A TEST FOR CELL AUTONOMY, BASED ON DI-CISTRONIC MESSENGER TRANSLATION

We have devised a test for cell autonomy of a gene that is switched on ectopically in a clone of cells, allowing us to ask whether the wild- type activity of this gene can influence neighbouring cells, To switch on the test gene, we used the yeast FRT system, and marked the FRT-ge nerated cell clone by co-expressing beta-galactosidase. Go-expression is achieved by a stretch of 5' untranslated mRNA from the homeotic gen e Ultrabithorax (Ubx), which is inserted between the two coding sequen ces, We show that this Ubx sequence mediates efficient and reliable di -cistronic mRNA translation in wing imaginal discs of Drosophila, Appl ying our test to Ubx, we find that ectopic Ubx in wing discs strictly coincides with beta-galactosidase expression, Consequently, wing cells are transformed into cells that appear to be intermediates between wi ng and haltere cells, contesting the view that homeotic genes act as b inary switches.