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25
OM&P
Section MOLECULAR NEUROSCIENCE
The cerebral cortex appears in stem amniotes and evolved in divergent manner in the two main amniote branches, namely the synapsids, that include premammals and mammals, and the sauropsids, now represented by reptiles and birds. Progress in our understanding of cortical neurogenesis, neuronal migration and layer formation allow to define common principles that are therefore presumably homologous and inherited from stem amniotes. On the other hand, critical features of mammalian cortex are absent in sauropsids and evolved after divergence of the two main radiations. Chief among those is the multilaminar organization of the mammalian cortex and its propensity to increase its surface by folding. Careful studies of human genetic disorders of cortical development and of animal models allow us to formulate mechanisms that can be tested using modern genetic and cellular technology. An integrated understanding of cortical development and evolution no longer seems an unattainable goal.
Cortical Expansion in the Development of Complex Mammalian Brains
Fumio Matsuzaki*
RIKEN Center for Developmental Biology, Japan. * Presenting e-mail: fumio@cdb.riken.jp
Introduction
Rapid expansion of brain size and complexity is a hallmark of mammalian evolution. The rodent dorsal brain, which is typically lissencephalic, forms a single primary germinal zone, the ventricular zone (VZ), which faces the ventricle on the apical side during development. In the VZ, self-renewing neural progenitors called radial glia undergo interkinetic nuclear movement and divide asymmetrically at the apical surface to give rise to a pair of daughter cells of distinct fates: another radial glial cell and an intermediate progenitor that divides once to generate a few neurons at the adjacent subventricular zone (SVZ). During the development of the complex brain, such as in ferret or primate, however, huge numbers of neurons are generated in the formation of the complex organization of the folded cortical structure. In such gyrencephalic brains, a new germinal zone, the outer SVZ (OSVZ), is formed during neurogenesis, and is thought to play important roles in the expansion of the neuronal population and fortmation of gyrencephaly.
Results and discussion
To gain a better understanding of the processes by which the OSVZ is formed from the VZ, we have used the ferret brain as a model of the complex brain in studies using long-term time-lapse imaging of brain slices, lineage analysis, and genetic perturbations (based on CRISPR/Cas9). We found that the cerebral cortex develops in a similar manner to the ganglionic eminence (the ventral side of the telencephalon) in ferret, unlike in rodent models. We discuss recent results from our group in light of this model of OSVZ formation.
References
1. Matsuzaki F, and Shitamukai A. Cell division modes and cleavage planes of neural progenitors during mammalian cortical development. Cold Spring Harb Perspect Biol. 2015; 7; a015719. doi: 10.1101/cshperspect.a015719 (2015).
2. Pilz GA, Shitamukai A, Reillo I, Pacary E, Schwausch J, Stahl R, Ninkovic J, Snippert HJ, Clevers H, Godinho L, Guillemot F, Borrell V, Matsuzaki F, Gote M. Amplification of progenitors in the mammalian telencephalon includes a new radial glial cell type. Nat Commun. 4:2125. doi: 10.1038/ncomms3125 (2013).
Distinct Epigenetic Functions of SOX2 in Self-Renewal and Differentiation
Flavio Cimadamore1, Alejandro Amador-Arjona1, Chun-Teng Huang1, Rusty Gage2, Alexey Terskikh1 *
1 Sanford Burnham Prebys Medical Discovery Institute, Neuroscience, La Jolla, CA;
2 Salk Institute, Laboratory of Genetics, La Jolla, CA. * Presenting e-mail: Terskikh@sbp.edu
28 Opera Med Physiol 2016 Vol. 2 (S1)
