Role Of Foxg1 Research Articles

FOXG1 regulates the proliferation and apoptosis of human lung cancer cells

FOXG1, a transcriptional factor belonging to the Forkhead Box (Fox) superfamily, is highly expressed in the brain tissue during brain development and plays an important role in cellular proliferation. Recently, FOXG1 was reported to play important roles in oncogenesis, wherein its abnormal expression regulates tumor cell proliferation. However, the expression and role of FOXG1 in lung cancer remain largely unknown. This study investigated the clinical significance, expression, and role of FOXG1 in lung cancer. We found that FOXG1 was highly expressed in lung cancer tissues. MTT, CCK-8 and colony formation assays showed that FOXG1 overexpression could enhance the proliferation of A549 lung cancer cells. Flow cytometry analysis revealed that FOXG1 promoted the cell cycle and suppressed cell apoptosis. Additionally, the expression levels of PTEN, phosphorylated AKT, mTOR, p53, and Bax were significantly altered in response to changes in FOXG1 expression, indicating that FOXG1 regulated the PI3K pathway. Furthermore, in the xenograft mouse model, the upregulated FOXG1 expression strongly promoted tumor growth. In conclusion, these results suggested that FOXG1 was a critical regulator of the proliferation of lung cancer cells and enhanced tumor growth in vivo.

FOXG1 is involved in mouse ovarian functions and embryogenesis

TGF-β superfamily has long been demonstrated to be essential for folliculogenesis and luteinization. Forkhead box G1 (FOXG1, also known as BF1), a member of the FOX family and an inhibitor of TGF-β signaling pathway, is a nucleocytoplasmic transcription factor that is essential for forebrain development. FOXG1 is involved in neurodevelopment and cancer pathology, however, little is known about the role of FOXG1 in reproduction. In this study, the spatiotemporal expression pattern of FOXG1 was examined during early mouse oocyte and embryonic development and its role during corpora luteum (CL) formation was further elucidated. The results showed that FOXG1 is localized in oocytes, theca cells (TCs) and CLs. After fertilization, FOXG1 is expressed at all stages during early embryogenesis, from zygotes to blastocysts. Following gonadotropin administration in immature mice, the expression of Foxg1 significantly increased along with steroidogenic genes, including Star, Hsd3β, Cyp11a1, as well as Cyp17a1 and Cyp19a1. The latter two first increased after pregnant mare serum gonadotropin stimulation, then decreased in response to hCG treatment. In addition, silencing of Foxg1 significantly reduced the concentration of testosterone and estrogen in cultured primary granulosa cells (GCs) and TCs (P < 0.05). Mechanistic studies demonstrated that the expression level of genes that are critical in estrogen synthesis were significantly reduced after Foxg1 silencing, including Cyp17a1 and Cyp19a1. In conclusion, FOXG1 is expressed in a stage-specific manner during folliculogenesis and embryogenesis and exerts a regulatory influence on testosterone and estrogen synthesis.

FOXG1 Contributes Adult Hippocampal Neurogenesis in Mice

Strategies to enhance hippocampal precursor cells efficiently differentiate into neurons could be crucial for structural repair after neurodegenerative damage. FOXG1 has been shown to play an important role in pattern formation, cell proliferation, and cell specification during embryonic and early postnatal neurogenesis. Thus far, the role of FOXG1 in adult hippocampal neurogenesis is largely unknown. Utilizing CAG-loxp-stop-loxp-Foxg1-IRES-EGFP (Foxg1fl/fl), a specific mouse line combined with CreAAV infusion, we successfully forced FOXG1 overexpressed in the hippocampal dentate gyrus (DG) of the genotype mice. Thereafter, we explored the function of FOXG1 on neuronal lineage progression and hippocampal neurogenesis in adult mice. By inhibiting p21cip1 expression, FOXG1-regulated activities enable the expansion of the precursor cell population. Besides, FOXG1 induced quiescent radial-glia like type I neural progenitor, giving rise to intermediate progenitor cells, neuroblasts in the hippocampal DG. Through increasing the length of G1 phase, FOXG1 promoted lineage-committed cells to exit the cell cycle and differentiate into mature neurons. The present results suggest that FOXG1 likely promotes neuronal lineage progression and thereby contributes to adult hippocampal neurogenesis. Elevating FOXG1 levels either pharmacologically or through other means could present a therapeutic strategy for disease related with neuronal loss.

The Role of FoxG1 in the Inner Ear.

Sensorineural deafness is mainly caused by damage to the tissues of the inner ear, and hearing impairment has become an increasingly serious global health problem. When the inner ear is abnormally developed or is damaged by inflammation, ototoxic drugs, or blood supply disorders, auditory signal transmission is inhibited resulting in hearing loss. Forkhead box G1 (FoxG1) is an important nuclear transcriptional regulator, which is related to the differentiation, proliferation, development, and survival of cells in the brain, telencephalon, inner ear, and other tissues. Previous studies have shown that when FoxG1 is abnormally expressed, the development and function of inner ear hair cells is impaired. This review discusses the role and regulatory mechanism of FoxG1 in inner ear tissue from various aspects – such as the effect on inner ear development, the maintenance of inner ear structure and function, and its role in the inner ear when subjected to various stimulations or injuries – in order to explain the potential significance of FoxG1 as a new target for the treatment of hearing loss.

Conditional Deletion of Foxg1 Alleviates Demyelination and Facilitates Remyelination via the Wnt Signaling Pathway in Cuprizone-Induced Demyelinated Mice

The massive loss of oligodendrocytes caused by various pathological factors is a basic feature of many demyelinating diseases of the central nervous system (CNS). Based on a variety of studies, it is now well established that impairment of oligodendrocyte precursor cells (OPCs) to differentiate and remyelinate axons is a vital event in the failed treatment of demyelinating diseases. Recent evidence suggests that Foxg1 is essential for the proliferation of certain precursors and inhibits premature neurogenesis during brain development. To date, very little attention has been paid to the role of Foxg1 in the proliferation and differentiation of OPCs in demyelinating diseases of the CNS. Here, for the first time, we examined the effects of Foxg1 on demyelination and remyelination in the brain using a cuprizone (CPZ)-induced mouse model. In this work, 7-week-old Foxg1 conditional knockout and wild-type (WT) mice were fed a diet containing 0.2% CPZ w/w for 5 weeks, after which CPZ was withdrawn to enable remyelination. Our results demonstrated that, compared with WT mice, Foxg1-knockout mice exhibited not only alleviated demyelination but also accelerated remyelination of the demyelinated corpus callosum. Furthermore, we found that Foxg1 knockout decreased the proliferation of OPCs and accelerated their differentiation into mature oligodendrocytes both in vivo and in vitro. Wnt signaling plays a critical role in development and in a variety of diseases. GSK-3β, a key regulatory kinase in the Wnt pathway, regulates the ability of β-catenin to enter nuclei, where it activates the expression of Wnt target genes. We then used SB216763, a selective inhibitor of GSK-3β activity, to further demonstrate the regulatory mechanism by which Foxg1 affects OPCs in vitro. The results showed that SB216763 clearly inhibited the expression of GSK-3β, which abolished the effect of the proliferation and differentiation of OPCs caused by the knockdown of Foxg1. These results suggest that Foxg1 is involved in the proliferation and differentiation of OPCs through the Wnt signaling pathway. The present experimental results are some of the first to suggest that Foxg1 is a new therapeutic target for the treatment of demyelinating diseases of the CNS.

RETRACTED ARTICLE: Forkhead box (FOX) G1 promotes hepatocellular carcinoma epithelial-Mesenchymal transition by activating Wnt signal through forming T-cell factor-4/Beta-catenin/FOXG1 complex

BackgroundForkhead box G1 (FOXG1) is a member of the Fox transcription factor family involved in regulation of many cancers. However, the role of FOXG1 in hepatocellular carcinogenesisis largely unclear. The present study aimed at examining the biological function and underlying mechanism of FOXG1 on hepatocellular carcinoma (HCC) tumor metastasis as well as its clinical significance.MethodsLevels of FOXG1 were determined by immunohistochemical and real-time PCR analysis in HCC cell lines and human HCC samples. The effect of FOXG1 on cancer cell invasion and metastasis was investigated in vitro and in vivo in either FOXG1-silenced or overexpressing human HCC cell lines. Immunoprecipitation and chromatin immunoprecipitation assays were performed to investigate the interaction of FOXG1, β-catenin, TCF4 and the effect on Wnt target-gene promoters.ResultsIn human HCC, the level of FOXG1 progressively increased from surrounding non tumorous livers to HCC, reaching the highest levels in metastatic HCC. Furthermore, expression levels of FOXG1 directly correlated with cancer cell epithelial-mesenchymal transition (EMT) phenotype. In FOXG1-overexpressing cells, FOXG1 promotes the stabilization and nuclear accumulation of β-catenin by directly binding to β-catenin and it associates with the lymphoid enhancer factor/T cell factor proteins (LEF/TCFs) on Wnt responsive enhancers (WREs) in chromatin.ConclusionsThe results show that FOXG1 plays a key role in mediating cancer cell metastasis through the Wnt/β-catenin pathway in HCC cells and predicts HCC prognosis after surgery. Targeting FOXG1 may provide a new approach for therapeutic treatment in the future.

Disruption of Foxg1 impairs neural plasticity leading to social and cognitive behavioral defects

The transcription factor Foxg1 is known to be continuously expressed at a high level in mature neurons in the telencephalon, but little is known about its role in neural plasticity. Mutations in human FOXG1 cause deficiencies in learning and memory and limit social ability, which is defined as FOXG1 syndrome, but its pathogenic mechanism remains unclear. To examine the role of Foxg1 in adults, we crossed Camk2a-CreER with Foxg1fl/fl mice and conditionally disrupted Foxg1 with tamoxifen in mature neurons. We found that spatial learning and memory were significantly impaired when examined by the Morris water maze test. The cKO mice also showed a significant reduction in freezing time during the contextual and cued fear conditioning test, indicating that fear conditioning memory was affected. A remarkable reduction in Schaffer-collateral long-term potentiation was also recorded. Morphologically, the dendritic arborization and spine densities of hippocampal pyramidal neurons were significantly reduced. Primary cell culture further confirmed altered dendritic complexity after Foxg1 deletion. Our results indicated that Foxg1 plays an important role in maintaining the neural plasticity, which is vital to high-grade function.

Loss of Foxg1 Impairs the Development of Cortical SST-Interneurons Leading to Abnormal Emotional and Social Behaviors.

FOXG1 syndrome is a severe encephalopathy that exhibit intellectual disability, emotional disorder, and limited social communication. To elucidate the contribution of somatostatin-expressing interneurons (SST-INs) to the cellular basis underlying FOXG1 syndrome, here, by crossing SST-cre with a Foxg1fl/fl line, we selectively ablated Foxg1. Loss of Foxg1 resulted in an obvious reduction in the number of SST-INs, accompanied by an altered ratio of subtypes. Foxg1-deficient SST-INs exhibited decreased membrane excitability and a changed ratio of electrophysiological firing patterns, which subsequently led to an excitatory/inhibitory imbalance. Moreover, cognitive defects, limited social interactions, and depression-like behaviors were detected in Foxg1 cKO mice. Treatment with low-dose of clonazepam effectively alleviated the defects. These results identify a link of SST-IN development to the aberrant emotion, cognition, and social capacities in patients. Our findings identify a novel role of Foxg1 in SST-IN development and put new insights into the cellular basis of FOXG1 syndrome.

FOXG1 Orchestrates Neocortical Organization and Cortico-Cortical Connections

The hallmarks of FOXG1 syndrome, which results from mutations in a single FOXG1 allele, include cortical atrophy and corpus callosum agenesis. However, the etiology for these structural deficits and the role of FOXG1 in cortical projection neurons remain unclear. Here we demonstrate that Foxg1 in pyramidal neurons plays essential roles in establishing cortical layers and the identity and axon trajectory of callosal projection neurons. The neuron-specific actions of Foxg1 are achieved by forming a transcription complex with Rp58. The Foxg1-Rp58 complex directly binds and represses Robo1, Slit3, and Reelin genes, the key regulators of callosal axon guidance and neuronal migration. We also found that inactivation of one Foxg1 allele specifically in cortical neurons was sufficient to cause cerebral cortical hypoplasia and corpus callosum agenesis. Together, this study reveals a novel gene regulatory pathway that specifies neuronal characteristics during cerebral cortex development and sheds light on the etiology of FOXG1 syndrome. VIDEO ABSTRACT.

The role of FOXG1 in the postnatal development and survival of mouse cochlear hair cells

The development of therapeutic interventions for hearing loss requires a detailed understanding of the genes and proteins involved in hearing. The FOXG1 protein plays an important role in early neural development and in a variety of neurodevelopmental disorders. Previous studies have shown that there are severe deformities in the inner ear in Foxg1 knockout mice, but due to the postnatal lethality of Foxg1 knockout mice, the role of FOXG1 in hair cell (HC) development and survival during the postnatal period has not been investigated. In this study, we took advantage of transgenic mice that have a specific knockout of Foxg1 in HCs, thus allowing us to explore the role of FOXG1 in postnatal HC development and survival. In the Foxg1 conditional knockout (CKO) HCs, an extra row of HCs appeared in the apical turn of the cochlea and some parts of the middle turn at postnatal day (P)1 and P7; however, these HCs gradually underwent apoptosis, and the HC number was significantly decreased by P21. Auditory brainstem response tests showed that the Foxg1 CKO mice had lost their hearing by P30. The RNA-Seq results and the qPCR verification both showed that the Wnt, Notch, IGF, EGF, and Hippo signaling pathways were down-regulated in the HCs of Foxg1 CKO mice. The significant down-regulation of the Notch signaling pathway might be the reason for the increased numbers of HCs in the cochleae of Foxg1 CKO mice at P1 and P7, while the down-regulation of the Wnt, IGF, and EGF signaling pathways might lead to subsequent HC apoptosis. Together, these results indicate that knockout of Foxg1 induces an extra row of HCs via Notch signaling inhibition and induces subsequent apoptosis of these HCs by inhibiting the Wnt, IGF, and EGF signaling pathways. This study thus provides new evidence for the function and mechanism of FOXG1 in HC development and survival in mice.

Foxg1 Regulates the Postnatal Development of Cortical Interneurons.

Abnormalities in cortical interneurons are closely associated with neurological diseases. Most patients with Foxg1 syndrome experience seizures, suggesting a possible role of Foxg1 in the cortical interneuron development. Here, by conditional deletion of Foxg1, which was achieved by crossing Foxg1fl/fl with the Gad2-CreER line, we found the postnatal distributions of somatostatin-, calretinin-, and neuropeptide Y-positive interneurons in the cortex were impaired. Further investigations revealed an enhanced dendritic complexity and decreased migration capacity of Foxg1-deficient interneurons, accompanied by remarkable downregulation of Dlx1 and CXCR4. Overexpression of Dlx1 or knock down its downstream Pak3 rescued the differentiation detects, demonstrated that Foxg1 functioned upstream of Dlx1-Pak3 signal pathway to regulate the postnatal development of cortical interneurons. Due to the imbalanced neural circuit, Foxg1 mutants showed increased seizure susceptibility. These findings will improve our understanding of the postnatal development of interneurons and help to elucidate the mechanisms underlying seizure in patients carrying Foxg1 mutations.

Collagen-derived dipeptide prolyl-hydroxyproline promotes osteogenic differentiation through Foxg1

Prolyl-hydroxyproline (Pro-Hyp) is one of the major constituents of collagen-derived dipeptides. We previously reported that Pro-Hyp promotes the differentiation of osteoblasts by increasing Runx2, osterix and Col1α1 mRNA expression levels. Here, to elucidate the mechanism of Pro-Hyp promotion of osteoblast differentiation, we focus on the involvement of Foxo1 in osteoblast differentiation via Runx2 regulation and the role of Foxg1 in Foxo1 regulation. The addition of Pro-Hyp had no effect on MC3T3-E1 cell proliferation in Foxo1- or Foxg1-knockdown cells. In Foxo1-knockdown cells, the addition of Pro-Hyp increased ALP activity, but in Foxg1-knockdown cells, it had no effect on ALP activity. An enhancing effect of Pro-Hyp on the Runx2 and osterix expression levels was observed in Foxo1-knockdown cells. However, no enhancing effect of Pro-Hyp on osteoblastic gene expression was observed when Foxg1 was knocked down. These results demonstrate that Pro-Hyp promotes osteoblastic MC3T3-E1 cell differentiation and upregulation of osteogenic genes via Foxg1 expression.

The Transcription Factor Foxg1 Promotes Optic Fissure Closure in the Mouse by Suppressing Wnt8b in the Nasal Optic Stalk.

During vertebrate eye morphogenesis, a transient fissure forms at its inferior part, known as the optic fissure. This will gradually close, giving rise to a healthy, spherical optic cup. Failure of the optic fissure to close gives rise to an ocular disorder known as coloboma. During this developmental process, Foxg1 is expressed in the optic neuroepithelium, with highest levels of expression in the nasal optic stalk. Foxg1−/− mutant mice have microphthalmic eyes with a large ventral coloboma. We found Wnt8b expression upregulated in the Foxg1−/− optic stalk and hypothesized that, similar to what is observed in telencephalic development, Foxg1 directs development of the optic neuroepithelium through transcriptional suppression of Wnt8b. To test this, we generated Foxg1−/−;Wnt8b−/− double mutants of either sex and found that the morphology of the optic cup and stalk and the closure of the optic fissure were substantially rescued in these embryos. This rescue correlates with restored Pax2 expression in the anterior tip of the optic fissure. In addition, although we do not find evidence implicating altered proliferation in the rescue, we observe a significant increase in apoptotic cell density in Foxg1−/−;Wnt8b−/− double mutants compared with the Foxg1−/− single mutant. Upregulation of Wnt/β-catenin target molecules in the optic cup and stalk may underlie the molecular and morphological defects in the Foxg1−/− mutant. Our results show that proper optic fissure closure relies on Wnt8b suppression by Foxg1 in the nasal optic stalk to maintain balanced apoptosis and Pax2 expression in the nasal and temporal edges of the fissure.SIGNIFICANCE STATEMENT Coloboma is an ocular disorder that may result in a loss of visual acuity and accounts for ∼10% of childhood blindness. It results from errors in the sealing of the optic fissure (OF), a transient structure at the bottom of the eye. Here, we investigate the colobomatous phenotype of the Foxg1−/− mutant mouse. We identify upregulated expression of Wnt8b in the optic stalk of Foxg1−/− mutants before OF closure initiates. Foxg1−/−;Wnt8b−/− double mutants show a substantial rescue of the Foxg1−/− coloboma phenotype, which correlates with a rescue in molecular and cellular defects of Foxg1−/− mutants. Our results unravel a new role of Foxg1 in promoting OF closure providing additional knowledge about the molecules and cellular mechanisms underlying coloboma formation.

Impaired Interneuron Development after Foxg1 Disruption.

Interneurons play pivotal roles in the modulation of cortical function; however, the mechanisms that control interneuron development remain unclear. This study aimed to explore a new role for Foxg1 in interneuron development. By crossing Foxg1fl/fl mice with a Dlx5/6-Cre line, we determined that conditional disruption of Foxg1 in the subpallium results in defects in interneuron development. In developing interneurons, the expression levels of several receptors, including roundabout-1, Eph receptor A4, and C-X-C motif receptor 4/7, were strongly downregulated, which led to migration defects after Foxg1 ablation. The transcription factors Dlx1/2 and Mash1, which have been reported to be involved in interneuron development, were significantly upregulated at the mRNA levels. Foxg1 mutant cells developed shorter neurites and fewer branches and displayed severe migration defects in vitro. Notably, Prox1, which is a transcription factor that functions as a key regulator in the development of excitatory neurons, was also dramatically upregulated at both the mRNA and protein levels, suggesting that Prox1 is also important for interneuron development. Our work demonstrates that Foxg1 may act as a critical upstream regulator of Dlx1/2, Mash1, and Prox1 to control interneuron development. These findings will further our understanding of the molecular mechanisms of interneuron development.

O05 * FOXG1 IS A CANDIDATE TRANSCRIPTIONAL MASTER REGULATOR IN NEURAL STEM CELLS AND GLIOBLASTOMA

INTRODUCTION: FOXG1 is a forebrain-specific forkhead box transcription factor, whose high level expression is necessary for telencephalic development in the embryo. Glioblastoma-derived cell cultures also consistently express high levels of FOXG1, and expression in the primary tumour is negatively correlated with patient survival. We and other groups have shown that FOXG1 cooperates with SOX2 to reprogram normal differentiated cells to a neural stem state. METHOD: We have investigated the function of FOXG1 in neural stem cells and their glioblastoma-derived equivalents, and using shRNA knockdown and Crispr/Cas knockout, as well as constitutive and inducible overexpression. We have characterised FOXG1's transcriptional targets using ChIP-Seq and Taqman array assays. We are in the process of exploring FOXG1's reprogramming capabilities in normal and neoplastic brain cell cultures. RESULTS: Functional data supports a role for FOXG1 in establishing and maintaining a neural stem identity, although some established tumour lines show evidence of escape from this regulation. We present a profile of downstream DNA-binding targets, including genes with established roles in self-renewal, lineage selection, cell cycle and chromatin regulation. CONCLUSION: FOXG1 is a candidate master regulator of neural stem cell identity. We believe that its consistent overexpression in GBM cell lines reflects a key role in glioma initiation, and we anticipate that FOXG1's downstream targets will present important novel therapeutic targets.

The Temporal Sequence of the Mammalian Neocortical Neurogenetic Program Drives Mediolateral Pattern in the Chick Pallium

The six-layered neocortex permits complex information processing in all mammalian species. Because its homologous region (the pallium) in nonmammalian amniotes has a different architecture, the ability of neocortical progenitors to generate an orderly sequence of distinct cell types was thought to have arisen in the mammalian lineage. This study, however, shows that layer-specific neuron subtypes do exist in the chick pallium. Deep- and upper-layer neurons are not layered but are segregated in distinct mediolateral domains in vivo. Surprisingly, cultured chick neural progenitors produce multiple layer-specific neuronal subtypes in the same chronological sequence as seen in mammals. These results suggest that the temporal sequence of the neocortical neurogenetic program was already inherent in the last common ancestor of mammals and birds and that mammals use this conserved program to generate a uniformly layered neocortex, whereas birds impose spatial constraints on the sequence to pattern the pallium.

FOXG1 Is Responsible for the Congenital Variant of Rett Syndrome

Rett syndrome is a severe neurodevelopmental disease caused by mutations in the X-linked gene encoding for the methyl-CpG-binding protein MeCP2. Here, we report the identification of FOXG1-truncating mutations in two patients affected by the congenital variant of Rett syndrome. FOXG1 encodes a brain-specific transcriptional repressor that is essential for early development of the telencephalon. Molecular analysis revealed that Foxg1 might also share common molecular mechanisms with MeCP2 during neuronal development, exhibiting partially overlapping expression domain in postnatal cortex and neuronal subnuclear localization.

FOXG1 dysregulation is a frequent event in medulloblastoma

Medulloblastomas represent 20% of malignant brain tumors of childhood. Although, they show multiple, non-random genomic alterations, no common, early genetic event involving all histologic types of medulloblastomas have been described. Nineteen medulloblastomas were analyzed using chromosomal comparative genomic hybridization (cCGH). Nine tumors with the most frequent number of genetic changes were further analyzed using bacterial artificial chromosome array CGH (aCGH). With aCGH, the frequency of gains and losses were higher than with cCGH. Chromosome 2p gains spanning 2p11-2p25 including N-myc locus, 2p24.1 were detected in 5/9 (55%) tumors while 14q12 gains were detected in 6/9 (67%) tumors. The 14q12 locus overlapped with the FOXGI gene locus. Quantitative real time PCR showed a 2-7-fold copy gain for FOXG1 in all the nine tumors. Protein expression was demonstrated by immunohistochemistry in all histologic types. The expression of FOXG1 and p21cip1 showed an inverse relationship. FOXG1 copy gain (>2 to 21 folds) was seen in 93% (55/59) of a validating set of tumors and showed a positive correlation with protein expression (Spearman's rank order correlation coefficient = 0.276; P = 0.038) representing the first report of FOXG1 dysregulation in medulloblastoma. Modulation of FOXG1 expression in DAOY cell line using siRNA showed a modest decrease in proliferation with a 2-fold upregulation of p21cip1. Current reports indicate that FOXG1 represses TGF-beta induced expression of p21cip1 and cytostasis, and forms a transcriptional repressor complex with Notch signaling induced hes1. Our findings are consistent with a role for FOXG1 in the inhibition of TGF-beta induced cytostasis in medulloblastoma.

FOXG1 is overexpressed in hepatoblastoma

Bacterial artificial chromosome array comparative genomic hybridization analysis of hepatoblastomas reveals a deletion in the 14q12 locus in 12 of 16 cases. A high frequency of copy gain is seen on chromosomes 1q, 2, 5p, 8, and 20. Frequent deletions are also seen at 6q, 17q, and 1p with less frequent gains on 4p, 6p, and 19p. 14q12 deletion locus analyses using quantitative real-time polymerase chain reaction reveals copy number gain/amplification in the region immediately telomeric to the deleted locus, including copy number gain (2- to 4-fold) of FOXG1 in 13 out of 16 tumors. This is associated with up-regulation (approximately 87-fold) of FOXG1 gene transcripts and increased protein expression. Immunostaining reveals an inverse relationship between FOXG1 expression and p21cip1 expression in all histologic subtypes. However, FOXG1 transcript levels were significantly higher (approximately 75-fold) in tumors with embryonal and small cell components when compared with pure fetal hepatoblastomas. FOXG1 has been implicated in the repression of transforming growth factor beta-induced expression of p21cip1 and cytostasis. Our findings are consistent with such a role for FOXG1. We propose that FOXG1 overexpression may contribute to the maintenance of the undifferentiated state in hepatoblastomas and could be a potential target for molecular therapeutics. This is the first report of a possible role for FOXG1 in hepatoblastoma and pediatric neoplasia.