Fig 2: Embryonic and adult skin is disrupted in the absence of Setd8. (A) Visualization of GFP as a reporter for Cre-activity in control (left hand panels) and K14CreSetd8Δ/Δ (right hand panels) embryos at the indicated embryonic days (E). (B, C) Mouse embryos at E18.5 with normal expression of Setd8 (control) (B) and deleted Setd8 (K14CreSetd8Δ/Δ) in skin (C). (D, E) Haematoxylin & Eosin staining of skin sections from control (D) and K14CreSetd8Δ/Δ (E) littermates at E15.5. (F–H) Skin sections of control (upper panels) and K14CreSetd8Δ/Δ (lower panels) littermates at E14.5 (F) and E15.5 (G, H) labelled with antibodies to Itga6 (green) and keratin 14 (K14; red) (F) or p63 (red) (G) or p53 (brown) (H). Arrows in (F) indicate the loss of an epithelial cell layers starting from E14.5. (I–L) Histological sections of adult skin expressing inducible Cre-recombinase under control of the K14 promoter (K14CreER) crossed with wild-type mice (Setd8wt/wt) (I), or animals heterozygous (Setd8Δ/wt) (K), homozygous (Setd8Δ/Δ) (J) for the floxed Setd8 allele, or mice carrying one floxed and one null allele for Setd8 (Setd8Δ/null) (L). (M, N) Labelling for FAS and Fabp5 (green) in the presence (K14CreERSetd8wt/wt) (left hand panels) or absence of Setd8 (K14CreERSetd8Δ/Δ) (right hand panels). Nuclei are counterstained with DAPI (blue) in (F, G, M, N). Arrows in (I–N) indicate sebaceous glands and arrowheads (I–L) point to IFE. Scale bars: 100 μm (F–N).

Fig 3: Epidermal response to different Myc levelsK14MycER and transgene negative (WT) dorsal skin was treated with the 4OHT doses indicated.A–D. Haematoxylin and eosin (H&E) staining. Doubleheaded arrows: SG enlargement (B); IFE thickening (C).E–H. Ki67 immunostaining.I. % Ki67 positive cells ± SEM in IFE basal layer.J. Maximum IFE thickness (µm) ± SEM.K–N, Q–S. Immunofluorescence staining for FAS (green, K–N) with DAPI nuclear counterstain (blue, K–N) or FABP5 (Q–S). Arrows indicate FAS expression. Brackets demarcate SG.O,P. H&E staining of IFE. Arrows show ectopic sebocytes. Scale bars: 10 µm (A–H, K–P), 75 µm (Q–S).

Fig 4: Epidermal response to MycAWT: transgene negative; Myc: K14MycER; MycA: K14MycAER. 4OHT doses are indicated.A–D. H&E stained sections of back skin. Arrowhead in (B) shows IFE thickening. Arrows (B–D): differentiated sebocytes.E,F. Ki67 labelling of back skin. Arrows: SG.G. % Ki67 positive IFE basal layer cells ± SEM.H. Maximum IFE thickness (µm) ± SEM.I. IFE basal (BL), spinous (SL), granular (GL) and cornified (CL) layers; 8 days, 0.5 mg 4OHT.J. FABP5 staining. Bracket: SG.K. Scatterplot of FABP5 positive area of individual SG; at least 28 SGs per condition. Red bar: median. *p<0.05, ***p<0.005.L. Summary of effects of Myc and MycA on proliferation of undifferentiated keratinocytes (UD) and differentiation into SG and IFE. Thickened arrows indicate stimulation relative to control, untreated epidermis. Scale bars: 10 µm (A–F), 50 µm (I), 75 µm (J).