Quantitative and ultrastructural analysis of the chondriome in ovogenesis and embriogenesis of the sea urchin Paracentrotus lividus.: 2.: Growth and proliferation of mitochondria in embriogenesis of the sea urchin Paracentrotus lividus

The dynamics of structural changes of the chondriome in the early development of the sea urchin Paracentrotus lividus was studied, Mature eggs and embryos at various stages of cleavage were used for quantitative and ultrastructural analysis based on computerized 3D reconstruction from serial ultrathin sections. The following structural transformations of the chondriome were shown to occur in the course of embryogenesis: 1) 15 min after fertilization the disintegration of mitochondrial clusters takes place, and mitochondrial division is induced. At two-blastomeres stage a population of mitochondria increases twofold; 2) the mitochondria divide by means of the contraction of both outer and inner membranes. The forming furrow divides the "maternal" mitochondrion into two equal "daughter" parts; 3) at the four-cell stage the division is ceased, and a prolonged growth of mitochondria begins, that leads to the increase in the mitochondrial length; 4) cellular differentiation stimulates elongation of rod-shaped mitochondria and brings about changes in the rod/spherical-shaped mitochondria ratio; 5) in unfertilized egg, the mitochondria of condensed form are present: after fertilization all the population of mitochondria is transformed to orthodox form. Modem concepts of chondriome proliferation in eukaryotic cells are discussed.