Neurons of the enteric nervous system (ENS), i.e. the enteric neurons, are located within the gastrointestinal (GI) tract, pancreas, and gall bladder. They control the movement, secretion, and absorption of the digestive system. Deficiency of enteric neurons causes abdominal distention and constipation, a condition of patients suffering from the Hirschsprung's disease. The receptor tyrosine kinase Ret is critical for ENS formation and mutations in RET have been associated with the Hirschsprung's disease. Recent studies showed that the protein product of the Growth arrest specific gene 1 (Gas1) could bind to Ret and modulate Ret signaling. My laboratory studies the role of Gas1 during mouse development. This proposal is based on our observation that Gas1 mutant mice have defects in the number, position, and axonal projection of enteric neurons. We have previously shown that Gas1 facilitates Sonic Hedgehog (Shh) signaling. The Shh mutant has similar defects in enteric neurons as the Gas1 mutant. We propose to test the hypothesis that Gas1 mediates Shh and Ret signaling to direct the positioning and axonal projection of enteric neurons.
In Aim 1, we will define the defects of the GI tract in the Gas1 mutant.
In Aim 2, we will examine whether the Gas1 mutant ENS has altered Shh and/or Ret signaling.
In Aim 3, we will determine whether Gas1 mediates a cross-talk between Shh and Ret signaling using in vitro explant and enteric neurospheres. We will test the hypothesis that Gas1 mediates Shh-directed inhibitory activity to keep enteric neuron cell bodies and their axons away from the gut epithelium, where Shh is expressed. We will also test whether Gas1 negatively regulates downstream effectors of Ret in the ENS. Our goal is to test the hypothesis that Gas1 modulates Shh and Ret signaling to control enteric progenitor/neuron positioning and axon arborization.

Public Health Relevance

We propose to study the molecular mechanism controlling the formation of the enteric nervous system. Two major signaling pathways have been implicated in enteric neuron positioning and axonal arborization, Ret and Shh signaling pathways. We plan to investigate the role of Gas1, a protein that can bind to Shh and to Ret, in enteric neuron positioning and axonal arborization. Results from these studies will help us to understand how the enteric nervous system is formed. As Shh and Ret pathways have been directly implicated in human diseases and cancers, our results may provide information for designing therapeutic means to correct diseases related to dys-regulated Shh and Ret signaling pathways.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Neurogenesis and Cell Fate Study Section (NCF)
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Carrington, Jill L
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Carnegie Institution of Washington, D.C.
United States
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Ren, Yi A; Liu, Zhilin; Mullany, Lisa K et al. (2016) Growth Arrest Specific-1 (GAS1) Is a C/EBP Target Gene That Functions in Ovulation and Corpus Luteum Formation in Mice. Biol Reprod 94:44
Jin, Shiying; Martinelli, David C; Zheng, Xiaobin et al. (2015) Gas1 is a receptor for sonic hedgehog to repel enteric axons. Proc Natl Acad Sci U S A 112:E73-80
Khonsari, Roman H; Seppala, Maisa; Pradel, Alan et al. (2013) The buccohypophyseal canal is an ancestral vertebrate trait maintained by modulation in sonic hedgehog signaling. BMC Biol 11:27
Biau, Sandrine; Jin, Shiying; Fan, Chen-Ming (2013) Gastrointestinal defects of the Gas1 mutant involve dysregulated Hedgehog and Ret signaling. Biol Open 2:144-55
Gurung, Buddha; Feng, Zijie; Iwamoto, Daniel V et al. (2013) Menin epigenetically represses Hedgehog signaling in MEN1 tumor syndrome. Cancer Res 73:2650-8
Pineda-Alvarez, Daniel E; Roessler, Erich; Hu, Ping et al. (2012) Missense substitutions in the GAS1 protein present in holoprosencephaly patients reduce the affinity for its ligand, SHH. Hum Genet 131:301-10
Ohazama, Atsushi; Haycraft, Courtney J; Seppala, Maisa et al. (2009) Primary cilia regulate Shh activity in the control of molar tooth number. Development 136:897-903
Martinelli, David C; Fan, Chen-Ming (2009) A sonic hedgehog missense mutation associated with holoprosencephaly causes defective binding to GAS1. J Biol Chem 284:19169-72