Glycosylation in S2 cells is very much like that in SF9, Sf21, and High Five cells. The nature of Drosophila N-linked glycosylation is less complex than mammalian glycosylation – it is generally of the paucimannose type, and is not trimmed and sialylated. O-linked glycosylation is similar, although not identical, to mammalian cells. However, correct glycosylation profiles are difficult to obtain, also glycosylation from CHO and HEK293 differ from human glycosylation. Human O-glycosylation can be divided into N-acetylGalactosamine linked (mucin type), N-acetylGlucosamine lined (O-GlcNAc type) and xylose linked (proteoglycans) families. The most abundant form is the mucin type, while O-GlcNac has only been found for cytoplasmic and nuclear proteins, the proteoglycans are of less interest here. In CHO cells, O-glycosylation results in terminally sialated mucin type glycans, with a low percentage core-1 structure (T-antigen) reported. In Drosophila S2, cell O-glycosylation is less complex than in human or mammalian cells. Unlike human proteins, O-GlcNAc has been found on an external protein. It appears that O-GlcNAc can occur in specific cases and are linked to the regulation of the protein, in this case the Notch receptor. However, mucin type glycosylation is the dominant O-glycosylation type in S2 cells and has been shown to be of the Tn-antigen (GalNAcalpha-Ser/Thr) and the core-1 structure (T-antigen) (Galbeta1-3GalNAcalpha-Ser/Thr) forms.