Ca²⁺ influx-linked protein kinase C activity regulates the β-catenin localization, micromere induction signalling and the oral-aboral axis formation in early sea urchin embryos.

Sea urchin embryos initiate cell specifications at the 16-cell stage by forming the mesomeres, macromeres and micromeres according to the relative position of the cells in the animal-vegetal axis. The most vegetal cells, micromeres, autonomously differentiate into skeletons and induce the neighbouring macromere cells to become mesoendoderm in the β-catenin-dependent Wnt8 signalling pathway. Although the underlying molecular mechanism for this progression is largely unknown, we have previously reported that the initial events might be triggered by the Ca2+ influxes through the egg-originated L-type Ca2+ channels distributed asymmetrically along the animal-vegetal axis and through the stretch-dependent Ca2+channels expressed specifically in the micromere at the 4th cleavage.

Larval arm resorption proceeds concomitantly with programmed cell death during metamorphosis of the sea urchin Hemicentrotus pulcherrimus.

Sea urchins are excellent models to elucidate metamorphic phenomena of echinoderms. However, little attention has been paid to the way that their organ resorption is accomplished by programmed cell death (PCD) and related cellular processes. We have used cytohistochemistry and transmission electron microscopy to study arm resorption in competent larvae of metamorphosing sea urchins, Hemicentrotus pulcherrimus, induced to metamorphose by L-glutamine treatment.

Larval and juvenile development of the Echinometrid sea urchin Colobocentrotus mertensii: emergence of the peculiar form of spines.

The development of Colobocentrotus mertensii from embryos to larvae and early juveniles was observed to give the first detailed description of larval and juvenile formation and skeletal structures in echinometrid sea urchins. The first larval spicules appeared at the mesenchyme blastula stage, whereas, in many echinoids, spicules were formed after gastrulation. From late eight-armed larva to juvenile, body color of C.

Mechanisms of calcium elevation in the micromeres of sea urchin embryos.

The micromeres, the first cells to be specified in sea urchin embryos, are generated by unequal cleavage at the fourth cell division. The micromeres differentiate autonomously to form spicules and dispatch signals to induce endomesoderm in the neighbouring macromeres cells in the embryo. Using a calcium indicator Fura-2/AM and a mixture of dextran conjugated Oregon green-BAPTA 488 and Rhodamine red, the intracellular calcium ion concentration ([Ca2+]i) was studied in embryos at the 16-cell stage.