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First published online 22 August 2007
doi: 10.1242/dev.02873
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1 Departamento de Biología del Desarrollo Cardiovascular, Centro Nacional
de Investigaciones Cardiovasculares, Instituto de Salud Carlos III, E-28029
Madrid, Spain.
2 Center for Genomic Regulation (CRG), Program on Systems Biology, Barcelona,
Spain.
* Author for correspondence (e-mail: mtorres{at}cnic.es)
Accepted 25 May 2007
Regionalization of embryonic fields into independent units of growth and patterning is a widespread strategy during metazoan development. Compartments represent a particular instance of this regionalization, in which unit coherence is maintained by cell lineage restriction between adjacent regions. Lineage compartments have been described during insect and vertebrate development. Two common characteristics of the compartments described so far are their occurrence in epithelial structures and the presence of signaling regions at compartment borders. Whereas Drosophila compartmental organization represents a background subdivision of embryonic fields that is not necessarily related to anatomical structures, vertebrate compartment borders described thus far coincide with, or anticipate, anatomical or cell-type discontinuities. Here, we describe a general method for clonal analysis in the mouse and use it to determine the topology of clone distribution along the three limb axes. We identify a lineage restriction boundary at the limb mesenchyme dorsoventral border that is unrelated to any anatomical discontinuity, and whose lineage restriction border is not obviously associated with any signaling center. This restriction is the first example in vertebrates of a mechanism of primordium subdivision unrelated to anatomical boundaries. Furthermore, this is the first lineage compartment described within a mesenchymal structure in any organism, suggesting that lineage restrictions are fundamental not only for epithelial structures, but also for mesenchymal field patterning. No lineage compartmentalization was found along the proximodistal or anteroposterior axes, indicating that patterning along these axes does not involve restriction of cell dispersion at specific axial positions.
Key words: Clonal analysis, Fate maps, Vertebrate limb, Lineage compartments, Lmx1b
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