Drosophila tan Encodes a Novel Hydrolase Required in Pigmentation and Vision

John R True,Tobias Kemme,Jianyong Li,Shian-Ren Liou,Shu-Dan Yeh,Ian A Meinertzhagen,Qian Han,Bernhard T Hovemann,Tara N Edwards,Gregory Barsh

doi:10.1371/journal.pgen.0010063

Abstract

Many proteins are used repeatedly in development, but usually the function of the protein is similar in the different contexts. Here we report that the classical Drosophila melanogaster locus tan encodes a novel enzyme required for two very different cellular functions: hydrolysis of N-β-alanyl dopamine (NBAD) to dopamine during cuticular melanization, and hydrolysis of carcinine to histamine in the metabolism of photoreceptor neurotransmitter. We characterized two tan-like P-element insertions that failed to complement classical tan mutations. Both are inserted in the 5′ untranslated region of the previously uncharacterized gene CG12120, a putative homolog of fungal isopenicillin-N N-acyltransferase (EC 2.3.1.164). Both P insertions showed abnormally low transcription of the CG12120 mRNA. Ectopic CG12120 expression rescued tan mutant pigmentation phenotypes and caused the production of striking black melanin patterns. Electroretinogram and head histamine assays indicated that CG12120 is required for hydrolysis of carcinine to histamine, which is required for histaminergic neurotransmission. Recombinant CG12120 protein efficiently hydrolyzed both NBAD to dopamine and carcinine to histamine. We conclude that D. melanogaster CG12120 corresponds to tan. This is, to our knowledge, the first molecular genetic characterization of NBAD hydrolase and carcinine hydrolase activity in any organism and is central to the understanding of pigmentation and photoreceptor function.

Highlights

One of the most important generalizations to emerge from contemporary developmental genetics is that gene products are typically used more than once during development
The products encoded by the Drosophila melanogaster ebony and tan genes, mutations in which cause reciprocal pigmentation defects but related neurological phenotypes, have been proposed as such a system [1,2,3,4,5,6]. ebony encodes N-balanyl dopamine (NBAD) synthase, which in epidermal cells converts the melanin precursor dopamine to N-b-alanyl dopamine, a precursor to tan-colored pigment, during cuticle development in late pupae [2,6]
The tan gene product has been proposed to catalyze the conversion of NBAD to dopamine via hydrolysis, which is the reverse of the activity catalyzed by the Ebony protein [2]

Summary

Introduction

One of the most important generalizations to emerge from contemporary developmental genetics is that gene products are typically used more than once during development. Multiple functions involve the protein performing the same task, e.g., activating transcription or binding to the cytoskeleton. The products encoded by the Drosophila melanogaster ebony and tan genes, mutations in which cause reciprocal pigmentation defects but related neurological phenotypes, have been proposed as such a system [1,2,3,4,5,6]. Ebony encodes N-balanyl dopamine (NBAD) synthase, which in epidermal cells converts the melanin precursor dopamine to N-b-alanyl dopamine, a precursor to tan-colored pigment, during cuticle development in late pupae [2,6]. The tan gene product has been proposed to catalyze the conversion of NBAD to dopamine via hydrolysis, which is the reverse of the activity catalyzed by the Ebony protein [2]. The reciprocal pigmentation effects of tan and ebony mutants can be explained: excess NBAD and deficient dopamine result in the abnormally light phenotype of tan, whereas excess dopamine and deficient NBAD result in the melanic phenotype of ebony, in which excess dopamine is converted to melanin

Methods

Results

Discussion

Conclusion