Research Highlights

Embryonic stem cells: The power of one

Lectins recognize specific terminal carbohydrates on glycan chains, making lectin panels or microarrays ideal for carbohydrate analysis. As specific carbohydrates are characteristic for certain cell types and developmental stages, lectins could in principle be used for the identification and classification of cells. In a study published in Stem Cells, Nash et al. now show that a single specific lectin is sufficient to identify mouse embryonic stem cells (mESCs).

Nash et al. tested the binding of several mESC markers, such as CD9 and alkaline phosphatase, to stem cells using fluorescence-activated cell sorting (FACS). The authors noticed that the disappearance of cell surface markers and the transition of stem cells to the next developmental stage did not coincide. For example, the reactivity of CD9 decreased when the stem cells developed into early primitive ectoderm-like (EPL) cells, but increased again shortly afterwards. The authors analyzed the binding of 18 different lectins to stem cells by FACS. Terminal carbohydrate structures recognized by Dolichos biflorus agglutinin (DBA) lectin showed a clear and uniform downregulation that preceded previously used cell surface markers. Additionally, treatment of the cell-DBA assay with N-acetylgalactosamine — but not with other carbohydrates — blocked binding of fluorescence-labeled DBA to mESCs.

Previously, EPL cells could only be distinguished from mESCs by laborious gene expression analysis. Nash et al. observed that DBA binding was restricted only to mESCs. Furthermore, stem cells could be sorted from a mixture containing both EPL cells and mESCs by FACS using the fluorescence-labeled DBA. DBA attaches only to cell surface N–acetylgalactosamine, and still bound to cells when N-glycans were removed from the cell membrane. This suggests that DBA lectin reacts specifically with N-acetylgalactosamine as the terminal carbohydrate of O-glycans or glycan chains of glycolipids.

The authors conclude that mESC recognition by DBA lectin is superior to that of previously used markers. Additionally, their study gives an example for the specificity of carbohydrate expression at specific developmental stages. Further work is needed to identify the protein structure of the O–glycans that are specifically expressed on the surface of mESCs as the search for similar defining glycan structures on human ESCs continues.

Author: Mirko von Elstermann