Abstract
Developing animal quartets removed surgically from 8-cell stage of Ascidia malaca and Phallusia mamillata have been treated for a short time with a low concentration of trypsin. The result is a differentiation of some neural structures, of pigment spots and of a tissue-specific enzyme, brain pigment cell tyrosinase. Tyrosinase activity, as detected histochemically, appeared in the pigment cells some hours before the normal time independently of any inductive interactions with related embryonic tissues. A study with the electron microscope has given evidence of the presence of presumed nervous cells and melanin granules related to them. An autoradiographic study using [ 3H]uridine has demonstrated presumed RNA synthesis which suggests gene activation. The results are discussed in relation to the possible role of the plasma membrane during embryonic development.
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