Abstract
Neuropeptides are small signaling molecules expressed in the tick central nervous system, i.e., the synganglion. The neuronal-like Ixodes scapularis embryonic cell line, ISE6, is an effective tool frequently used for examining tick–pathogen interactions. We detected 37 neuropeptide transcripts in the I. scapularis ISE6 cell line using in silico methods, and six of these neuropeptide genes were used for experimental validation. Among these six neuropeptide genes, the tachykinin-related peptide (TRP) of ISE6 cells varied in transcript expression depending on the infection strain of the tick-borne pathogen, Anaplasma phagocytophilum. The immunocytochemistry of TRP revealed cytoplasmic expression in a prominent ISE6 cell subpopulation. The presence of TRP was also confirmed in A. phagocytophilum-infected ISE6 cells. The in situ hybridization and immunohistochemistry of TRP of I. scapularis synganglion revealed expression in distinct neuronal cells. In addition, TRP immunoreaction was detected in axons exiting the synganglion via peripheral nerves as well as in hemal nerve-associated lateral segmental organs. The characterization of a complete Ixodes neuropeptidome in ISE6 cells may serve as an effective in vitro tool to study how tick-borne pathogens interact with synganglion components that are vital to tick physiology. Therefore, our current study is a potential stepping stone for in vivo experiments to further examine the neuronal basis of tick–pathogen interactions.
Highlights
The North American black-legged deer tick Ixodes scapularis and the European castor-bean tick Ixodes ricinus are both medically important arthropod vectors
The presence of 37 neuropeptide transcripts was confirmed in the ISE6 Sequence Read Archive (SRA)
We introduce the existence of neuropeptide transcripts in ISE6 cells and present their neuropeptidergic features
Summary
The North American black-legged deer tick Ixodes scapularis and the European castor-bean tick Ixodes ricinus are both medically important arthropod vectors These two allopatric tick species are well recognized for transmitting a wide spectra of bacterial, viral, and protozoan pathogens [1,2]. Developing effective tick control strategies to prevent A. phagocytophilum transmission requires a better understanding of specific interactions between this pathogen and the tick [5] To address this limitation, researchers may utilize the I. scapularis embryo-derived cell line, ISE6, as an in vitro analytical tool, since ISE6 cells are commonly used in propagating various TBPs [6,7,8,9,10]. The ISE6 cell line is successful in isolating and analyzing tick-borne bacteria (i.e., Rickettsia, Ehrlichia, Borrelia, and Anaplasma) [8,10,11,12,13,14], as well as propagating arboviruses and vector-borne flaviviruses (i.e., Semiliki Forest, Hazara, or the Langat viruses) [15,16]
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