Evolution of regulatory elements producing a conserved gene expression pattern in Caenorhabditis

Summary Natural selection acts at the level of function, not at the logistical level of how organisms achieve a particular function. Consequently, significant DNA sequence and regulatory differences can achieve the same function, such as a particular gene expression pattern. To investigate how regulatory features underlying a conserved function can evolve, we compared the regulation of a conserved gene expression pattern in the related species Caenorhabditis elegans and C. briggsae. We find that both C. elegans and C. briggsae express the ovo‐related zinc finger gene lin‐48 in the same pattern in hindgut cells. However, the regulation of this gene by the Pax‐2/5/8 protein EGL‐38 differs in two important ways. First, specific differences in the regulatory sequences of lin‐48 result in the presence of two redundant EGL‐38 response elements in C. elegans, whereas the redundancy is absent in C. briggsae. Second, there is a single egl‐38 gene in C. briggsae. In contrast, the gene is duplicated in C. elegans, with only one copy retaining the ability to regulate lin‐48 in vivo. These results illustrate molecular changes that can occur despite maintenance of conserved gene function in different species.