Evolutionary analysis of thedec-1eggshell gene in Drosophila yakuba and Drosophila virilis
Abstract
Dec-1 is a complex gene that plays an important role in Drosophila eggshell development. Product diversity is generated through developmentally regulated alternative splicing and proteolytic processing events. Alternative splicing generates three transcripts which produce three dec-1 products which share common N-terminal sequences, but have unique C-terminal sequences. One transcript represents the quantitatively major component of the dec-1 locus, while the other two are quantitatively minor. Complementation studies have demonstrated that in addition to the quantitatively major product, at least one of the two quantitatively minor products are required for function. The quantitatively major product of the dec-1 locus is fc106. The two minor products are fc125 and fc177. Homozygous female dec-1 null mutants lay eggs with gross eggshell deformities. The amino acid composition of dec-1 is distinctive in terms of several unique regions. These include a 26 kDa N-terminal region, a central glutamine-methionine rich repeating region consisting of five perfect and seven imperfect 26 amino acid repeats, and a cysteine rich region. In an effort to elucidate those aspects of dec-1 that may be important for function, an evolutionary approach has been taken. Protein analysis has identified conservation of processing, temporal and cell specificity and methionine content of dec-1 products in both D. yakuba and D. virilis. Developmental Northern analysis has identified conservation of both the expression profile and two size classes of transcripts in D. yakuba. Sequence comparisons between D. melanogaster and the D. yakuba dec-1 homolog demonstrated overall identity of 85% at the amino acid level. While overall identity between D. melanogaster and D. yakuba was found to be 85%, regions differed. These differences included unique sequences as well as regions of extended or limited homology. Analysis of the D. yakuba dec-1 homolog identified two sizable insertions. The first, a 24 amino acid insertion, consisted of a 4 amino acid repeating motif found near the N-terminus of all dec-1 products. The second, a 19 amino acid insertion, was found near the C-terminus of fc125. Analysis of the N-terminal region identified a proline-alanine rich region that demonstrated that while sequence identity was diminished (51%), the proline-alanine content of the region remain essentially unchanged. Analysis of the central glutamine-methionine rich repeating region demonstrated conservation of repeat length and sequence between the two species. However, two of the first five repeats are deleted in D. yakuba relative to D. melanogaster. Analysis of the cysteine rich domain demonstrated conservation of the existence and spacing of the cysteines.
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