Identification of microtubule-organizing centers in interphase melanophores of Xenopus laevis larvae in vivo

The morphological characteristics of microtubule-organizing centers (MTOCs) in dermal interphase melanophores of Xenopus laevis larvae in vivo at 51-5 3 stages of development has been studied using immunostained semi-thick sec tions by fluorescent microscopy combined with computer image analysis. Comp uter image analysis of melanophores with aggregated and dispersed pigment g ranules, stained with the antibodies against the centrosome-specific compon ent (CTR210) and tubulin, has revealed the presence of one main focus of mi crotubule convergence in the cell body, which coincides with the localizati on of the centrosome-specific antigen, An electron microscopy of those mela nophores has shown that aggregation or dispersion of melanosomes is accompa nied by changes in the morphological arrangement of the MTOC/centrosome, Th e centrosome in melanophores with dispersed pigment exhibits a conventional organization, and their melanosomes are situated in an immediate vicinity of the centrioles. In melanophores with aggregated pigment, MTOC is charact erized by a three-zonal organization: the centrosome with centrioles, the c entrosphere, and an outlying radial arrangement of microtubules and their a ssociated inclusions. The centrosome in interphase melanophores is presumed to contain a pair of centrioles or numerous centrioles. Because of an inability of detecting additional MTOCs, it has been consider ed that an active MTOC in interphase melanophores of X, laevis is the centr osome, We assume that remaining intact microtubules in the cytoplasmic proc esses of mitotic melanophores (Rubina et al,, 1999) derive either from the aster or the centrosome active at the interphase.