Corneal lens secretion in newly emerged Drosophila melanogaster examined by electron microscope autoradiography.

Drosophila corneal lens secretion was studied by electron microscope autoradiography of [3H]amino acids (leucine, lysine, phenylalanine, proline and tyrosine) and [3H]sugars (glucosamine and mannose) in newly emerged flies. Ommatidial lenses were homogeneously labelled with both tracers at low levels, suggesting that lens materials turn over continuously after lens formation is completed. In contrast, ocellar lenses were heavily labelled, indicating that deposition of ocellar lens cuticle is still active at this stage. [3H]amino acids and [3H]sugars were deposited in distinct patterns in ocelli. Although over 90% of [3H] sugars remained, even after 3 h after application, within 1 micron of the apices of corneagenous cells associated with lens bases, [3H]amino acids distributed diffusely. There was an obvious gradient of [3H]sugars from center to periphery of the lens base, suggesting that structure of the corneal lens in dorsal ocelli is determined by spatially regulated secretion of chitin by corneagenous cells.