A high-resolution genetic map of mouse chromosome 15 encompassing the Dominant megacolon (Dom) locus

Histochemical study of Dom mouse: A model for Waardenburg-Hirschsprung's phenotype

BACKGROUND/PURPOSE

The spontaneous mouse mutant Dominant megacolon (Dom) represents the model of the Waardenburg-Hirschsprung's disease, a syndromic pathology, characterized by the association of pigmentation defects (PD), deafness, and Hirschsprung's disease (HD). The defect in Dom mouse is caused by a spontaneous mutation of the gene encoding the Sry-related transcription factor Sox10. This mutation affects several aspects of neural crest development leading to combined enteric innervation and pigmentation defects, both in mouse and human. The purpose of this report is to define, by enzymo-histochemical techniques routinely used for the diagnosis of human Hirschsprung's disease (AChE, LDH, NADPH-diaphorase), the innervative patterns of the affected gut.

METHODS

Fifty-four siblings of Heterozygous Dom/+ mice underwent autopsy and were genotyped by direct sequencing of polymerase chain reaction (PCR) products for Sox10 mutations. The enteric nervous system of all the mice was studied by histochemical techniques indicated above.

RESULTS

Genotyping showed that 43 mice were Dom/+ and 11 were Wild type +/+. Wild-type +/+ mice were used as control. The correspondence between genotype and at least 1 phenotypic aspect (PD or dysganglionosis) was present in 93% of cases (41 of 43). Among the Dom/+ mice, dysganglionosis was present in 79% of cases and PD in 90% of cases. Moreover, among Dom/+ mice, excluding those whose mantle was not evaluated as dead just after birth, PD and dysganglionosis (complete phenotype) were present in 68% of cases.

CONCLUSIONS

The histochemical methods that we used proved to be useful for identification of different aganglionic (AG), hypoganglionic (HG), and normoganglionic segments of Dom/+ mouse gut studied in longitudinal sections. Unlike humans, control mice (Wild type +/+) presented a rich component of AChE nerve fibers, whereas Dom/+ mice with dysganglionosis presented a decrease in AChE-positive nerve fibers. These data confirm the variable phenotypic penetrance in heterozygous mice. Because dysganglionosis in this animal model (Dom/+) was evident in 79% of cases (AG or HG), we concluded that Dom mice could represent important models for further experimental studies.

Mouse models for four types of Waardenburg syndrome

Waardenburg syndrome (WS) is an auditory-pigmentary syndrome caused by a deficiency of melanocytes and other neural crest-derived cells. Depending on a variety of symptoms associated with the auditory-pigmentary symptoms, WS is classified into four types: WS type 1 (WS1), WS2, WS3, and WS4. Six genes contributing to this syndrome--PAX3, SOX10, MITF, SLUG, EDN3 and EDNRB--have been cloned so far, all of them necessary for normal development of melanocytes. Mutant mice with coat color anomalies were helpful in identifying these genes, although the phenotypes of these mice did not necessarily perfectly match those of the four types of WS. Here we describe mice with mutations of murine homologs of WS genes and verify their suitability as models for WS with special interest in the cochlear disorder. The mice include splotch (Sp), microphthalmia (mi), Slugh-/-, WS4, JF1, lethal-spotting (ls), and Dominant megacolon (Dom). The influence of genetic background on the phenotypes of mice mutated in homologs of WS genes is also addressed. Finally, possible interactions among the six WS gene products are discussed.

Mutation of the Sry-related Sox10 gene in Dominant megacolon, a mouse model for human Hirschsprung disease

The spontaneous mouse mutant Dominant megacolon (Dom) is a valuable model for the study of human congenital megacolon (Hirschsprung disease). Here we report that the defect in the Dom mouse is caused by mutation of the gene encoding the Sry-related transcription factor Sox10. This assignment is based on (i) colocalization of the Sox10 gene with the Dom mutation on chromosome 15; (ii) altered Sox10 expression in the gut and in neural-crest derived structures of cranial ganglia of Dom mice; (iii) presence of a frameshift in the Sox10 coding region, and (iv) functional inactivation of the resulting truncated protein. These results identify the transcriptional regulator Sox10 as an essential factor in mouse neural crest development and as a further candidate gene for human Hirschsprung disease, especially in cases where it is associated with features of Waardenburg syndrome.

Sox10 mutation disrupts neural crest development in Dom Hirschsprung mouse model

Hirschsprung disease (HSCR, MIM #142623) is a multigenic neurocristopathy (neural crest disorder) characterized by absence of enteric ganglia in a variable portion of the distal colon. Subsets of HSCR individuals also present with neural crest-derived melanocyte deficiencies (Hirschsprung-Waardenburg, HSCR-WS, MIM #277580). Murine models have been instrumental in the identification and analysis of HSCR disease genes. These include mice with deficiencies of endothelin B receptor (Ednrb(s-l); refs 1,2) endothelin 3 (Edn3(ls): refs 1,3) the tyrosine kinase receptor cRet and glial-derived neurotrophic factor. Another mouse model of HSCR disease, Dom, arose spontaneously at the Jackson Laboratory. While Dom/+ heterozygous mice display regional deficiencies of neural crest-derived enteric ganglia in the distal colon, Dom/Dom homozygous animals are embryonic lethal. We have determined that premature termination of Sox10, a member of the SRY-like HMG box family of transcription factors, is responsible for absence of the neural crest derivatives in Dom mice. We demonstrate expression of Sox10 in normal neural crest cells, disrupted expression of both Sox10 and the HSCR disease gene Ednrb in Dom mutant embryos, and loss of neural crest derivatives due to apoptosis. Our studies suggest that Sox10 is essential for proper peripheral nervous system development. We propose SOX10 as a candidate disease gene for individuals with HSCR whose disease does not have an identified genetic origin.