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Biology

Iain Shepherd
Cellular and Genetic Characterization of the Zebrafish Enteric Nervous System Mutant Enema

Delalande J.M.1, Guyote M.1, Stensby D.1, Talbot W. S.2, Raible D. W.3 and Shepherd I.T.1
1. Dept of Biology, Emory University, RRC 1510 Clifton Rd, Atlanta GA 30322
2. Department of Developmental Biology, Stanford University School of Medicine, Stanford CA 94305
3. Department of Biological Structure, University of Washington, Box 357420, Seattle WA 98195

The enteric nervous system (ENS) is the largest most complicated subdivison of the peripheral nervous system and is completely derived from the neural crest. In zebrafish the entire ENS appears to be derived from only post-otic neural crest cells. Enema (enm) was identified in a genetic screen that looked for zebrafish ENS development mutants. enm mutants have a significant reduction in the number of enteric neurons at 96hpf. In addition to its ENS phenotype this mutation is also characterized by other abnormalities affecting development of the eyes, the thymus, the jaw cartilages and the heart. With the exception of the eyes, all of these structures are entirely derived, or receive cellular contributions, from the post-optic NCCs. This suggests that the enm mutation is in a gene that is essential for the normal development of this NCC population. To determine if the enm mutation affects the initial specification and migration of the post-otic neural crest we have examined the expression pattern of crestin. Expression of this marker is unchanged in mutant embryos as compared to wild type siblings. To determine the earliest stage at which we could identify a defect in ENS development in enm mutants, we examined the expression of phox2b. Preliminary results suggest that the enm mutation affects the ability of ENS precursors to colonize the gut. Experiments are currently being undertaken to assess if the decrease in enteric precursors is due to reduced proliferation or increased apoptosis in the enm ENS precursors. To determine the genetic basis of the enm mutation we have generated a mapping hybrid. We have fine mapped the mutation and find that it is tightly linked to the pax9 locus. We will report our progress in determining the genetic basis for the enm mutation.