Expression of the aquaglyceroporin HC-9 in a freeze-tolerant amphibian that accumulates glycerol seasonally.

As ambient temperatures fall in the autumn, freeze-tolerant Cope's gray treefrogs, (formerly ), accumulate glycerol as a cryoprotective agent. We hypothesized that these treefrogs express an ortholog of the mammalian aquaglyceroporin AQP9 and that AQP9 expression is upregulated in the cold to facilitate glycerol transport. We sequenced 1790 bp from cloned cDNA that codes for a 315 amino acid protein, HC-9, containing the predicted six transmembrane spanning domains, two Asn-Pro-Ala (NPA) motifs, and five amino acid residues characteristic of aquaglyceroporins.