Fig. 10.

Frzb shifts Wnt8 from N-sulfo-rich to N-acetyl-rich HS clusters. a Frzb inhibits the accumulation of Wnt8 on ndst1 overexpressing cells. Experimental procedures were as illustrated. Although mV-Wnt8 was accumulated on ndst1-overexpressing cells (upper right), mV-Frzb was not accumulated on ndst1-overexpressing cells (lower left). When coexpressed with Frzb, mV-Wnt8 was not accumulated on ndst1 overexpressing cells similar to Frzb (lower right). b Frzb inhibits internalization of Wnt8. Left panels, the characteristic puncta of mV-Frzb (asterisks, source cells of mV-Frzb). Middle panels, mV-Wnt8 in the intercellular space (white arrowheads) and inside the cells (orange arrowheads) (asterisks, source cells of mV-Wnt8). Right panels, in the presence of Frzb, punctate staining of mV-Wnt8 (asterisks, source cells of mV-Wnt8) became smoother in the intercellular space (white arrowheads) and was barely detected inside the cell. Lower panels, magnified images of the boxed regions in the upper panels. mV-wnt8 and frzb mRNAs were separately injected into different blastomeres. c A model of the N-sulfo-rich and N-acetyl-rich HS cluster system for the regulation of the extracellular distribution and signal reception of the Wnt morphogen. d A model for the initiation of signalosome formation. N-sulfo-rich HS clusters (magenta) work as a pre-existing core to accumulate Wnt8 (green) prior to the recruitment of the Fzd receptor and following phosphorylation of LRP6. Images are a representative of at least two independent experiments. Amounts of mRNAs (ng/embryo): mV-wnt8, 1.0 (a) or 2.0 (b); mV-frzb, 0.39 (a) or 2.0 (b); frzb, 0.48 (a) or 2.5 (b); ndst1, 0.5. Scale bars, 20 μm. a.u., arbitrary units