Heat-shock DNA homology in distantly related species of Drosophila

Heat shock proteins: a history of study in Russia

This review describes a brief history of the discovery and studies in Russia and associated countries of the main stress protein (Hsp70) that plays important roles both in the normal function of the cell and body as well as under various stressful stimuli. Research on this protein at the Institute of Molecular Biology (Moscow) began with the elucidation of its adaptive functions at the cellular level and at the level of the whole organism. These studies examined the function of Hsp70 under normal and extreme conditions using a wide range of model and non-model animal species, from Leishmania and Drosophila to camels and humans. These analyses made it possible to elucidate the primary regulations in the evolution and function of heat shock (HS) genes in the studied organisms. Next, we studied the structure and characteristic features of heat shock genes and proteins in species with contrasting habitat temperatures. The systems of Hsp70 expression and isolation we developed using various research objects allowed us to proceed to study the protective properties of human recombinant Hsp70 in normal-aging animal models as well as animal models experiencing sepsis, Alzheimer's disease, and stroke. The results obtained open the prospects of using recombinant Hsp70 for the treatment of various neuropathologies in humans. This review describes the logic and history of investigation of Hsp70 performed by one group of scientists from Engelhardt Institute of Molecular Biology, Russian Academy of Sciences. It was not the goal of this paper to give a comprehensive general picture of other similar studies carried out in Russia during this period.

Molecular mechanisms underlying thermal adaptation of xeric animals

For many years,we and our collaborators have investigated the adaptive role of heat shock proteins in different animals,including the representatives of homothermic and poikilothermic species that inhabit regions with contrasting thermal conditions. Adaptive evolution of the response to hyperthermia has led to different results depending upon the species. The thermal threshold of induction of heat shock proteins in desert thermophylic species is, as a rule, higher than in the species from less extreme climates. In addition,thermoresistant poikilothermic species often exhibit a certain level of heat shock proteins in cells even at a physiologically normal temperature. Furthermore,there is often a positive correlation between the characteristic temperature of the ecological niche of a given species and the amount of Hsp70-like proteins in the cells at normal temperature. Although in most cases adaptation to hyperthermia occurs without changes in the number of heat shock genes, these genes can be amplified in some xeric species. It was shown that mobile genetic elements may play an important role in the evolution and fine-tuning of the heat shock response system,and can be used for direct introduction of mutations in the promoter regions of these genes.

Unusual arrangement of thehsp68locus in thevirilisspecies group ofDrosophilaimplicates evolutionary loss of anhsp68gene

Unlike all other Drosophila species studied to date, species in the virilis group of Drosophila have 2 complete copies of hsp68 arranged in inverted head-to-head orientation. Evidence for this conclusion includes Southern blots for D. virilis, D. lummei, and D. montana, PCR analysis of the former 2 species, in situ hybridization in D. virilis × D. lummei hybrids, and the complete nucleotide sequence of the locus in D. lummei. This organization resembles the primitive state of hsp70 in Diptera. Moreover, the Hsp68 peptide sequence for D. virilis and D. lummei is intermediate between that of Hsp70 and Hsp68 from other Drosophila spp. Therefore, we suggest that the hsp68 locus may have arisen via duplication of the hsp70 locus (or vice versa) early in the history of the genus Drosophila, with 1 hsp68 copy subsequently lost in most other Drosophila species groups.Key words: hsp68, Drosophila, Drosophila virilis, evolution, molecular chaperone, heat-shock protein, molecular evolution, gene duplication, gene loss.

Use of surface-enhanced laser desorption ionization-time-of-flight to identify heat shock protein 70 isoforms in closely related species of the virilis group of Drosophila

The 70-kDa heat shock protein (Hsp) family in all Drosophila species includes 2 environmentally inducible family members, Hsp70 and Hsp68. Two-dimensional gel electrophoresis revealed an unusual pattern of heat shock-inducible proteins in the species of the virilis group. Trypsin fingerprinting and microsequencing of tryptic peptides using ProteinChip Array technology identified the major isoelectric variants of Hsp70 family, including Hsp68 isoforms that differ in both molecular mass and isoelectric point from those in Drosophila melanogaster. The peculiar electrophoretic mobility is consistent with the deduced amino acid sequence of corresponding hsp genes from the species of the virilis group.

Evolution and arrangement of the hsp70 gene cluster in two closely related species of the virilis group of Drosophila

To investigate the genetic basis of differing thermotolerance in the closely related species Drosophila virilis and Drosophila lummei, which replace one another along a latitudinal cline, we characterized the hsp70 gene cluster in multiple strains of both species. In both species, all hsp70 copies cluster in a single chromosomal locus, 29C1, and each cluster includes two hsp70 genes arranged as an inverted pair, the ancestral condition. The total number of hsp70 copies is maximally seven in the more thermotolerant D. virilis and five in the less tolerant D. lummei, with some strains of each species exhibiting lower copy numbers. Thus, maximum hsp70 copy number corresponds to hsp70 mRNA and Hsp70 protein levels reported previously and the size of heat-induced puffs at 29C1. The nucleotide sequence and spacing of the hsp70 copies are consistent with tandem duplication of the hsp70 genes in a common ancestor of D. virilis and D. lummei followed by loss of hsp70 genes in D. lummei. These and other data for hsp70 in Drosophila suggest that evolutionary adaptation has repeatedly modified hsp70 copy number by several different genetic mechanisms.

Evolution of thermotolerance and the heat-shock response: evidence from inter/intraspecific comparison and interspecific hybridization in the virilis species group of Drosophila. I. Thermal phenotype

Species in the virilis group of Drosophila (fruit flies), which overlap or replace one another along climatic gradients, exhibit corresponding differences in basal thermotolerance, inducible thermotolerance and the heat-shock response. The low-latitude species D. virilis exceeds the high-latitude species D. lummei in these measures of thermotolerance, the temperature threshold for heat-shock factor (HSF) activation and the ability to express hsp70 mRNA and diverse heat-shock proteins (e.g. Hsp70, Hsp83 and small Hsps) after intense heat shock (e.g. 40-41 degrees C). The xeric species D. novamexicana differs from the mesic species D. texana in much the same way for many of these traits. By contrast, intraspecific variation in these traits is small. Because D. virilis and D. lummei can readily be crossed to yield partially fertile progeny, genetic analysis of interspecific differences is possible. Interspecific hybrids are intermediate to the parental species in basal thermotolerance and inducible thermotolerance and resemble D. virilis in Hsp concentrations after intense heat shock and Hsp70 protein electromorphs.

A DROSOPHILA MELANOGASTER Strain From Sub-Equatorial Africa Has Exceptional Thermotolerance But Decreased Hsp70 Expression

Drosophila melanogaster collected in sub-equatorial Africa in the 1970s are remarkably tolerant of sustained laboratory culture above 30°C and of acute exposure to much warmer temperatures. Inducible thermotolerance of high temperatures, which in Drosophila melanogaster is due in part to the inducible molecular chaperone Hsp70, is only modest in this strain. Expression of Hsp70 protein and hsp70 mRNA is likewise reduced and has slower kinetics in this strain (T) than in a standard wild-type strain (Oregon R). These strains also differed in constitutive and heat-inducible levels of other molecular chaperones. The lower Hsp70 expression in the T strain apparently has no basis in the activation of the heat-shock transcription factor HSF, which is similar in T and Oregon R flies. Rather, the reduced expression may stem from insertion of two transposable elements, H.M.S. Beagle in the intergenic region of the 87A7 hsp70 gene cluster and Jockey in the hsp70Ba gene promoter. We hypothesize that the reduced Hsp70 expression in a Drosophila melanogaster strain living chronically at intermediate temperatures may represent an evolved suppression of the deleterious phenotypes of Hsp70.

Chromosomal homology and molecular organization of Muller's elements D and E in the Drosophila repleta species group

Thirty-three DNA clones containing protein-coding genes have been used for in situ hybridization to the polytene chromosomes of two Drosophila repleta group species, D. repleta and D. buzzatii. Twenty-six clones gave positive results allowing the precise localization of 26 genes and the tentative identification of another nine. The results were fully consistent with the currently accepted chromosomal homologies and in no case was evidence for reciprocal translocations or pericentric inversions found. Most of the genes mapped to chromosomes 2 and 4 that are homologous, respectively, to chromosome arms 3R and 3L of D. melanogaster (Muller's elements E and D). The comparison of the molecular organization of-these two elements between D. melanogaster and D. repleta (two species that belong to different subgenera and diverged some 62 million years ago) showed an extensive reorganization via paracentric inversions. Using a maximum likelihood procedure, we estimated that 130 paracentric inversions have become fixed in element E after the divergence of the two lineages. Therefore, the evolution rate for element E is approximately one inversion per million years. This value is comparable to previous estimates of the rate of evolution of chromosome X and yields an estimate of 4.5 inversions per million years for the whole Drosophila genome.

One- and two-dimensional polyacrylamide gel analysis of the heat shock proteins of the virilis group of Drosophila

The heat shock proteins of the virilis group of Drosophila are analyzed by one- and two-dimensional polyacrylamide gel analysis. This group consists of the two closely related but distinct virilis and montana phylads. The analysis reveals that some of the heat shock proteins are highly conserved among the two phylads while others are not. The 83-, 72-, and 69-kdalton proteins comigrate in all species examined. There is, however, a noticeable trend toward greater molecular weight variability in the smaller heat shock proteins. In general, the heat shock protein patterns within each phylad follow the proposed phylogenetic relationships with some exceptions. D. ezoana and D. littoralis, both members of the montana phylad, exhibit heat shock protein patterns more similar to those of the virilis phylad. The data also demonstrate that the montana phylad has almost two times the heat shock allele members that the virilis phylad has. It is also shown that F1 and F2 hybrid flies of crosses between Drosophila species having different patterns of heat shock proteins show Mendelian segregation of alleles. After several generations of inbred growth, however, the pattern of heat shock protein synthesis in reciprocal hybrids each resembles that of the paternal parent. The implications of these findings are discussed.

Transposition of mobile genetic elements in interspecific hybrids of Drosophila

In situ hybridization of labeled DNA of four mobile dispersed genetic elements (mdg), isolated from D. melanogaster and C. virilis genomes, with polytene chromosomes of the larvae of several Drosophila species has been carried out. The data show that the mdg elements exhibit a high degree of species specificity. The same conclusions are derived from filter hybridization using 32P-labeled D. melanogaster and D. virilis DNA and cloned mdg sequences immobilized on nitrocellulose filters. We attempted to induce transpositions ("jumping") of mdg elements specific for D. virilis chromosomes to the chromosomes of related species (e.g. D. littoralis Meigen) originally lacking the representatives of this family of repeats. For this purpose we produced hybrid stocks with "synthetic" karyotoypes characterized by different combinations of D. virilis homologous chromosomes and "hybrid" chromosomes. In one of such stocks we did find by in situ hybridization the insertion of a D. virilis mdg element into the fifth chromosome of D. littoralis Meigen. The transposition ("jumping") took place in the only region where somatic pairing between the fifth chromosomes of D. virilis and D. littoralis occurs more or less regularly in the hybrids. Since crossing-over in hybrid chromosomes of males is excluded in such "synthetic" stocks, gene conversion may be responsible for this transposition. The possible bearing of the phenomenon observed on the problem of hybrid dysgenesis is discussed.

Rapid sequence divergence in a heat shock locus of Drosophila

In situ hybridization of cRNA transcribed from cloned D. melanogaster heat shock sequences to D. hydei chromosomes has shown that the D. hydei locus 2--32 A corresponds to the D. melanogaster locus 87 A/C and the D. hydei locus 2--36 A to the D. melanogaster locus 95 D, while the D. hydei locus 4--81 B corresponds to the D. melanogaster locus 63 BC. No hybridization to D. hydei chromosomes was found with cRNA transcribed from a clone containing the alpha beta sequences encoded by the D. melanogaster locus 87 C. Neither D. melanogaster heat shock RNA nor D virilis heat shock RNA hybridized significantly to the D. hydei heat shock locus 2--48 B. Furthermore, D. hydei heat shock RNA did not hybridize to the cytological homologs of locus 2--48 B found in D. repleta or in D. virilis. D. hydei heat shock. RNA did hybridize to the cytological homologs of locus 2--48 B in D. neohydei and D. eohydei, both of which belong to the hydei subgroup.

The analysis of a temperature-sensitive (ts) mutation influencing the expression of heat shock-inducible genes in Drosophila melanogaster

The effect of a ts-mutation belonging to the cell-lethal type on protein and RNA synthesis under heat shock conditions has been investigated. The mutation studied, l(l)ts-403, localized in the X-chromosome has significant effect on the kinetics of protein synthesis in salivary gland subjected to heat treatment under in vivo and in vitro conditions. The animals homozygous for l(l)ts-403 are characterized by a rapid drop of label incorporation into heat shock proteins. It is shown that the mutation affects not only the kinetics of heat-shock proteins synthesis but their electrophoretic pattern as well. The experiments performed enable us to conclude that the presumptive regulatory gene realized its action at the level of transcription of heat shock loci.