C. Sotgia et al., REGULATION OF ECTODERMAL DIFFERENTIATION IN XENOPUS-LAEVIS ANIMAL CAPS TREATED WITH TPA AND AMMONIUM-CHLORIDE, Development, growth & differentiation, 40(1), 1998, pp. 75-84
Animal caps isolated from Xenopus laevis embryos at the blastuia stage
were treated sequentially with NH4Cl, a known cement gland inducer, a
nd with 12-O-tetradecanoyl phorbol-13-acetate (TPA), a known neural in
ducer. The two artificial inducers were also used in reverse order to
see if they can mimic the natural inducers acting during the progressi
ve determination of the ectodermal organ. Immunofluorescence and whole
-mount in situ hybridization were used to study the expression of tubu
lin, taken to indicate an early step on the pathway of cell elongation
, and neural cell adhesion molecule (N-CAM) taken to indicate an early
step in the determination of the nervous system. The expression of XC
G-1, a marker of early specification of the cement gland, was also stu
died. The results showed that the two artificial inducers can mimic th
e effects of the natural inducers in animal cap explants. The TPA beha
ves like a neural inducer, reducing the number and the extension of th
e cement gland when added to the medium in addition to NH4Cl, before o
r after NH4Cl treatment. In the process of cement gland/neural inducti
on, it is possible to redirect the ectoderm already specified as cemen
t gland to neural tissue, but it does not seem possible to respecify t
he neural tissue as cement gland. Moreover, the animal caps were also
cut into dorsal and ventral parts and the two halves were treated sepa
rately. The results were similar to those obtained with treatment of t
he entire animal cap, suggesting that a dorsal-ventral pattern is not
yet established before the gastrula stage, and that in normal embryos
there are boundaries between the effects of different inducers.