Calcium-containing, smooth-surfaced endoplasmic reticulum and vacuoles in cells of the blastopore-forming region during gastrulation of the newt, Cynops pyrrhogaster

Abstract

Ultrastructural changes in cells of the blastopore-forming region (BFR) were examined during gastrulation of the newt, Cynops pyrrhogaster. Smooth-surfaced endoplasmic reticulum (sER), tubular in shape and with two types of vacuole, empty vacuoles and multilamellar vacuoles, appeared in cells of the BFR at the beginning of formation of the blastopore. The extent of the tubular sER increased during formation of the blastopore. With the deepening of the blastoporal groove, the tubular sER and multilamellar vacuoles disappeared in cells of the BFR. The empty vacuoles increased in number and appeared throughout the cytoplasm of the cells in the BFR and the marginal zone as formation of the archenteron progressed. Many large empty vacuoles were closely associated with deformed lipid droplets. Cytochemistry and X-ray microanalysis revealed the accumulation of calcium in the tubular sER and in some of the empty vacuoles. These results suggest important roles for the calcium-containing tubular sER in the regulation of the intracellular concentration of calcium during formation of the blastopore, as well as a role for empty vacuoles in the dissolution and consumption of lipid droplets during early gastrulation.