High
glycogen levels in the Pacific oyster (<i>Crassostrea
gigas</i>) contribute to its flavor, quality, and hardiness.
Glycogenin (CgGN) is the priming glucosyltransferase that initiates
glycogen biosynthesis. We characterized the full sequence and function
of <i>C. gigas CgGN</i>. Three <i>CgGN</i> isoforms
(CgGN-α, β, and γ) containing alternative exon regions
were isolated. <i>CgGN</i> expression varied seasonally
in the adductor muscle and gonadal area and was the highest in the
adductor muscle. Autoglycosylation of CgGN can interact with glycogen
synthase (CgGS) to complete glycogen synthesis. Subcellular localization
analysis showed that CgGN isoforms and CgGS were located in the cytoplasm.
Additionally, a site-directed mutagenesis experiment revealed that
the Tyr200Phe and Tyr202Phe mutations could affect CgGN autoglycosylation.
This is the first study of glycogenin function in marine bivalves.
These findings will improve our understanding of glycogen synthesis
and accumulation mechanisms in mollusks. The data are potentially
useful for breeding high-glycogen oysters
