טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentChapovetsky Victoria
SubjectCharacterization of Stress Response (HSP) in Toads at
Differential Experimental Conditions
DepartmentDepartment of Biology
Supervisor Professor Uri Katz


Abstract


Exposure of organisms to elevated temperatures and other environmental insults induce stress response, based on increased expression of HSP (heat shock proteins). These proteins are believed to be involved in the maintenance of protein structure and cell organization when external conditions, particularly temperature, are disturbed. This molecular system has been studied quite extensively in mammals and cell cultures, and a model has been suggested that describes the sequence of reactions leading to the increase in cellular HSP. The induction of the HSP70, for example, is mediated by HSF1 (heat shock factor 1) that is constitutively expressed in the cell as inactive monomer. Following the stress, HSF1 undergoes trimerization and locates in the nucleus. There it binds to HSE (heat shock element) on the hsp gene promotor and acts as transcription inducer of HSP70 protein. Homeotherms do not experience but a narrow range of body temperature, whereas poikilotherms such as amphibians and reptiles, experience a much larger range. However, not many studies have been published on HSP in poikilotherms, and it is questioned if the same model applies to them. Very little is known in amphibians, perhaps most vulnerable among vertebrates, in respect to HSP system, and we have decided to study it in closely related species of toads that differ markedly in their sensitivity to low temperature. The expression of heat shock proteins and parts of stress-response system were studied in the tissues of cold-resistant (Bufo viridis) and cold-sensitive (Bufo regularis) toads. The toads are poikilotherms, and their body temperature equilibrates with the ambient.