Infectivity and genes differentially expressed between young and aging theront cells of the marine fish parasite Cryptocaryon irritans

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.

Cryptocaryon irritans (Brown, 1951) is a serious threat to aquaculture of marine fish

“…14,45,51 Shen et al 36 indicated that the loss of theront infectivity is associated with reduced swimming ability and body cilia number, and they speculated that energy attenuation is the main reason for the loss of infectivity. Chi et al 52 demonstrated that the genes related to energy production were down-regulated at 10 h compared with 1 h post-excystment.…”

Host responses against the fish parasitizing ciliate Cryptocaryon irritans

“…To date, no commercial vaccines against C. irritans are available, although good protection can be achieved by experimental vaccines using live, inactivated and subunit preparations and DNA vaccine candidates. Expressed sequence tag libraries of trophont, tomont and theront stages of C. irritans have been sequenced, 124,133,136 which will provide many opportunities for identification of diagnostic and protective antigens. We expect that this C. irritans transcription profiles will boost bioinformatic studies, including basic and applied discoveries.…”

Honokiol induces apoptosis-like death in Cryptocaryon irritans Tomont

“…The apoptosis-like death pathway has also been found in many protozoa, such as Leishmania, Plasmodium falciparum , Tetrahymena thermophila , Trypanosoma cruzi , Blastocystis hominis , Toxoplasma gondii , and Ichthyophthirius multifiliis [ 12 – 21 ], providing a new way to treat parasitic diseases. Many apoptosis-related genes of C. irritans have been found via transcriptome analysis [ 22 – 26 ], which indicates that C. irritans might have an apoptosis-like death pathway. Honokiol, one of the main active components of Magnolia officinalis , has been reported to induce apoptosis of cancer cells and Candida albicans via the endoplasmic reticulum (ER) stress pathway [ 27 – 30 ].…”