2
1.1 Introduction
The brain is the most complex organ in the human body. It has increased in size and
complexity throughout human evolution, supporting capabilities such as language,
planning, and social behavior. During early neural development, the anlage of the
central nervous system first forms as a neural plate in the dorsal ectoderm. Then the
neural plate folds and rolls up into a neural tube (Rubenstein et al. 1998 ; Lumsden
and Krumlauf 1996 ). Subsequently, the neural tube is regionalized into distinct pro-
genitor domains along the anterior–posterior (AP) and dorsal–ventral (DV) axes by
the effects of secreted factors and their downstream transcription factors (Lee and
Jessell 1999 ). The distinct progenitor domains give rise to a variety of neurons and
glia, which have different morphological and functional properties (Shen et al.
2006 ). The regional pattern along the AP axis is determined at an early embryonic
stage, and subsequently the regional pattern along the DV axis is fixed (Levine and
Brivanlou 2007 ). In vivo, the telencephalon develops from the forebrain, which is
derived from the rostral portion of the neural tube (Wilson and Houart 2004 )
(Fig. 1.1a). The telencephalon further subdivides into dorsal and ventral telencepha-
lon along the DV axis. The dorsal telencephalon consists of the choroid plexus,
cortical hem, medial pallium (giving rise to the hippocampus) and dorsolateral pal-
lium (giving rise to the cerebral cortex), whereas the ventral telencephalon consists
of the lateral, medial, and caudal ganglionic eminence (LGE, MGE, and CGE; giv-
ing rise to the striatum and globus pallidus as well as telencephalic GABAergic
interneurons) (Sousa and Fishell 2010 ; Suzuki and Vanderhaeghen 2015 ) (Fig. 1.1b).
Classical embryological studies in amphibians proposed the “neural default
model” in which ectodermal cells undergo differentiation into neural progenitors in
the absence of exogenous inhibitory factors (Levine and Brivanlou 2007 ; Godsave
and Slack 1989 ; Grunz and Tacke 1989 ; Sasai et al. 1995 ; Piccolo et al. 1996 ; Sasai
and De Robertis 1997 ; Sato and Sargent 1989 ). This model has been thought to be
applicable to in vitro differentiation; neural differentiation spontaneously occurs in
embryonic stem (ES) cells cultured in medium containing minimal extrinsic signals
(Tropepe et al. 2001 ; Ying et al. 2003 ; Watanabe et al. 2005 ; Smukler et al. 2006 ).
Based on this idea, we developed a versatile 3D differentiation system, called SFEB/
SFEBq (serum-free floating culture of embryoid body-like aggregates with quick
reaggregation) (Watanabe et al. 2005 , 2007 ; Wataya et al. 2008 ; Eiraku et al. 2008 ,
Sasai 2013a, b) (Fig. 1.1c). In the SFEBq culture, dissociated mouse and human
ESCs are reaggregated using low-cell-adhesion 96-well culture plate. The floating
aggregates cultured in serum-free medium that contains no or minimal growth fac-
tors can efficiently differentiate into neural progenitors.
The telencephalon is one of the most interesting regions of the brain because its
dysfunction is linked to various neurological and neuropsychiatric diseases such as
dementia, autism, schizophrenia, and mood disorders (depression and bipolar dis-
ease). Using a variety of animal models, we have increased our knowledge about the
development, function, and structures of the telencephalon. However, the human
brain has not been sufficiently examined, partly because of limited access to human
tissues. Recent advances in 3D differentiation technologies of PSCs (ES cells and
T. Kadoshima et al.