Microtubule-organizing centers in the mitotic melanophores of Xenopus laevis larvae in vivo: ultrastructural study.

Mitotic melanophores of Xenopus laevis larvae at 51-53 stages of development were morphologically studied using light and electron microscopy, with special reference to their microtubule-organizing centers. These melanophores represented a highly branched cell shape in mitosis, each cell process is distributed with melanosomes without exhibiting any responsiveness to hormonal (melatonin) stimulation, and upon completion of mitosis, recovered the ability to translocate these granules in response to such a stimulus. At the metaphase, these cells contained bipolar or multipolar spindles, whose poles were composed of three zones: the centrosome with centrioles; the centrosphere; and an outlying radial arrangement of microtubules and their associated inclusions.