A. J. Howells

Developmental patterns of 3-hydroxykynurenine accumulation in white and various other eye color mutants of Drosophila melanogaster.

Several points of biochemical similarity between white and scarlet mutants suggest that both are defective in the transport of xanthommatin precursors. In both, accumulation of 3-hydroxykynurenine is negligible during larval life and occurs at only a slow rate during adult development. Larvae of both mutants also excrete 3H-3-hydroxykynurenine and 3H-kynurenine rapidly, which probably accounts for the normal levels of kynurenine during larval life. 3-Hydroxykynurenine levels are abnormal in all white mutants which were studied, although in two alleles which are strongly pigmented (wsat and wcol) accumulation is enhanced rather than diminished. In wa, larval accumulation is normal but accumulation during adult development is greatly diminished, suggesting that this mutation has a tissue-specific effect. Similar levels were found in zeste females. Of the 11 other eye color mutants tested, abnormal levels of 3-hydroxykynurenine were found in eight. In four of these (claret, light, lightoid, and pink), larval accumulation is negligible, suggesting that these have defects in the kynurenine transport system like scarlet and white. In three others, however (brown, karmoisin, and rosy), accumulation during larval life is enhanced. In cardinal accumulation is normal during larval life but is excessive during adult development. This evidence supports the suggestion that the cd mutation blocks the final step of xanthommatin synthesis.

Control of drosopterin synthesis in Drosophila melanogaster: mutants showing an altered pattern of GTP cyclohydrolase activity during development.

The reaction catalyzed by GTP cyclohydrolase is the first unique step of pteridine biosynthesis in Drosophila melanogaster and is therefore likely to be an important control point. GTP cyclohydrolase activity varies during development, showing two distinct peaks of activity—one at pupariation and a much larger peak at emergence. Most of the early pupal enzyme is located in the body region, whereas in late pupal and early adult life most of the activity is found in the head. Mixing experiments indicate that developmental changes in activity are not due to changes in the level of a direct effector of GTP cyclohydrolase. The mutants raspberry and prune show an increased GTP cyclohydrolase activity at pupariation relative to wild type, but a decreased enzyme activity at emergence. The changes in GTP cyclohydrolase activity are reflected in changes in pteridine levels in these mutants. Several lines of evidence suggest that neither locus is the structural gene for GTP cyclohydrolase. The raspberry and prune gene products may play a specific role in regulating GTP cyclohydrolase activity during development.

Xanthommatin biosynthesis in wild-type and mutant strains of the Australian sheep blowfly Lucilia cuprina.

The synthesis of eye pigments has been studied in the seven eye color mutants of the Australian sheep blowfly, Lucilia cuprina. Six appear to be affected primarily in the synthesis of xanthommatin. In wild type, the onset of xanthommatin biosynthesis occurs midway through metamorphosis. Developmental patterns of accumulation of the xanthommatin precursors tryptophan, kynurenine, and 3-hydroxykynurenine have also been established for wild type. By determining the levels of these precursors in late pupae of the mutants, it has been shown that the mutant yellowish accumulates excess tryptophan and the mutant yellow accumulates excess kynurenine. The implications of these results—that yellowish lacks tryptophan oxygenase, thus failing to convert tryptophan to kynurenine, and that yellow lacks kynurenine hydroxylase (blocked in the conversion of kynurenine to 3-hydroxykynurenine)—have been confirmed. This has involved in vitro assays of tryphophan oxygenase and precursor feeding experiments. The precursor accumulation patterns are less clear for the other mutants.

The ommochrome biosynthetic pathway in Drosophila melanogaster: the head particulate phenoxazinone synthase and the developmental onset of xanthommatin synthesis.

Particulate fractions from the heads of Drosophila melanogaster catalyze the conversion of o-aminophenols to phenoxazinones. This particulate enzyme is stimulated by Mn2+. It has a number of features which distinguish it clearly from the Mn2+-dependent activity found in the soluble fraction. The particulate enzyme has a characteristic developmental pattern, showing a marked increase in activity at about the time of onset of xanthommatin synthesis. In addition, it is much reduced in activity in a number of xanthommatin-deficient mutants (v, cn, st, cd, and w). We believe that the head particulate enzyme is involved in xanthommatin biosynthesis and that the developmental onset of synthesis of this pigment is brought about by the synthesis or activation of this enzyme.

A biochemical study of the scarlet eye-color mutant of Drosophila melanogaster

Abstract3-Hydroxykynurenine is virtually absent from st larvae but accumulates during adult development in the puparium. Over the period of adult emergence, the accumulated 3-hydroxykynurenine is excreted so that st adults contain none. Larvae of st fed on tryptophan-C14 medium produce labeled 3-hydroxykynurenine, at a reduced rate, perhaps, compared to wild type. Xanthurenic acid levels in st pupae are similar to those in wild type. Thus the failure of st larvae to accumulate 3-hydroxykynurenine does not seem to be due either to an inability to synthesize this compound or to an excessive rate of its conversion to xanthurenic acid. Rather, it appears that the mechanism of 3-hydroxykynurenine storage during larval life is defective, so that this compound is excreted at an abnormally high rate. The inability of the pigment cells of the eyes of st to synthesize xanthommatin may result from a similar defect in their ability to take up or store 3-hydroxykynurenine.

The cuticle proteins of Lucilia cuprina: Stage specificity and immunological relatedness

Abstract Proteins extracted from larval, pupal and adult cuticles of the sheep blowfly, Lucilia cuprina , have been compared electrophoretically and immunologically. Larval, pupal and adult cuticles each possess a largely unique set of cuticle proteins. Cuticles from the three larval instars contain some shared proteins; of the nine major 3rd instar larval cuticle proteins, three appear to be present in the 1st instar and four in the 2nd instar. Immunological evidence suggests that these proteins are specific to the integument (i.e. to the epidermis plus cuticle) and are not transported to the cuticle via the haemolymph. Pupariation involves a concerted crosslinking of the major larval cuticle proteins, such that most extractable protein is rendered insoluble within 24 h of white puparium formation. Protein extracted from pupal cuticle resolves into seven major bands and that from adult cuticle into nine major bands on native polyacrylamide gels. The electrophoretic profile of proteins extracted from the pupal cuticle (which remains unsclerotized) is relatively constant throughout pupal life. In contrast, the profiles of proteins extracted from the adult cuticle (which becomes sclerotized) change markedly during development. Regional variation in pupal and adult cuticle protein composition is also found. Immunological cross-reactivity is obtained between an antiserum raised against L. cuprina larval cuticle proteins and proteins from the larval cuticle of Drosophila melanogaster .

Larval cuticle proteins of Lucilia cuprina: electrophoretic separation, quantification and developmental changes

Abstract Proteins from isolated cuticles of third instar larvae of the sheep blowfly, Lucilia cuprina , have been solubilized with water or 7 M urea or 2% SDS. While 7 M urea or 2% SDS extract significantly more protein than water, the same major proteins, in the same relative proportions, are extracted by all three solutions. More than 80% of the cuticular protein is extracted by 7 M urea or 2% SDS. Extracted proteins resolve into nine major bands when analysed by gradient polyacrylamide gel electrophoresis. These proteins are anionic, relatively low in molecular weight (13–28 kd) and are essentially free of carbohydrate. Only minor differences exist between the proteins of two morphologically distinct cuticular regions. Cuticle proteins, extracted from larvae at different developmental stages (first, second and third instars) display quantitatively and qualitatively unique electrophoretic profiles. A number of proteins are common to all stages however. The electrophoretic profiles of proteins extracted from larval cuticles at various times within an instar also differ although the differences are largely quantitative. This is particularly evident during the transition from the feeding to the wandering stages of the third instar; the weight of the cuticle relative to that of the larva increases and this is accompanied by marked changes in the electrophoretic profile of the cuticle proteins.

Levels of RNA and DNA in Drosophila melanogaster at different stages of development: A comparison between one bobbed and two phenotypically non-bobbed stocks

AbstractA bobbed mutant stock of Drosophila melanogaster from which bobbed larvae, pupae, and flies can easily be selected is described in this paper. The RNA levels in these bobbed insects, whether expressed per insect or per milligram of tissue, are lower than in either a wild-type or a non-bobbed

Functions of the white and topaz loci of Lucilia cuprina in the production of the eye pigment xanthommatin

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