Fig. 2. Expression of differentiation markers in HK1.fos/5Pten tumours. (A) HK1.fos papillomas exhibit a delay in onset of suprabasal keratin K1 expression (green), consistent with expansion of the proliferative basal cell compartment, counterstained with K14 (red). HK1.fos/5Pten^flx KAs exhibit strong, atypical K1 expression in proliferative basal cells of differentiated regions (no separate K14/red is visible), suggesting an accelerated terminal differentiation. (B,C) Late-stage differentiation markers (B) loricrin and (C) filaggrin remained confined to the granular layer in HK1.fos papillomas. By contrast, HK1.fos/5Pten^flx KAs display premature elevated loricrin and filaggrin expression indicative of an accelerated disordered nature to differentiation, e.g. loricrin in micro-cysts. (D) HK1.fos papillomas expressed tumour progression marker keratin K13, which was focally expressed in papillomatous HK1.fos/5Pten^flx areas, whereas K13 expression was lost in differentiated KA histotypes.