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Bromodeoxyuridine Specifically Labels the Regenerative Stem Cells of Planarians

Summary: Bromodeoxyuridine Specifically Labels the
Regenerative Stem Cells of Planarians
Phillip A. Newmark1
and Alejandro Sa´nchez Alvarado
Department of Embryology, Carnegie Institution of Washington,
115 West University Parkway, Baltimore, Maryland 21210
The singular regenerative abilities of planarians require a population of stem cells known as neoblasts. In response to
wounding, or during the course of cell turnover, neoblasts are signaled to divide and/or differentiate, thereby replacing lost
cell types. The study of these pluripotent stem cells and their role in planarian regeneration has been severely hampered by
the reported inability of planarians to incorporate exogenous DNA precursors; thus, very little is known about the
mechanisms that control proliferation and differentiation of this stem cell population within the planarian. Here we show
that planarians are, in fact, capable of incorporating the thymidine analogue bromodeoxyuridine (BrdU), allowing neoblasts
to be labeled specifically during the S phase of the cell cycle. We have used BrdU labeling to study the distribution of
neoblasts in the intact animal, as well as to directly demonstrate the migration and differentiation of neoblasts. We have
examined the proposal that a subset of neoblasts is arrested in the G2 phase of the cell cycle by double-labeling with BrdU
and a mitosis-specific marker; we find that the median length of G2 ( 6 h) is sufficient to account for the initial mitotic
burst observed after feeding or amputation. Continuous BrdU-labeling experiments also suggest that there is not a large,
slow-cycling population of neoblasts in the intact animal. The ability to label specifically the regenerative stem cells,
combined with the recently described use of double-stranded RNA to inhibit gene expression in the planarian, should serve
to reignite interest in the flatworm as an experimental model for studying the problems of metazoan regeneration and the


Source: Alvarado, Alejandro Sánchez - Department of Neurobiology and Anatomy, University of Utah
Newmark, Phillip A. - Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign


Collections: Biology and Medicine