The balance between MN and V2a IN development is sensitive to Isl
protein levels. (A-J) Immunolabeling to detect
Isl1/2+ and Hb9+ MNs, and
Chx10+ V2a INs in E11.5 cervical spinal cords. Wild-type
(Ctrl; A,B), Isl2 null (Isl2 KO; C,D), Isl1 hypo
(E,F), Isl1 hypo; Isl2 KO (G,H) and Isl1 cKO (I,J)
embryos were examined. (K) Quantification of Hb9+ MNs and
Chx10+ V2a INs in transverse sections of E11.5 embryos. The loss of
Isl labeling was found to correlate with an increase in V2a IN (Chx10)
labeling. Each bar represents the average of eight sections collected from
three different embryos. Mean±s.e. is shown. Asterisks indicate
statistically significant differences compared with control or groups marked
with bracket (*P<0.05; **P<0.01,
paired Student's t-test). (L) Diagram depicting the hexameric
2-NLI: 2-Lhx3: 2-Isl1 transcription complex in wild-type and Isl mutant
embryos. As Isl protein level drops, the formation of 2-NLI: 2-Lhx3 complexes
for V2a IN development are likely to predominate. Scale bar: in J, 40 μm
for A-J.