Our goal is to find new ways to diagnose, treat and prevent life-threatening bowel motility disorders like chronic intestinal pseudo-obstruction (CIPO) and Hirschsprung Disease (HSCR). Bowel motility is essential for life and is coordinated by a complex, gut-intrinsic network of neurons and glia called the enteric nervous system (ENS). Children with neuropathic CIPO have enteric neurons throughout the bowel, but have defects in neuron function that cause inadequate gut motility for survival and growth. In contrast, children with HSCR are born without enteric neurons at the end of the bowel. This causes tonic distal bowel contraction and functional obstruction. HSCR is treated by surgical removal of bowel without neurons, but bowel motility problems often persist after surgery, suggesting that neuron function in more proximal bowel regions is impaired despite the presence of enteric neurons. Twenty years ago, mutations in the Dlx1 and Dlx2 transcription factors were reported to cause deadly bowel motility defects in mice, but this observation was never pursued. Dlx1-/- mice die at one month of age, while Dlx2-/- mice, and mice lacking both DLX1 and DLX2, die shortly after birth with defective intestinal peristalsis and massive proximal small bowel distention due to air accumulation. Although DLX1 and DLX2 are essential for central nervous system (CNS) interneuron differentiation, survival, and migration, their role in ENS development and function is not known. The ENS is derived primarily from vagal neural crest precursors that invade the foregut and migrate rostro-caudally down the bowel before differentiating into neurons and glia. DLX1 and DLX2 are expressed in the developing ENS at ages relevant to neuron precursor migration, differentiation, and development. My preliminary data show that mice lacking DLX1 and DLX2 have delayed intestinal transit and reduced or absent neurally-mediated contractions in their small intestine. However, these mice have neurons throughout their bowel. Therefore, I hypothesize that DLX1 and DLX2 are essential for differentiation of specific subtypes of enteric neurons, consistent with the role of these proteins in the developing CNS. Because the ENS depends on integrated circuits and contains ~20 different neuron types, defects in enteric neuron differentiation and function can cause the observed bowel phenotype. To test this hypothesis, I will identify structural and functional defects in the ENS of Dlx1-/-, Dlx2-/-, and Dlx1/2-/- mice. I will also investigate genes regulated by DLX1 and DLX2 in the ENS using RNA-Seq and qRT-PCR. In addition, I will test the hypothesis that bowel motility defects in Dlx1-/- and Dlx2-/- mice occur because DLX1 and DLX2 regulate Zfhx1b in the ENS. Zfhx1b is a transcriptional regulator that is known to be controlled by DLX1 and DLX2 in some CNS neurons. ZFHX1B mutations cause HSCR, as well as CNS defects in humans and mice. These studies will elucidate unexplored roles for DLX1 and DLX2 during ENS maturation, and should facilitate development of new treatments for CIPO and HSCR, two life-threatening bowel motility disorders.
Bowel motility is essential for life and is coordinated by a complex, gut-intrinsic network of neurons and glia called the enteric nervous system (ENS). Defects in ENS development can cause life-threatening bowel motility disorders including Chronic Intestinal Pseudo-Obstruction and Hirschsprung Disease. This proposal details experiments designed to characterize the role of two transcription factors (DLX1 and DLX2) in enteric nervous system precursor differentiation and function.
