Ticks are obligate blood-sucking ectoparasites of vertebrates throughout the world. They can transmit a wide variety of pathogens causing several human and animal diseases. Hard and soft ticks display different feeding strategies: hard ticks feed on blood for a few days to over one week, whereas soft ticks typically feed on blood for minutes to hours. Kunitz/BPTI proteins are abundant in the salivary glands and have different functions and domain architectures in soft and hard ticks. How these differences emerged and whether they are associated with the evolution of long-term blood feeding in hard ticks remain unknown.

Under the supervision of Prof. HUANG Jingfei, Dr. DAI Shaoxing and his colleagues from the group of Bioinformatics and System Biology at Kunming Institute of Zoology, CAS (http://bsb.kiz.ac.cn/), systematically examined the evolution, expansion and expression of Kunitz/BPTI gene family in Ixodes scapularis.

This study reveals the great differences in the Kunitz/BPTI family between soft and hard ticks. Multi-domain Kunitz/BPTI proteins were created in hard ticks after the split between hard and soft ticks. Groups II and III, which exhibit significantly higher expression during long-term blood feeding, are only present and expanded in the genus Ixodes. Positive selection drove the expansion of the Kunitz/BPTI family and the evolution of new functions in group II such as ion channel-modulating ability, which can enhance blood-feeding efficiency. Results suggest that the differences in the Kunitz/BPTI family between soft and hard ticks may be linked to the evolution of long-term blood feeding in hard ticks and the six genes identified in this study may be candidate target genes for tick control.

The result has been published on BMC Evolutionary Biology 2012, 12:4( http://www.biomedcentral.com/1471-2148/12/4) .This work was supported by the National Basic Research Program of China and the National Natural Science Foundation of China for JFH.