Do the BEAF insulator proteins regulate genes involved in cell polarity and neoplastic growth?

It was reported that a chromosome with the BEAF(NP6377) (NP6377) allele leads to a loss of cell polarity and neoplastic growth in Drosophila melanogaster when homozygous (Gurudatta et al., 2012). We had previously generated the BEAF(AB-KO) (AB-KO) allele by homologous recombination and did not note these phenotypes (Roy et al., 2007). Both alleles are null mutations. It was unclear why two null alleles of the same gene would give different phenotypes. To resolve this, we performed genetic tests to explore the possibility that the chromosome with the NP6377 allele contained other, second site mutations that might account for the different phenotypes. We found that the chromosome with NP6377 has at least two additional mutations. At least one of these, possibly in combination with the NP6377 allele, is presumably responsible for the reported effects on gene expression, cell polarity and neoplastic growth.