Scanning electron microscopical study of the inside of sea urchin embryos ( Pseudocentrotus depressus) : Effects of aryl β-xyloside, Tunicamycin and deprivation of sulfate ions

Abstract

The deprivation of sulfate ions as well as the addition of p-nitrophenyl β- d-xyloside and Tunicamycin gave rise to the arrest of gastrulation and the inhibition of skeletal formation in Pseudocentrotus embryos. Scanning electron microscopical (SEM) observations of the inside of embryos revealed some impairment of the formation of pseudopodia and filamentous structures, especially in the secondary mesenchyme cells and accordingly of the migration of the mesenchyme cells. The intercellular organization or adhesion of mesenchyme cells (primary and secondary) or columnar cells (in the blastular wall) appeared more or less impaired in the absence of sulfate or the presence of aryl xyloside and, moreover, cellular fragmentation was observed in the presence of Tunicamycin. In the normal mid-gastrula the secondary mesenchyme cells were localized between the animal pole and the tip of invaginating archenteron and long, thick pseudopodia protruding from the two ends of each cell in opposite directions were observed, apparently reflecting a role in the invagination of archenteron.