HES1 and neoplasm: In particular, Hes1 expression predominated in normal rat pituitary when compared to prolactin secreting cell lines and xenografts, Hey1 showed higher levels in the GH3 tumor relative to MMQ cells and normal gland, and the target Hey2 was detected in the GH3 xenograft model and in the normal pituitary but was almost absent in the tumor MMQ and GH3 cell lines, similarly to results found in AtT20 cells for this transcription factor (Figure 5C).