Molecular biology and regulation of tick storage proteins

Female specific, multiple yolk proteins (Vg) and multiple non-sex linked hemolymph storage proteins (carrier protein, CP) have been sequenced from the American dog tick, Dermacentor variabilis. The molecular biology and phylogeny of these proteins will be discussed along with their site of tissue origin, importance in heme sequestration and transport, and function in tick female reproduction. In addition, the molecular biology of the ovarian Vg receptor will be discussed. Where possible, considerations will be made of the structure of the storage protein genes, including introns and exons, and their upstream functional elements. Significant advances have recently been made in understanding the hormonal regulation of tick vitellogenesis and egg development. A consensus mode will be presented that summarizes our current understanding of the critical elements of this process. This will include the role of a male pheromone in the initiation of tick female reproduction, possible brain hormones and their regulation of ecdysteroid biosynthesis, and the importance of VgR in egg maturation. This model will be discussed relative to what we currently know about the structure and function of the insect and crustacean neuroendocrine systems and their hormones that regulate reproduction with the goal of better understanding the evolution of arthropod hormones not only relative to reproduction but also their role in metamorphosis.