Fig. 1. HNT is expressed in sensory neuron precursor cells in larval discs. Third instar larval and pupal discs stained with -HNT antibody: (A-D) larval eye discs; (E) pupal eye disc; (F) wing disc; (G,H) leg discs. (A) In wild type, HNT accumulates posterior to the morphogenetic furrow of the eye disc (arrow) in the nuclei of all R cells before their differentiation as neurons, in all sensory neuron precursor cells in the antennal disc (black arrowhead points to a subset of these cells) and in the ocellar precursor cells (gray arrowhead). (B) Eye disc from a larva carrying a dpp-lacZ enhancer trap (see Materials and Methods) double-stained with -HNT antibody (green) and an -ß-gal antibody to visualize dpp-reporter expression (red). The most anterior boundary of HNT expression is in the middle of the furrow, partially overlapping with dpp-reporter expression. (C) HNT expression in the furrow is restricted to clusters of cells, with non-staining cells in between (the arrow marks the furrow). (D) More posteriorly, HNT is found in the nuclei of all R cells in the developing clusters (the arrow marks the furrow). Inset: there is higher accumulation of HNT in the R3 and R4 precursor cells (white arrowheads). (E) HNT accumulates in the bristle precursor cell nuclei in the basal plane of a pupal eye disc. (F,G) HNT accumulates in sensory precursor cells in third instar wing (F) and leg (G) discs. (H) In a leg disc from a N^ts1/Y fly pulsed at the restrictive temperature, HNT accumulates in the additional cells that are now destined to become neurons.