The Notch signalling pathway regulates many developmental processes in
metazoan embryos and adults such as cell proliferation, stem cell maintenance, cell fate
specification and apoptosis. Despite the importance of this pathway, few targets have
been identified, with the Hes (Hairy and Enhancer-of-split) protein family being the
best-characterised group of downstream effectors.
I have established transgenic mice carrying Biotin Acceptor Peptide (BAP)-
tagged versions of Notch1. The tagged protein is fully functional and is biotinylated
after crossing to mice expressing the biotinylase from E. coli. Biotinylation was
confirmed in a range of different tissues. However, streptavidin chromatin pull-down
(bioChIP) experiments from these tissues showed no significant enrichment of known
Notch1 target sequences. A possible explanation could be the indirect and transient
nature of the interaction between Notch, its DNA binding partner CSL and the promoter
of the target gene.
A transgenic mouse line expressing a BAP-tagged version of the transcription
factor Hes7, a downstream effector of Notch signalling and key regulator of
somitogenesis, was similarly generated. Although the tagged Hes7 protein is functional
and gets biotinylated in cell culture assays, the transgenic mice exhibit a severe
somite/skeletal phenotype indicating that the tagged allele is hypomorphic. A detailed
analysis of the phenotype revealed differential axial requirements for Hes7
