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Ecological transcriptomics: a non-lethal sampling approach for endangered fire salamanders

ABSTRACT: The analysis of transcriptomes is well-established and increasingly affordable in studies at the interface of ecology and evolution. Expression analysis of thousands of genes in parallel reveals functions and pathways involved in relevant phenotypic differentiation. The application of such methods typically involves the sacrifice of the analysed organisms, which is potentially subject to ethical and legal constraints. As an alternative to lethal sampling, transcriptome analyses can be performed using small biopsies of dispensable tissues. It has to be verified, however, to what extent such results are representative of the whole organism. Here, we use a custom microarray to compare transcriptomes of tail-clip samples with those of the remaining whole-body of fire salamander larvae (Salamandra salamandra). The microarray was calibrated using target RNA to validate the performance of each probe. We varied water temperature to test whether the thermal response in gene expression can be characterized in both types of sample. A large fraction (51 %) of the differentially expressed genes showed parallel changes for both tail clips and whole bodies in response to temperature. While sets of differentially expressed were not identical, they largely belonged to the same functional categories. The gene functions thus revealed a common thermal response of larvae irrespective of the sampled tissue. This included an overexpression of mitochondrial transcripts, an expected thermal acclimatization response of ectotherms. Hence, ecological transcriptomics based on small biopsies represent an alternative to the analysis of lethally sampled tissues in situations where the sacrifice of individuals is not an option.

ORGANISM(S): Salamandra salamandra

PROVIDER: GSE70054 | GEO | 2015/06/20

SECONDARY ACCESSION(S): PRJNA287546

REPOSITORIES: GEO

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Project description:The analysis of transcriptomes is well-established and increasingly affordable in studies at the interface of ecology and evolution. Expression analysis of thousands of genes in parallel reveals functions and pathways involved in relevant phenotypic differentiation. The application of such methods typically involves the sacrifice of the analysed organisms, which is potentially subject to ethical and legal constraints. As an alternative to lethal sampling, transcriptome analyses can be performed using small biopsies of dispensable tissues. It has to be verified, however, to what extent such results are representative of the whole organism. Here, we use a custom microarray to compare transcriptomes of tail-clip samples with those of the remaining whole-body of fire salamander larvae (Salamandra salamandra). The microarray was calibrated using target RNA to validate the performance of each probe. We varied water temperature to test whether the thermal response in gene expression can be characterized in both types of sample. A large fraction (51 %) of the differentially expressed genes showed parallel changes for both tail clips and whole bodies in response to temperature. While sets of differentially expressed were not identical, they largely belonged to the same functional categories. The gene functions thus revealed a common thermal response of larvae irrespective of the sampled tissue. This included an overexpression of mitochondrial transcripts, an expected thermal acclimatization response of ectotherms. Hence, ecological transcriptomics based on small biopsies represent an alternative to the analysis of lethally sampled tissues in situations where the sacrifice of individuals is not an option. Larvae of European Fire salamander were exposed to two different temperatures (9°C & 17°C; n(cold) = 6, n(warm) = 6, n(total) = 12). The transcriptome response to temperature was assessed based on RNA extracted from tail tips, which can be sampled without sacrificing the individual, and based on RNA extracted from the remaining whole body. Results from the analysis of both tissues were compared.

Project description:Fever implies a significant increase in corporal temperature that aids toward the resolution of infective processes such as viral disease. The majority of vertebrate species are not homeothermic therefore must rely upon the environment for temperature regulation. Here we show that in the zebrafish an artificial viral infection, induced by poly (I:C), induces a fever response regulated by the behavioral choice of temperature. We recorded 12 h of the diurnal cycle in zebrafish previously treated (first 12 hours dark cycle) with the pyrogen, poly (I:C) [10 μg⋅kg-1]. Fish, n=10, were held in a thermal gradient (36-180C) separated into 7 interconnected chambers. Presence or absence of individuals in each chamber was recorded each 15 minutes throughout the 12 hour period. After the experimental period we dissected whole brains for microarray analysis. In monitored zebrafish intraperitoneal treatment with poly (I:C) induced a febrile behaviour with significantly elevated temperature preference (T of about 32ºC) in stark contrast with the observed frequency for saline-injected fish (28ºC). Microarray analyses uncovered significant shifts in transcriptional activity that were highly directed in the poly (I:C)-treated fish housed in the thermal gradient. When compared to gene expression profiles from poly (I:C)-treated fish deprived of a thermal gradient we observed a less intense specific to the poly (I:C) challenge and interestingly observed a scattered generalised stress response. Our results highlight the influence of temperature preference in the development of the immune response in zebrafish. Fever induced gene expression in zebrafish brain was measured at 24 after intra peritoneal injection with 1mg*Kg-1 of Poly (I:C) in zebrafish. Four independent experiments were performed to explore the transcriptomic profile induced by animals injected by Poly (I:C) with/whithout thermal gradient, saline solution (PBS), or control using different animals for each experiment.

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Ecological transcriptomics: a non-lethal sampling approach for endangered fire salamanders

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