O-sulfotransferases modify heparan sulfate proteoglycans (HSPGs) by catalyzing the transfer of a sulfate to a specific position
on heparan sulfate glycosaminoglycan (GAG) chains. Although the roles of specific HSPG modifications have been described in
cell culture and invertebrates, little is known about their functions or abilities to modulate specific cell signaling pathways
in vertebrate development. Here, we report that 2-O-sulfotransferase (2-OST) is an essential component of canonical Wnt signaling
in zebrafish development. 2-OST-defecient embryos have reduced GAG chain sulfation and are refractory to exogenous Wnt8 overexpression.
Embryos in which maternally encoded 2-OST is knocked down have normal activation of several zygotic mesoderm, endoderm and
ectoderm patterning genes, but have decreased deep cell adhesion and fail to initiate epiboly, which can be rescued by re-expression
of 2-OST protein. Reduced cell adhesion and altered cell cycle regulation in 2-OST-deficient embryos are associated with decreased
β-catenin and E-cadherin protein levels at cell junctions, and these defects can be rescued by reactivation of the intracellular
Wnt pathway, utilizing stabilized β-catenin or dominant-negative Gsk3, but not by overexpression of Wnt8 ligand. Together,
these results indicate that 2-OST functions within the Wnt pathway, downstream of Wnt ligand signaling and upstream of Gsk3β
and β-catenin intracellular localization and function.