Figure 5

Defects in nociceptor specification in the Brn3a^-/- TG. The TG of Brn3a knockout and control embryos were examined at various stages for the expression of TrkA, TrkB, and Runx1. (A, B) At E10.5, TrkA and TrkB are extensively co-expressed in control (A) and Brn3a knockout (B) ganglia. Runx1 is not expressed at this stage. (C, D) At E12.5, Runx1 is expressed in control ganglia (C) but is markedly diminished in the knockout (D). Arrows mark rare Runx1⁺ cells. (E, F) At E13.5, TrkA and TrkB expressing neurons normally segregate into discrete populations (E) but fail to do so in Brn3a knockout ganglia (F). Exposure time for TrkA in (F) is increased to reveal co-expression; see (I, J) for equal exposures. Arrowheads in (F) indicate examples of numerous abnormal TrkA⁺/TrkB⁺ cells. (G, H) At E13.5, Runx1 expression is markedly diminished in the knockout. The few Runx1⁺ neurons detected at this stage do not express TrkB (H, arrows). Scale bar = 50 μM.