SP1 and esophageal squamous cell carcinoma: RT-qPCR with variant-specific primer sets revealed that the levels of EMX2 splice variant 1 (sp1) and variant 2 (sp2) were highly correlated in both groups of ESCC cell lines (Figure 2A), ESCC tissues (Figure 2B), and normal esophageal epithelial tissues (Figure 2C), and the sp1 level was always higher than the sp2 level (p < 0.0001).