Transcriptional regulation governs lineage specification in all tissues including themammary gland, yet our understanding of the mechanisms controlling transcription remains limited. Enhancers fine-tune transcriptional programs and are critical for cell differentiation process. Regulation of cellular differentiation programs can go wrong in cancer. Understanding the gene regulation of lineage specification is vital, as it is likely that breast cancer development occurs through alterations in cells along different stages of the differentiation hierarchy. Transcription factors (TF) are proteins that coordinate lineage specificity. Mutations in transcription factor networks are associated with cancer. We hypothesise that cis-regulatory elements, primarily enhancers, of lineage specific TFs are critical to the differentiation of the two epithelial lineages of the mammary gland. We utilised CRISPR-activation (CRISPRa) to interrogate the role of putative enhancer elements in driving expression of lineage TFs during differentiation. We designed multiple guides, covering several putative enhancer regions to activate expression of lineage specific TFs in a murine mammary epithelial cell line. The effects of this putative enhancer activation on target gene transcription and expression were analysed by Western blot and qPCR. The transduction and cell sorting strategies were optimised. Guides targeting putative enhancers of ΔNp63, Snai2, Msx2, Elf5 and Gata3 TFs increased target gene expression using the CRISPRa system. We are currently undertaking work to analyse the transcriptomic and epigenetic effects of CRISPRa enhancer activation and using this system to activate cis-regulatory elements in primary mammary cells to characterise shifts in mammary gland lineage.