| As one of the few vertebrates in which large-scale genetic screens are feasible, thanks to its large clutch size, external development, and genetic tractability, the zebrafish has quickly become one of the foremost model systems for the study of vertebrate development. Thousands of mutations defining hundreds of essential genes have been isolated in forward genetic screens, and the molecular and phenotypic characterization of the mutations that have been cloned has provided novel insights into a number of developmental pathways. However, only a small fraction of the genes disrupted by these mutations have been identified. In the first part of this thesis, I report the construction of a first-generation single nucleotide polymorphism (SNP) genetic map for zebrafish as well as the development of a high throughput microarray-based method to score the SNPs. These two advances will significantly hasten genetic mapping and hence the cloning of zebrafish mutations, facilitating the genetic dissection of multiple developmental mechanisms.;Classical forward genetic screens have uncovered a number of zebrafish genes involved in the formation of the dorsoventral axis, greatly advancing our understanding of vertebrate axis formation and providing a genetic foundation for models of dorsoventral patterning. It is clear, however, that certain classes of genes have been overlooked in these screens, including genes with subtle phenotypic effects and genes with redundant or partially redundant roles. In the second part of this thesis, I describe the results of a sensitized genetic screen that we performed to identify novel genes involved in dorsoventral patterning. We isolated multiple new alleles of the transcriptional effector smad5, uncovered a new role for the T-box transcription factor spadetail/tbx16 in dorsoventral patterning and discovered the first zebrafish mutation in bmp4. We show that BMP4 is required for dorsoventral patterning of the tail in zebrafish and suggest a model for BMP4 function with respect to BMP2b and BMP7. |
