La respuesta de shock térmico y el dimorfismo en Leishmania

Abstract

Protozoa of the Leishmania genus are intracellular parasites having two different stages, promastigote and amastigote, which are present during their life cycle in the invertebrate host and the mammal host respectively. During its life cycle, the parasite suffers dramatic temperature changes and the transformation success between one and the other form is crucial for its survival and reproduction. The response of the organisms to temperature or heat shock response has been well studied in Leishmania, promastigotes having been obtained at 26°C and amastigotes at 35°C respectively, and their reconversion when the temperature is increased or lowered has been demonstrated. These changes in parasite morphology are accomplished by biochemical and molecular variations with differences in enzyme activity and protein synthesis. These processses increase the production of heat shock proteins, specifically HSP70 and HSP83, which continue to be expressed as pari of the Leishrnania amastiyotes as a way of adaptation to vertebrate host environment. At a molecular level, it has been demonstrated that almost al1 heat shock proteins structural genes are arranged in tandem repetition, being transcribed in polycystronic RNA and finally processed by poly-adenylation and trans-splicing. Nevertheless, it has not been possible to identify any transcription promoter in these parasites. Furthermore, studies of transcriptional regulation have demonstrated that the regulation of heat shock proteinsr gene éxpression in Leishmania occurs by post-transcriptional processes. This demonstration has marked a fundamental difference between Leishmania and the other non-protozoal eucariotes.