Genetic mechanism regulating diversity in the placement of eyes on the head of animals.

Abstract

Despite the conservation of genetic machinery involved in eye development, there is a strong diversity in the placement of eyes on the head of animals. Morphogen gradients of signaling molecules are vital to patterning cues. During <i>Drosophila</i> eye development, Wingless (Wg), a ligand of Wnt/Wg signaling, is expressed anterolaterally to form a morphogen gradient to determine the eye- versus head-specific cell fate. The underlying mechanisms that regulate this process are yet to be fully understood. We characterized <i>defective proventriculus (dve)</i> (<i>Drosophila</i> ortholog of human SATB1), a K50 homeodomain transcription factor, as a dorsal eye gene, which regulates Wg signaling to determine eye versus head fate. Across <i>Drosophila</i> species, Dve is expressed in the dorsal head vertex region where it regulates <i>wg</i> transcription. Second, Dve suppresses eye fate by down-regulating retinal determination genes. Third, the <i>dve</i>-expressing dorsal head vertex region is important for Wg-mediated inhibition of retinal cell fate, as eliminating the Dve-expressing cells or preventing Wg transport from these <i>dve</i>-expressing cells leads to a dramatic expansion of the eye field. Together, these findings suggest that Dve regulates Wg expression in the dorsal head vertex, which is critical for determining eye versus head fate. Gain-of-function of SATB1 exhibits an eye fate suppression phenotype similar to Dve. Our data demonstrate a conserved role for Dve/SATB1 in the positioning of eyes on the head and the interocular distance by regulating Wg. This study provides evidence that dysregulation of the Wg morphogen gradient results in developmental defects such as hypertelorism in humans where disproportionate interocular distance and facial anomalies are reported.