A hybrid dysgenesis syndrome occurs in Drosophila virilis when males from an established laboratory strain are crossed to females obtained from the wild, causing the simultaneous mobilization of several different transposable elements. The insertion sequence responsible for the mutant phenotype of a dysgenic yellow allele has been characterized and named Penelope. In situ hybridization and Southern analyses reveal the presence of more than 30 copies of this element in the P-like parental strain, whereas Penelope is absent in all M-like strains tested. Penelope contains one 2.5-kb-long ORF that could encode products with homology to integrase and reverse transcriptase. Northern analysis and whole-mount in situ hybridization show strong induction of a 2.6-kb RNA in the ovaries of dysgenic females that is expressed at very low levels in the parental strains or in the progeny from the reciprocal cross. Injection of Penelope-containing plasmids into preblastoderm embryos of an M-like strain results in mutant progeny caused by insertion of Ulysses and perhaps other transposons, suggesting that Penelope expression might be responsible for the observed dysgenesis syndrome and the simultaneous mobilization of other transposable elements.Hybrid dysgenesis in Drosophila melanogaster results in high sterility and mutation rates, male recombination, segregation distortion, and chromosome nondisjunction (1-3). The transposase-encoding P element is responsible for the P-M hybrid dysgenesis syndrome in this species (4, 5). A second hybrid dysgenesis system, designated I-R, also leads to similar abnormalities. Although the dysgenic traits that arise in P-M and I-R crosses are similar, the nature of the transposable elements involved is very different. The I transposable element differs from the P element in that it encodes a protein with sequence similarities to reverse transcriptase (RT) (6). Some dysgenic traits have also been observed in systems involving the hobo family of transposable elements, which can promote high rates of chromosomal rearrangements and other dysgenic traits (7).A similar dysgenic syndrome takes place in Drosophila virilis in unidirectional crosses between males of a strain named 160 and females of strain 9 (8). These two strains are respectively designated P-like and M-like based on the parallels in their behavior with P and M strains in D. melanogaster. The above cross results in characteristic traits in the progeny such as a high level of gonadal sterility in F 1 males and females, chromosomal nondisjunction and rearrangements, male recombination, and the occurrence of multiple visible mutations, although it was shown that neither P nor I elements are present in this species (8). A white mutation (w d9 ) isolated from the progeny of a dysgenic cross has been characterized, and the insertion sequence responsible for the mutant phenotype has been isolated (9, 10). This sequence is a 10.6-kb long terminal repeat-containing retrotransposon named Ulysses. The transcription pattern of Ulysses is the...

We report that two structurally similar transposable elements containing reverse transcriptase (RT), Penelope in Drosophila virilis and Athena in bdelloid rotifers, have proliferated as copies containing introns. The ability of Penelope-like elements (PLEs) to retain introns, their separate phylogenetic placement and their peculiar structural features make them a novel class of eukaryotic retroelements.

Colonization of a host by an active transposon can increase mutation rates or cause sterility, a phenotype termed hybrid dysgenesis. As an example, intercrosses of certain Drosophila virilis strains can produce dysgenic progeny. The Penelope element is present only in a subset of laboratory strains and has been implicated as a causative agent of the dysgenic phenotype. We have also introduced Penelope into Drosophila melanogaster, which are otherwise naive to the element. We have taken advantage of these natural and experimentally induced colonization processes to probe the evolution of small RNA pathways in response to transposon challenge. In both species, Penelope was predominantly targeted by endo-small-interfering RNAs (siRNAs) rather than by piwi-interacting RNAs (piRNAs). Although we do observe correlations between Penelope transcription and dysgenesis, we could not correlate differences in maternally deposited Penelope piRNAs with the sterility of progeny. Instead, we found that strains that produced dysgenic progeny differed in their production of piRNAs from clusters in subtelomeric regions, possibly indicating that changes in the overall piRNA repertoire underlie dysgenesis. Considered together, our data reveal unexpected plasticity in small RNA pathways in germ cells, both in the character of their responses to invading transposons and in the piRNA clusters that define their ability to respond to mobile elements.

We studied various aspects of heat-shock response with special emphasis on the expression of heat-shock protein 70 (hsp70) genes at various levels in two congener species of littoral endemic amphipods (Eulimnogammarus cyaneus and E. verrucosus) from Lake Baikal which show striking differences in their vertical distribution and thermal tolerance. Although both the species studied demonstrate high constitutive levels of Hsp70, the thermotolerant E. cyaneus exhibited a 5-fold higher basal level of Hsp70 proteins under normal physiological conditions (7 °C) and significantly lower induction of Hsp70 after temperature elevation compared with the more thermosensitive E. verrucosus. We isolated the hsp70 genes from both species and analysed their sequences. Two isoforms of the cytosolic Hsp70/Hsc70 proteins were detected in both species under normal physiological conditions and encoded by two distinct hsp/hsc70 family members. While both Hsp70 isoforms were synthesized without heat shock, only one of them was induced by temperature elevation. The observed differences in the Hsp70 expression patterns, including the dynamics of Hsp70 synthesis and threshold of induction, suggest that the increased thermotolerance in E. cyaneus (compared with E. verrucosus) is associated with a complex structural and functional rearrangement of the hsp70 gene family and favoured the involvement of Hsp70 in adaptation to fluctuating thermal conditions. This study provides insights into the molecular mechanisms underlying the thermal adaptation of Baikal amphipods and represents the first report describing the structure and function of the hsp70 genes of endemic Baikal species dwelling in thermally contrasting habitats.

A population of Stratiomys japonica, a species belonging to the family Stratiomyidae (Diptera), common name 'soldier flies', occurs in a hot volcanic spring, which is apparently among the most inhospitable environments for animals because of chemical and thermal conditions. Larvae of this species, which naturally often experience temperatures more than 40 degrees C, have constitutively high concentrations of the normally inducible heat-shock protein Hsp70, but very low level of corresponding mRNA. Larvae of three other species of the same family, Stratiomys singularior, Nemotelus bipunctatus and Oxycera pardalina, are confined to different type semi-aquatic habitats with contrasting thermal regime. However, all of them shared the same pattern of Hsp70 expression. Interestingly, heat-shock treatment of S. japonica larvae activates heat-shock factor and significantly induces Hsp70 synthesis, whereas larvae of O. pardalina, a species from constant cold environment, produce significantly less Hsp70 in response to heat shock. Adults of the four species also exhibit lower, but detectable levels of Hsp70 without heat shock. Larvae of all species studied have very high tolerance to temperature stress in comparison with other Diptera species investigated, probably representing an inherent adaptive feature of all Stratiomyidae enabling successful colonization of highly variable and extreme habitats.

The synthesis of heat shock proteins (hsps) at normal physiological and elevated temperatures has been correlated with the natural adaptation of an organism to heat in nine lizard species studied. These species differ drastically by their adaptation to elevated temperature and represent a spectrum of forms isolated from various geographical regions of the Union of Soviet Socialist Republics. The synthesis of hsps belonging to the hsp7O family and their correspondent mRNAs have been compared at different temperature regimes. This analysis has shown that lizards inhabiting the Middle Asia deserts are characterized by a higher content of hsp7O-like proteins at normal physiological temperatures (2-to 5-fold differences) when compared with the forms from central and northern regions of the European part of the Union of Soviet Socialistic Republics. Analysis of hsp7O mRNA at different temperatures substantiated these observations, showing evident correlation between adaptation of a given form to hyperthermia and the quantity of hsp7O mRNA in the cells under non-heat-shock conditions. The results obtained with a wide spectrum of ecologically different lizard species, coupled with other relevant data, enable us to propose a general rule applicable to poikilothermic organisms. This rule postulates the direct correlation between the characteristic temperature of the ecological niche of a given species and the amount of hsp7O-like proteins in the cells at normal temperature.Heat or other environmental stresses have been shown to induce the synthesis of a family of proteins, the so-called heat shock proteins (hsps), in a wide variety of cells from yeast to mammalian systems (for reviews, see refs. 1-3). Recent work has focused on the role of hsps in the assembly, folding, and transport of other cellular proteins under different conditions. The level of these special activities of hsps, often termed "chaperonins", depends on the state of the general translational machinery of the cell (4-6). One of the more interesting aspects of thermal biology in different systems is the interrelation between the induction of hsp synthesis and the development of thermoresistance. Hsps are thought to protect cells from the toxic effects of short-term environmental stress (1-3). However, although much information about the structure of hsps and their cellular function has been accumulated, almost all these data were obtained by studying culture cells or isolated organs and tissues. Only scattered facts concern the role of hsps in providing wholebody adaptation to the close species inhabiting ecological niches with strikingly different temperature regimes (7)(8)(9)(10).Our studies focus on the heat shock response in nine lizard species that inhabit different environments and exhibit various levels ofthermoresistance. We found a direct correlation between the level of thermoresistance of a species and both the quantity of hsps belonging to the hsp70 family and the correspondent mRNA in the cells at normal physiological temperature. MAT...

Brain deterioration resulting from "protein folding" diseases, such as the Alzheimer's disease (AD), is one of the leading causes of morbidity and mortality in the aging human population. Heat shock proteins (Hsps) constitute the major cellular quality control system for proteins that mitigates the pathological burden of neurotoxic protein fibrils and aggregates. However, the therapeutic effect of Hsps has not been tested in a relevant setting. Here we report the dramatic neuroprotective effect of recombinant human Hsp70 in the bilateral olfactory bulbectomy model (OBX mice) and 5XFAD mouse models of neurodegeneration. We show that intranasally-administered Hsp70 rapidly enters the afflicted brain regions and mitigates multiple AD-like morphological and cognitive abnormalities observed in model animals. In particular, in both cases it normalizes the density of neurons in the hippocampus and cortex which correlates with the diminished accumulation of amyloid-β (Aβ) peptide and, in the case of 5XFAD mice, reduces Aβ plaque formation. Consistently, Hsp70 treatment also protects spatial memory in OBX and 5XFAD mice. These studies demonstrate that exogenous Hsp70 may be a practical therapeutic agent for treatment of neurodegenerative diseases associated with abnormal protein biogenesis and cognitive disturbances, such as AD, for which neuroprotective therapy is urgently needed.

Here we describe a new class of retroelements termed PLE (Penelope-like elements). The only transpositionally active representative of this lineage found so far has been isolated from Drosophila virilis. This element, Penelope, is responsible for the hybrid dysgenesis syndrome in this species, characterized by simultaneous mobilization of several unrelated TE families in the progeny of dysgenic crosses. Several lines of evidence favor the hypothesis of recent Penelope invasion into D. virilis. Moreover, when D. virilisPenelope was introduced by P element-mediated transformation into the genome of D. melanogaster, it underwent extensive amplification in the new host and induced several traits of the dysgenesis syndrome, including gonadal atrophy and numerous mutations. The single ORF encoded by PLE consists of two principal domains: reverse transcriptase (RT) and endonuclease (EN), which is similar to GIY-YIG intron-encoded endonucleases. With the appearance of a large number of PLEs in genome databases from diverse eukaryotes, including amoebae, fungi, cnidarians, rotifers, flatworms, roundworms, fish, amphibia, and reptilia, it becomes possible to resolve their phylogenetic relationships with other RT groups with a greater degree of confidence. On the basis of their peculiar structural features, distinct phylogenetic placement, and structure of transcripts, we conclude that PLE constitute a novel class of eukaryotic retroelements, different from non-LTR and LTR retrotransposons.