Progenitor Outgrowth from the Niche in Drosophila Trachea Is Guided by FGF from Decaying Branches

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Science  10 Jan 2014:
Vol. 343, Issue 6167, pp. 186-189
DOI: 10.1126/science.1241442

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Out with the Old, In with the New

In adult animals, resident stem or progenitor cells residing in niches replenish old tissues with new cells, but how they form new tissue is not well understood. Chen and Krasnow (p. 186) examined how progenitor cells in the fruit fly form new tracheae as the old tracheae are destroyed during metamorphosis. Proliferating progenitors move out of their niche by crawling along the surface of decaying tracheal branches. The decaying branches express the chemoattractant FGF (fibroblast growth factor) and create a track that directs progenitors.


Although there has been progress identifying adult stem and progenitor cells and the signals that control their proliferation and differentiation, little is known about the substrates and signals that guide them out of their niche. By examining Drosophila tracheal outgrowth during metamorphosis, we show that progenitors follow a stereotyped path out of the niche, tracking along a subset of tracheal branches destined for destruction. The embryonic tracheal inducer branchless FGF (fibroblast growth factor) is expressed dynamically just ahead of progenitor outgrowth in decaying branches. Knockdown of branchless abrogates progenitor outgrowth, whereas misexpression redirects it. Thus, reactivation of an embryonic tracheal inducer in decaying branches directs outgrowth of progenitors that replace them. This explains how the structure of a newly generated tissue is coordinated with that of the old.

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