Characterization of Dystrophin Dp71 Expression and Interaction Partners in Embryonic Brain Development: Implications...

Duchenne/Becker muscular dystrophy (DMD/BMD) manifests progressive muscular dystrophy and non-progressive central nervous disorder. The neural disorder is possibly caused by abnormalities in the developmental period; however, basic research to understand the mechanisms remains underdeveloped. The responsible gene, Dmd (dystrophin), generates multiple products derived from several gene promoters. Here, we aim to characterize the expression of the shortest product, Dp71, during embryonic brain development and to identify its interaction proteins by using Dp71-specific tag-insertion mice. We showed that Dp71 and Dp140 were major dystrophin products significantly detectable in the mouse embryonic brains and Dp71 was the only dystrophin product derived from intron-62 gene promoter in the physiological mouse brains. Although both Dp71f (exon 78-exclusive form) and Dp71d (exon 78-inclusive form) existed in the embryonic brains, Dp71f and Dp71d were dominant forms in the prenatal and postnatal periods, respectively. We histologically found that Dp71 was prominently expressed in the neuroepithelium of the dorsal and medial telencephalon, which gives rise to the primordial cerebral cortex and hippocampus. Deeper analysis using in vitro primary culture verified Dp71 expressions in Nestin-positive neural stem/progenitor, Fabp7-positive radial glia, and Gfap-positive astrocytic cell populations. Interestingly, Dp71 was downregulated upon neuronal differentiation from stem/progenitor cells into TuJ1-positive immature neurons; however, Dp71 became detectable at Gephyrin-positive inhibitory postsynapses within mature neurons. Importantly, interactome analysis revealed dystroglycan, dystrobrevins, and syntrophins as dominant Dp71-partners in the embryonic neural stem/progenitor cells. Thus, the presence of Dp71-dystroglycan macromolecular complex was clearly established at an early stage of embryonic brain development, which sheds light on relations between fetal abnormalities and intellectual disabilities in DMD/BMD.