Former question: Where and how happen these operations in the Wnt signaling pathway?
I have read about the signaling pathway on wikipedia:
Wnt comprises a diverse family of secreted lipid-modified signaling glycoproteins that are 350–400 amino acids in length. The lipid modification of all Wnts is palmitoleoylation of a single totally conserved serine residue. Palmitoleoylation is necessary because it is required for Wnt to bind to its carrier protein Wntless (WLS) so it can be transported to the plasma membrane for secretion and it allows the Wnt protein to bind its receptor Frizzled  Wnt proteins also undergo glycosylation, which attaches a carbohydrate in order to ensure proper secretion. In Wnt signaling, these proteins act as ligands to activate the different Wnt pathways via paracrine and autocrine routes
Where happen these chemical reactions described in this quote ? My understanding is that they happen outside of cells, before the arrival of the Wnt ligand on the receptor that is located at the surface of the cell. Am I correct? If yes, were does this happen precisely in the body? Where the ligand comes from?
EDIT: From comments: The Wnt ligand is secreted by other cells and transmitted from cell to cell, this is an autocrine process.
The question is: Under which conditions does this process start in one cell?