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N-Glycolylneuraminic Acid Deficiency in Mice: Implications for Human Biology and Evolution

Glycobiology Research and Training Center, Departments of Medicine,¹ Pathology,² Pediatrics,³ Surgery,⁴ Neurosciences,⁵ Cellular & Molecular Medicine, University of California, San Diego, and VA Medical Center, La Jolla, California 92093-0687,⁶ Laboratory of Membrane Biochemistry and Biophysics, Graduate School of Biostudies, Kyoto University, Kyoto,⁷ Supra-biomolecular System Research Group, RIKEN Frontier Research System, Wako, Saitama,⁸ Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi, Japan⁹

Received 1 March 2007/ Accepted 28 March 2007

Humans and chimpanzees share >99% identity in most proteins. One rare difference is a human-specific inactivating deletion in the CMAH gene, which determines biosynthesis of the sialic acid N-glycolylneuraminic acid (Neu5Gc). Since Neu5Gc is prominent on most chimpanzee cell surfaces, this mutation could have affected multiple systems. However, Neu5Gc is found in human cancers and fetuses and in trace amounts in normal human tissues, suggesting an alternate biosynthetic pathway. We inactivated the mouse Cmah gene and studied the in vivo consequences. There was no evidence for an alternate pathway in normal, fetal, or malignant tissue. Rather, null fetuses accumulated Neu5Gc from heterozygous mothers and dietary Neu5Gc was incorporated into oncogene-induced tumors. As with humans, there were accumulation of the precursor N-acetylneuraminic acid and increases in sialic acid O acetylation. Null mice showed other abnormalities reminiscent of the human condition. Adult mice showed a diminished acoustic startle response and required higher acoustic stimuli to increase responses above the baseline level. In this regard, histological abnormalities of the inner ear occurred in older mice, which had impaired hearing. Adult animals also showed delayed skin wound healing. Loss of Neu5Gc in hominid ancestors 2 to 3 million years ago likely had immediate and long-term consequences for human biology.

Published ahead of print on 9 April 2007.