Dyrk1b: Dual-specificity Tyrosine-regulated kinase 1B SO: sarcopenic obesity MetS: metabolic syndrome myoD1: myoblast determination protein 1 Fgf: Fibroblast growth factor Shh: Sonic Hedgehog mTORC1: mechanistic target of rapamycin C1 4e-bp1: Eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1
ABSTRACTThe advent of human genetics has provided unprecedented opportunities for discovery of novel disease pathways. Mutations in DYRK1B have been associated with metabolic syndrome and sarcopenic obesity in humans, underscoring the critical role of the encoded protein in skeletal muscle development and homeostasis. By the novel creation of Dyrk1b knockout zebrafish models we demonstrate that Dyrk1b kinase activity is critical for specification of the paraxial myoD. Mechanistically, Dyrk1b mediates and amplifies Fgf signaling in the paraxial domain by the transcriptional suppression of its negative feedback inhibitor sprouty1. In the adaxial myoD domain, Dyrk1b amplifies Shh signaling and partially rescues defects caused by its disruption. The investigations of C2C12 terminal differentiation revealed that Dyrk1b also plays a critical role in myofiber fusion. Combined biochemical and proteomic analysis of C2C12 myoblasts undergoing differentiation showed that Dyrk1b kinase activation is induced by shh inhibition, and triggers differentiation by inhibiting mTOR, subsequent upregulation of 4e-bp1 and induction of autophagy. In conclusion, we demonstrate that Dyrk1b plays a critical role in sustaining myocyte specification and differentiation by integrating Fgf, Shh and mTORC1 signaling pathways. determination, inherited metabolic syndrome. E lateral views, F-G dorsal views, H and I are cross-sections at regions indicated by red lines on G. Red asterisks on F and G indicate the unstained axial domain. Red asterisks on I denote somites, red arrow denotes notochord, NT=neural tube. J,K are group shots of zebrafish embryos stained with anti-sense and the control sense probe. L. Schematic diagram of the dyrk1b locus in the zebrafish genome. Boxes indicate the exons (not drawn to scale). The dotted lines from second exon indicate the translation start site (in red). Guide RNA is highlighted in yellow and PAM region in green. wildtype and dyrk1b+/-sequence are shown, 7bp insertion induced by CRISPR/Cas9 is highlighted in blue. M Schematic showing Dyrk1b CRISPR/Cas9 injection and transmission of induced mutation. N T7 assay with one band for Wildtype and two bands for dyrk1b+/-, indicating the heteroduplex formed by CRISPR/Cas9 activity. O. Sanger sequencing images of amplified segments of wildtype and dyrk1b+/-, demonstrating the site of 7bp insertion (red arrow) and the ensuing frame shift. P. dyrk1b mRNA expression levels (mean + s.e.m) in the wildtype and Dyrk1b+/-zebrafish embryo at 24hpf (*** p≤ 0.001, Students ttest, 2 tailed, n=30 pooled embryos).