The use of gene silencing to study the role of dopa decarboxylase in mosquito melanization reactions.

Mosquito melanization involves hydroxylation of tyrosine to dopa, which then is oxidized to dopaquinone by phenoloxidase, or decarboxylated to dopamine by dopa decarboxlase (DDC). An Armigeres subalbatus cDNA encoding DDC was cloned and real-time PCR analysis revealed increased transcripts in blood-fed and microfilariae (mf)-inoculated mosquitoes. A double subgenomic Sindbis virus was used to silence DDC and assess its role in melanization of mf. DDC transcription and activity were significantly decreased in silenced mosquitoes, as was the degree of mf melanization 48 h postinoculation; however, melanization increased after 72 and 96 h, demonstrating that DDC influences the rate of melanization. DDC-silenced mosquitoes also exhibit high mortality, over-feeding and abnormal movement, consistent with an involvement of DDC in neurotransmission.