Receptor tyrosine kinases (RTKs) are a large group of integral membrane signaling molecules. Mutations in the RTK anaplastic lymphoma kinase (Alk) protein have been linked with non-Hodgkin lymphoma, but the normal function of Alk had remained unclear. Two papers in the October 2 Nature describe the use of Drosophila as a model to show that Alk is activated by the secreted protein Jelly belly (Jeb) and that this ligand and the Alk receptor combine to determine visceral muscle development.

Muscle tissue is derived from the embryonic mesoderm, and in fruit flies, the formation of the muscles that move food through the gut—visceral muscles—begins with fusion of two cell types, known as muscle founders and fusion competent cells. Activation of the Alk RTK triggers a signaling cascade that imposes founder cell identity, but the ligand for Alk had not been identified.

In the first paper, Camilla Englund, Christina...

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