100
Brain Development
Anterior
Posterior
Forebrain
(Prosencephalon)
Midbrain
(Mesencephalon)
Hindbrain
(Rhombencephalon)
Spinal column
Telencephalon
Diencephalon
Neural Retina
Mesencepahlon
Metencephalon
(Pons and cerebellum)
Myelencepahlon
(Medulla)
Spinal cord
E10.5
5-somite
A/B
A/B?
MHB
Mouse
Midline
FMB
p4/5?
p2/3?
p4/5
FMB
MHB?
POS
p2/3 (ZLI)
POS(=r2/3)
Nkx2.2
Nkx2.1
Pax6/Cad6
Emx2
Otx1
p1
r1
r2
r3
r4
r5
r6
r7
p2
p3
p4
p5
p6
me
(a)
Anterior
Chick
HH6
HH20
ZLI
Six3
Pax6
Otx2
Pax2
En1
Irx3
Gbx2
te
di
me
mt
my
MHB
FMB
A/B
(b)
(c)
each segmental unit (Fig. 7a). Interest-
ingly, the homeotic selector genes, con-
taining a unique DNA-binding motif with
60 amino acids called ‘‘
homeodomain
,’’
make a cluster in
Drosophila
chromosome
3su
chth
a
tth
e
i
ra
r
r
an
g
em
en
ti
sc
o
l
in
-
ear to the expression domain along the
A–P axis of the organism (Fig. 7b). Lewis
proposed a model in which the combi-
natorial expression of this class of genes
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