pyramus and thisbe: FGF genes that pattern the mesoderm of Drosophila embryos.
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.
Stathopoulos
Angelike
A
Department of Molecular and Cell Biology, Division of Genetics & Development, University of California, Berkeley 94720-3204, USA.
Tam
Bergin
B
Ronshaugen
Matthew
M
Frasch
Manfred
M
Levine
Michael
M
D000818:Animals; D019521:Body Patterning; D004330:Drosophila / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D005775:Gastrula / Q000502:physiology; D008648:Mesoderm / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D029721:Drosophila Proteins; D017468:Receptors, Fibroblast Growth Factor; D005346:Fibroblast Growth Factors; D011505:Protein-Tyrosine Kinases; C102667:htl protein, Drosophila