Limb reduction defects in endothelial nitric oxide synthase-deficient mice

Nitric oxide synthases are a family of enzymes capable of converting L-argi nine to L-citrulline with the subsequent release of nitric oxide (NO). NO h as been shown to have multiple biologic effects depending on the isoform re sponsible for its production and its tissue of origin. Murine endothelial n itric oxide synthase (eNOS) is encoded by Nos3, located on mouse chromosome 5. NO produced from this isoform causes vascular smooth muscle relaxation. Other investigators have shown that the administration of nonspecific inhi bitors of nitric oxide synthases to pregnant rats induces limb reduction de fects. However, mice deficient in Nos3 have not previously been noted to sh ow such abnormalities. To explore the importance of eNOS during development , we produced mice deficient in eNOS using embryonic stem cell technology. Limb reduction defects were seen in similar to 10% of the null animals. We also observed increased neonatal loss of homozygous deficient pups. One fun ctional copy of Nos3 eliminates the risk of limb defects observed in our mo use strain. These findings have implications for understanding genetic pred isposition to sporadic limb reduction defects in humans.