OLIG2 and glioblastoma: Hence, we focused on two other markers YKL-40 and OLIG2 for proneural and mesenchymal subtypes segregation using the strategy shown in Figure 4A. Glioblastoma tissue sections stained for YKL-40 and OLIG2 were screened in lower power fields (20×; 5 regions/sections in a minimum of 2–3 serial sections) and scored for YKL-40- and OLIG2-positive areas.