died soon after birth, and the analysis of epidermis from these mice revealed hyperplasia, decreased expression of spinous and granular markers of differentiation and a role for E2F in the hyperplastic epidermis [28]. While we observed similar changes in basal cell hyperproliferation and defects in spinous markers of differentiation, we did not observe the granular changes reported in developing skin. For example, we did not observe diminished keratohyalin granules, filaggrin, and involucrin expression in adult epidermis and we did observe an uncoupling of involucrin and loricrin expression in adult epidermis. Collectively, these results indicate that there are significant differences between the effects of co-deletion of C/EBPa and C/EBPb in embryonic development and postnatal differentiation. Notch signaling is important in both the early and later stages of epidermal development where it regulates the basal to spinous transition in a Hes1 independent manner and the spinous to granular transition in a Hes1 dependent manner [18–20]. AP-2a and AP-2c also have essential roles in both the early and later stages of epidermal development and recently it was reported that both AP-2 and Notch signaling converge on the regulation of the expression of C/EBPa and C/EBPb [21]. Results reported in our current study demonstrate C/EBPa and C/EBPb have critical roles in the early stages of squamous differentiation and our results are consistent with a model where C/EBPs function downstream of AP-2 and Notch signaling to regulate the basal to spinous transition. As described in the introduction, the knockin of C/EBPb into the C/EBPa locus rescues the lethality of C/EBPa2/2 mice and supports the notion of functional redundancies between these family members [27,43]. 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