The Drosophila black enigma: The molecular and behavioural characterization of the black1 mutant allele

Abstract

The cuticular melanization phenotype of black flies is rescued by h-alanine, but h-alanine production, by aspartate decarboxylation, was reported to be normal in assays of black mutants, and although black/Dgad2 is expressed in the lamina, the first optic ganglion, no electroretinogram (ERG) or other visual defect has been demonstrated in black flies. The purpose of this study was to investigate the black gene, and protein, in black 1 mutants of Drosophila melanogaster in order to resolve the apparent paradox of the black phenotype. Using black 1 mutant flies we show that (1) aspartate decarboxylase activity is significantly reduced in adults and at puparium formation, consistent with defects in cuticular and non-cuticular processes, (2) that the black 1 mutation is a frameshift, and black 1 flies are nulls for the black/ DGAD2 protein, and (3) that behavioural experiments using Buridan's paradigm, demonstrate that black responds abnormally to visual cues. No ERG, or target recognition defects can be demonstrated suggesting a problem with higher order visual functions in black mutants. D

A Member of the p38 Mitogen-Activated Protein Kinase Family Is Responsible for Transcriptional Induction ofDopa decarboxylasein the Epidermis ofDrosophila melanogasterduring the Innate Immune Response

“…Presumably, DA is metabolized by the enzymes responsible for the production of sclerotin since no melanin deposits are evident within the epidermis. Consistent with this prediction, the gene black, whose protein product is an enzyme involved in NBAD synthesis (30,62,82), is also upregulated in the Drosophila immune response (34). Future research will reveal the extent of the antimicrobial role of quinone production in the innate immune response.…”

The metabolism of histamine in theDrosophilaoptic lobe involves an ommatidial pathway: β-alanine recycles through the retina

“…Indeed the presence of Black in the epithelial glia (Phillips et al, 1993), co-expressed with Ebony (Richardt et al, 2002), provides good evidence for the hypothesis that the aspartate pathway is the major source of -alanine in these cells. The normal ERG in black mutants (Phillips et al, 2005) indicates only that -alanine derived from uracil is sufficient to maintain normal transmission at the first synapse, even though the increase in head histamine we see when black 1 mutants drink 5% uracil only partially rescues the wild-type head histamine phenotype. However, we have previously shown that flies mutant for black show a large increase in head histamine when given -alanine to drink, attaining a value seen in wild-type heads (Borycz et al, 2002).…”

“…This flexibility may explain why Drosophila black mutants, despite the obvious cuticular melanization and significantly reduced aspartate decarboxylase activity, still have an ERG with normal transients and behavioural responses to visual cues (Phillips et al, 2005). However, the normal availability of uracil is apparently not sufficient to maintain head -alanine at control levels as -alanine is significantly reduced in black 1 , but these levels must still be sufficient to supply the carcinine cycle and to support the normal ERG seen in this mutant.…”

“…However, the normal availability of uracil is apparently not sufficient to maintain head -alanine at control levels as -alanine is significantly reduced in black 1 , but these levels must still be sufficient to supply the carcinine cycle and to support the normal ERG seen in this mutant. This sufficiency indicates that the role of black within the lamina's epithelial glia (Phillips et al, 1993) may be dispensable for vision (Phillips et al, 2005). We therefore infer that recycling is efficient and that even greatly diminished -alanine levels are sufficient to maintain this recycling and to support synaptic transmission at photoreceptors, at least as revealed by the transients of the ERG in black 1 (Phillips et al, 2005), as well as in su (r) 1 r C ;b 1 flies, which have defects in one or both -alanine biosynthesis pathways.…”

“…The biosynthesis of -alanine by decarboxylation of L-aspartate is regulated by an aspartate decarboxylase that in Drosophila is encoded by the gene black (Hodgetts, 1972). This is expressed along with ebony in the epithelial glial cells of the first optic neuropile, or lamina, that surround the terminals of photoreceptor neurons R1-R6 (Phillips et al, 2005). The strength and location of its expression have understandably focused attention on Black as the main regulator for the supply of -alanine.…”