Gtp-bp transcripts are expressed at high levels throughout embryogenesis with a peak between 12 and 18 hrs. They are found lateral to the dorsal-most regions of the ventral midline and show a segmentally repeating pattern.

In germ band extended embryos, Gtp-bp protein is detected in cells dorsal to the ectoderm and is distributed in a continuous layer from the stomodeal opening to the end of the germ band. It is also found at the anterior tip of the clypeolabrum and in the posterior gut. During germ band retraction, it becomes confined within the ventral midline, dorsal to the delaminating neuroblasts. The midline cells expressing Gtp-bp protein send a broad process across the midline just ventral to the yolk sac to the contralateral neuromere. At this stage, a single cell in each neuromere is detected. Later, protein is detected on axons that cross the midline and in other cells and processes in lateral regions of each neuromere. Starting in stage 13, Gtp-bp protein is detected in ventral, lateral and dorsal sensilla of the PNS. In later embryos, protein is detected in the intersegmental nerve and the segmental nerve on axons and on subsets of PNS cell soma.