Abstract
Heat shock protein 70 (Hsp70) is a molecular chaperone providing tolerance to heat and other challenges at the cellular and organismal levels. We sequenced a genomic cluster containing three hsp70 family genes linked with major histocompatibility complex (MHC) class III region from an extremely heat tolerant animal, camel (Camelus dromedarius). Two hsp70 family genes comprising the cluster contain heat shock elements (HSEs), while the third gene lacks HSEs and should not be induced by heat shock. Comparison of the camel hsp70 cluster with the corresponding regions from several mammalian species revealed similar organization of genes forming the cluster. Specifically, the two heat inducible hsp70 genes are arranged in tandem, while the third constitutively expressed hsp70 family member is present in inverted orientation. Comparison of regulatory regions of hsp70 genes from camel and other mammals demonstrates that transcription factor matches with highest significance are located in the highly conserved 250-bp upstream region and correspond to HSEs followed by NF-Y and Sp1 binding sites. The high degree of sequence conservation leaves little room for putative camel-specific regulatory elements. Surprisingly, RT-PCR and 5′/3′-RACE analysis demonstrated that all three hsp70 genes are expressed in camel's muscle and blood cells not only after heat shock, but under normal physiological conditions as well, and may account for tolerance of camel cells to extreme environmental conditions. A high degree of evolutionary conservation observed for the hsp70 cluster always linked with MHC locus in mammals suggests an important role of such organization for coordinated functioning of these vital genes.
Highlights
Among multiple changes in cellular activity and physiology, the most remarkable event in stressed cells of all organisms studied so far is the rapid production of a highly conserved set of stress proteins usually termed ‘‘Heat Shock Proteins’’ or Hsps because these proteins were originally described in Drosophila melanogaster after temperature elevation [1]
Individual members belonging to this family exhibit exceptionally high levels of homology even when distant organisms are compared, various phylogenetic groups of organisms exhibit strikingly different trends in the evolution and organization of hsp70 gene clusters
In our previous studies on Diptera species including representatives of virilis group species of Drosophila and various species belonging to Stratiomyidae family, we have shown that the hsp70 gene cluster is involved in active rearrangement processes, and closely related species and even geographical strains may differ by number and relative position of individual hsp70 copies comprising the cluster [10,19]
Summary
Among multiple changes in cellular activity and physiology, the most remarkable event in stressed cells of all organisms studied so far is the rapid production of a highly conserved set of stress proteins usually termed ‘‘Heat Shock Proteins’’ or Hsps because these proteins were originally described in Drosophila melanogaster after temperature elevation [1]. There is a wealth of experimental data suggesting that members of Hsp family play an important role in whole body adaptation of animals to adverse environmental conditions [3,7,8]. It should be emphasized that the Hsp family is most diverse and includes many stress-inducible as well as constitutive proteins playing various roles in different cell compartments and under different cellular conditions [4,8,9]. After the discovery of heat shock proteins in Drosophila, we decided to investigate whether there is a correlation between the general pattern of Hsps synthesis and the whole body adaptation in various animals inhabiting thermally contrasting conditions. In our studies we usually compared Hsps synthesis in close species existing under conditions that differ sharply in mean temperature and other parameters of their ecological niches [5,6,7]
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