Fig. 2. Altered neurogenesis and neuronal differentiation patterns in the Hoxa1, Hoxb1 and Hoxb2 mutant hindbrains. Ventricular views of flat-mounted wild-type (A,E,I,J), Hoxb1 (B,F,J,N), Hoxb2 (C,G,K,O) and Hoxa1 (D,H,L,P) mutant hindbrains labelled with a Math3 (A-H), Phox2b (I-L) or GATA2 (M-P) riboprobes. (A-H) At 10.5 and 11.5 dpc, Math3 expression resolved into longitudinal stripes and was particularly strong in a ventral r4 column (Vc) (black arrowheads, A) and in a medial column (Mc) extending from r4 through to r6 (bar, A). There was also some upregulation at a more dorsal column (Dc). At 11.5 dpc, the ventral r4 column segregates into two adjacent stripes (black arrowheads, E). There is no r4-specific upregulation of the ventral column in either Hoxb1 (white arrowheads, B,F) or Hoxa1 (white arrowheads, D,H) mutants. Some upregulation was evident in Hoxb2 mutants at 10.5 (black arrowheads, C), but not at 11.5 dpc (white arrowheads, G). Expression within the dorsal column extended throughout only two rhombomeres in the Hoxb1 mutants (bar, B,F) and one rhombomere in Hoxa1 mutants (bar, D,H), but appeared normal in the Hoxb2 mutants (bar, C,G). (I-L) Phox2b expression at 10.5 dpc. In the wild-type hindbrain, expression was strongest in a ventral r4 column (black arrowheads), but it was also upregulated in a medial column extending from r2 to r6, and a dorsal column extending from r4 posteriorly (I). The medial and dorsal columns overlap in three rhombomeres: r4, r5 and r6 (black bar, I). In Hoxb1 (J) and Hoxa1 (L) mutants, there was no r4-specific upregulation (white arrowheads). The medial and dorsal columns overlap by only two rhombomeres in Hoxb1 mutants (J, bar) and one rhombomere in Hoxa1 mutants (L, bar). In Hoxb2 mutants (K), expression levels in ventral r4 were lower than in wild type, but remained elevated when compared with neighbouring rhombomeres (black arrowheads). (M-P) Gata2 expression at 10.25 dpc. In wild-type hindbrain, Gata2 expression is strongly upregulated in ventral r4 (M, black arrowheads). Gata2 expression is absent in this domain in Hoxb1 mutants (N, white arrowheads) and slightly reduced in the Hoxb2 mutants (O, black arrowheads). Both the width and the strength of this domain were greatly reduced in the Hoxa1 mutants (P, black arrowheads).

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