Analysis of SOX10 mutations identified in Waardenburg‐Hirschsprung patients: Differential effects on target gene regulation

Abstract

SOX10 is a member of the SOX gene family related by homology to the high-mobility group (HMG) box region of the testis-determining gene SRY. Mutations of the transcription factor gene SOX10 lead to Waardenburg-Hirschsprung syndrome (Waardenburg-Shah syndrome, WS4) in humans. A number of SOX10 mutations have been identified in WS4 patients who suffer from different extents of intestinal aganglionosis, pigmentation, and hearing abnormalities. Some patients also exhibit signs of myelination deficiency in the central and peripheral nervous systems. Although the molecular bases for the wide range of symptoms displayed by the patients are still not clearly understood, a few target genes for SOX10 have been identified. We have analyzed the impact of six different SOX10 mutations on the activation of SOX10 target genes by yeast one-hybrid and mammalian cell transfection assays. To investigate the transactivation activities of the mutant proteins, three different SOX target binding sites were introduced into luciferase reporter gene constructs and examined in our series of transfection assays: consensus HMG domain protein binding sites; SOX10 binding sites identified in the RET promoter; and Sox10 binding sites identified in the P0 promoter. We found that the same mutation could have different transactivation activities when tested with different target binding sites and in different cell lines. The differential transactivation activities of the SOX10 mutants appeared to correlate with the intestinal and/or neurological symptoms presented in the patients. Among the six mutant SOX10 proteins tested, much reduced transactivation activities were observed when tested on the SOX10 binding sites from the RET promoter. Of the two similar mutations X467K and 1400del12, only the 1400del12 mutant protein exhibited an increase of transactivation through the P0 promoter. While the lack of normal SOX10 mediated activation of RET transcription may lead to intestinal aganglionosis, overexpression of genes coding for structural myelin proteins such as P0 due to mutant SOX10 may explain the dysmyelination phenotype observed in the patients with an additional neurological disorder.

Neural crest origin of olfactory ensheathing glia

“…Heterotopic grafts further showed that hindbrain-and spinal cord-derived NCCs can form OECs. We also identified Sox10 as a molecular marker for OECs: this is consistent both with the maintenance of Sox10 expression in all NCC-derived glia (23) and with the fact that Sox10 directly regulates the "myelin" P0 gene (24), an OEC marker in chick and rat (22,25,27 YFP embryos, in which NCCs are permanently labeled genetically (32,33), yielded results entirely consistent with our fate-mapping experiments in avian embryos. Hence, OECs are derived from the neural crest, not from the olfactory placodes.…”

Review and update of mutations causing Waardenburg syndrome

“…A few mutations, such as Ser135Thr, differentially influenced expression of target genes, an observation that might account for the phenotypic differences observed [Chan et al, 2003;Lang and Epstein, 2003;Yokoyama et al, 2006a]. When cotransfected in vitro with wild-type SOX10 in a dose-dependent manner, truncated SOX10 proteins, irrespective of their associated phenotypes (WS4 or PCWH), displayed a similar dominant-negative effect.…”

“…Four missense or small in frame insertions are described in the HMG domain. Remarkably, there is a significant number of nonstop mutations (i.e., mutations of the stop codon that lengthen the protein), which are thought to exert a dominant negative effect due to the extended tail [Chan et al, 2003;Inoue et al, 1999;Sham et al, 2001]. Partial or full gene deletions represent a significant proportion of SOX10 mutations [Bondurand et al, 2007].…”

The contribution of associated congenital anomalies in understanding Hirschsprung’s disease

“…The iris is pathologically involved in the Waardenburg-Shah association [25,94] and chromosome 13 deletions [95,96] as well as frame-shift and missense Sox10 mutations [97][98][99].…”