Expression is first detected in 4 neuronal cells at around 350 min post-fertilization, which is the time at which the BAG and URX neurons are born. Expression is restricted to these 4 neurons during embryogenesis. At the first larval stage,
egl-13 expression is observed in the BAG and URX neurons plus occasionally in a small number of unidentified cells in the head and tail (including the AQR and PQR neurons). Later during larval development,
egl-13 expression is observed in body wall muscle and vulval cells (data not shown). Neuronal expression is restricted to the O2 and CO2-sensing neurons in the adult.