An evolutionary and genetic analysis of dec-1 protein function in Drosophila
Abstract
All organisms are faced with the challenging task of functioning in a three-dimensional world. This demands that cells be able to produce a complex array of intra- and extracellular lattices. How such macromolecular structures are assembled to produce a functional framework is a central question in developmental biology. The eggshell of Drosophila is an example of a complex structure that lends itself to such an examination. The defective chorion 1 gene (dec-1 ) produces several mature proteins that have been shown to be components of the eggshell. The absence of dec-1 proteins results in abnormalities in eggshell morphology and a female sterile phenotype, suggesting dec-1 proteins play a critical role in the architecture of the mature eggshell. In an effort to identify specific amino acid sequences that are critical for dec-1 function, an evolutionary approach involving an interspecies comparison of dec-1 genes from D. melanogaster and D. virilis was employed. In this study, cloning and sequencing of the D. virilis dec-1 gene has revealed that dec-1 is one of the most rapidly evolving genes in the Drosophila genome yet described. It has also shown that the amino acid identity that does exist between the D. virilis and D. melanogaster dec-1 proteins is found in discrete blocks. Mutagenesis experiments were performed in which conserved blocks were deleted so as to determine their functional significance. The effects these deletions had on dec-1 function were assayed by introducing the altered dec-1 genes into the D. melanogaster genetic background. These experiments have revealed; (1) additional steps in the processing of dec-1 proproteins, (2) sequences necessary for proteolytic processing, (3) the use of cryptic cleavage sites, (4) that failure to separate putative functional domains by proteolysis can result in dominant negative effects and (5) that processing of some dec-1 proteins may proceed through the formation of homodimers or higher order complexes. Additional blocks of conservation identified during the interspecies comparison of the dec-1 genes will provide a basis for future mutagenesis studies aimed at dissecting the roles of dec-1 proteins in eggshell assembly.
This paper has been withdrawn.