Evidence that Evolution of the Diabetes Susceptibility Gene SLC30A8 that Encodes the Zinc Transporter ZnT8 Drives Variations in Pancreatic Islet Zinc Content in Multiple Species.

Pancreatic islet zinc levels vary widely between species. Very low islet zinc levels in Guinea pigs were thought to be driven by evolution of the INS gene that resulted in the generation of an isoform lacking a histidine at amino acid 10 in the B chain of insulin that is unable to bind zinc. However, we recently showed that the SLC30A8 gene, that encodes the zinc transporter ZnT8, is a pseudogene in Guinea pigs, providing an alternate mechanism to potentially explain the low zinc levels. We show here that the SLC30A8 gene is also inactivated in sheep, cows, chinchillas and naked mole rats but in all four species a histidine is retained at amino acid 10 in the B chain of insulin. Zinc levels are known to be very low in sheep and cow islets. These data suggest that evolution of SLC30A8 rather than INS drives variation in pancreatic islet zinc content in multiple species.