Organ Regeneration Based on Developmental Biology

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expression of Coup-TF1 and also reverse expression of SP8 as seen in early fetal
cortex (Kadoshima et al. 2013 ) (Fig. 1.4b). Moreover, a higher level of phospho- ERK
signals is observed on the side opposite to Coup-TF1 expression (Fig. 1.4b), sug-
gesting the involvement of upstream signals of ERK activation at the region. Indeed,
treatment with extrinsic FGF8 causes broad expression of Sp8 at the expense of
Coup-TF1 expression (Kadoshima et al. 2013 ) (Fig. 1.4b). These data indicate that
exogenous FGF8 signaling induces rostralization of early cortical tissues in vitro,
mimicking the in vivo situation. Besides arealization along the AP axis, subregion-
alization of the cortical lobe, such as the occipital lobe, frontal lobe, and parietal
lobe, was also observed in cerebral organoids (Lancaster et al. 2013 ). In addition to
FGF signals, artificial manipulation of cortical arealization by exogenous signals in
3D PSC culture will be an interesting topic for future study. These advances move
us closer to being able to efficiently generate an intended cortical area.
Lastly, induction of 3D cortical tissues allows the examination of human oRG-
like cells that requires markers and a morphological character to detect proper dif-
ferentiation. In human ESC-derived cortical tissue in SFEBq culture, a large number
of Pax6+/Sox2+/Tbr2− progenitors appear outside the VZ on day 91, whereas they
are hardly present on day 70 (Fig. 1.3b). Phospho-vimentin (M phase-specific phos-
phorylation) staining reveals that they have a basal process but not an apical process
during mitosis, like in vivo oRG cells. Moreover, the cleavage plane of the human

A B

Sp8

COUP-TF1

RC

M

L

cortex

olfactory

bulb

COUP-TF1

Sp8

in vivo cortical tissue in vitro human ESCs-derived cortical tissue

+FGF8

pErk

FGF8

Fig. 1.4 Cortical arealization in vivo and in vitro. (a) The transcription factors COUP-TF1 and
Sp8 are expressed in gradients along the rostrocaudal axis of the fetal cortex. FGF8 is secreted
from the anterior patterning center, the anterior neural ridge, which later becomes the commissural
plate. (b) Graded expression of COUP-TF1 and Sp8 in human ESC-derived cortical neuroepithe-
lium. Phosphorylated ERK is localized in the cortical neuroepithelium on the side with strong Sp8
expression. Treatment with exogenous FGF8 causes broad expression of Sp8 at the expense of
COUP-TF1 expression

T. Kadoshima et al.