Compensatory action of different types of <i>cis</i> -regulatory elements buffers the striped expression of <i>Drosophila</i> pair-rule genes

The striped expression of pair-rule genes in Drosophila embryos is a paradigm for understanding transcriptional control of development. Pair-rule striped expression is regulated by two types of cis-regulatory elements: stripe-specific elements respond to non-periodic cues in different regions of the embryo to establish individual stripes while 7-stripe elements simultaneously regulate all stripes, responding to pair-rule genes expressed in stripes. Here, we assess roles of stripe-specific versus 7-stripe elements for the pair-rule gene ftz. We show that loss of a ftz stripe 2 element is compensated by 7-stripe elements, even though they respond to different spatiotemporal cues. We next investigate whether similar rules apply to the classic eve stripe2 element. Animals homozygous for a genomic deletion of eve stripe2 are viable and fertile; stripe 2 expression is perturbed early but re-establishes sufficiently to regulate downstream target genes. However, temperature or genetic stress decrease viability of ftz and eve stripe 2 deletion mutants. Thus, these stripe-specific elements contribute to robustness but are not absolutely required for segment formation. Two separate routes to establishing stripes, stripe-specific and 7-stripe elements, buffer each other, adding complexity to embryonic patterning.