Targeted disruption of a murine glucuronyl C5-epimerase gene results in heparan sulfate lacking L-iduronic acid and in neonatal lethality

The glycosaminoglycan, heparan sulfate (HS), binds proteins to modulate signaling events in embryogenesis. All identified protein-binding HS epitopes contain L-iduronic acid ( IdoA). We report that targeted disruption of the murine D-glucuronyl C5-epimerase gene results in a structurally altered HS lacking IdoA. The corresponding phenotype is lethal, with renal agenesis, lung defects, and skeletal malformations. Unexpectedly, major organ systems, including the brain, liver, gastrointestinal tract, skin, and heart, appeared normal. We find that IdoA units are essential for normal kidney, lung, and skeletal development, albeit with different requirement for 2-O-sulfation. By contrast, major early developmental events known to critically depend on heparan sulfate apparently proceed normally even in the absence of IdoA.