In vivo studies of the Drosophila insulator factor CTCF reach a Catch 22

Mutations in the proteins that bind insulator DNA elements that define the boundaries of chromatin domains can give morphogenetic readouts in Drosophila, as recently reported in BMC Biology by Bonchuk et al. in the Georgiev laboratory. But disentangling the effects on the phenotype may not be simple. See research article: http://www.biomedcentral.com/1741-7007/13/63