The brain-specific POU-box gene Brn4 is a sex-linked transcription factor located on the human and mouse X chromosomes

A New Pathogenic Variant in POU3F4 Causing Deafness Due to an Incomplete Partition of the Cochlea Paved the Way for Innovative Surgery

Incomplete partition type III (IP-III) is a relatively rare inner ear malformation that has been associated with a POU3F4 gene mutation. The IP-III anomaly is mainly characterized by incomplete separation of the modiolus of the cochlea from the internal auditory canal. We describe a 71-year-old woman with profound sensorineural hearing loss diagnosed with an IP-III of the cochlea that underwent cochlear implantation. Via targeted sequencing with a non-syndromic gene panel, we identified a heterozygous c.934G > C p. (Ala31Pro) pathogenic variant in the POU3F4 gene that has not been reported previously. IP-III of the cochlea is challenging for cochlear implant surgery for two main reasons: liquor cerebrospinalis gusher and electrode misplacement. Surgically, it may be better to opt for a shorter array because it is less likely for misplacement with the electrode in a false route. Secondly, the surgeon has to consider the insertion angles of cochlear access very strictly to avoid misplacement along the inner ear canal. Genetic results in well describes genotype-phenotype correlations are a strong clinical tool and as in this case guided surgical planning and robotic execution.

[Presentation of a rare case of hereditary hearing loss with X-linked recessive inheritance associated with the POU3F4 gene]

Congenital hearing loss is one of the most frequent inherited human pathologies, occurring in 1-2 out of 1000 newborns. X-linked hearing loss occurs in 1-5% of all congenital hearing impairments. The proband (a man) and his affected brother have profound prelingual non-syndromic neurosensory hearing loss. Their parents are healthy. The aim of the study was to determine the cause of hearing loss in a given family and to assess the population frequency of the revealed pathogenic genetic variant. NGS analysis identified a pathogenic variant c.907C>T (p.Pro303Ser) in the POU3F4 gene mapped to the Xq21.1 locus. This is the second case of X-linked hearing loss (DFNX2, OMIM 304400) in Europe, caused by the c.907C>T variant in the POU3F4 gene. DFNX2-hearing loss is manifested with abnormalities of the inner ear, predisposing to the "gusher effect" - otoliquorrhea during stapedoplasty. The brother was diagnosed with a c.907C>T variant in the POU3F4 gene in the hemizygous state while in their mother - in the heterozygous state. Their father had no variant c.907C>T. Molecular genetic analysis showed that the genetic variant c.907C>T was not detected in the control sample of healthy female from the Nogai population, which suggests its low frequency in the population.

A novel pathogenic variant c.975G>A (p.Trp325*) in the POU3F4 gene in Yakut family (Eastern Siberia, Russia) with the X-linked deafness-2 (DFNX2)

Here, we report a novel hemizygous transition c.975G>A (p.Trp325*) in POU3F4 gene (Xq21) found in two deaf half-brothers from one Yakut family (Eastern Siberia, Russia) with identical inner ear abnormalities ("corkscrew" cochlea with an absence of modiolus) specific to X-linked deafness-2 (DFNX2). Comprehensive clinical evaluation (CT and MR-imaging, audiological and stabilometric examinations) of available members of this family revealed both already known (mixed progressive hearing loss) and additional (enlargement of semicircular canals and postural disorders) clinical DFNX2 features in affected males with c.975G>A (p.Trp325*). Moreover, mild enlargement of semicircular canals, postural abnormalities and different types of hearing thresholds were found in female carrier of this POU3F4-variant.

Regulatory roles of Oct proteins in the mammary gland

The expression of Oct-1 and -2 and their binding to the octamer motif in the mammary gland are developmentally and hormonally regulated, consistent with the expression of milk proteins. Both of these transcription factors constitutively bind to the proximal promoter of the milk protein gene β-casein and might be involved in the inhibition or activation of promoter activity via interactions with other transcription factors or cofactors at different developmental stages. In particular, the lactogenic hormone prolactin and glucocorticoids induce Oct-1 and Oct-2 binding and interaction with both the signal transducer and activator of transcription 5 (STAT5) and the glucocorticoid receptor on the β-casein promoter to activate β-casein expression. In addition, increasing evidence has shown the involvement of another Oct factor, Oct-3/4, in mammary tumorigenesis, making Oct-3/4 an emerging prognostic marker of breast cancer and a molecular target for the gene-directed therapeutic intervention, prevention and treatment of breast cancer. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

The role of octamer binding transcription factors in glioblastoma multiforme

A group of transcription factors (TF) that are master developmental regulators of the establishment and maintenance of pluripotency during embryogenesis play additional roles to control tissue homeostasis and regeneration in adults. Among these TFs, members of the octamer-binding transcription factor (OCT) gene family are well documented as major regulators controlling the self-renewal and pluripotency of stem cells isolated from different adult organs including the brain. In the last few years a large number of studies show the aberrant expression and dysfunction of OCT in different types of cancers including glioblastoma multiforme (GBM). GBM is the most common malignant primary brain tumor, and contains a subpopulation of undifferentiated stem cells (GSCs), with self-renewal and tumorigenic potential that contribute to tumor initiation, invasion, recurrence, and therapeutic resistance. In this review, we have summarized the current knowledge about OCT family in GBM and their crucial role in the initiation, maintenance and drug resistance properties of GSCs. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

X-linked deafness-2 (DFNX2) phenotype associated with a paracentric inversion upstream of POU3F4

PURPOSE

The authors report on a 7-year-old male, designated FR, who has severe sensorineural hearing loss. Features include a round face, hypertelorism, epicanthal folds, and flat nasal root. Although there were early developmental concerns regarding FR, all but his speech delay resolved when he was placed in an educational program that accommodated his hearing loss. Genetic studies were performed to investigate genetic causes for his hearing loss.

METHOD

History, physical examination, audiologic assessment, and imaging were performed according to usual practice. FMR1,GJB2,GJB6, and POU3F4 genes were sequenced. Chromosomal studies consisted of karyotyping and breakpoint analysis by fluorescence in situ hybridization (FISH).

RESULTS

Results from FMR1,GJB2,GJB6, and POU3F4 sequencing and echocardiography, electrocardiogram, and abdominal ultrasound were normal. A computed tomography (CT) scan revealed a large fundus of the internal auditory canals and absence of the bony partition between the fundus and the adjacent cochlear turns, with a widened modiolus bilaterally. FR's CT findings were consistent with those described in persons with X-linked deafness-2 (DFNX2) hereditary deafness. FR's karyotype was 46,inv(X)(q13q24),Y.ish inv(X)(XIST+)mat. FISH refined the breakpoints to inv(X)(q21.1q22.3). The Xq21.1 breakpoint was narrowed to a 25-kb region 450 kb centromeric to the DFNX2 gene, POU3F4. There are rare case reports of DFNX2 patients with chromosomal rearrangements positioned centromeric to POU3F4 and no mutations within the gene.

CONCLUSION

Authors hypothesized that FR's hearing loss was caused by dysregulation of POU3F4 due to separation from regulatory elements affected by the inversion.

Cochlear implantation in children with congenital X-linked deafness due to novel mutations in POU3F4 gene

OBJECTIVES

We report novel mutations in the POU3F4 gene resulting in congenital X-linked deafness DFN3, and describe the results of cochlear implantation in 4 boys (3 siblings) followed for an average of 3.5 years.

METHODS

The diagnosis of DFN3 was made in infant boys on the basis of the radiologic criteria of an underdeveloped modiolus, a wide cochlear fossette, and the presence of all cochlear turns. The POU3F4 gene was sequenced. A standard, transmastoid, facial recess approach was used for cochlear implantation. A lumbar drain was placed before the operation.

RESULTS

The identified mutations in the POU3F4 gene were novel (p.R167X in the 3 siblings) or recently reported (p.S310del). A high-flow cerebrospinal fluid leak through the cochleostomy was encountered in each patient and was ultimately controlled. Although the implants functioned properly, the auditory perceptual abilities did not progress past sound detection in the 3 siblings, or past closed-set word identification in the non-sibling, who achieved better speech perception with contralateral amplification. Three boys (2 siblings) show signs of other learning disorders; 1 boy was too young for a complete assessment.

CONCLUSIONS

Preoperative gene mutation analysis in DFN3 patients who are considering cochlear implantation may help in long-term counseling and in avoidance of postoperative complications. Limited auditory perception and language acquisition may result. Amplification may sometimes be a better alternative than cochlear implantation, despite the severity of the hearing loss.

Transcript map of a 900-kb genomic region in Xp22.1-p22.2: identification of 12 novel genes

The Xp22.1-p22.2 interval is a focus of interest as a number of hereditary disease loci have been mapped to this region, including X-linked nonsyndromic sensorineural deafness (DFN6), X-linked juvenile retinoschisis (RS), and several X-linked mental retardation syndromes. In the course of cloning the RS gene we have assembled YAC and PAC contigs of the 900-kb candidate region delimited by DXS418 and DXS999. In this study, we now report the construction of a first transcript map of this chromosomal interval by combining exon trapping, EST mapping, and computational gene identification methods. Overall, this strategy has led to the assembly of at least 12 novel transcripts positioned within the DXS418-DXS999 region, one of these encoding a putative protein kinase motif with significant homology to the rat p58/GTA protein kinase domain and another a putative neuronal protein with strong homology to a Drosophila transcriptional repressor.

Transcribed sequences encoded in the region involved in contiguous deletion syndrome that comprises X-linked stapes fixation and deafness

We have used a direct cDNA selection protocol to isolate expressed sequences from yeast artificial chromosome clones that contain approximately 900 Kb of genomic DNA from Xq21 band that is deleted in contiguous gene syndromes comprising of mixed deafness associated with stapes fixation (DFN3). In addition to identifying Brn4 (POU3f4), a POU domain containing transcription factor that is involved in DFN3 phenotype, we have isolated seven short fragment cDNAs mapping to the deleted region. Some of the selected fragments showed X-chromosome specificity and hybridized to autosomal DNA fragments, indicating the presence of a low abundance interspersed repeat in the cDNAs or their homology to some uncharacterized family of genes. In conformity with the inertness of Xq21 band our results demonstrate that the region encodes far less than the average density of genes in other parts of the genome.

Class III POU genes: generation of homopolymeric amino acid repeats under GC pressure in mammals

The class III POU transcription factor genes play an important role in the nervous system. Comparison of their entire amino acid sequences disclosed a remarkable feature of particular mammalian class III POU genes. Alanine, glycine, and proline repeats were present in the mammalian Brain-1 gene, whereas most of these repeats were absent in the nonmammalian homologue. The mammalian Brain-2 gene had alanine, glycine, proline, and glutamine repeats, which were missing in the nonmammalian homologue. The mammalian Scip gene had alanine, glycine, proline, and histidine repeats, but the nonmammalian homologue completely lacked these repeats. In contrast, the mammalian Brain-4 gene had no amino acid repeats like its nonmammalian homologue. The mammalian genes containing the characteristic amino acid repeats had another feature, higher GC content. We found a positive correlation between the GC content and the amino acid repeat ratio. Those amino acids were encoded by triplet codons with relatively high GC content. These results suggest that the GC pressure has facilitated generation of the homopolymeric amino acid repeats.

Checklist: vertebrate homeobox genes

Up to now around 170 different homeobox genes have been cloned from vertebrate genomes. A compilation of the various isolates from mouse, chick, frog, fish and man is presented in the form of a concise checklist, including the designations from the original publications. Putative homologs from different species are aligned, and key characteristics of embryonic or adult expression domains, as well as mutant phenotypes are briefly indicated.

Cloning and characterization of a murine brain specific gene Bpx and its human homologue lying within the Xic candidate region

The X inactivation centre (Xic) is a cis-acting locus thought to play a key role in the initiation of X-inactivation. We have cloned and characterized a new gene, Bpx, lying distal to the murine Xist. Bpx, which is specifically expressed in the brain, shows strong homology to genes encoding nucleosome assembly proteins and is normally X-inactivated in mice. Isolation and localization of BPX, its human homologue, has shown the gene to be located centromeric to XIST in man. The Xq13 region, whose orientation is apparently globally conserved between man and mouse, must therefore contain an inversion of at least 600 kb spanning the XIST sequence and including the CDX4 and BPX genes.

POU homeodomain genes and myogenesis

We show that members of the POU homeodomain family are among the transcription factors expressed in developing mouse skeletal muscle. From a cDNA library prepared from fetal muscle mRNA, we cloned a cDNA identical to that of Brn-4, a POU class II gene previously cloned from neural tissues. In limb muscle, we found that Brn-4 mRNA expression was highest at embryonic days 15-18, declined-after birth, and was undetectable in adults. The mRNAs of two additional POU genes, Emb (POU class VI) and Oct-1 (POU class II), were also expressed in developing muscle and, unlike Brn-4, continued to be expressed in postnatal and adult muscles. In skeletal muscle, expression of Brn-4 is myogenin-dependent, because muscles from myogenin-deficient fetuses contained much less Brn-4 mRNA than muscles from myogenin-expressing littermates. In contrast, expression of Emb was the same in the presence or absence of myogenin. The distinct pattern of Brn-4 mRNA expression and its dependence on a myogenic regulatory factor suggest that Brn-4 is part of the network of interacting transcription factors that control muscle-specific gene expression during mammalian myogenesis.

Mapping and cloning hereditary deafness genes

In the past two years, considerable progress has been made in the mapping and cloning of human deafness genes. Highlights are the chromosomal localization of at least five genes for autosomal forms of non-syndromic deafness and, more recently, the cloning of an X-linked deafness gene, DFN3, and the Usher syndrome type IB gene. This last gene encodes a myosin-like protein and was identified as the human homolog of the mouse shaker-1 gene. The DFN3 gene Brain 4 encodes a POU domain containing transcription factor that is involved in the development of the inner ear.

Association between X-linked mixed deafness and mutations in the POU domain gene POU3F4

Deafness with fixation of the stapes (DFN3) is the most frequent X-linked form of hearing impairment. The underlying gene has been localized to a 500-kilobase segment of the Xq21 band. Here, it is reported that a candidate gene for this disorder, Brain 4 (POU3F4), which encodes a transcription factor with a POU domain, maps to the same interval. In five unrelated patients with DFN3 but not in 50 normal controls, small mutations were found that result in truncation of the predicted protein or in nonconservative amino acid substitutions. These findings indicate that POU3F4 mutations are a molecular cause of DFN3.