Developmental regulation of the alpha-methyldopa hypersensitive gene of Drosophila melanogaster.

The insect cuticle is a highly differentiated structure exhibiting considerable variety and specialization. Part of this specialization is achieved by regulating the nature and/or extent of sclerotization. The dopa decarboxylase (Ddc) and alpha-methyldopa hypersensitive (l(2)amd) genes of Drosophila are structurally related and it has been shown that the Ddc gene is required for the proper sclerotization of pigmented cuticle as well as for neurotransmitter production. The physiological role of the amd gene is unknown. Following the pattern of amd expression during development, we find that it is expressed in tissues that secrete clear flexible (arthrodial) cuticle both internally and in specialized external structures. We present electron microscopic evidence that loss of amd function leads to cuticle defects in a region of amd expression. We also find that amd is expressed in the larval CNS and ring gland where it may be involved in neurotransmitter metabolism similar to its paralog, Ddc. Lymph glands also express amd suggesting a possible role in the immune response. The expression of amd in segmentally repeating stripes at the end of dorsal closure suggests that amd may be a terminal target of the segmentation gene hierarchy which specifies segments.