Laboratory of Genetics and Functional Genomics, Regional Center for Genomic Studies, Faculty of Exact Sciences, National University of La Plata, Bvd 120, 1459, La Plata, 1900, Argentina.
Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas Filho, 373, bloco D. Prédio do CCS, Ilha do Fundão, Rio de Janeiro, 21941-902, Brazil; Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular (INCT-EM), Rio de Janeiro, Brazil.
Insect Biochem Mol Biol. 2019 May;108:24-31. doi: 10.1016/j.ibmb.2019.03.006. Epub 2019 Mar 15.
Cuticle tanning occurs in insects immediately after hatching or molting. During this process, the cuticle becomes dark and rigid due to melanin deposition and protein crosslinking. In insects, different from mammals, melanin is synthesized mainly from dopamine, which is produced from DOPA by the enzyme DOPA decarboxylase. In this work, we report that the silencing of the RpAadc-2 gene, which encodes the putative Rhodnius prolixus DOPA decarboxylase enzyme, resulted in a reduction in nymph survival, with a high percentage of treated insects dying during the ecdysis process or in the expected ecdysis period. Those treated insects that could complete ecdysis presented a decrease in cuticle pigmentation and hardness after molting. In adult females, the knockdown of AADC-2 resulted in a reduction in the hatching of eggs; the nymphs that managed to hatch failed to tan the cuticle and were unable to feed. Despite the failure in cuticle tanning, knockdown of the AADC-2 did not increase the susceptibility to topically applied deltamethrin, a pyrethroid insecticide. Additionally, our results showed that the melanin synthesis pathway did not play a major role in the detoxification of the excess (potentially toxic) tyrosine from the diet, an essential trait for hematophagous arthropod survival after a blood meal.
角质层鞣制发生在昆虫孵化或蜕皮后立即。在此过程中，由于黑色素沉积和蛋白质交联，角质层变得黑暗和坚硬。在昆虫中，与哺乳动物不同，黑色素主要由多巴胺合成，多巴胺由多巴胺脱羧酶从 DOPA 产生。在这项工作中，我们报告说，沉默 RpAadc-2 基因，该基因编码假定的 Rhodnius prolixus DOPA 脱羧酶，导致若虫存活率降低，大量处理过的昆虫在蜕皮过程中或预期的蜕皮期死亡。那些能够完成蜕皮的处理过的昆虫在蜕皮后角质层的色素沉着和硬度下降。在成年雌性中，AADC-2 的敲低导致卵孵化减少；设法孵化的若虫无法鞣制角质层，也无法进食。尽管角质层鞣制失败，但 AADC-2 的敲低并没有增加对局部施用拟除虫菊酯类杀虫剂溴氰菊酯的敏感性。此外，我们的结果表明，黑色素合成途径在从饮食中解毒过量（潜在有毒）酪氨酸方面没有发挥主要作用，这是吸血节肢动物在饱餐后生存的一个重要特征。
