Fig. 5. dA4 neurons and their derivative, the inferior olivary nucleus, are absent in Olig3 mutant mice. (A,B,D,E,F,H) Immunohistological analysis of control (A,B,D) and Olig3 mutant (E,F,H) mice using antibodies against Brn3a and Foxd3. In control mice at E11.5 (A), Brn3a⁺/Foxd3⁺ dA4 neurons emerged in the dorsal alar plate. Foxd3/Brn3a co-expression marks specifically dA4; other neuronal types expressed either Foxd3 (a ventral population, asterisk) or Brn3a (dorsal neuronal subtypes). At E12.5 (B), a stream of Foxd3⁺/Brn3a⁺ dA4 neurons (arrowheads) extended ventrally and appeared to assemble close the ventral midline (arrow). In Olig3 mutant mice at E11.5 (E) and at E12.5 (F), Foxd3⁺/Brn3a⁺ dA4 neurons were absent. At E18.5. Foxd3⁺/Brn3a⁺ neurons were located in the inferior olivary nucleus of control mice (arrow, D), but were absent in Olig3 mutants (H). (C,G) In situ hybridization analysis of control (C) and Olig3 mutant (G) mice at E15.5 using a Foxd3-specific probe (arrow in C). The insets show the whole-mount in situ hybridization of the corresponding hindbrains prior to sectioning. Scale bars: 50 µm in F,G; 100 µm in H.