Heterodimers of tgo/trh are involved in the control of breathless expression. Plays a role in the cellular or tissue response to oxygen deprivation. Efficient DNA binding requires dimerization with another bHLH protein. Heterodimer with ahr, trh or sim. At stage 11, expression is detected in tracheal pits. At later stages, strong expression is also detected in the CNS. Expressed both maternally and zygotically in pupae at a low level.