Mechanisms of Acclimation to Low Temperature in Zebrafish (Danio rerio)
Date Issued
2009
Date
2009
Author(s)
Abstract
Abstractctothermic vertebrates are different from mammals that are sensitive to hypothermia and they have to maintain core temperature for survival. Why and how ectothermic animals can survive, grow and reproduce in low temperature have been for a long time a scientifically challenging and important inquiry to biologists. We used a microarray to profile the gill transcriptome in zebrafish (Danio rerio) after exposure to low temperature. Adult zebrafish were acclimated to a low temperature of 12 °C for 1 day only (1-d) and up to 30 days (30-d), and the gill transcriptome was compared to wild types by oligonucleotide microarray hybridization. The gill transcriptome profiles revealed that ionoregulation-related genes were highly upregulated in cold-acclimated zebrafish. This paved way to investigate the role of ionoregulatory genes in zebrafish gills during cold acclimation. Cold acclimation caused upregulation of genes that are essential for ionocyte specification, differentiation, ionoregulation, acid/base balance, and increased cell number among cells expressing these genes. For instance, epithelial Ca2+ channel (ECaC), an ionoregulatory gene mRNA expression was increased in parallel with the level of Ca2+ influx, revealing a functional compensation after long-term acclimation to cold. Phospho-histone H3 and TUNEL staining showed that the cell turnover rate was retarded in cold-acclimated gills. These results suggest that gills may sustain their functions by yielding mature ionocytes from preexisting undifferentiated progenitors in low-temperature environments.e further adopt a transcript screening approach to compare the cold responses in zebrafish gills and brain. Principle component analysis of the gene expression profiles indicated that gills developed different strategies depending on the durations of coldxposure while brain remained more stable. Based on ANOVA, clustering analysis, and sub-network enrichment analysis (SNEA), gill exhibits higher cell activities and 3 stress responses while brain activates more genes related to cellular protection during cold acclimation. We also extended the study on the interactions between these two organs during cold acclimation. A transcription factor gene, orthopedia (otp), which is associated with isotocin neuronal development, was stimulated by cold in the zebrafish brain. A group of isotocin-related genes were also stimulated by cold in the zebrafish brain. Otp knockdown decreased the mRNA expressions of these ionocyte-related genes, the numbers of ionocytes, and ion uptake functions. Moreover, two isotocin receptor isoforms were cloned, and the mRNA expressions of these two genes were found to be upregulated in zebrafish gills during cold acclimation. These data suggest that the hypothalamic neurohormone, isotocin, plays some roles in the control pathways of iono/osmoregulatory mechanisms in zebrafish. Taken together, the present study not only identify cold induced genes in zebrafish gill and brain but also provide molecular evidences to elucidate the interactions between these two organs during cold acclimation.
Subjects
Cold acclimation
Ionocyte
Ion regulation
Type
thesis
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