Sialic acid is a unique sugar moiety that resides in the distal and most
accessible position of the glycans on mammalian cell surface and
extracellular glycoproteins and glycolipids. The potential for sialic
acid to obscure underlying structures has long been postulated, but the
means by which such structural changes affect directly biological
processes continues to be elucidated. Here, we appraise the growing body
of literature detailing the importance of sialic acid for the
generation, differentiation, function, and death of hematopoietic cells.
We conclude that sialylation is a critical post-translational
modification utilized in hematopoiesis to meet the dynamic needs of the
organism by enforcing rapid changes in availability of lineage-specific
cell types. Though long thought to be generated only cell-autonomously
within the intracellular ER-Golgi secretory apparatus, emerging data
also demonstrate previously unexpected diversity in the mechanisms of
sialylation. Emphasis is afforded to the mechanism of extrinsic
sialylation, whereby extracellular enzymes remodel cell surface and
extracellular glycans, supported by charged sugar donor molecules from
activated platelets.