Putative transcription factor required for axon growth and guidance in the central and peripheral nervous systems. Repels CNS axons away from the midline by promoting the expression of the midline repellent sli and its receptor robo. Some isoforms may be generated by alternative trans-splicing of exons sequentially encoded by the same DNA strand. Expressed in both mesoderm and ectoderm with expression highest in the mesectoderm by stage 11. Becomes enriched in a cluster of brain cells, in abdominal histoblasts, and in the embryonic imaginal disks during later stages. Expressed both maternally and zygotically. At least one isoform is present at each developmental stage. C-terminal exons may be joined by a trans-splicing event. The exons are coded by the same DNA strand.