Abstract
Tick cell lines are an easy-to-handle system for the study of viral and bacterial infections and other aspects of tick cellular processes. Tick cell cultures are often continuously cultivated, as freezing can affect their viability. However, the long-term cultivation of tick cells can influence their genome stability. In the present study, we investigated karyotype and genome size of tick cell lines. Though 16S rDNA sequencing showed the similarity between Ixodes spp. cell lines at different passages, their karyotypes differed from 2n = 28 chromosomes for parental Ixodes spp. ticks, and both increase and decrease in chromosome numbers were observed. For example, the highly passaged Ixodes scapularis cell line ISE18 and Ixodes ricinus cell lines IRE/CTVM19 and IRE/CTVM20 had modal chromosome numbers 48, 23 and 48, respectively. Also, the Ornithodoros moubata cell line OME/CTVM22 had the modal chromosome number 33 instead of 2n = 20 chromosomes for Ornithodoros spp. ticks. All studied tick cell lines had a larger genome size in comparison to the genomes of the parental ticks. Thus, highly passaged tick cell lines can be used for research purposes, but possible differences in encoded genetic information and downstream cellular processes, between different cell populations, should be taken into account.
Highlights
Tick cell lines are an easy-to-handle system for the study of viral and bacterial infections and other aspects of tick cellular processes
We included an early passage of the ISE18 cell line that had been stored in liquid nitrogen for 8 years and resuscitated for this study, and karyotypes of the two I. ricinus cell lines carried out 10 years previously
We found that the chromosome numbers differed between passage levels of the same tick cell line (Fig. 1), and they were different from the expected diploid chromosome numbers of 28 in the ticks I. scapularis and I. ricinus[23,26], and 20 in the tick O. moubata[27]
Summary
Tick cell lines are an easy-to-handle system for the study of viral and bacterial infections and other aspects of tick cellular processes. Cryopreservation of tick cell lines during short periods of inactivity is not recommended due to unpredictable viability and a possible lengthy recovery period following resuscitation[20,28]. Instead, they may be cultured continuously, and some cell lines can be held for several weeks or months at temperatures between 4 and 15 °C22,28–30. We aimed to analyze the genome stability of different tick cell lines during long-term cultivation. We performed an analysis of karyotype and genome size of I. scapularis, I. ricinus and O. moubata cell lines and compared these data with the known genome sizes of the corresponding ticks. We noted that long-term continuous passaging of tick cells could increase the probability of genomic changes
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