Genome-Wide Screen for New Components of the Drosophila melanogaster Torso Receptor Tyrosine Kinase Pathway

Patterning of the Drosophila embryonic termini by the Torso (Tor) receptor pathway has long served as a valuable paradigm for understanding how Receptor Tyrosine Kinase (RTK) signalling is controlled. However, the mechanisms that underpin the control of Tor signalling remain to be fully understood. In particular, it is unclear how the Perforin-like protein Torso-like (Tsl) localises Tor activity to the embryonic termini. To shed light on this, together with other aspects of Tor pathway function, we conducted a genome-wide screen to identify new pathway components that operate downstream of Tsl. Using a set of molecularly-defined chromosomal deficiencies, we screened for suppressors of ligand-dependent Tor signalling induced by unrestricted Tsl expression. This approach yielded 59 genomic suppressor regions, 11 of which we mapped to the causative gene, and a further 29 that were mapped to less than 15 genes. Of the identified genes, six represent previously unknown regulators of embryonic Tor signalling. These include twins, which encodes an integral subunit of the protein phosphatase 2A complex, and α-tubulin at 84B, a major constituent of the microtubule network, suggesting that these may play an important role in terminal patterning. Together these data comprise a valuable resource for the discovery of new Tor pathway components. Many of these may also be required for other roles of Tor in development, such as in the larval prothoracic gland where Tor signalling controls the initiation of metamorphosis.

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