Developmental profiles of ecdysteroids, ecdysteroid receptor mRNAs and DNA binding properties of ecdysteroid receptors in the Ixodid tick Amblyomma americanum (L.).

Total body ecdysteroid titers were determined at specific stages during the larval and nymphal life of Amblyomma americanum (L.). One ecdysteroid peak was observed following the completion of larval apolysis. However, two distinct ecdysteroid peaks occurred at a comparable stage in the nymphal molting cycle. The first occurred following apolysis and the second peak occurred at about the time of ecdysis. When whole body profiles of EcR and RXR mRNAs were examined during the molting cycle using RT-PCR, the expression of both AamEcR and AamRXR mRNAs was shown to be correlated with the ecdysteroid titer. Using an electrophoretic gel mobility shift assay, it was demonstrated that AamEcR*AamRXR1, but not AamEcR*AamRXR2, exhibits broad DNA binding specificity, forming complexes with a variety of synthetic direct repeat and palindromic nuclear response elements with the half-site consensus AGGTCA. These data suggest that functional differences may exist between the AamRXR1 and AamRXR2 proteins.