Tick proteins functioning in vital physiological processes such as blood meal uptake,
digestion and reproduction are potential targets for anti-tick vaccines, since vaccination
could inhibit these essential functions and ultimately affect tick survival. In this study we
identified metzincin metalloproteases from Rhipicephalus microplus as potential vaccine
candidates since they are implicated as essential to blood-cavity formation, bloodmeal
digestion and reproduction in ixodid ticks. Eight transcripts encoding proteins that contain
the characteristic metzincin zinc-binding motif HEXXHXXG/NXXH/D and a unique
methionine containing “methionine-turn” were identified from native and in-house
assembled R. microplus expressed eequence tag (EST) databases. These were
representative of five reprolysin-like and three astacin-like metzincin metalloproteases.
Reverse transcription-PCR analysis indicated that the reprolysins were most abundantly
expressed in the salivary glands, whereas the astacins were most abundant in the midgut
and ovaries. In vivo gene silencing was performed to assess a possible phenotype of
these metalloproteases during adult female R. microplus blood feeding and reproduction.
RNA interference (RNAi) against two of the reprolysins and one of the astacins
significantly affected the average egg weight and oviposition rate. Evidently, this reverse
genetic approach enabled the evaluation of the overall vital impact of tick proteins. Finally,
integrated real time-PCR studies also revealed an extensive cross organ network between
the R. microplus metzincin transcripts, supporting the use of a combinatorial metzincinbased
anti- R. microplus vaccine.