DNA (cytosine-5) methyltransferase turnover and cellular localization in developing Paracentrotus lividus sea urchin embryo

The turnover and localization of the enzyme DNA (cytosine-5) methyltransfer ase (Dnmt 1) were studied during Paracentrotus lividus sea urchin embryo de velopment using antibody preparations against the NH2 and COOH-terminal reg ions of the molecule. The antibodies reveal, by Western blots and whole-mou nt analyses, that the enzyme is differently required during embryonic devel opment. The changeover point is at blastula stage, where a proteolytic mech anism hydrolyses the enzyme present in all embryonic cells by removing a pe ptide of about 45 kDa from the amino terminal region of the 190 kDa enzyme initially synthesized on maternal transcripts. The resulting 145 kDa enzyme shows modified catalytic properties, different antibody reactivity and is rapidly destroyed in the few hours before gastrulation. At more advanced st ages of development the enzyme is newly synthesized but only in particular cell types. among which neurons. The data show that Dnmt I is removed from embryonic cells before gastrulation to be synthesized again at different le vels in different cell types, indicating that the concentration of Dnmt I i s critical for the various differentiated cells of the developing sea urchi n embryo. (C) 2001 Elsevier Science B.V. All rights reserved.