Cell lineage analysis of pattern formation in the tubifex embryo. II. Segmentation in the ectoderm

A. Nakamoto, A. Arai, T. Shimizu

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23 Citations (Scopus)


Ectodermal segmentation in the oligochaete annelid Tubifexis a process of separation of 50-μm-wide blocks of cells from the initially continuous ectodermal germ band (GB), a cell sheet consisting of four bandlets of blast cells derived from ectoteloblasts (N, O, P and Q). In this study, using intracellular lineage tracers, we characterized the morphogenetic processes that give rise to formation of these ectodermal segments. The formation of ectodermal segments began with formation of fissures, first on the ventral side and then on the dorsal side of the GB; the unification of these fissures gave rise to separation of a 50-μm-wide block of-30 cells from the ectodermal GB. A set of experiments in which individual ectoteloblasts were labeled allowed that as development proceeded, an initially linear array of blast cells in each ectodermal bandlet gradually changed its shape and that its contour became indented in a lineage-specific manner. These morphogenetic changes resulted in the formation of distinct cell clumps, which were separated from the handler to serve as segmental elements (SEs). SEs in the N and Q lineages were each comprised of clones of two consecutive primary blast cells. In contrast, in the O and P lineages, individual blast cell clones were distributed across SE boundaries; each SE was a mixture of a part of a more anterior clone and a part of the next more posterior clone. Morphogenetic events, including segmentation, in an ectodermal handler proceeded normally in the absence of neighboring ectodermal bandlets. Without the underlying mesoderm, separated SEa failed to space themselves at regular intervals along the anteroposterior axis. We suggest that ectodermal segmentation in Tubifex consists of two stages, autonomous morphogenesis of each bandlet leading to generation of SEs and the ensuing mesoderm-dependent alignment of separated SEs.

Original languageEnglish
Pages (from-to)797-805
Number of pages9
JournalInternational Journal of Developmental Biology
Issue number7
Publication statusPublished - 2000 Dec 27
Externally publishedYes


  • Cell lineage
  • Ectodermal segmentation
  • Germ band
  • Mesodermal control
  • Tubifex

ASJC Scopus subject areas

  • Embryology
  • Developmental Biology


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