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Studies on the potential of micromeres to induce archenteron differentiation in embryos of a direct-developing sand dollar, Peronella japonica

Published online by Cambridge University Press:  16 July 2018

Minoru Iijima
Affiliation:
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo, Japan
Yasuhiro Ishizuka
Affiliation:
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo, Japan
Takuya Minokawa
Affiliation:
Department of Life Science, Tokyo Institute of Technology, Kanagawa, Japan
Shonan Amemiya
Affiliation:
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo, Japan Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Tokyo, Japan

Extract

Echinoid embryos of indirect developers comprise three tiers at the 16-cell stage: eight mesomeres, four macromeres and four micromeres. Micromeres differentiate autonomously into skeletogenic mesenchyme cells and induce adjoining macromeres to form a vegetal plate, resulting in archenteron invagination (Ransick & Davidson, 1995). It has been shown that micromeres have the potential to induce archenteron differentiation of presumptive ectoderm (Hörstadius, 1939).

Direct development, in which the larval stages are more or less abbreviated, has evolved in several phylogenetic lineages of echinoids. In most of them, the fourth cleavage of the embryos produces 16 blastomeres of almost the same size (Raff, 1987). Because of their indistinguishability, the inductive potential of vegetal-most blastomeres of direct developers remained to be studied.

The 16-cell stage embryos of the direct-developing sand dollar, Peronella japonica, are an exception and produce three tiers, the same as indirect developers. The embryos develop into two-armed pluteus-like larvae and metamorphose within 3 days after fertilisation without feeding. The micromeres of the species had been shown to differentiate into the skeletogenic mesenchyme cells (Amemiya & Arakawa, 1996). In the present study, we investigated the potential of the micromeres to induce or promote archenteron invagination in Peronella japonica.

Type
Special Lecture for Citizens
Copyright
Copyright © Cambridge University Press 1999

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References

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