__SP__ __NODE__ protein in cell culture increases phosphorylation of __SP__ __NODE__ protein in fibroblasts from mutant 160.5 day old embryonic __SP__ with a homozygous knockout of __SP__ __NODE__ to phosphorylated ( S473 ) __SP__ __NODE__ protein in fibroblasts from mutant 160.5 day old embryonic __SP__ with a homozygous knockout of __SP__ __NODE__ .