Universlty of Manitoba, ln Partîal Fulfiìlment - MSpace at the ...

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t971), Gal lus and Xenopus (l'lessier, 1969; Kêrfunkel , 1971). These nicrotubules
are dlsrupted by vînblastine and colchicine (Karfunkel, 1971; 1972) ,
w¡th arrest of neurulation and flattening of neuroepÌthel ial cells. Burnside
(197t) foun¿ that the m¡crotubules were distributed obl iquely, suggesting
that they might produce cell elongatÎon by displacing cytoplasm towards
the expanding cell bases, rêther than by'direét elongation.
A system of contractíle microfilâments has also been described in
the apical cytoplasm of neuroepithel ial cells in Hyla and Xenopus (Baker
and Schroeder, 1967) and in Rana, Ambìystoma, and Gallus (Schroeder, 1969)-'
Neurulatîon is associated with a short períod of contrêction in these microfl
laments. Disruptìon of the microfilaments in neuroepitheliaì¡ cells of
the chick embryo, (by vinblastine or cytochâlasin B), inhibits neurulation,
v,rt th loss of apical wedging but no reduction in columnar heíght of the
neural plate cells (Karfunkel, 1971 ; 1972)'
Ambellan (1955; l95B; 1962) showed that treatment of frog neurulae
with A.T.P., A.D.P., and A.l'1.P. - 3 caused accelerated n"ut.ul"tion, in direct
proportion to the number of phosphate groups in the nucleotides' Microfi
lament contraction may be ca I c i um-dependen t (Gingell , 1970, ì,tessels 1971).
It would be of great înterest to examine the uìtrastructural changes in
the neural tis'sue of chick embryos after windowing.
ln wîndowed embryos with hemimyel ia, the neural plate was absent
caudal ly. As only five embryos were examined histologically ît was not
clear whether this couìd be attributed to a faîlure of neural induction at
the caudal level, or to necrosîs of presumptive neurectodermal cells'
ln amphibîan embryos, differentiation of neural epithel ium resul ts
from the actlon of t¡ssues ín the archenteric roof on overlyÎng ectoderm
(Spemann, 1938). Experîmentally, however, neural ijìduction can be produced
by: larval or adult neural tissue; certain other tissues such as kidney,