Ticks are blood-sucking arthropods that act as vectors for many animal pathogens. As a result, ticks act to transmit diseases such as Lyme borreliosis, tick-borne encephalitis, babesiosis, and tularemia. One way to control the transmission of human, livestock, and wildlife diseases is to interrupt the tick life-cycle. My research is directed at improving our understanding of tick physiology and reproduction with the long-term goal of reducing tick populations and, therefore, transmission of tick-borne diseases.
My research falls into three general areas.
1) Tick embryo development. Very little research has been done to describe the progression of embryonic growth within the tick egg. Using microscopy techniques including SEM and fluorescence staining, I have been working to identify the anatomical milestones that occur during development in two ixodid tick species: Amblyomma hebraeum and Dermacentor andersoni. Likewise, the molecular mechanisms that control tick embryogenesis have not been explored. I am focused on identifying two highly conserved, developmentally important gene families in these ticks: the hox and the wnt families. Hox genes code for transcriptional regulator proteins that initiate many developmental events, including the formation of the general body axis as well as more specific anatomical features (e.g. appendages). The wnt family codes for a group of secreted cell signaling proteins that establish boundaries between neighboring tissues. Like the Hox proteins, the Wnt proteins regulate a wide range of developmental events including establishing segmentation patterns in insects and other arthropods. Members of the hox and wnt families can be found in all other animal groups but have not yet been identified in ticks.
2) Tick egg production. Research done during my doctorate focused on identifying some key endocrine events that lead to egg production in female ticks. Following a blood meal, an engorged female transforms ingested nutrients into energy-rich yolk (vitellin) that is accumulated in eggs and then used as an energy source for developing embryos. My research helped establish the role of the arthropod hormones, the ecdysteroids, in stimulating the synthesis of vitellin.
3) Tick feeding and engorgement. I am currently developing an in vitro tick feeding system based on the previous work of Kröber and Guerin (2007 Trends Parasitol.23:445) from the University of Neuchâtel. In this method, ticks feed through a synthetic ‘skin’ composed of cellulose rayon-reinforced silicone stretched across one end of an acrylic glass tube. This method has been demonstrated to be effective for feeding several species of ticks. The in vitro tick feeding method will allow the successful completion of the tick life cycle without the use of an animal host. This method offers an opportunity to experimentally control the content of the tick blood meal as well as to measure secretions found in tick saliva (i.e. pathogens, anticoagulants, analgesics, etc.).
Friesen KJ, Kaufman WR. 2009. Salivary gland degeneration and vitellogenesis in the ixodid tick Amblyomma hebraeum: Surpassing a critical weight is the prerequisite and detachment from the host is the trigger. Journal of Insect Physiology 55:936-42.
Seixas A, Friesen KJ, Kaufman WR. 2008. Effect of 20-hydroxyecdysone and haemolymph on oogenesis in the ixodid tick Amblyomma hebraeum. Journal of Insect Physiology 54: 1175-8.
Friesen KJ, Kaufman WR. 2004. Effects of 20-hydroxyecdysone and other hormones on egg development, and identification of a vitellin-binding protein in the ovary of the tick, Amblyomma hebraeum. Journal of Insect Physiology 50: 519-529.
Friesen KJ, Kaufman WR. 2002. Quantification of vitellogenesis and its control by 20-hydroxyecdysone in the ixodid tick, Amblyomma hebraeum. Journal of Insect Physiology 48(8): 773-782
Friesen, KJ, Kaufman, WR. 2011. Steps toward characterizing the morphological and molecular aspects of embryo development in the African cattle tick, Ambylomma hebraeum (Koch). 7th International Conference on Ticks and Tick-Borne Pathogens, Zaragoza, Spain.