The tricornered and furry genes of Drosophila are important for maintaining the integrity of cellular extensions during morphogenesis

The wings of adult Drosophila melanogaster are covered by a large number of small distally pointing hairs, which are formed in the pupal stage from microvilli like prehairs by individual epidermal cells. This dissertation describes my work on the tricornered (trc) and furry (fry) genes of Drosophila. Mutations in both trc and fry cause an extreme multiple wing hair phenotype that appears to result from the dramatic splitting of a single prehair early in its elongation. Thus these genes seem to be essential for maintaining prehair integrity.;We have molecularly cloned trc using a P insertion that marks the gene. trc encodes the Drosophila Ndr kinase, a well conserved serine/threonine protein kinase also found in Caenorhabditis elegans and humans. Trc is related to a number of kinases that have been shown to regulate cellular morphology. Further evidence that trc encodes the fly Ndr protein kinase was obtained by sequencing EMS induced trc point mutations and by transformation rescue with trc cDNA. Transgenic flies carrying FLAG/(His) 6 tagged trc cDNA were made, and the immunostaining of their tissues showed that the Trc fusion protein is primarily nuclear.;fry was recovered in a FLP/FRT based mutant screen for isolating wing hair polarity mutants. We used a P element insertion allele as a tag to clone the fry gene. About 20 kb genomic DNA flanking the P insertion site was cloned and sequenced. Four cDNA candidates from this region were recovered and three of them were subsequently ruled out either by complementation test or by sequencing EMS induced fry alleles. A clone of the fourth cDNA candidate was identified and later the full-length cDNA sequence was recovered by fellow graduate student Jingli Cong. She confirmed that this cDNA indeed encodes the fry locus by sequencing point mutations. fry was found to be a large and complicated gene that encodes a pair of large conserved proteins of unknown biochemical function. Data from double mutant analysis have argued that fry and trc are likely to function in the same genetic pathway that is independent of the frizzled tissue polarity pathway.