BackgroundGenetic canalization reflects the capacity of an organism’s phenotype to remain unchanged in spite of mutations. As selection on genetic canalization is weak and indirect, whether or not genetic canalization can reasonably evolve in complex genetic architectures is still an open question. In this paper, we use a quantitative model of gene regulatory network to describe the conditions in which substantial canalization is expected to emerge in a stable environment.ResultsThrough an individual-based simulation framework, we confirmed that most parameters associated with the network topology (complexity and size of the network) have less influence than mutational parameters (rate and size of mutations) on the evolution of genetic canalization. We also established that selecting for extreme phenotypic optima (nil or full gene expression) leads to much higher canalization levels than selecting for intermediate expression levels. Overall, constrained networks evolve less canalization than networks in which some genes could evolve freely (i.e. without direct stabilizing selection pressure on gene expression).ConclusionsTaken together, these results lead us to propose a two-fold mechanism involved in the evolution of genetic canalization in gene regulatory networks: the shrinkage of mutational target (useless genes are virtually removed from the network) and redundancy in gene regulation (so that some regulatory factors can be lost without affecting gene expression).Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0801-2) contains supplementary material, which is available to authorized users.

Although the majority of genomic binding sites for the insulator protein CCCTC-binding factor (CTCF) are constitutively occupied, a subset show variable occupancy. Such variable sites provide an opportunity to assess context-specific CTCF functions in gene regulation. Here, we have identified a variably occupied CTCF site in the Drosophila Ultrabithorax (Ubx) gene. This site is occupied in tissues where Ubx is active (third thoracic leg imaginal disc) but is not bound in tissues where the Ubx gene is repressed (first thoracic leg imaginal disc). Using chromatin conformation capture, we show that this site preferentially interacts with the Ubx promoter region in the active state. The site lies close to Ubx enhancer elements and is also close to the locations of several gypsy transposon insertions that disrupt Ubx expression, leading to the bx mutant phenotype. gypsy insertions carry the Su(Hw)-dependent gypsy insulator and were found to affect both CTCF binding at the variable site and the chromatin topology. This suggests that insertion of the gypsy insulator in this region interferes with CTCF function and supports a model for the normal function of the variable CTCF site as a chromatin loop facilitator, promoting interaction between Ubx enhancers and the Ubx transcription start site.