Heat shock genes: regulatory role for differentiation in parasitic protozoa.

The parasitic protozoa Trypanosoma brucei and Leishmania major are transmitted by insect vectors to their mammalian hosts. The temperature difference between the hosts (25 degrees and 37 degrees C) may induce a heat shock response in the parasite. Transcripts of heat shock genes (homologous to Hsp70 and Hsp83) were 25 to 100 times more abundant in Trypanosoma brucei bloodstream forms (trypomastigotes) than in insect (procyclic) stages. In Leishmania major the patterns of heat shock gene expression in promastigotes (insect-adapted) and amastigotes (mammal-adapted) were different. A temperature shift in vitro induced differentiation of Leishmania major from promastigotes to amastigotes. Therefore, heat shock genes may be responsible for differentiation of these vector-borne parasites.