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Fig. 1. Altered olivocochlear efferent and facial visceral motoneuron development
in reeler mutant hindbrain. Motoneuron distribution was determined by
using an islet 1 riboprobe on whole-mount preparations. Pial side view of
flat-mounted control (A,C,E,G) and reeler (B,D,F,H) embryos at E12.5,
E13.5, E14.5 and E15.5. (A) In control embryos at E12.5, islet 1 expression is
observed in the Vth (trigeminal motor) and VIIth (facial) migrating nuclei,
and in a discrete lateral column of cells (arrows) between these two nuclei
that includes a sub-population of the trigeminal, the facial
visceromotoneurons (FVM) and the olivocochlear neurons (OC). At this stage
many facial motoneurons are still in the process of migrating caudally from
their birthplace in rhombomere 4 to their settling position in rhombomere 6.
(B) In reeler embryos, VII neuron migration is comparable to control,
whereas the OC/FVM column is reduced in its rostrocaudal extension (arrows).
(C) In control embryos at E13.5, islet 1 expression is clearly observed in the
main Vth nucleus, in the OC/FVM motoneurons, and in the VIIth nucleus. (D) In
reeler mutants, the OC/FVM group of motoneurons is barely detectable
(arrow). (E-H) At E14.5 (E,F) and E15.5 (G,H), FVM (and/or associated OC) are
not labeled by islet 1 at the pial side in reeler embryos (F,H;
arrows). At this stage most of the migrations have already occurred or are in
the final stages. By E15.5, the facial nucleus forms two lobes, medial and
lateral, in control embryos (G, arrowheads). In reeler embryos (H,
arrowhead), the medial lobe seems reduced when compared with the control.
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