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Fig. 5. Her3 and Her9 repress the expression of proneural genes. (A-H) Expression
of neurod4 in the wild-type control embryos (A,E), embryos that
received an injection of 2 ng her9ATG-MO (H9MO; B,F), mib
mutant embryos (C,G) and mib mutant embryos that received an
injection of her9ATG-MO (D,H) at the one-somite stage. Dorsal views
(A-D) and dorsolateral views (E-H). neurod4 was expressed in the
inter-proneuronal domain between the RB neurons and primary interneurons in
the her9ATG-MO-injected wild-type and mib mutant embryos,
where neurod4 was not expressed in the control embryos. (I-L) The
her9-MO-injected embryos had a reduced and narrow fourth ventricle at
30 hours post fertilization (hpf) (J,L), compared with the control embryos
(I,K). atoh1 marks neuronal precursor cells located in the
subventricular zone of the fourth ventricle. Lateral views (I,J) and dorsal
views of the hindbrain region (K,L). (M-N) Expression of neurog1 in 1
ng of control MO (M) and her3-MO1-injected embryos (H3MO; N) at the
one-somite stage. Dorsal views for the anterior hindbrain. Ectopic expression
of neurog1 was detected only in rhombomeres 2 and 4 of the
her3 morphant embryos. (O-R) Her9 functions as a transcriptional
repressor. RNAs for Myc-tagged Her9 (Her9MT, 5 pg; O,P), Her9-VP16 fusion
protein (Her9VP16, 5 pg; Q) or Myc-tagged Her3 (Her3MT, 20 pg; R) together
with 50 pg ß-galactosidase RNA, were injected into one blastomere of two-
to four-cell stage embryos. The embryos were fixed at the one-cell stage, and
stained with X-gal and the neurod4 probe. In the majority of the
her9MT RNA-injected embryos, cells that received her9MT RNA
were distributed to only the inter-proneuronal domains (O). However, when the
cells were located in the proneuronal domains, the neurod4 expression
was reduced or abrogated (P). Expression of Her9VP16 led to an ectopic but
spotty expression of neurod4 in the neural plate (Q). Expression of
Her3MT led reduction of the neurod4 expression in the proneuronal
domains (R). Quantification of the results is shown in
Table 1.
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