Zebrafish and cellular models of SELENON-Congenital myopathy exhibit novel embryonic and metabolic phenotypes.

Background: SELENON-Congenital Myopathy (SELENON-CM) is a rare congenital myopathy caused by mutations of the SELENON gene characterized by axial muscle weakness and progressive respiratory insufficiency. Muscle histopathology may be non-specific, but commonly includes multiminicores or a dystrophic pattern. The SELENON gene encodes selenoprotein N (SelN), a selenocysteine-containing redox enzyme located in the endo/sarcoplasmic reticulum membrane where it colocalizes with mitochondria-associated membranes. However, the molecular mechanism(s) by which SelN deficiency cause SELENON-CM remain poorly understood. A hurdle is the lack of cellular and animal models that show easily assayable phenotypes.

Methods: Using CRISPR-Cas9 we generated three zebrafish models of SELENON-CM, which were then studied by spontaneous coiling, hatching, and activity assays. We also performed selenon coexpression analysis using a single cell RNAseq zebrafish embryo-atlas. SelN-deficient myoblasts were generated and assayed for glutathione, reactive oxygen species, carbonylation, and nytrosylation levels. Finally, we tested Selenon-deficient myoblasts' metabolism using a Seahorse cell respirometer.

Results: We report deep-phenotyping of SelN-deficient zebrafish and muscle cells. SelN-deficient zebrafish exhibit changes in embryonic muscle function and swimming activity in larvae. Analysis of single cell RNAseq data in a zebrafish embryo-atlas revealed coexpression of selenon and genes involved in the glutathione redox pathway. SelN-deficient zebrafish and mouse myoblasts exhibit altered glutathione and redox homeostasis, as well as abnormal patterns of energy metabolism, suggesting roles for SelN in these functions.

Conclusions: These data demonstrate a role for SelN in zebrafish early development and myoblast metabolism and provide a basis for cellular and animal model assays for SELENON-CM.