Gene expression and function of T. bryosalmona

Tetracapsuloides bryosalmonae is an enigmatic myxozoan parasite which causes proliferative kidney disease in salmonid fish. Previous studies have identified European and North American strains of the parasite which are adapted to brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss), respectively. Significantly, European T. bryosalmonae do not form mature spores in rainbow trout. To date, there is a paucity of knowledge on parasite gene expression and function, and on the genetic background of the host immune response. This project will compare the expression profiles of rainbow trout and brown trout infected with European T. bryosalmonae, to elucidate the genetic background for the observed incomplete development. Additionally, first data will be obtained on gene regulation of development of T. bryosalmonae in fish and those genes involved in the host immune response against the parasite. Brown trout and rainbow trout will be experimentally infected by spores of European T. bryosalmonae obtained from our existing laboratory culture of the parasite. Infection progress will be monitored by histological examination to detect the beginning of sporogony in the kidney. Suppression subtractive hybridization (SSH) will be used to detect transcripts differentially expressed in kidney tissue from T. bryosalmonae-infected and non- infected brown trout to identify genes relevant for the normal development of the parasite, and the fish genes involved in the immune response. Moreover, this technique will enable us to compare gene expression in infected brown trout and rainbow trout to identify the genes of host or parasite that are responsible for the incomplete development of T. bryosalmonae in rainbow trout. Ultrastructural analysis of infected trout tissue will be conducted to link the genetic information to morphological changes of parasite stages. Differentially expressed genes will be further analysed and characterized by quantitative real-time PCR at different time points during infection and by sequence analysis of the full reading frame obtained by 5`/3` RACE PCR. Results obtained from this project will help to explain the observed differences in the development of T. bryosalmonae between the two fish hosts, brown trout and rainbow trout.

Tetracapsuloides bryosalmonae is an enigmatic myxozoan parasite which causes proliferative kidney disease in salmonids in Europe and North America. Proliferation of T. bryosalmonae induces a granulomatous cellular response in the interstitial tissue, which leads to swelling of the spleen and kidney. In Europe, spores of T. bryosalmonae develop in the kidney of infected brown trout Salmo trutta and are released via urine to infect the freshwater bryozoan Fredericella sultana. We were interested in discovering host genes that are responsible for normal development of sporogenesis of the European strain of T. bryosalmonae in brown trout but not in rainbow trout. For this study, brown trout and rainbow trout were experimentally infected by European strain of T. bryosalmonae and kidneys were sampled at different time points of infection. Transmission of parasite spores from both infected fish species to the invertebrate host bryozoan F. sultana colonies was observed. Physical parameters (body length and weight), numbers of parasite stages and parasite load were examined and analyzed. The transcriptomes of both infected fish species kidneys were compared using suppressive subtractive hybridization and differentially expressed transcripts were identified and validated by quantitative real time PCR of kidney samples from both fish species. Results of this project demonstrated that; the parasite was successfully transmitted from infected brown trout to the bryozoa host but not from infected rainbow trout. The infection of parasite influences the body length and weight of rainbow trout but not in brown trout. Parasite load was higher in infected brown trout compared with rainbow trout. High numbers of intra-luminal sporogonic stages of parasite were detected in the renal tubules of brown trout but it was not seen in rainbow trout. Furthermore, we discovered novel transcripts in the kidneys of both fish species and their expression levels were differentially up-and down-regulated in both fish species at different time points of parasite development. Differential expression of host anti-inflammatory, humoral immune and endocytic pathway responses, signal transduction activities, cell proliferation and cell growth processes do not inhibit the development of intra-luminal sporogonic stages of the European strain of T. bryosalmonae in brown trout but suppress it in rainbow trout. The project provided fundamental information for understanding trout response and the modulation of the candidate genes during developmental stages of T. bryosalmonae.