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. By stage 11, isoform W, isoform X and isoform Y are expressed throughout the mesoderm, whereas isoform O is expressed in both mesoderm and ectoderm. From stage 15, expression of isoform O expands to all tissues, whereas expression of isoform W, isoform X and isoform Y becomes restricted during later stages; starting from stage 14 to 16, isoform W, isoform X and isoform Y are expressed in muscle. From stages 14 and 15, isoform W and isoform Y are expressed in the gut. For some isoforms, expression is also seen in specific types of cells in the embryo; isoform O is expressed in the ventral furrow at stage 5 and in the dorsal epidermis from stage 7. Isoform Y shows prominent expression in the gonad starting at stage 15. Expressed both maternally and zygotically. At least one isoform is present at each developmental stage.