The function of ENSG00000173852 (DPY19L1, dpy-19 like C-mannosyltransferase 1) is as follows. C-mannosyltransferase that mediates the C-mannosylation tryptophan residues on target proteins. The reaction occurs on the luminal side of the endoplasmic reticulum and involves the transfer of a mannose unit from a dolichylphosphate mannose (Dol-P-Man) donor to an acceptor protein containing a WxxW consensus sequence (By similarity). C-mannosylates the first two tryptophans in the WxxWxxWxxC motif in thrombospondin (TSP) type-1 of UNC5A (By similarity). Regulates neurite extension during development (By similarity). .