Extracellular activity of NBAD-synthase is responsible for colouration of brown spots in Ceratitis capitata wings

Abstract

After the emergence of the Ceratitis capitata imago, the pale and folded wings are expanded and sclerotized to acquire the definitive form and to stabilize the cuticle. The wings of this fly show a specific pattern of brownish and black spots. Black spots are pigmented by melanin, whereas there was scarce information about the development of the brownish spots. N-beta-alanydopamine (NBAD) is the main tanning precursor in C. capitata body cuticle, and we hypothesized that it may be responsible for the colouration of the brownish spots. We determined the topology and timing of NBAD synthesis and deposition to attain the species-specific colouration pattern. We demonstrated that during the first hours the colour of the brownish spots was principally determined by the tanning of the hairs. Haemolymph circulation through the veins is required to tan the wings. We confirmed that soon after wing spreading, most of the wing epidermal cells disappeared. Thus, the tanning of the brown spots was accomplished when the wing lamina was devoid of cells. NBAD synthase (NBAD-S; Ebony protein in D. melanogaster) activity in wings was detected in pharate adults and lasted several days after the emergence, even after the end of the tanning process. This observation is in contrast to epidermal NBAD-S activity in the body, where it was nearly undetectable 48 h post emergence. Our results indicate that NBAD-S was exported and deposited into the extracellular matrix of the brown spot areas before cell death and that tanning occurs through gradual export of NBAD precursors (dopamine and b-alanine) from veins.

Completion of metamorphosis after adult emergence in Ceratitis capitata (Diptera: Tephritidae)

“…Our studies complement previously published studies ( Perez et al., 2018 ) describing the tanning process in the wings of newly emerged adults of C. capitata . First, the increased activity of NBAD synthase in the body temporarily coincided with the definitive tanning of the head, thorax, and abdominal cuticles and coincided with the acquisition of a definitive body shape (2 h after adult emergence).…”

“…One hour after ecdysis in adults, the characteristic brown and black spots of Ceratitis began to be recognized. However, the definitive pattern of colouration is attained 24 h after emergence ( Perez et al., 2018 ). Our results indicate that while the shape of the body and the final position of the wings would be reached within the first two hours after emergence, the final colouration of the wings was completed after 24 hours.…”

“…Studies in several flies have shown that wing expansion requires an increase in haemolymph pressure ( Johnson and Milner, 1987 ; Zdarek and Denlinger, 1992 ). We previously studied Ceratitis capitata wing expansion followed by final steps of cuticle tanning and colouration ( Perez et al., 2018 ). After emergence, the pale and folded wings are expanded and sclerotized to acquire the definitive form and to stabilize the cuticle.…”

The genetic basis of the black pupae phenotype in tephritid fruit flies

“…The role of Ebony in the pigmentation of C . capitata wings was investigated by Pérez et al 49 . Using biochemical assays, the authors showed that Ebony is spatially pre-patterned in the yellowish-brown bands of the medfly wings during early adult development, maintaining an extracellular activity long after epithelial cells disappear from the lamina.…”

“…The mechanism behind this effect is unclear, but it seems to follow a phylogenetic pattern and therefore could be related to a species-specific distribution of pigment precursors through their wing veins. The role of Ebony in the pigmentation of C. capitata wings was investigated by Pérez et al 49 . Using biochemical assays, the authors showed that Ebony is spatially pre-patterned in the yellowish-brown bands of the medfly wings during early adult development, maintaining an extracellular activity long after epithelial cells disappear from the lamina.…”