Mesomere-derived glutamate decarboxylase-expressing blastocoelar mesenchyme cells of sea urchin larvae

Author:

Katow Hideki1,Katow Tomoko1,Abe Kouki12,Ooka Shioh13,Kiyomoto Masato4,Hamanaka Gen4

Affiliation:

1. Division of Developmental Biology, Research Center for Marine Biology, Tohoku University, Asamushi, Aomori 039-3501, Japan

2. Present address: Nara Institute of Science and Technology, Laboratory of Neuronal Cell Morphogenesis, Graduate School of Biological Sciences, Ikoma 630-0192, Japan

3. Present address: Tokyo University of Marine Science and Technology, Field Science Center, Tateyama Station (Banda), Chiba 294-0308, Japan

4. Marine and Coastal Research Center, Ochanomizu University, Tateyama, Chiba 294-0301, Japan

Abstract

Summary The ontogenetic origin of blastocoelar glutamate decarboxylase (GAD)-expressing cells (GADCs) in larvae of the sea urchin Hemicentrotus pulcherrimus was elucidated. Whole-mount in situ hybridisation (WISH) detected transcription of the gene that encodes GAD in H. pulcherrimus (Hp-gad) in unfertilised eggs and all blastomeres in morulae. However, at and after the swimming blastula stage, the transcript accumulation was particularly prominent in clumps of ectodermal cells throughout the embryonic surface. During the gastrula stage, the transcripts also accumulated in the endomesoderm and certain blastocoelar cells. Consistent with the increasing number of Hp-gad transcribing cells, immunoblot analysis indicated that the relative abundance of Hp-Gad increased considerably from the early gastrula stage until the prism stage. The expression pattern of GADCs determined by immunohistochemistry was identical to the pattern of Hp-gad transcript accumulation determined using WISH. In early gastrulae, GADCs formed blastocoelar cell aggregates around the blastopore with primary mesenchyme cells. The increase in the number of blastocoelar GADCs was inversely proportional to the number of ectodermal GADCs ranging from a few percent of total GADCs in early gastrulae to 80% in late prism larvae; this depended on ingression of ectodermal GADCs into the blastocoel. Some of the blastocoelar GADCs were fluorescein-positive in the larvae that developed from the 16-cell stage chimeric embryos; these comprised fluorescein-labeled mesomeres and unlabelled macromeres and micromeres. Our finding indicates that some of the blastocoelar GADCs are derived from the mesomeres and thus they are the new group of mesenchyme cells, the tertiary mesenchyme cells.

Publisher

The Company of Biologists

Subject

General Agricultural and Biological Sciences,General Biochemistry, Genetics and Molecular Biology

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