Cleavages

From cleavage and until the blastula stage, AChE activity, which had disappeared during fertilisation, starts to be present and active once more (Fig. 8A), starting from the perinuclear envelope; this, at least in vertebrate muscle cells (Miki and Mizoguti 1981), is the first site of synthesis. Also, at these stages, the final destination of the molecules is at the blastomere surface where presumably they play a role in cell-to-cell interaction (Fig. 8B). Extensive studies conducted by Buznikov and coworkers demonstrated that, during these events, the typical neurotransmitters mainly involved in regulating cell-to-cell interaction are represented by biogenic amines (Buznikov et al. 2001); these are responsible for inducing messages among blastomeres (Shmukler and Buznikov 1998).

Fig. 8A, B. AChE histochemical reaction in Paracentrotus lividus. A Zygote, showing dark labelling around the nucleus, in the cytoplasm and in the sperm pathway from the fertilisation cone (arrow) to the point of contact with the female pronucleus. B Two-blastomere stage, showing the enzyme activity product around the nuclei and in the furrow between the blastomeres. In toto mount, bar 80 |m

Fig. 8A, B. AChE histochemical reaction in Paracentrotus lividus. A Zygote, showing dark labelling around the nucleus, in the cytoplasm and in the sperm pathway from the fertilisation cone (arrow) to the point of contact with the female pronucleus. B Two-blastomere stage, showing the enzyme activity product around the nuclei and in the furrow between the blastomeres. In toto mount, bar 80 |m

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