A Drosophila Dystrophin-related protein, MSP-300, is required for embryonic muscle morphogenesis

Proteins from the spectrin superfamily contribute to cell polarity and shape during the morphogenetic that accompany embryogenesis. Drosophila MSP-300, a member of the spectrin superfamily, is expressed in somatic, visceral and heart embryonic muscles. Cloning and sequence analysis of various spliced forms of MSP-300 reveals functional and structural similarities between MSP-300 and vertebrate Dystrophin, the product of the Duchenne Muscular Dystrophy gene. The identification of a strain mutant for the MSP-300 gene is described. Analysis of the somatic muscle phenotype in MSP-300 mutant embryos suggests that the protein contributes to the integrity of the somatic and visceral muscle during periods of significant morphogenetic change. Functional synergism between MSP-300 and laminin is demonstrated by the analysis of the phenotype of embryos mutant for both genes. The enhancement of aberrant muscle phenotype in the double mutants suggests a link between MSP-300 and laminin function in mediating proper extension of the myotube towards the epidermal muscle attachment site. In addition, both genes function to establish gut integrity. In view of the functional and structural similarities between MSP-300 and Dystrophin, it is postulated that Dystrophin is not only required for proper muscle function in adult life but also contributes to muscle morphogenesis during the development of the vertebrate embryo.