Data from: Ancient mechanisms for the evolution of the bicoid homeodomain's function in fly development

The ancient mechanisms that caused developmental gene regulatory networks
to diversify among distantly related taxa are not well understood. Here we
use ancestral protein reconstruction, biochemical experiments, and
developmental assays of transgenic animals carrying reconstructed
ancestral genes to investigate how the transcription factor Bicoid (Bcd)
evolved its central role in anterior-posterior patterning in flies. We
show that most of Bcd's derived functions are attributable to
evolutionary changes within its homeodomain (HD) during a phylogenetic
interval >140 million years ago. A single substitution from this
period (Q50K) accounts almost entirely for the evolution of Bcd's
derived DNA specificity in vitro. In transgenic embryos expressing the
reconstructed ancestral HD, however, Q50K confers activation of only a few
of Bcd's transcriptional targets and yields a very partial rescue of
anterior development Adding a second historical substitution (M54R)
confers regulation of additional Bcd targets and further rescues anterior
development. These results suggest that two epistatically interacting
mutations played a major role in the evolution of Bcd's controlling
regulatory role in early development.