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Open AccessArticle

Blood Digestion by Trypsin-Like Serine Proteases in the Replete Lyme Disease Vector Tick, Ixodes scapularis

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Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Reno, NV 89557, USA
2
Department of Agriculture, Veterinary and Rangeland Sciences, University of Nevada, Reno, Reno, NV 89557, USA
*
Authors to whom correspondence should be addressed.
Insects 2020, 11(3), 201; https://doi.org/10.3390/insects11030201 (registering DOI)
Received: 20 February 2020 / Revised: 9 March 2020 / Accepted: 20 March 2020 / Published: 23 March 2020
(This article belongs to the Special Issue Vectors and Vector-borne Diseases)
Ixodes scapularis is the major vector of Lyme disease in the Eastern United States. Each active life stage (larva, nymph, and adult) takes a blood meal either for developing and molting to the next stage (larvae and nymphs) or for oviposition (adult females). This protein-rich blood meal is the only food taken by Ixodes ticks and therefore efficient blood digestion is critical for survival. Studies in partially engorged ticks have shown that the initial stages of digestion are carried out by cathepsin proteases within acidic digestive cells. In this study, we investigated the potential role of serine proteases in blood digestion in replete ticks. RNA interference was used for functional analysis and a trypsin-benzoyl-D, L-arginine 4-nitoanilide assay was used to measure active trypsin levels. Hemoglobinolytic activity was determined in vitro, with or without a serine protease inhibitor. Our data suggest that trypsin levels increase significantly after repletion. Knockdown of serine proteases negatively impacted blood feeding, survival, fecundity, levels of active trypsin in the midgut, and resulted in lower hemoglobin degradation. Incubation of midgut extract with a trypsin inhibitor resulted in 65% lower hemoglobin degradation. We provide evidence of the serine proteases as digestive enzymes in fully engorged, replete females. Understanding the digestive profile of trypsin during blood meal digestion in I. scapularis improves our understanding of the basic biology of ticks and may lead to new methods for tick control. View Full-Text
Keywords: ticks; Ixodes scapularis; serine protease; blood digestion; trypsin ticks; Ixodes scapularis; serine protease; blood digestion; trypsin
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MDPI and ACS Style

Reyes, J.; Ayala-Chavez, C.; Sharma, A.; Pham, M.; Nuss, A.B.; Gulia-Nuss, M. Blood Digestion by Trypsin-Like Serine Proteases in the Replete Lyme Disease Vector Tick, Ixodes scapularis. Insects 2020, 11, 201.

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