Organ Regeneration Based on Developmental Biology

162

Thus, similar to the process of somitogenesis, the IM develops in an anterior- to-
posterior direction alongside caudal trunk elongation. Notably, the position of the
anteriorly located IM is not at the most rostral part of the embryo, but is located in
between the caudal forelimb edge and the rostral hind limb border level. Therefore,
this region could be more appropriately referred to as a middle IM (Figs. 9.4, 9.5,
and 9.6).

Posterior Intermediate Mesoderm

a

b

(= future metanephric mesenchyme)

Osr 1 +/Wt 1 +/Pax 2 -/Six 2 -/Gdnf-Hox 11 +

Osr 1 +/Wt 1 +/Pax 2 +/Six 2 +/Gdnf+/Hox 11 -

Middle Intermediate Mesoderm

(= future mesonephros)

Forelimb

E9.5 (side view)

Somite

Wolffian duct

Nephrogenic cord

Neural tube

E9.5 (sectioned image)

D

V

Fig. 9.4 Schematic of an E9.5 embryo. (a) Side view of an E9.5 embryo. Green indicates the
intermediate mesoderm. The middle intermediate mesoderm is located in the anterior region of the
body trunk and contributes to the mesonephros. The posterior intermediate mesoderm is located in
the caudal region of the embryo and gives rise to the metanephric mesenchyme. The dashed line
indicates the sectioned level of panel B. (b) Sectioned image of the E9.5 embryo at the middle
intermediate mesoderm level. The middle intermediate mesoderm forms a condensate called the
nephrogenic cord. Arrow indicates the direction of dorsal (D)-to-ventral (V) axis

A. Taguchi and R. Nishinakamura