Fig. S1. Induction of Ets1 changes expression of keratinocyte structural proteins. Lysates from the skin of E18.5 day WT and BT embryos were used in western blotting to detect the expression of filaggrin, loricrin and K6 as well as the Ets1 transgene using antibodies to the HA-tag and to Ets1. GAPDH is a loading control.

Fig. S2. Induction of Ets1 results in delayed involucrin expression. Immunofluorescent staining of epidermal differentiation markers on dorsal skin of E18.5 BT and WT mice. Sections were counterstained with DAPI to detect nuclei and β4-integrin to mark the basement membrane. The following markers were used to assess the differentiation pattern of WT and BT epidermis: (A) keratin 14 (K14), (B) keratin 10 (K10), (C) involucrin (INV), (D) filaggrin (FIL) and (E) loricrin (LOR). White arrow in WT skin sections marks a well-defined stratum corneum, while it is absent in the BT skin (grey arrow).

Fig. S3. Expression of Ets1 in differentiating oral keratinocytes induces hyperproliferation. (A) Hematoxylin and eosin staining of oral epithelium of WT and BT newborn pups shows mild hyperplasia in ventral tongue and palate mucosa in addition to parakeratosis (arrowheads). (B) Immunostaining for PCNA, counterstained with DAPI, shows hyper-proliferation of the ventral tongue and palate.

Fig. S4. Induction of Ets1 alters the differentiation program of oral keratinocytes. Sections from palate, and from the dorsal and ventral surfaces of the tongue were immunostained for (A) keratin 5, (B) keratin 6, (C) keratin 13 and (D) loricrin, and counterstained with DAPI.

Fig. S5. Early stages of hair follicle formation are unaffected by HA-Ets1 induction. Skin sections of E15.5 day old WT and BT embryos stained with (A) hematoxylin and eosin, (B) for E-cadherin, and (C) for P-cadherin. Sections were counterstained with β4-integrin to mark the basement membrane (asterisks denote the location of mesenchymal fibroblasts). Black arrowheads in A indicate elongating hair germs and blue arrowheads indicate younger hair follicle progenitors. (D, E, F) same as above for E16.5 embryonic skin.

Fig. S6. Validation of microarray results with semi-quantitative RT-PCR. Primers specific for some of the genes that demonstrated alterations in expression by microarray were used in RT-PCR with cDNA derived from E18.5 day skin of WT and BT embryos. Also shown in RT-PCR with primers that recognize the HA-Ets1 transgene and with primers to Hprt1, a housekeeping gene whose expression was not affected in microarray analysis and which serves as an internal control for cDNA quality.

Fig. S7. Myeloid cells infiltrate the skin of BT mice. Immuno-staining for CD11b (Itgam) in the skin of WT and BT embryos at E18.5. Sections are co-stained with K6 to mark the epidermis in the BT sample and the hair follicles in the WT sample.