 (Ins2) promoter by binding directly to two GlisBS elements located at -263 and -99 within the Ins2 promoter. Phosphomimetic mutation of Ser(245) inhibited the binding of Glis2 to GlisBS and dramatically affected its transactivation of the Ins2 promoter and its ability to inhibit GlisBS-dependent transactivation by Gli1. In this study, we demonstrate that Glis2 can function as a transcriptional activator and that post-translational modification within its DNA-binding domain can regulate its transcriptional activity. This control may play a critical role in the Glis2-dependent regulation of target genes and renal function.

Expression and phylogenetic analysis of the zic gene family in the evolution and development of metazoans

Background

zic genes are members of the gli/glis/nkl/zic super-family of C2H2 zinc finger (ZF) transcription factors. Homologs of the zic family have been implicated in patterning neural and mesodermal tissues in bilaterians. Prior to this study, the origin of the metazoan zic gene family was unknown and expression of zic gene homologs during the development of early branching metazoans had not been investigated.

Results

Phylogenetic analyses of novel zic candidate genes identified a definitive zic homolog in the placozoan Trichoplax adhaerens, two gli/glis/nkl-like genes in the ctenophore Mnemiopsis leidyi, confirmed the presence of three gli/glis/nkl-like genes in Porifera, and confirmed the five previously identified zic genes in the cnidarian Nematostella vectensis. In the cnidarian N. vectensis, zic homologs are expressed in ectoderm and the gastrodermis (a bifunctional endomesoderm), in presumptive and developing tentacles, and in oral and sensory apical tuft ectoderm. The Capitella teleta zic homolog (Ct-zic) is detectable in a subset of the developing nervous system, the foregut, and the mesoderm associated with the segmentally repeated chaetae. Lastly, expression of gli and glis homologs in Mnemiopsis. leidyi is detected exclusively in neural cells in floor of the apical organ.

Conclusions

Based on our analyses, we propose that the zic gene family arose in the common ancestor of the Placozoa, Cnidaria and Bilateria from a gli/glis/nkl-like gene and that both ZOC and ZF-NC domains evolved prior to cnidarian-bilaterian divergence. We also conclude that zic expression in neural ectoderm and developing neurons is pervasive throughout the Metazoa and likely evolved from neural expression of an ancestral gli/glis/nkl/zic gene. zic expression in bilaterian mesoderm may be related to the expression in the gastrodermis of a cnidarian-bilaterian common ancestor.

Transcription factor Glis3, a novel critical player in the regulation of pancreatic beta-cell development and insulin gene expression

In this study, we report that the Krüppel-like zinc finger transcription factor Gli-similar 3 (Glis3) is induced during the secondary transition of pancreatic development, a stage of cell lineage specification and extensive patterning, and that Glis3(zf/zf) mutant mice develop neonatal diabetes, evidenced by hyperglycemia and hypoinsulinemia. The Glis3(zf/zf) mutant mouse pancreas shows a dramatic loss of beta and delta cells, contrasting a smaller relative loss of alpha, PP, and epsilon cells. In addition, Glis3(zf/zf) mutant mice develop ductal cysts, while no significant changes were observed in acini. Gene expression profiling and immunofluorescent staining demonstrated that the expression of pancreatic hormones and several transcription factors important in endocrine cell development, including Ngn3, MafA, and Pdx1, were significantly decreased in the developing pancreata of Glis3(zf/zf) mutant mice. The population of pancreatic progenitors appears not to be greatly affected in Glis3(zf/zf) mutant mice; however, the number of neurogenin 3 (Ngn3)-positive endocrine cell progenitors is significantly reduced. Our study indicates that Glis3 plays a key role in cell lineage specification, particularly in the development of mature pancreatic beta cells. In addition, we provide evidence that Glis3 regulates insulin gene expression through two Glis-binding sites in its proximal promoter, indicating that Glis3 also regulates beta-cell function.

Glis3 is associated with primary cilia and Wwtr1/TAZ and implicated in polycystic kidney disease

In this study, we describe the generation and partial characterization of Krüppel-like zinc finger protein Glis3 mutant (Glis3(zf/zf)) mice. These mice display abnormalities very similar to those of patients with neonatal diabetes and hypothyroidism syndrome, including the development of diabetes and polycystic kidney disease. We demonstrate that Glis3 localizes to the primary cilium, suggesting that Glis3 is part of a cilium-associated signaling pathway. Although Glis3(zf/zf) mice form normal primary cilia, renal cysts contain relatively fewer cells with a primary cilium. We further show that Glis3 interacts with the transcriptional modulator Wwtr1/TAZ, which itself has been implicated in glomerulocystic kidney disease. Wwtr1 recognizes a P/LPXY motif in the C terminus of Glis3 and enhances Glis3-mediated transcriptional activation, indicating that Wwtr1 functions as a coactivator of Glis3. Mutations in the P/LPXY motif abrogate the interaction with Wwtr1 and the transcriptional activity of Glis3, indicating that this motif is part of the transcription activation domain of Glis3. Our study demonstrates that dysfunction of Glis3 leads to the development of cystic renal disease, suggesting that Glis3 plays a critical role in maintaining normal renal functions. We propose that localization to the primary cilium and interaction with Wwtr1 are key elements of the Glis3 signaling pathway.

CD spectra show the relational style between Zic-, Gli-, Glis-zinc finger protein and DNA

Zic family proteins have five C2H2-type zinc finger motifs. The Zic-zinc finger domains show high homology to the corresponding domains of the Gli and Glis families, which also contain five C2H2-type zinc finger motifs. The zinc finger motifs of the proteins of these three protein families form an alpha-helix conformation in solution. The addition of oligo DNA that included a Gli-binding sequence increased the alpha-helix content estimated by using circular dichroism spectroscopy. Comparison of the Zic-, Gli-, and Glis-zinc fingers indicated that the alpha-helix content after the addition of oligo DNA correlated well with the affinity of each zinc finger for the oligo DNA (correlation coefficient, 0.85). The importance of the zinc ion for protein folding was reflected in a reduction in the alpha-helix content upon removal of the zinc ion. Owing to the compact globular structure, the alpha-helix structure of the proteins of these three protein families is extremely thermally stable. These results suggest that the alpha-helix structure is important for DNA binding and profoundly related to functional and structural diversity among the three families.

Functional analysis of the zinc finger and activation domains of Glis3 and mutant Glis3(NDH1)

The Krüppel-like zinc finger protein Gli-similar 3 (Glis3) plays a critical role in pancreatic development and has been implicated in a syndrome with neonatal diabetes and hypothyroidism (NDH). In this study, we examine three steps critical in the mechanism of the transcriptional regulation by Glis3: its translocation to the nucleus, DNA binding and transcriptional activity. We demonstrate that the putative bipartite nuclear localization signal is not required, but the tetrahedral configuration of the fourth zinc finger is essential for the nuclear localization of Glis3. We identify (G/C)TGGGGGGT(A/C) as the consensus sequence of the optimal, high-affinity Glis3 DNA-binding site (Glis-BS). All five zinc finger motifs are critical for efficient binding of Glis3 to Glis-BS. We show that Glis3 functions as a potent inducer of (Glis-BS)-dependent transcription and contains a transactivation function at its C-terminus. A mutation in Glis3 observed in NDH1 patients results in a frameshift mutation and a C-terminal truncated Glis3. We demonstrate that this truncation does not effect the nuclear localization but results in the loss of Glis3 transactivating activity. The loss in Glis3 transactivating function may be responsible for the abnormalities observed in NDH1.

Kruppel-like zinc finger protein Glis2 is essential for the maintenance of normal renal functions

To obtain insight into the physiological functions of the Krüppel-like zinc finger protein Gli-similar 2 (Glis2), mice deficient in Glis2 expression were generated. Glis2 mutant (Glis2(mut)) mice exhibit significantly shorter life spans than do littermate wild-type (WT) mice due to the development of progressive chronic kidney disease with features resembling nephronophthisis. Glis2(mut) mice develop severe renal atrophy involving increased cell death and basement membrane thickening in the proximal convoluted tubules. This development is accompanied by infiltration of lymphocytic inflammatory cells and interstitial/glomerular fibrosis. The severity of the fibrosis, inflammatory infiltrates, and glomerular and tubular changes progresses with age. Blood urea nitrogen and creatinine increase, and Glis2(mut) mice develop proteinuria and ultimately die prematurely of renal failure. A comparison of the gene expression profiles of kidneys from 25-day-old/60-day-old WT and Glis2(mut) mice by microarray analysis showed increased expressions of many genes involved in immune responses/inflammation and fibrosis/tissue remodeling in kidneys of Glis2(mut) mice, including several cytokines and adhesion and extracellular matrix proteins. Our data demonstrate that a deficiency in Glis2 expression leads to tubular atrophy and progressive fibrosis, similar to nephronophthisis, that ultimately results in renal failure. Our study indicates that Glis2 plays a critical role in the maintenance of normal kidney architecture and functions.

The C. elegans M3 neuron guides the growth cone of its sister cell M2 via the Krüppel-like zinc finger protein MNM-2

The invariant cell-cell interactions occurring during C. elegans development offer unique opportunities to discover how growing axons may receive guidance cues from neighboring cells. The mnm-2 mutant was isolated because of its defects in the axon trajectory of the bilateral M2 pharyngeal neurons in C. elegans. We found that mnm-2 enhances the effects of many growth cone guidance mutations on these axons, suggesting that it performs a novel function during axon guidance. We cloned mnm-2 and found that it encodes a protein with three C2H2 zinc finger domains related to the Krüppel-like Factor protein family. mnm-2 is expressed only transiently in the M2 neuron, but exhibits a sustained expression in its sister cell, the M3 neuron. Strikingly, the expression of mnm-2 is not sustained in the M3 cell of the mnm-2 mutant, indicating that this gene positively regulates itself in that cell. Electropharyngeograms also indicate that the M3 cell is functionally impaired in the mnm-2 mutant. We used an M3-specific promoter to show that the M2 axon defect can be rescued by expression of mnm-2 in its sister cell M3. The same promoter was used to express the pro-apoptotic gene egl-1 to kill the M3 cell, which resulted in an M2 axon guidance defect similar to that found in the mnm-2 mutant. Our results suggest an M2 axon guidance model in which the M3 cell provides an important signal to the growth cone of its sister M2 and that this signal and the proper differentiation of M3 both depend on mnm-2 expression. This mechanism of axon guidance regulation allows fine-tuning of trajectories between sister cells.

The transcriptional repressor Glis2 is a novel binding partner for p120 catenin

In epithelial cells, p120 catenin (p120) localizes at cell-cell contacts and regulates adhesive function of the cadherin complex. In addition, p120 has been reported to localize in the nucleus, although the nuclear function of p120 is not fully understood. Here, we report the identification of Gli-similar 2 (Glis2) as a novel binding protein for p120. Glis2 is a Krüppel-like transcriptional repressor with homology to the Gli family, but its physiological function has not been well characterized. In this study, we show that coexpression of Glis2 and Src induces nuclear translocation of p120. Furthermore, p120 induces the C-terminal cleavage of Glis2, and this cleavage is further enhanced by Src. The cleaved form of Glis2 loses one of its five zinc finger domains, but it is still able to bind DNA. Functional studies in chick neural tube indicate that full-length Glis2 can affect neuronal differentiation, whereas the cleaved form requires coexpression of p120 to have a similar effect. These data indicate that p120 has additional novel functions in the nucleus together with Glis2.

The Krüppel-like zinc finger protein Glis2 functions as a negative modulator of the Wnt/beta-catenin signaling pathway

To gain insight into the mechanism by which Gli-similar 2 (Glis2) regulates transcription, we performed yeast-two hybrid cDNA library screening using Glis2 as bait. This screening identified beta-catenin as a potential Glis2-interacting protein. Mammalian two-hybrid, co-immunoprecipitation, and GST-pulldown analyses supported the interaction between Glis2 and beta-catenin. Pulldown analyses with several Glis2 deletion mutants indicated that the 1st zinc finger motif of Glis2 is critical for its interaction with beta-catenin, while the armadillo repeats of beta-catenin are important in its interaction with Glis2. Reporter analyses showed that Glis2 represses T-cell factor (TCF)-mediated transcriptional activation. In addition, Glis2 represses the expression of the TCF target gene cyclin D1. Our results indicate that Glis2 interacts with beta-catenin and suggest that Glis2 functions as a negative modulator of beta-catenin/TCF-mediated transcription.

Identification of shared transcriptional targets for the proneural bHLH factors Xath5 and XNeuroD

Proneural basic helix-loop-helix (bHLH) transcription factors are critical positive regulators of neuronal differentiation in a variety of species and are required for proper differentiation of various subtypes of neurons. Although bHLH factors demonstrate some unique functions during neural development, they share the ability to regulate neuronal differentiation, potentially by targeting overlapping sets of genes. To assess this, we performed a screen in ectoderm animal cap tissue to identify direct transcriptional targets shared by two Xenopus ato-related bHLH factors, Xath5 and XNeuroD. Candidate target genes identified in this screen include several transcriptional regulators (Xebf2, Xebf3, XETOR and NKL), an RNA binding protein (elrC), a cell cycle component (Xgadd45gamma) and several novel genes. Overexpression of either Xath5 or XNeuroD induced ectopic in vivo expression of these candidate target genes. Conversely, blocking ato-related bHLH activity prevented endogenous nervous system expression of these genes. Therefore, we have identified a set of genes that can be regulated by multiple ato-related bHLH factors and may function as critical effectors of proneural bHLH-mediated differentiation.

Regulatory role for Krüppel-like zinc-finger protein Gli-similar 1 (Glis1) in PMA-treated and psoriatic epidermis

In this study, we analyze the expression and potential function of the Krüppel-like zinc-finger protein Gli-similar protein 1 (Glis1) in normal and inflammatory skin and in the differentiation of epidermal keratinocytes. Glis1 mRNA is not expressed in normal human epidermis, but is significantly induced in psoriatic epidermis and in mouse skin upon treatment with the tumor promoter phorbol-12-myristate-13-acetate (PMA). The expression of Glis1 is restricted to the suprabasal layers. These observations suggest that Glis1 expression is associated with hyperplastic, inflammatory epidermis. Consistent with these findings, Glis1 mRNA is not expressed in undifferentiated or differentiated normal human epidermal keratinocytes (NHEK) in culture, but is dramatically induced after the addition of PMA or interferon gamma. A similar induction of Glis1 mRNA by PMA treatment was observed in the immortalized epidermal keratinocyte cell line NHEK-HPV, whereas PMA did not induce Glis1 in HaCaT cells or in several squamous cell carcinoma cell lines. To obtain insight into its function, Glis1 and a C-terminal deletion mutant Glis1DeltaC were expressed in NHEK-HPV cells and changes in epidermal differentiation and gene expression examined. Microarray analysis revealed that Glis1DeltaC promoted PMA-induced epidermal differentiation, as indicated by increased expression of many differentiation-specific genes. This, in association with its induction in psoriasis, suggests that transcriptional factor Glis1 is involved in the regulation of aberrant differentiation observed in psoriatic epidermis.

The expression and function of MTG/ETO family proteins during neurogenesis

The proneural basic helix-loop-helix (bHLH) proteins promote neurogenesis by inducing changes in gene expression required for neuronal differentiation. Here we characterize one aspect of this differentiation program by analyzing a small family of putative corepressors encoded by MTG genes. We show that MTG genes are expressed sequentially during neurogenesis as cells undergo neuronal differentiation in both the chick spinal cord and in the Xenopus primary nervous system. Using in ovo electroporation, we show that misexpressing wild-type forms of MTG proteins in the developing chick spinal cord does not detectably alter neuronal differentiation. By contrast, the number of differentiated neurons is markedly reduced when a putative dominant-negative mutant of the MTG proteins is expressed in neural precursors in a manner that can be rescued by wild-type MTGR1. Together, these results suggest that MTG family members act downstream of proneural proteins, presumably as corepressors, to promote neuronal differentiation.

The role of Zic genes in neural development

The Zic family of zinc-finger proteins plays a crucial role in neural development. Zic genes are vertebrate homologs of odd-paired, the Drosophila pair-rule gene. Their gene products have zinc-finger domains similar to those of Gli proteins, which act as transcriptional regulators in hedgehog signaling. Recent studies of human, mouse, frog, fish and ascidian Zic homologs have provided evidence that Zic genes are involved in a variety of developmental processes, including neurogenesis, myogenesis, skeletal patterning, and left-right axis establishment. Zic genes appear to have multiple roles in neural development. They control the initial phase during which ectoderm differentiates into neuroectoderm, and they may act as bridges between secreted neural tissue induction signals and the basic-helix-loop-helix class of neurogenesis-inducing transcriptional regulatory factors. Studies of loss-of-function mutations with differing Zic gene subtypes show that the Zic family of genes controls the process of neurulation. Mutations result in neural tube defects, which are seen at different rostrocaudal levels depending on which Zic gene subtype has been affected. Development of holoprosencephaly, forebrain anomalies, and cerebellar dysgenesis indicate that region-specific morphogenesis of the CNS is also controlled by Zic genes. The underlying molecular actions of Zic gene products, which allow them to control development, remain a mystery. Recent molecular characterization has shown that Zic proteins are able to bind Gli-binding DNA sequences in a sequence-specific manner, but with lower affinity than Gli proteins. Zic proteins also can activate transcription from several promoters. Furthermore, Zic and Gli proteins interact physically via their zinc-finger domains, raising the possibility that Zic proteins can act as transcriptional cofactors and modulate the hedgehog-signaling pathway. Clarification of the specific cooperating factors is therefore required in each case. Other evidence also suggests that Zic proteins can inhibit neuronal differentiation by activating Notch signals. This association might be is a clue toward understanding of the multifunctional property of Zic proteins because Notch signaling also is implicated in the control of several developmental processes.

NELL2 promotes motor and sensory neuron differentiation and stimulates mitogenesis in DRG in vivo

We previously identified a secreted glycoprotein, neural epidermal growth factor-like like 2 (NELL2), in a subtraction screen designed to identify molecules regulating sensory neurogenesis and differentiation in the chick dorsal root ganglion (DRG). Characterization of NELL2 expression during embryogenesis revealed that NELL2 was specifically expressed during the peak periods of both sensory and motor neuron differentiation, and within the neural crest was restricted to the sensory lineage. We now provide evidence for a function for NELL2 during neuronal development. We report here that NELL2 acts cell autonomously within CNS and PNS progenitors, in vivo, to promote their differentiation into neurons. Additionally, neuron-secreted NELL2 acts paracrinely to stimulate the mitogenesis of adjacent cells within the nascent DRG. These studies implicate dual functions for NELL2 in both the cell autonomous differentiation of neural progenitor cells while simultaneously exerting paracrine proliferative activity.

Difference in the maternal and zygotic contributions of tumorhead on embryogenesis

Tumorhead (TH) is a maternally expressed gene in Xenopus laevis, that when overexpressed, increased proliferation of ectodermal derivatives and inhibited neural and epidermal differentiation. However, injection of anti-TH antibodies inhibited cleavage of all blastomeres, not only those contributing to the ectoderm. The injection of TH morpholino antisense oligonucleotide (TH-MO), which inhibits translation of TH mRNA, did not affect early cleavage but inhibited cell division in both the neural field and epidermis. This was accompanied by the inhibition of neural and epidermal markers. TH-MO did not affect the formation and differentiation of mesoderm and endoderm derivatives. Our overexpression and loss-of-function studies demonstrated that TH plays an important role in differentiation of the ectoderm by regulating cell proliferation. They also supported the conclusion that the maternal component of TH may affect the cell cycle in all cells, while the zygotic component has a germ layer-specific effect on the ectoderm.

Nutrient control of gene expression in Drosophila: microarray analysis of starvation and sugar-dependent response

We have identified genes regulated by starvation and sugar signals in Drosophila larvae using whole-genome microarrays. Based on expression profiles in the two nutrient conditions, they were organized into different categories that reflect distinct physiological pathways mediating sugar and fat metabolism, and cell growth. In the category of genes regulated in sugar-fed, but not in starved, animals, there is an upregulation of genes encoding key enzymes of the fat biosynthesis pathway and a downregulation of genes encoding lipases. The highest and earliest activated gene upon sugar ingestion is sugarbabe, a zinc finger protein that is induced in the gut and the fat body. Identification of potential targets using microarrays suggests that sugarbabe functions to repress genes involved in dietary fat breakdown and absorption. The current analysis provides a basis for studying the genetic mechanisms underlying nutrient signalling.

Xiro homeoproteins coordinate cell cycle exit and primary neuron formation by upregulating neuronal-fate repressors and downregulating the cell-cycle inhibitor XGadd45-gamma

The iroquois (iro) homeobox genes participate in many developmental processes both in vertebrates and invertebrates, among them are neural plate formation and neural patterning. In this work, we study in detail Xenopus Iro (Xiro) function in primary neurogenesis. We show that misexpression of Xiro genes promotes the activation of the proneural gene Xngnr1 but suppresses neuronal differentiation. This is probably due to upregulation of at least two neuronal-fate repressors: XHairy2A and XZic2. Accordingly, primary neurons arise at the border of the Xiro expression domains. In addition, we identify XGadd45-gamma as a new gene repressed by Xiro. XGadd45-gamma encodes a cell-cycle inhibitor and is expressed in territories where cells will exit mitosis, such as those where primary neurons arise. Indeed, XGadd45-gamma misexpression causes cell cycle arrest. We conclude that, during Xenopus primary neuron formation, in Xiro expressing territories neuronal differentiation is impaired, while in adjacent cells, XGadd45-gamma may help cells stop dividing and differentiate as neurons.

A novel gene, GliH1, with homology to the Gli zinc finger domain not required for mouse development

The Sonic hedgehog (Shh)-Gli signaling pathway regulates development of many organs, including teeth. We cloned a novel gene encoding a transcription factor that contains a zinc finger domain with highest homology to the Gli family of proteins (61-64% amino acid sequence identity) from incisor pulp. Consistent with this sequence conservation, gel mobility shift assays demonstrated that this new Gli homologous protein, GliH1, could bind previously characterized Gli DNA binding sites. Furthermore, transfection assays in dental pulp cells showed that whereas Gli1 induces a nearly 50-fold increase in activity of a luciferase reporter containing Gli DNA binding sites, coexpression of Gli1 with Gli3 and/or GliH1 results in inhibition of the Gli1-stimulated luciferase activity. In situ hybridization analysis of mouse embryos demonstrated that GliH1 expression is initiated later than the three Gli genes and has a more restricted expression pattern. GliH1 is first detected diffusely in the limb buds at 10.0 days post coitus and later is expressed in the branchial arches, craniofacial interface, ventral part of the tail, whisker follicles and hair, intervertebral discs, teeth, eyes and kidney. LacZ was inserted into the GliH1 allele in embryonic stem cells to produce mice lacking GliH1 function. While this produced indicator mice for GliH1-expression, analysis of mutant mice revealed no discernible phenotype or required function for GliH1. A search of the Celera Genomics and associated databases identified possible gene sequences encoding a zinc finger domain with approximately 90% homology to that of GliH1, indicating there is a family of GliH genes and raising the possibility of overlapping functions during development.

Identification of Glis1, a novel Gli-related, Kruppel-like zinc finger protein containing transactivation and repressor functions

In this study, we describe the identification and characterization of a novel Krüppel-like protein named Gli-similar 1 (Glis1). The Glis1 gene encodes an 84.3-kDa proline-rich protein. Its five tandem zinc finger motifs exhibit highest homology with those of members of the Gli and Zic subfamilies of Krüppel-like proteins. Glis1 was mapped to mouse chromosome 4C6. Northern blot analysis showed that expression of the 3.3-kb Glis1 mRNA is most abundant in placenta and adult kidney and expressed at lower levels in testis. Whole mount in situ hybridization on mouse embryos demonstrated that Glis1 is expressed in a temporal and spatial manner during development; expression was most prominent in several defined structures of mesodermal lineage, including craniofacial regions, branchial arches, somites, vibrissal and hair follicles, limb buds, and myotomes. Confocal microscopic analysis showed that Glis1 is localized to the nucleus. The zinc finger region plays an important role in the nuclear localization of Glis1. Electrophoretic mobility shift assays demonstrated that Glis1 is able to bind oligonucleotides containing the Gli-binding site consensus sequence GACCACCCAC. Although monohybrid analysis showed that in several cell types Glis1 was unable to induce transcription of a reporter, deletion mutant analysis revealed the presence of a strong activation function at the carboxyl terminus of Glis1. The activation through this activation function was totally suppressed by a repressor domain at its amino terminus. Constitutively active Ca(2+)-dependent calmodulin kinase IV enhanced Glis1-mediated transcriptional activation about 4-fold and may be mediated by phosphorylation/activation of a co-activator. Our results suggest that Glis1 may play a critical role in the control of gene expression during specific stages of embryonic development.

Characterization of Glis2, a novel gene encoding a Gli-related, Krüppel-like transcription factor with transactivation and repressor functions. Roles in kidney development and neurogenesis

In this study, we describe the characterization of a gene encoding a novel Krüppel-like protein, named Glis2. Glis2 encodes a relatively proline-rich, basic 55.8-kDa protein. Its five tandem Cys(2)-His(2) zinc finger motifs exhibit the highest homology to those of members of the Gli and Zic subfamilies of Krüppel-like proteins. Confocal microscopic analysis demonstrated that Glis2 localizes to the nucleus. Analysis of the genomic structure of the Glis2 gene showed that it is composed of 6 exons separated by 5 introns spanning a genomic region of more than 7.5 kb. Fluorescence in situ hybridization mapped the mouse Glis2 gene to chromosome 16A3-B1. Northern blot analysis showed that the Glis2 gene encodes a 3.8-kb transcript that is most abundant in adult mouse kidney. By in situ hybridization, expression was localized to somites and neural tube, and during metanephric development predominantly to the ureteric bud, precursor of the collecting duct, and inductor of nephronic tubule formation. One-hybrid analysis using Glis2 deletion mutants identified a novel activation function (AF) at the N terminus. The activation of transcription through this AF domain was totally suppressed by two repressor functions just downstream from the AF. One of the repressor functions is contained within the first zinc finger motif. The level of transcriptional activation and repression varied with the cell line tested, which might be due to differences in cell type-specific expression of co-activators and co-repressors. Our results suggest that Glis2 behaves as a bifunctional transcriptional regulator. Both the activation and repressor functions may play an important role in the regulation of gene expression during embryonic development.

Strain-specific complementation between NRIF1 and NRIF2, two zinc finger proteins sharing structural and biochemical properties

The zinc finger protein NRIF (neurotrophin receptor interacting factor) was originally identified by virtue of its interaction with the neurotrophin receptor p75NTR and its participation in embryonic apoptosis. Targeted deletion of the nrif gene in mice is embryonically lethal in the C57BL6 genetic background, where it blocks cell cycle progression, but not in the Sv129 strain. We have now identified a second, highly homologous nrif gene, designated nrif2, encoding a protein with similar structural and biochemical properties as well as subcellular distribution as NRIF1, and whose over-expression in transfected fibroblasts also correlates with impaired BrdU incorporation. Unexpectedly, the nrif2 transcript becomes significantly upregulated in nrif1-/- mice only in Sv129, the genetic background where the mutants are viable, suggesting that the functional complementation of the two nrif genes may be strain-specific.

The secreted glycoprotein Noelin-1 promotes neurogenesis in Xenopus

Neurogenesis in Xenopus neural ectoderm involves multiple gene families, including basic helix-loop-helix transcription factors, which initiate and control primary neurogenesis. Equally important, though less well understood, are the downstream effectors of the activity of these transcription factors. We have investigated the role of a candidate downstream effector, Noelin-1, during Xenopus development. Noelin-1 is a secreted glycoprotein that likely forms large multiunit complexes. In avians, overexpression of Noelin-1 causes prolonged and excessive neural crest migration. Our studies in Xenopus reveal that this gene, while highly conserved in sequence, has a divergent function in primary neurogenesis. Xenopus Noelin-1 is expressed mainly by postmitotic neurogenic tissues in the developing central and peripheral nervous systems, first appearing after neural tube closure. Its expression is upregulated in ectopic locations upon overexpression of the neurogenic genes X-ngnr-1 and XNeuroD. Noelin-1 expression in animal caps induces expression of neural markers XBrn-3d and XNeuroD, and co-expression of secreted Noelin-1 with noggin amplifies noggin-induced expression of XBrn-3d and XNeuroD. Furthermore, in animal caps neuralized by expression of noggin, co-expression of Noelin-1 causes expression of neuronal differentiation markers several stages before neurogenesis normally occurs in this tissue. Finally, only secreted forms of the protein can activate sensory marker expression, while all forms of the protein can induce early neurogenesis. This suggests that the cellular localization of Noelin-1 may be important to its function. Thus, Noelin-1 represents a novel secreted factor involved in neurogenesis.

Genomic structure of the gene encoding the human GLI-related, Krüppel-like zinc finger protein GLIS2

In this study, we describe the sequence and genomic structure of the human GLIS2 gene, encoding a new member of the Krüppel-like zinc finger protein family. GLIS2 is a relatively proline-rich, basic protein of 55.7 kDa in size. It contains five tandem Cys(2)-His(2) zinc finger motifs consisting of the consensus sequence X-Cys-X(2,4)-Cys-X(12,15)-His-X(3,4)-His-X. The sequence of the zinc finger domain exhibits highest homology with those of members of the GLI and ZIC subfamilies of Krüppel-like proteins. The zinc finger domain of GLIS2 exhibits highest (58%) homology with that of GLI-1. The human GLIS2 gene consists of six exons and five introns, and spans more than 7.5 kb. Primer extension identified several putative transcription initiation sites. GLIS2 mRNA is most abundantly expressed in human kidney suggesting a role in the regulation of certain kidney functions. The GLIS2 gene maps to human chromosome 16p13.3, a locus implicated in several human kidney diseases. The sequence and structure of human GLIS2 will be useful tools to study the regulation of GLIS2 and its potential role in human disease.