Abstract
The ciliated protozoan Cryptocaryon irritans infects a wide range of marine fish and causes the highly lethal white spot disease. This parasite possesses three morphologically and physiologically distinct life stages: an infectious theront, a parasitic trophont, and an asexually reproductive tomont. In the past few years, several attempts have been made to help elucidate how C. irritans transforms from one stage to another using transcriptomic or proteomic approaches. However, there has been no research studying changes in transcription profiles between different time points of a single C. irritans life stage—the development of this parasite. Here we use RNA-seq and compare gene expression profiles of theront cells collected by 1 and 10 hrs after they emerged from tomonts. It has been shown that infectivity of theront cells declines 6–8 hours post-emergence, and we used this characteristic as a physiological marker to confirm the aging of theront cells. We identified a total of 41 upregulated and 90 downregulated genes that were differentially expressed between young and aging theront cells. Using Blast2Go to further analyze functions of these genes, we show that genes related to energy production are downregulated, but quite surprisingly many genes involved in transcription/translation processes are upregulated. We also show that expression of all nine detectable agglutination/immobilization antigen genes, with great sequence divergence, is invariably downregulated. Functions of other differentially expressed genes and indications are also discussed in our study.
Highlights
Unicellular eukaryotes often need to respond dynamically to changes in their living environments
Two different ages of C. irritans theronts (1 hr and 10 hrs post-excystment) were used to infect L. calcarifer at a nonlethal dosage, and numbers of tomonts released from fish were counted
Raw reads were aligned to a C. irritans transcriptome published by Lokanathan and colleagues which contains 1,806,497 base pairs in 2,610 unique transcripts [24]
Summary
Unicellular eukaryotes often need to respond dynamically to changes in their living environments. The ability to meet conditional demands promptly is important for parasitic protozoans because their physiological priorities might be different before, during, and after establishing successful infections on hosts. Infectivity and genes differentially expressed in different ages of C. irritans theronts
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