Document Detail

Cell lineage analysis of pattern formation in the Tubifex embryo. II. Segmentation in the ectoderm.
MedLine Citation:
PMID:  11128574     Owner:  NLM     Status:  MEDLINE    
Ectodermal segmentation in the oligochaete annelid Tubifex is a process of separation of 50-microm-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-microm-wide block of approximately 30 cells from the ectodermal GB. A set of experiments in which individual ectoteloblasts were labeled showed 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 bandlet 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 bandlet proceeded normally in the absence of neighboring ectodermal bandlets. Without the underlying mesoderm, separated SEs 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.
A Nakamoto; A Arai; T Shimizu
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Publication Detail:
Type:  Comparative Study; Journal Article    
Journal Detail:
Title:  The International journal of developmental biology     Volume:  44     ISSN:  0214-6282     ISO Abbreviation:  Int. J. Dev. Biol.     Publication Date:  2000 Oct 
Date Detail:
Created Date:  2000-12-20     Completed Date:  2001-03-01     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8917470     Medline TA:  Int J Dev Biol     Country:  Spain    
Other Details:
Languages:  eng     Pagination:  797-805     Citation Subset:  IM    
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
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MeSH Terms
Annelida / cytology,  embryology*
Blastomeres / metabolism
Body Patterning
Cell Division
Cell Lineage*
Ectoderm / cytology*
Mesoderm / cytology
Models, Biological
Oligochaeta / cytology,  embryology*
Organ Culture Techniques
Species Specificity
Stem Cells / cytology
Time Factors

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