(D) Outline of strategy to map single MNs to a position along the AP axis (see also Materials and Methods). Upper panel: Intensities of Hox protein expression along the ventral nerve cord measured by immunofluorescence (upper left panel) and co-expression patterns of Hox gene transcripts measured by scRNA-Seq (upper right panel) were used as input. Upper right panel depicts a heatmap of color-coded Hox gene expression levels; columns correspond to n=758 single twitlow MNs. Lower panel: AP position is inferred form scRNA-Seq data by probabilistically mapping Hox gene expression pattern in each individual cell to the immunofluorescence reference data. 