Molecular analysis of the Drosophila miniature-dusky (m-dy) gene complex: m-dy mRNAs encode transmembrane proteins with similarity to C. elegans cuticulin

Abstract

Mutations in the Drosophila miniature-dusky ( m-dy) gene complex were first reported by Morgan and Bridges about 90 years ago. m-dy mutants have abnormally small wings, a phenotype attributed to a cell-autonomous reduction in the size of the epidermal cells comprising the differentiated wing. Using a molecular genetic approach, we have characterized the m-dy chromosomal interval and identified a pair of adjacent transcription units corresponding to m and dy. A dy mutant known as dy (And) has a single base substitution within the protein-coding region that is predicted to result in an amber stop codon and premature translational termination. We show that dy mRNA is expressed at two discrete periods during the life cycle--one during embryonic development and early larval instars, the second during adult development, coincident with wing differentiation. In agreement with the phenotypic similarity of m and dy mutants, sequence comparisons reveal a similarity between the predicted MINIATURE and DUSKY proteins, and indicate that the m and dy genes are members of a larger Drosophila gene family. Both m and dy, as well as other members of this superfamily, are predicted to encode transmembrane proteins with similarity to C. elegans cuticle proteins known as cuticulins. We postulate that m, dy and other members of this protein superfamily function as structural components of the Drosophila cuticulin layer. Such a role for m and dy products in wing differentiation is sufficient to explain the morphological phenotypes associated with m-dy mutants.

Gene Expression During Drosophila Wing Morphogenesis and Differentiation

“…Some of these are suggestive of a specific role for the gene in the differentiation of the pupal wing during the time covered by our experiment. Among the most striking are miniature and dusky, which encode related proteins (DiBartolomeis et al 2002;Roch et al 2003). Mutations in both of these genes result in small dark wings.…”

RNA interference from a CAX trinucleotide repeat

“…As mentioned previously, it is known that m and dy show sequence similarity (DiBartolomeis et al, 2002), and given that the two genes are located in adjacent genomic intervals, we postulate that they arose via a duplication event. However, the apparent targeting of m or other genes is not a consequence of extensive se- quence identity between the UAS-dy-dsRNA and other Drosophila RNAs.…”

“…1a). The m and dy genes share sequence similarity and both encode fly Cuticulin proteins (DiBartolomeis et al, 2002) that are required at the pupal stage of development (Newby and Jackson, 1995) for normal wing differentiation. In the absence of m-dy products, the wing is reduced in size, due to an autonomous effect on the size and/or shape of wing epidermal cells (Newby et al, 1991).…”

“…While studying the function of the Drosophila miniature-dusky (m-dy) gene complex (DiBartolomeis et al, 2002), we produced transgenic flies expressing a dsRNA that would permit silencing of the dy gene (P{UAS-dy-dsRNA}; Fig. 1a).…”

“…However, the apparent targeting of m or other genes is not a consequence of extensive se- quence identity between the UAS-dy-dsRNA and other Drosophila RNAs. Indeed, we designed the dy silencing vector using sequence from an N-terminal coding region not present in m or other dy-related genes (DiBartolomeis et al, 2002), so as to avoid such illegitimate mRNA targeting. To determine the reason for the apparent targeting of m, we reexamined the dy-dsRNA and m-mRNA sequences.…”