Do Rodents Have a Gene Encoding Glycogenin‐2, the Liver Isoform of the Self‐Glucosylating Initiator of Glycogen Synthesis?

The discovery of a second human gene, GYG2, encoding a liverspecific isoform of glycogenin, the self‐glucosylating initiator of glycogen biosynthesis, raised the possibility for differential controls of this protein in liver and muscle. The new protein, glycogenin‐2, had several properties similar biochemically to the muscle isoform, glycogenin‐1, but unlike glycogenin‐1, stable expression in fibroblasts led to a significant overaccumulation of glycogen. Ensuing attempts to generate reagents suitable for use with rodents, to examine the physiological regulation of glycogenin‐2 by nutritional and hormonal factors, have been unsuccessful. Proof of a negative is difficult but the weight of the evidence is beginning to mitigate against the existence of a second glycogenin gene in rodents leading us to hypothesize that the presence of the GYG2 gene is limited to primates.