Developmental origin of the Pair1 descending interneuron.

Pair1 is part of a larval locomotor circuit that promotes backward locomotion by inhibiting forward locomotion. We hypothesize that lineage related neurons may function in neuronal circuits together. Testing this hypothesis requires knowing the progenitor of each neuron within this locomotor circuit, and here we focus exclusively on Pair1. During embryogenesis, unique neuroblasts form by inheriting the spatial transcription factors (TFs) expressed in their birth location within the neuroectoderm. We examine the Pair1 neurons using immunofluorescence to determine which neuroblast the Pair1s derive from. Our results show that Pair1 is derived from gnathal neuroblast 5-3 which expresses Gooseberry (Gsb) and Intermediate neuroblasts defective (Ind). When Gsb or Ind were overexpressed in the Pair1 lineage, extra neurons formed with similar Pair1 morphology.