Biosynthesis of core 1 and core 2 O-glycans. Core 2 β6GnT generates a biantennary structure in O-glycans, and sLe^x is synthesized at the terminus of N-acetyl lactosamine disaccharide repeats on the core 2 branch. Core 1 β3GalT, core 1 β-1,3-galactosyltransferase; core 2 β6GnT, core 2 β-1,6-N-acetylglucosaminyltransferase; β4GalT, β-1,4-galactosyltransferase; α-1,3-FucT, α-1,3-fucosyltranferase; α-2,3-ST, α-2,3-sialyltransferase; β3GnT, β-1,3-N-acetylglucosaminyltransferase (i-extension enzyme).