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Published March 15, 2004 | Published
Journal Article Open

pyramus and thisbe: FGF genes that pattern the mesoderm of Drosophila embryos

Abstract

The Heartless (Htl) FGF receptor is required for the differentiation of a variety of mesodermal tissues in the Drosophila embryo, yet its ligand is not known. Here we identify two new FGF genes, thisbe (ths) and pyramus (pyr), which probably encode the elusive ligands for this receptor. The two genes exhibit dynamic patterns of expression in epithelial tissues adjacent to Htl-expressing mesoderm derivatives, including the neurogenic ectoderm, stomadeum, and hindgut. Embryos that lack ths+ and pyr+ exhibit defects related to those seen in htl mutants, including delayed mesodermal migration during gastrulation and a loss of cardiac tissues and hindgut musculature. The misexpression of Ths in wild-type and mutant embryos suggests that FGF signaling is required for both cell migration and the transcriptional induction of cardiac gene expression. The characterization of htl and ths regulatory DNAs indicates that high levels of the maternal Dorsal gradient directly activate htl expression, whereas low levels activate ths. It is therefore possible to describe FGF signaling and other aspects of gastrulation as a direct manifestation of discrete threshold readouts of the Dorsal gradient.

Additional Information

© 2004 Cold Spring Harbor Laboratory Press. The Authors acknowledge that six months after the full-issue publication date, the Article will be distributed under a Creative Commons CC-BY-NC License (Attribution-NonCommercial 4.0 International License, http://creativecommons.org/licenses/by-nc/4.0/). Received October 31, 2003; revised version accepted February 13, 2004. We thank S. Roth and H. Nguyen for providing antibodies and A. Michelson and the Bloomington Stock Center for providing fly stocks. We are grateful to Kevin Cook for information regarding the BSC25 deficiency, Yutaka Satou for help with the FGF classification, and Kate Senger for comments on the manuscript. This work was funded from grants from the NIH: GM46638 to M.L., HD30832 to M.F., and GM20352 to A.S. The publication costs of this article were defrayed in part by payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

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August 22, 2023
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