Sequence and the developmental and tissue-specific regulation of the first complete vitellogenin messenger RNA from ticks responsible for heme sequestration

Neuropeptide signaling sequences identified by pyrosequencing of the American dog tick synganglion transcriptome during blood feeding and reproduction

“…In insects, the female gonadotropic hormone that initiates vitellogenesis is JH (Gilbert et al, 2000), with the exception of mosquitoes where this role is filled by ecdysteroids (Shapiro et al, 1986). In ticks, ecdysone is clearly the initiator of the vitellogenin message and its synthesis (vitellogenesis) and not JH (Neese et al, 2000;Thompson et al, 2005Thompson et al, , 2007Roe et al, 2008), although these studies are based on only one tick species in the former and one hard tick and one soft tick species in the latter. The function of ASTs in ticks may or may not be related to the JH synthesis pathway.…”

Molecular characterization of two vitellogenin genes from the tick, Amblyomma hebraeum (Acari: Ixodidae)

“…These repeats do not appear to be present in other Vgs, though a number of the proline, histidine and tyrosine sites appear to be conserved in one of the putative IsVgs (XP 002415224). As noted by Thompson et al (2007), although these repeats are found only in haem-binding Vgs, they are not present in all haem-binding Vgs, nor are they associated with the closely related haem-binding CPs. The mechanism by which haem binds to Vg in ticks is unknown, as is the function of the above repeats.…”

“…In insects, the recognition site is generally [R/K]-X-[R/K]-R, although RXXR is also used (Sappington and Raikhel, 1998). This site has also been found in tick Vg sequences, but there is currently no conclusive evidence confirming that tick Vgs described are actually cleaved at these sites (Thompson et al, 2007;Horigane et al, 2010;Boldbaatar et al, 2010;Khalil et al, 2011). Generally, in order for cleavage to occur, the recognition site alone is not sufficient; rather, PC mediated processing occurs only if the recognition site is directly adjacent to a predicted ␤-turn, or is part of an -loop and, as such, is more readily accessible to the PC (Brakch et al, 2000;Rholam and Fahy, 2009).…”

“…However, Vg is produced in both the fat body and midgut in a number of tick species (Coons et al, 1989;Rosell and Coons, 1992;Thompson et al, 2007;Boldbaatar et al, 2010;Horigane et al, 2010;Khalil et al, 2011). Following synthesis, Vg is released into the haemolymph and taken up into the developing oocyte by receptormediated endocytosis, where the Vg may be further processed and stored Sappington and Raikhel, 1998;Tufail and Takeda, 2008;Ogihara and Taylor, 2013).…”

“…Although there is a wealth of knowledge regarding vitellogenesis and its regulation in insects, our knowledge of this process is much more limited in ticks. The first complete tick Vg cDNA sequence was reported in 2007 from the American dog tick Dermacentor variabilis (Thompson et al, 2007). Since then, complete Vg sequences have been described from two additional tick species: Ornithodoros moubata (Horigane et al, 2010) and Haemaphysalis longicornis (Boldbaatar et al, 2010), with multiple Vg genes described from both D. variabilis (Khalil et al, 2011) and H. longicornis (Boldbaatar et al, 2010).…”