Analysis of mutants from a genetic screening reveals the control of intestine and liver development by many common genes in zebrafish.

Both the intestine and liver develop from the endoderm, yet little is known how these two digestive organs share and differ in their developmental programs, at the molecular level. A classical forward genetic screen, with no gene bias, is an effective way to address this question by examining the defects of the intestine and liver in obtained mutants to assess mutated genes responsible for the development of either organ or both. We report here such a screen in zebrafish. ENU was used as the mutagen because of its high mutagenic efficiency and no site preference. Embryos were collected at 3.5 dpf for RNA whole mount in situ hybridization with a cocktail probe of the intestine marker ifabp and the liver marker lfabp to check phenotypes and determine their parental heterozygosis. A total of 52 F2 putative mutants were identified, and those with general developmental defects were aborted. To rule out non-inheritable phenotypes caused by high mutation background, F2 putative mutants were outcrossed with wild type fish and a re-screen in F3 generations was performed. After complementation tests between F3 mutants with similar phenotypes originating from the same F2 families, a total of 37 F3 mutant lines originated from 22 F2 families were identified after screening 78 mutagenized genomes. Classification of mutant phenotypes indicated that 31 out of the 37 mutants showed defects in both the intestine and liver. In addition, four "intestine specific mutants" and two "liver specific mutants" showed selectively more severe phenotype in the intestine and liver respectively. These results suggested that the intestine and liver share a substantial number of essential genes during both organs development in zebrafish. Further studies of the mutants are likely to shed more insights into the molecular basis of the digestive system development in the zebrafish and vertebrate.