Natural Science Forum / Biology / Biology / February 2008

Development, Growth & Differentiation
Volume 22 Issue 5 Page 805-812, October 1980

AKITO OHARA 1 1 Biological Institute, Faculty of Science, Nagoya
University, Nagoya 464, Japan*
*Department of Biology, Shiga University of Medical Science, Seta,
Otsu 520-21, Japan

Brain formation in variously aged presumptive ectoderms of Cynops
pyrrhogaster under the influence of the head organizer was examined by
the sandwich method. The head organizer was obtained from the middle
portion of the archenteron roof at the slit-blastopore stage. The
presumptive ectoderm was taken from 0- to 36-hr exogastrulae.
Exogastrulae were prepared from the earliest gastrulae just before
invagination (0-hr embryos). The presumptive neural plate overlying
the archenteron roof used as organizer was cultivated in an envelope
of belly ectoderm from an early neurula.

The following results were obtained: 1) Brain induction was almost
entirely restricted to explants covered with 6-hr ectoderm and its
frequency was low. 2) The presumptive neural plate above the head
organizer was almost completely determined as neural tissues. 3) The
head organizer showed a tendency to differentiate into more endodermal
and less mesodermal tissues than those expected from its prospective
fate.

Brain induction in normal development and the relationship between
neural tissue formation in variously aged presumptive ectoderms and
the time necessary for neural induction are discussed.