We also identified a striking expression pattern for the helix-loop-helix TF
hlh-15, in which expression is confined to a single neuron in the tail (DVA) and a single paired neuron in the head (AVKL/R). A previous study generated a promoter::GFP transgene for
hlh-15 and likewise reported expression in a single tail neuron and a single paired head neuron (Grove et al. 2009) but tentatively assigned the expression to the DVA and RIF neurons based on cell position and morphology. To clarify the discrepancy, we obtained the hlh- 15p::GFP transgene and crossed it with nuclear red fluorescent transgenes (H2B::mCherry) expressed in only the DVA neuron or only the AVK neuron (Wang et al. 2017). We found that the DVA mCherry marks the nucleus of the cell identified in the tail, and the AVK mCherry marks the nucleus of the paired head neurons, confirming VISTA's cell-type identification for
hlh-15 gene expression.