Arrowhead encodes a LIM homeodomain protein that distinguishes subsets of Drosophila imaginal cells

The Arrowhead gene encodes a LIM-homeodomain transcription factor required for establishment of a subset of imaginal tissues: the abdominal histoblasts and the salivary gland imaginal rings. Consistent with its role in development, during embryogenesis Arrowhead is expressed in each abdominal segment and in the labial segment. Late in embryonic development, expression is refined to the abdominal histoblasts and salivary gland imaginal ring cells themselves. When ectopically expressed in imaginal disc cells, Arrowhead causes programmed cell death and loss of corresponding adult structures. Therefore, Arrowhead expression is required for development of one set of imaginal cells and is incompatible with development of another, emphasizing the specificity of Arrowhead and the sensitivity of different target cells to its expression. Loss-of-function mutations in Arrowhead affect conserved or invariant amino acids in the LIM- and homeo-domains demonstrating the importance of these residues in LIM homeodomain protein activity.