| Popis: |
N - β -Alanyldopamine (NBAD) metabolism was investigated in wild-type and melanic mutant niger strains of the Mediterranean fruit fly, Ceratitis capitata , during the process of pupariation. When radioactive β-alanine (BALA) was injected at the onset of pupariation, the wild-type puparium incorporated 70% of the label, whereas less than 5% was detected in the niger puparium. BALA was catabolized and eliminated as carbon dioxide substantially more in the mutant than the wild-type strain. Significant differences between the two strains were found in the composition of catecholamines extracted from fully sclerotized puparial cuticle. NBAD levels in niger were five times lower than those in the wild type, whereas dopamine (DA) levels were 20 times higher. The concentration of NBAD in hemolymph also was greatly reduced in niger , whereas DA and N-acetyldopamine levels remained high during pupariation. The synthesis of NBAD was assayed both in vivo and in vitro , revealing that the conversion of BALA into NBAD was several fold higher in the wild-type than in the niger strain. Because NBAD hydrolase activity was found to be similar in both strains, an impairment in NBAD synthesis appears to be responsible for the melanic phenotype. We also found that NBAD synthesis in the wild type was restricted to a narrow developmental window, which overlaps the time period in which puparial tanning occurs. Because we were able to induce niger -wild-type cuticle mosaics in heterozygous embryos, NBAD synthetase appears to be expressed by the epidermis. We conclude that the niger mutant is defective in NBAD synthesis and that this defect prevents normal pigmentation. |
Full Text from ScienceDirect