Amiel, J., Laudier, B., Attie-Bitach, T., Trang, H., de Pontual, L., Gener, B. et al. Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome. Nat. Genet. 33, 459-461
ABSTRACT Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5-9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans.
Full-textDOI: · Available from: Pierre Ray, Aug 28, 2015
- SourceAvailable from: Roberta Benfante
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- "Interestingly, co-transfection of the deleted proteins with the wild-type protein reduced promoter activity in comparison with the full transactivation observed with PHOX2B WT alone only in the case of the PHOX2B Δaa 200–290 mutant (Fig. 7D, compare hatched bars with white bar). These data are in line with the fact that in-frame polyalanine contraction variants (with 7, 13, 14 or 15 repeats in the polyalanine tract) are also found in the control population (Amiel et al., 2003; Hung et al., 2007; Matera et al., 2004; Toyota et al., 2004). Finally, our data support the idea that the portion of the protein downstream of the homeodomain containing the polyalanine tract modulates the DNA binding and transactivation function of the PHOX2B protein, and it is reasonable to hypothesize that the deletion of a large C-terminal region of the protein encompassing the polyalanine stretch can affect the correct orientation, folding and/or protein–protein interaction properties of the remaining portion of the protein generating a mutant variant with dominant-negative effects on a subset of promoters. "
ABSTRACT: The PHOX2B transcription factor plays a crucial role in autonomic nervous system development. In humans, heterozygous mutations of the PHOX2B gene lead to Congenital Central Hypoventilation Syndrome (CCHS), a rare disorder characterized by a broad variety of symptoms of autonomic nervous system dysfunction including inadequate control of breathing. The vast majority of patients with CCHS are heterozygous for a polyalanine repeat expansion mutation involving a polyalanine tract of twenty residues in the C-terminus of PHOX2B. Although several lines of evidence support a dominant-negative mechanism for PHOX2B mutations in CCHS, the molecular effects of PHOX2B mutant proteins on the transcriptional activity of the wild-type protein have not yet been elucidated. As one of the targets of PHOX2B is the PHOX2B gene itself, we tested the transcriptional activity of wild-type and mutant proteins on the PHOX2B gene promoter, and found that the transactivation ability of proteins with polyalanine expansions decreased as a function of the length of the expansion, whereas DNA binding was severely affected only in the case of the mutant with the longest polyalanine tract (+13 alanine). Co-transfection experiments using equimolar amounts of PHOX2B wild-type and mutant proteins in order to simulate a heterozygous state in vitro and four different PHOX2B target gene regulatory regions (PHOX2B, PHOX2A, DBH, TLX2) clearly showed that the polyalanine expanded proteins alter the transcriptional activity of wild-type protein in a promoter-specific manner, without any clear correlation with the length of the expansion. Moreover, although reduced transactivation may be caused by retention of the wild-type protein in the cytoplasm or in nuclear aggregates, this mechanism can only be partially responsible for the pathogenesis of CCHS because of the reduction in cytoplasmic and nuclear accumulation when the +13 alanine mutant is co-expressed with wild-type protein, and the fact that the shortest polyalanine expansions do not form visible cytoplasmic aggregates. Deletion of the C-terminal of PHOX2B leads to a protein that correctly localizes in the nucleus but impairs PHOX2B wild-type transcriptional activity, thus suggesting that protein mislocalization is not the only mechanism leading to CCHS. The results of this study provide novel in vitro experimental evidence of a transcriptional dominant-negative effect of PHOX2B polyalanine mutant proteins on wild-type protein on two different PHOX2B target genes.Neurobiology of Disease 10/2012; 50(1). DOI:10.1016/j.nbd.2012.10.019 · 5.20 Impact Factor
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- "The homozygous disruption of the PHOX2B gene has been reported to result in the absence of enteric ganglia, a feature which is reminiscent of HSCR (Elworthy et al., 2005). Amiel et al. (2003) reported that PHOX2B is the primary disease locus in congenital central hypoventilation syndrome (CCHS). They found that mutations in PHOX2B not only exist in isolated cases of CCHS but also in individuals with a more complex neural crest involvement including CCHS and HSCR (Haddad syndrome). "
ABSTRACT: Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cells to fully colonize the gut during embryonic development. It is characterized by the absence of the enteric ganglia in a variable length of the intestine. Substantial progress has been made in understanding the genetic basis of HSCR with the help of advanced genetic analysis techniques and animal models. More than 11 genes have been found to be involved in the pathogenesis of HSCR. The RET gene is the most important susceptibility gene involved in HSCR with both coding and non- coding sequence mutations. Due to phenotypic diversity and genetic complexity observed in HSCR, mutational analysis has limited practical value in genetic counseling and clinical practice. In this review, we discuss the progress that has been made in understanding the molecular genetics of HSCR and summarize the currently identified genes as well as interactions between pathways and gene-modifying loci in HSCR. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 10/2012; 295(10):1628-38. DOI:10.1002/ar.22538 · 1.53 Impact Factor
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- "In vertebrates, CO2-sensing neurons are critical regulators of respiration . Their dysfunction is proposed to underlie disorders such as sudden infant death syndrome  and congenital hypoventilation syndrome . CO2 is also sensed by animals as an ethologically relevant environmental cue. "
ABSTRACT: Many animals possess neurons specialized for the detection of carbon dioxide (CO(2)), which acts as a cue to elicit behavioral responses and is also an internally generated product of respiration that regulates animal physiology. In many organisms how such neurons detect CO(2) is poorly understood. We report here a mechanism that endows C. elegans neurons with the ability to detect CO(2). The ETS-5 transcription factor is necessary for the specification of CO(2)-sensing BAG neurons. Expression of a single ETS-5 target gene, gcy-9, which encodes a receptor-type guanylate cyclase, is sufficient to bypass a requirement for ets-5 in CO(2)-detection and transforms neurons into CO(2)-sensing neurons. Because ETS-5 and GCY-9 are members of gene families that are conserved between nematodes and vertebrates, a similar mechanism might act in the specification of CO(2)-sensing neurons in other phyla.PLoS ONE 03/2012; 7(3):e34014. DOI:10.1371/journal.pone.0034014 · 3.23 Impact Factor