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Background: The ETS transcription factor Elf5 (also known as ESE-2) is highly expressed in the mammary gland and plays an important role in its development and differentiation. Indeed studies in mice have illustrated an essential role for Elf5 in directing alveologenesis during pregnancy. Although the molecular mechanisms that underlie the developmental block in Elf5 null mammary glands are beginning to be unraveled, this investigation has been hampered by limited information about the identity of Elf5-target genes. To address this shortcoming, in this study we have performed ChIP-cloning experiments to identify the specific genomic segments that are occupied by Elf5 in pregnant mouse mammary glands., Results: Sequencing and genomic localization of cis-regulatory regions bound by Elf5 in vivo has identified several potential target genes covering broad functional categories. A subset of these target genes demonstrates higher expression levels in Elf5-null mammary glands suggesting a repressive functional role for this transcription factor. Here we focus on one putative target of Elf5, the Ccnd2 gene that appeared in our screen. We identify a novel Elf5-binding segment upstream of the Ccnd2 gene and demonstrate that Elf5 can transcriptionally repress Ccnd2 by directly binding to the proximal promoter region. Finally, using Elf5-null mammary epithelial cells and mammary glands, we show that loss of Elf5 in vivo leads to up regulation of Ccnd2 and an altered expression pattern in luminal cells., Conclusions: Identification of Elf5-targets is an essential first step in elucidating the transcriptional landscape that is shaped by this important regulator. Our studies offer new toolbox in examining the biological role of Elf5 in mammary gland development and differentiation.

Background: Genetic experiments have clarified that p63 is a key transcription factor governing the establishment and maintenance of multilayered epithelia. Key to our understanding of p63 strategy is the identification of target genes. We perfomed an RNAi screening in keratinocytes for p63, followed by profiling analysis., Results: C/EBPdelta, member of a family with known roles in differentiation pathways, emerged as a gene repressed by p63. We validated C/EBPdelta as a primary target of DeltaNp63alpha by RT-PCR and ChIP location analysis in HaCaT and primary cells. C/EBPdelta is differentially expressed in stratification of human skin and it is up-regulated upon differentiation of HaCaT and primary keratinocytes. It is bound to and activates the DeltaNp63 promoter. Overexpression of C/EBPdelta leads to alteration in the normal profile of p63 isoforms, with the emergence of DeltaNp63beta and gamma, and of the TA isoforms, with different kinetics. In addition, there are changes in the expression of most p63 targets. Inactivation of C/EBPdelta leads to gene expression modifications, in part due to the concomitant repression of DeltaNp63alpha. Finally, C/EBPdelta is found on the p63 targets in vivo by ChIP analysis, indicating that coregulation is direct., Conclusion: Our data highlight a coherent cross-talk between these two transcription factors in keratinocytes and a large sharing of common transcriptional targets.