The effect of heat and cold exposure on HSP70 expression and development of deformities during embryogenesis of Atlantic salmon (Salmo salar)

Temperature stress is recognized as a teratogenic factor that induces deformities during the embryonic development of teleosts. In order to further elaborate the mechanisms involved, Atlantic salmon (Salmo salar) embryos were heat (16 °C) and cold (1 °C) shocked at eight and four different embryonic stages, respectively, during the period from gastrulation until the completion of somitogenesis. Additionally, embryos were subjected to a long-term heat exposure at 12 °C from the ∼ 1st until the ∼ 20th somite stage. Real-time RT-PCR results showed that the HSP70 mRNA expression was dependent on the stage of development. Whereas temperature shock was found to induce HSP70 mRNA up-regulation at the gastrula stage, the ∼ 9th, the ∼ 15th, the ∼ 20th and the ∼ 45th somite stage, the additional three investigated stages showed no up-regulation. The highest HSP70 expression levels were induced at the ∼ 45th somite stage as shown by a 12- and 4-fold increase after heat and cold shock, respectively. Embryos subjected to the prolonged heat exposure showed a stronger HSP70 expression than embryos that were given a 1-h heat shock. Intriguingly, a high incidence (17%) of situs inversus of abdominal organs was found in fry subjected to the long-term exposure, supporting that early somitogenesis is an important period of left-right determination in teleosts. In general, the 1-h temperature shock was not sufficient to induce high frequencies of deformities. Though, a 14% incidence of vertebral deformities was observed both at the ∼ 45th somite stage and at the completion of somitogenesis after cold shock. The results provide new insight regarding the tolerance of high and low temperature stress in Atlantic salmon embryos.