Acts as a transcription regulator (PubMed:20713707). Binds to the sequence motif 5'-TCAGGTT-3' (PubMed:20335356). Binds to the cis-regulatory element of proapoptotic factor egl-1 gene and together with eya-1 activates egl-1 expression to promote motor neuron M4 sister cell apoptosis (PubMed:20713707). Also promotes apoptosis of I1 pharyngeal neuron sister cell (PubMed:20713707). Together with eya-1, required to specify the coelomocyte fate in embryonic and postembryonic precursors (PubMed:19427847, PubMed:20335356). Interacts (via N-terminus) with eya-1 (via C-terminus). Expression starts at the embryonic bean stage and continues throughout larval and adult stages in few anterior body wall muscle cells and in unidentified cells in the head (PubMed:19427847). Expressed predominantly in pharyngeal cells during embryogenesis and throughout larval and adult stages (PubMed:20713707). In L1 larvae, expressed in all pharyngeal neurons (M4, I1, MI, I3, M3, NSM, MC, I2, I4, I5, I6, M1, M2, and M5), some pharyngeal muscle cells (pm1 and pm2) and pharyngeal epithelial cells (e1 and e3), and some body wall muscles around the anterior pharynx (PubMed:20713707). Expressed transiently in the M lineage-derived coelomocyte precursor cells M.dlpa and M.drpa before their differentiation into coelomocytes (PubMed:19427847, PubMed:20335356). Expressed in the M4 motor neuron sister cell (PubMed:20713707). RNAi-mediated knockdown in embryos causes lethal arrest at the embryonic 3-fold stage or at the L1 larval stage with abnormal anterior morphology (PubMed:19427847). The few surviving animals lack 1 or both pairs of embryonic MS lineage-derived coelomocytes as well as the 2 post embryonic M lineage-derived coelomocytes (PubMed:19427847). RNAi-mediated knockdown in L1 larvae causes the loss of the M lineage-derived coelomocytes due to the abnormal differentiation of coelomocyte precursors M.drpa and M.dlpa into body wall muscle cells (PubMed:19427847). In 38 percent of animals, the motor neuron M4 sister survived (PubMed:20713707). Belongs to the SIX/Sine oculis homeobox family.