Transcriptional repressor. Activity as a repressor is enhanced by binding to the corepressor tle3a. Interacts with tle3a. Detected in the presumptive ectoderm at the late blastula stage. During the gastrula stage, expression refines to the ventrolateral ectoderm and the dorsal-midline ectoderm. Expressed in primary neurons during the segmentation stage, with strongest expression in primary motoneurons and interneurons and lower expression in Rohon-Beard neurons. The expression domain is restricted to regions posterior of rhombomere 4. During the late segmentation and pharyngula stages, expression decreases in an anterior-to-posterior direction and is largely absent by 48 hours post-fertilization. Morpholino knockdown of the protein results in impaired neurogenesis in posterior regions. Expression of the neural precursor marker ngn1 is reduced at the one- to three-somite stage. At later stages, there is a significant reduction in islet1-expressing primary motoneurons and defective axon outgrowth from motoneurons. Formation of Rohon-Beard neurons is initially abnormal but later recovers. Development of secondary neurons is not affected. Belongs to the NK-1 homeobox family.