Yellow-y Functions in Egg Melanization and Chorion Morphology of the Asian Tiger Mosquito, Aedes albopictus

Abstract

The Asian tiger mosquito, Aedes albopictus, is one of the most serious public health pests, which can transmit various vector-borne diseases. Eggs from this mosquito species become dark black shortly after oviposition and exhibit high desiccation resistance. Some of the Yellow proteins that act as dopachrome conversion enzymes (DCEs) are involved in the tyrosine-mediated tanning (pigmentation and sclerotization) metabolic pathway that significantly accelerates melanization reactions in insects. In this research, we analyzed the function of one of the yellow genes, yellow-y (AalY-y), in eggshell/chorion melanization of Ae. albopictus eggs. Developmental and tissue-specific expression measured by real-time PCR showed that AalY-y transcripts were detected at all stages of development analyzed, with significantly higher levels in the ovaries from blood-fed adult females. Injection of double-stranded RNA for AalY-y (dsAalY-y) had no significant effect on fecundity. However, unlike dsEGFP-treated control eggs that become black by 2–3 h after oviposition (HAO), dsAalY-y eggs were yellow-brown at 2 HAO, and reddish-brown even at 48 HAO. dsEGFP eggs exhibited resistance to desiccation at 48 HAO, whereas approximately 50% of the dsAalY-y eggs collapsed when they were moved to a low humidity condition. In addition, TEM analysis revealed an abnormal morphology and ultrastructure of the outer-endochorion in the dsAalY-y eggs. These results support the hypothesis that AalY-y is involved in the tyrosine-induced melanin biosynthetic pathway, plays an important role in black melanization of the chorion and functions in conferring proper morphology of the outer-endochorion, a structure that is presumably required for egg desiccation resistance in Ae. albopictus.

High-efficiency gene editing inAnopheles sinensisusing ReMOT control

“…The hatching and eclosion rates of Asyellow mutants were significantly lower compared with WT mosquitoes (data not shown). Similar results were previously noted in Aedes albopictus and Agrotis ypsilon (Noh et al ., 2020; Noh et al ., 2021; Chen et al ., 2018). In addition, mosaic phenotypes in small sclerotized regions are difficult to observe.…”

Comparative Proteomic Analysis Provides New Insights into the Molecular Basis of Thermal-Induced Parthenogenesis in Silkworm (Bombyx mori)

“…Following thermal induction, 14 chorion proteins were differentially expressed, and 13 were increased in abundance in PL, such as chorion class B protein L12-like, chorion class B protein M2410-like, and chorion class A protein M2774-like, suggesting their role in egg activation. Tyrosine and dopamine are major precursors for synthesis of black melanin and N-acylquinoid-derived pigments [ 84 ]. Dopachrome tautomerase is an enzyme responsible for melanisation in egg chorion tanning [ 85 ].…”

Characterization of Spontaneous Melanization by Fluorescence Spectroscopy: A Basis for Analytical Application to Biological Substrates

“…The above-described fluorescence data from the pure compound preparations, along with the available literature on the presence of melanin in biological samples [ 60 , 70 ], have been used to interpret the spectra from the aqueous extract solutions prepared from mosquito eggs and black cat hairs. The solution obtained from the mosquito eggs excited at wavelengths ranging from 310 to 440 nm showed well-defined emission spectra in the 350–600 nm range, in parallel with excitation bands in the 320–420 nm interval observed at wavelengths varying from 420 nm to 530 nm.…”

“…All these results are in keeping with the presence of melanin compounds in the mosquito eggs, as previously shown in Ae. albopictus [ 70 ]. The preparation from black cat hairs, in turn, shows much lower signals in the spectral region typical of melanin compounds.…”

“…Consistently, some of the commonly indicated yellow proteins have been demonstrated to participate in the enzyme conversion of dopachrome along the tyrosine-dependent pathway of tanning, favoring the rapid pigmentation and sclerotization of the chorion of Ae. albopictus eggs [ 70 , 75 ]. Implications on mosquito reproduction deriving from melanization effects on the cuticle mechanical stiffness may also regard some structures of adult insects.…”