Rx transcripts are first observed at embryonic stage 8 in two dorsolateral spots in the procephalic region. At the end of stage 8, additional staining is seen in the dorsal region that will give rise to the clypeolabrum. The head region expression becomes more pronounced by stage 9 and additional staining appears in the CNS. Later expression is observed in the antenno-maxillary complex. Staining at the medial edges of the two brain lobes, in the clypeolabrum, and in the antenno-maxillary complex persists until the end of embryogenesis.

(Eggert et al., 1998)

Rx transcripts are detected by in situ hybridization during early embryogenesis in the eye disc primordia. They are also observed in a patch of cells in the anterior of the embryo corresponding to the clypeolabrum, in a region that gives rise to the epiphysis.

(Mathers et al., 1997)

During embryogenesis, Rx is expressed in a subset of Nrt positive brain cells, including 8-10 dpn positive neuroblasts, 4 of which are the mushroom body neuroblasts. This expression, and co-expression with dpn, persists throughout larval development where it also overlaps with Scer\GAL4^insc-Mz1407 and Scer\GAL4^NP1316. During the first larval instar stage, Rx positive mushroom body neuroblasts are seen within the cortex of the ey positive larval mushroom body. At the L3 stage, there are ~10 Rx and dpn co-expressing neuroblasts per hemisphere including the mushroom body neuroblasts, 2 of the dorso-lateral protocerebral DPLc lineage and ~2 that are part of the protocerebral CP or posterior deutocerebral CM lineages. Rx expression also overlaps with pros in a subset of mushroom body cells at this stage. Rx is also expressed in distally located, elav positive differentiated neurons of the type II DM neuroblast lineage, but not in neuroblasts, precursor cells or ganglion mother cells of this lineage. Finally, Rx is expressed in a subset of young Scer\GAL4^insc-Mz1407 labelled Kenyon cells in adults but is not observed in mature Kenyon cells.

(Kraft et al., 2016)

In stage 12 embryos, Rx protein is detected in a cluster of neuroectodermal cells alongside the dorsal midline, posterior to the pars lateralis primordium.

(de Velasco et al., 2007)

Protein is detected in stage 13 embryos in a restricted pattern in the central nervous system with staining in the embryonic brain hemispheres near the midline. Protein is expressed in larval central nervous system in several cell clusters near the midline. Additional expression in larvae is observed in a subset of cells in the clypeo-labral disc. Expression is detected in dorsal and posterior regions of the adult brain.

(Davis et al., 2003)