FOXG1 Gene

Abstract: Duplications of FOXG1 gene at 14q12 have been reported in patients with infantile spasms and developmental delay of variable severity1, 2, 3 FOXG1 encodes the forkhead protein G1, a brain-specific transcriptional repressor, regulating corticogenesis in the developing brain and neuronal stem cell self-renewal in the postnatal brain4 Recently, Amor et al5 reported on this journal an interstitial duplication of ∼88 kb at 14q12 in a father–son pair with hemifacial microsomia and normal neurocognitive phenotype The duplication contains only two polypeptide-encoding genes, FOXG1 and C14orf23, suggesting that FOXG1 duplication may be benign or at least incompletely penetrant That makes the involvement of FOXG1 duplication in the pathogenesis of the neurocognitive impairment and epilepsy controversial As also discussed by Brunetti-Pierri et al,6 we feel that this statement needs special caution Functional consequences of chromosomal microduplication and microdeletion rely on the final gene dosage, which is strongly influenced by the location of the breakpoint In this context, the understanding of the contribution of regulatory sequences in gene transcription is critical to understand the relationship between CNVs and human diseases With this purpose, the Encyclopedia of DNA Elements (ENCODE) project has recently performed a systematic analysis of transcriptional regulation in different human cell lines, providing new understanding about transcription start sites, including their relationship with specific regulatory sequences and histone modification and features of chromatin accessibility7, 8 Interestingly, analysis of histone modifications from the ENCODE project revealed the presence of a putative regulatory element upstream FOXG1 gene between 28 188 and 28 217 kb (UCSC genome browser, NCBI Build 36/hg18) (Figure 1) This conserved region localizes about 130 kb upstream FOXG1 gene and contains histone modifications typical of enhancers of gene transcription (eg, histone H3 and Lysine 4 monomethylation) in eight different human cells lines Analysis of regulatory potential scores, comparing frequencies of short alignment patterns between known regulatory elements and neutral DNA,9 also disclose two additional putative elements typical of cis-regulatory modules within this region (Figure 1) Moreover, it contains a DNaseI hypersensitive site (DHS) DHSs reflect genomic regions thought to be enriched for regulatory information and many DHSs reside at or near transcription start site Notably, no other polypeptide-encoding genes or non-coding RNAs and pseudogenes are present in the region, suggesting that this regulatory element might regulate FOXG1 transcription Analysis of duplication breakpoints previously reported on 14q12 revealed that duplications associated with an epileptic phenotype localizes uniquely upstream this regulatory element, whereas downstream duplications were identified only in the cases without seizures (Figure 1) On the basis of this finding, we suggest that FOXG1 duplication including this putative regulatory region allows the efficient transcription of the supernumerary copy of FOXG1 gene, resulting in an effective increase in FOXG1 expression and, thereby, in brain hyperexcitability In contrast, duplications starting downstream this putative regulatory site do not allow efficient transcription of FOXG1, which may underlie the lack of neurological phenotype in the case reported by Amor et al5 Figure 1 UCSC genome browser (NCBI36/hg18) schematic view of reported 14q12 duplications encompassing FOXG1 gene Histone modifications from the ENCODE project7 in eight cells lines (GM12878, H1-hESC, HMEC, HSMM, HUVEC, K562, NHEK and NHLF) indicate the presence Even if the functional relevance of this putative long-range regulatory element on FOXG1 transcription deserves to be experimentally verified, it provides an interesting clue to dissect genotype–phenotype correlation in FOXG1 microduplication and to uncover the real actual contribution of FOXG1 in the neurodevelopmental phenotype associated with 14q12 duplication Notably, chromosome rearrangements disrupting or displacing putative cis-regulatory elements distal to FOXG1 gene in patients with severe cognitive disabilities has been also reported,10, 11 pointing out the relevance of regulatory sequences in the expression of FOXG1 gene

Abstract: Foxg1 (previously named BF1) is a winged-helix transcription factor with restricted expression pattern in the telencephalic neuroepithelium of the neural tube and in the anterior half of the developing optic vesicle. Previous studies have shown that the targeted disruption of the Foxg1 gene leads to hypoplasia of the cerebral hemispheres with severe defect in the structures of the ventral telencephalon. To further investigate the molecular mechanisms by which Foxg1 plays essential roles during brain development, we have adopted a strategy to isolate genes whose expression changes immediately after introduction of Foxg1 in cultured neural precursor cell line, HiB5. Here, we report that seventeen genes were isolated by ordered differential displays that are up-regulated by over-expression of Foxg1, in cultured neuronal precursor cells. By nucleotide sequence comparison to known genes in the GeneBank database, we find that nine of these clones represent novel genes whose DNA sequences have not been reported. The results suggest that these genes are closely related to developmental regulation of Foxg1.

Abstract: Rett Syndrome (RTT) is an X-linked dominant neurodevelopmental disorder which specifically affecting females. Majority of the cases of RTT is caused because of mutation in methyl-CpG-binding protein (MECP2) gene; besides few cases are caused because of mutation in CDKL5 and FOXG1 gene as well. Since the RTT is a severe disorder and MECP2 and CDKL5 are X linked disorder, therefore, only females are affected. Since, males are hemizygous for X chromosome, therefore, males could not survive with these mutations. In contrast, RTT in males is because of mutations in FOXG1 gene, an autosomal gene. Microcephaly is the prominent phenotype among Rett patients characterized by progressive loss of intellectual functioning, development of stereotypic hand movement, seizures etc. To study the disease pathogenesis, live patients’ neurons are the best suited model system, however, getting patients live brain cells are impossible from an affected individual and also ethically not permissible. Therefore, development of a model system to recapitulate the phenotype of the syndrome with same genome as that of patient is essential. This can be done by using induced pluripotent stem cells (iPSCs) techniques. The main advantage of iPSCs is that it can be used to generate any type of brain cells, even a miniature brain organoid called cerebral organoid can also be generated which can be used to study cross talk between genes and their effects on different brain tissues. The first iPSCs model for Rett was developed by Ellis group in 2009. Subsequently, various researchers successfully generated Rett-iPSCs to evaluate different mutations pertaining to Rett phenotypes. The neurons differentiated from patient-specific iPSCs exhibits similar phenotypes as that of the patients, like reduced soma and nuclear size, decreased dendritic spine density, fewer synapse, altered calcium signaling, etc. It was demonstrated through iPSCs that there is overexpression of GABAergic gene products with MECP2 mutant iPSC-derived neurons while reduced functional synaptic contact and impaired neuronal activity were demonstrated in CDKL5 mutant iPSCs-derived neurons. Moreover, iPSCs-derived neurons from FOXG1-mutated patients showed increased level of GRID1 mRNA levels that regulate synaptic differentiation and thus have altered effect on normal development. Besides the disease pathogenesis study, efforts are also on for cellular therapy as well as evaluating different drug candidates. With the help of latest gene editing technique CRISPR/Cas9, various groups are trying to restore the functionality of MECP2 gene which can lead to a promising way toward treatment for Rett. This technique of iPSCs will be helpful not only for studying RTT in depth but also can pave a path toward drug development to ease the quality of life of the affected children.