Role of syndecan in the elongation of postoral arms in sea urchin larvae.

Abstract

Ac-SYN is the core protein of a cell surface proteoglycan of the sea urchin Anthocidaris crassispina. To examine the functions of Ac-SYN, embryos were cultured in the presence of affinity-purified antibody against Ac-SYN. At the late pluteus stage, severe inhibition of elongation of the postoral arms was seen in treated embryos compared with control embryos. Blastocoeleic microinjection of the antibody did not affect morphogenesis. The relationship between the number of cells in the postoral arms and the length of the postoral rods was investigated in normal embryos. This showed that postoral arm elongation has two phases: the first phase accompanies the increase in cell numbers while the second does not. The syndecan antibody inhibited the increase in cell numbers in the postoral arms. Furthermore, in the treated embryos, cell numbers continued to increase normally until 31 h post fertilization (hpf), while cell division stopped after 31 hpf. These results suggest that Ac-SYN participates in postoral arm formation via cell division in sea urchin embryos.