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. Mostly neuronal. Expressed both maternally and zygotically. At least one isoform is present at each developmental stage.