Intragenic CpG islands and imprinting In mammals, DNA methylation is essential for development and differentiation and targets mainly the cytosines located in the CpG context. Whereas the genome is globally depleted in this dinucleotide, there are clusters of CpGs known as CpG islands (CGI). When associated with promoter regions, CGIs are globally devoid of DNA methylation but where these regions are methylated, this is correlated with repression. By contrast, CGIs localised in the gene body (or intragenic CGIs, iCGIs), are prone to acquiring DNA methylation during differentiation and development. Interestingly, most of this iCGIs also show tissue-specific promoter activity and expression from the host gene and the CGI is important in the regulation of this tissue- and developmental stage-specific methylation patterns. This suggests important crosstalk between iCGIs and their host genes and an important role for iCGIs in cell fate specification. This is supported by our studies, in mouse, at the imprintedMcts2/H13 locus where the expression of the imprinted retrogene Mcts2 from an iCGI leads to alternative polyadenylation at the host gene transcript (H13). In this context, our project is to elucidate how intragenic promoter activity is regulated and how this activity could influence the transcript diversity from the host gene with a special focus on alternative polyadenylation. To answer these questions, our group combine genome-wide studies on in vitro differentiation systems and detailed molecular analysis at the Mcts2/H13locus model.