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Shinichi AIZAWA, Ph. D. 
All
vertebrate species share certain features in the development of the brain,
in that all vertebrate brains comprise four regions – telencephalon,
diencephalon, mesencephalon and metencephalon (or cerebellum) – an organizational
trait that is thought to have appeared with the advent of the vertebrate
lineage. However, dramatic changes in this organization took place during
the divergence of jawed (gnathostome) fishes from their jawless (agnathan)
ancestors. Evolutionary modifications of the telencephalon first manifested
in the reptiles, becoming even more pronounced with the development of
a neocortex stratified into six layers regionalized by distinct physiological
functions. However, the mechanisms that instruct the brain's laminar
regions to conform to anterior-posterior and dorsal-ventral axis patterning
programs, and the means by which each individual region is formed, remain
unknown.
The
head is the most highly layered of the body's structures and its
development begins with anterior-posterior axis formation. This A-P axis
patterning is one of the most primary phenomena in animal development,
and the emergence of the vertebrate lineage has been accompanied by widespread
adaptations to this fundamental rule, as evidenced by the diversity of
mechanisms by which vertebrate taxa achieve the common ends of axis formation
and jaw induction.
A
long road lies ahead in the search for the origins of the Bauplan of the
vertebrate head, but application of powerful new molecular biological
techniques to the study of multiple vertebrate model species has now made
it possible to study the question more comprehensively and in greater
detail than ever before. Our laboratory is focusing on the ontogenetic
and phylogenetic roles played by the Otx/Emx family of head gap
genes as a route toward a better understanding of brain development. The
question of what molecular mechanisms underlie the development of neocortical
regions is central to that pursuit.
