Organ Regeneration Based on Developmental Biology

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9.5.2 Lateral Patterning of the IM During Post-migration

In addition to the pre-patterning within the PS (before migration), previous studies
proposed a patterning signal in the post-migration phase. Studies utilizing chick
embryos demonstrated the importance of PAM-derived signals and an appropriate

Bmp

Activin/Nodal

Wnt

?

Putative Wnt signal

gradient model

Extra embryonic mesoderm

Lateral plate mesoderm

Intermediate mesoderm

Paraxial mesoderm

Endoderm

Activin/Nodal

Wnt

Wnt

Bmp

A P

Ectoderm

E7.5

Primitive streak

b

a

LPM

IM

PAM

NT

Primitive Streak

E8.5 (upper view)

A

D

V

P P

A

Rostral
(anterior)

Caudal

(posterior)

E8.5 (side view) E8.5 (sectioned image)

Fig. 9.3 Schematic of early lineage specification at E7.5 and E8.5. (a) Signal gradients within the
primitive streak at E7.5. The anterior activin/Nodal signal and posterior Bmp signal together with
Wnt signal patterns in the primitive streak (left). Hypothetical Wnt signal gradient within the prim-
itive streak (right). (b) Schematic images of E8.5 embryo: side view (left), upper view (middle),
and sectioned image (right). Continuous cell differentiation from the caudal immature population
(primitive streak) produces the caudal body trunk. The anteroposterior position within the primi-
tive streak largely determines the future dorsoventral patterning within the mesodermal tissues.
The dashed line in the middle panel indicates the sectioned level of right panel image. Arrows
indicate the direction of anterior (A)-to-posterior (P) axis (middle panel) or dorsal (D)-to-ventral
(V) axis (right panel)

A. Taguchi and R. Nishinakamura