Strain-specific alleles of <i>Phox2B</i> differentially modify <i>Sox10^Dom</i> aganglionosis

Abstract

Hirschsprung disease (HSCR) is characterized by a lack of enteric ganglia in a variable portion of the distal bowel. The complex inheritance pattern of this disorder has led researchers to focus on genetic effects other than the putative disease mutation. Mouse models provide a controlled background for these types of studies. <i>Sox10</i> is an essential gene for the development of the enteric nervous system (ENS). <i>Sox10^Dom</i> mice on a mixed genetic background exhibit the variable aganglionosis seen in HSCR cases. Congenic lines of <i>Sox10^Dom</i> mice on distinct inbred genetic backgrounds, C57BL/6J (B6) and C3HeB/FeJ (C3Fe), differ in penetrance and extent of aganglionosis. A linkage screen for modifiers of <i>Sox10^Dom</i> aganglionosis was undertaken in a large B6 X C3Fe F₂ population. Several potential modifier regions were identified, with the most significant located on chromosome five (<i>Sox10m3</i>). The most relevant candidate gene in this region was <i>Phox2B</i>, an essential factor in autonomic neurogenesis. This goal of this dissertation was to understand the developmental differences between the congenic <i>Sox10^Dom</i> lines and how <i>Phox2B</i> impacts those differences. This study involved exploring differential expression of <i>Phox2B</i>, genetic variation at this locus between inbred strains, and the effects of different alleles of <i>Phox2B</i> on ENS development. The results suggest that <i>Phox2B</i> is differentially expressed between the B6 and C3Fe strains. The putative differences in expression are most likely due to genetic variation at key regulatory regions that are associated with aganglionic severity across multiple inbred strains. Strain-specific alleles at <i>Phox2B</i> modulate the effect of the <i>Sox10^Dom</i> mutation on ENS development. The work presented in this dissertation confirms the identification of <i>Phox2B</i> as the <i>Sox10m3</i> modifier and demonstrates the effects of genetic background on complex phenotypes such as HSCR-related aganglionosis. By extending the principles used in this work to other genes and inbred strains, a greater understanding of the pathogenesis of HSCR can be achieved.