Increased Apoptosis of Myoblasts in Drosophila Model for the Walker-Warburg Syndrome

Morio Ueyama,Shoko Nishihara,Ryu Ueda,Tomomi Ichimiya,Toshiro Aigaki,Yoshihiro Akimoto,Hayato Kawakami,Mel B Feany

doi:10.1371/journal.pone.0011557

Abstract

Walker-Warburg syndrome, a progressive muscular dystrophy, is a severe disease with various kinds of symptoms such as muscle weakness and occasional seizures. The genes of protein O-mannosyltransferases 1 and 2 (POMT1 and POMT2), fukutin, and fukutin-related protein are responsible for this syndrome. In our previous study, we cloned Drosophila orthologs of human POMT1 and POMT2 and identified their activity. However, the mechanism of onset of this syndrome is not well understood. Furthermore, little is known about the behavioral properties of the Drosophila POMT1 and POMT2 mutants, which are called rotated abdomen (rt) and twisted (tw), respectively. First, we performed various kinds of behavioral tests and described in detail the muscle structures by using these mutants. The mutant flies exhibited abnormalities in heavy exercises such as climbing or flight but not in light movements such as locomotion. Defective motor function in mutants appeared immediately after eclosion and was exaggerated with aging. Along with motor function, muscle ultrastructure in the tw mutant was altered, as seen in human patients. We demonstrated that expression of RNA interference (RNAi) for the rt gene and the tw mutant was almost completely lethal and semi-lethal, respectively. Flies expressing RNAi had reduced lifespans. These findings clearly demonstrate that Drosophila POMT mutants are models for human muscular dystrophy. We then observed a high density of myoblasts with an enhanced degree of apoptosis in the tw mutant, which completely lost enzymatic activity. In this paper, we propose a novel mechanism for the development of muscular dystrophy: POMT mutation causes high myoblast density and position derangement, which result in apoptosis, muscle disorganization, and muscle cell defects.

Highlights

Congenital muscular dystrophies (CMDs) are genetic diseases that cause progressive muscle weakness and wasting [1,2]
Behavioral defects in rt and tw mutants Patients with progressive muscular dystrophy show muscle weakness and motor dysfunction with age
The number of dividing myoblasts in the wing disc did not differ between wild-type flies and tw mutants (Fig. S4). These results showed that apoptosis was enhanced in myoblasts of the tw mutant while the number of dividing cells was not altered

Summary

Introduction

Congenital muscular dystrophies (CMDs) are genetic diseases that cause progressive muscle weakness and wasting [1,2]. CMDs result from dystrophin glycoprotein complex (DGC) dysfunction [3]. DGC, which connects the extracellular matrix to the intracellular cytoskeleton, comprises several kinds of proteins such as laminin 2, dystrophin, sarcoglycan, and dystroglycan [4]. Walker-Warburg Syndrome (WWS), the most severe CMD, is a rare recessive inherited disorder characterized by muscular dystrophy, severe brain malformations, and eye abnormalities [5,6,7,8,9]. The POMT1/2 complex transfers mannose to the Ser/Thr residues of a-dystroglycan [18], one of the components of the DGC, and plays an important role in the first step of O-mannosylation. O-Mannosylation contributes to the stabilization of sarcolemma by binding to laminin, which attaches to the basal membrane [3,19,20,21]

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Results

Conclusion