Differential expression of heat-shock proteins and spontaneous synthesis of HSP70 during the life cycle of Blastocladiella emersonii

Small heat shock protein genes are developmentally regulated during stress and non-stress conditions in Blastocladiella emersonii

Small heat shock proteins (sHsps) are molecular chaperones of low molecular weight involved in an early association with misfolded proteins. In response to heat shock, B. emersonii induces the synthesis of a number of proteins. As sHsps are still poorly studied in B. emersonii and in fungi overall, the aim of this work was to carry out a in-depth characterization of sHsps during B. emersonni life cycle, as well as in response to thermal stress. We verified a strong induction of the hsp17 gene in cells exposed to heat shock both in germination and sporulation stages, and that Hsp17 protein levels show the same pattern of variation of its mRNA. Unlike hsp17 and hsp30, hsp16 gene is not significantly induced during heat shock, in germination or sporulation cells. However, at normal temperatures, the hsp16 gene presents high mRNA levels in sporulation cells, whereas the hsp30 gene presents high mRNA levels in germination cells. Interestingly, heat shock mRNA levels for hsp17 and hsp30 genes are 10 times higher in germination cells than in sporulation cells. Thus, our data show that the expression of these sHsp genes is quite distinct, both under normal temperature as during heat shock.

Stress response in tardigrades: differential gene expression of molecular chaperones

Semi-terrestrial tardigrades exhibit a remarkable tolerance to desiccation by entering a state called anhydrobiosis. In this state, they show a strong resistance against several kinds of physical extremes. Because of the probable importance of stress proteins during the phases of dehydration and rehydration, the relative abundance of transcripts coding for two alpha-crystallin heat-shock proteins (Mt-sHsp17.2 and Mt-sHsp19.5), as well for the heat-shock proteins Mt-sHsp10, Mt-Hsp60, Mt-Hsp70 and Mt-Hsp90, were analysed in active and anhydrobiotic tardigrades of the species Milnesium tardigradum. They were also analysed in the transitional stage (I) of dehydration, the transitional stage (II) of rehydration and in heat-shocked specimens. A variable pattern of expression was detected, with most candidates being downregulated. Gene transcripts of one Mt-hsp70 isoform in the transitional stage I and Mt-hsp90 in the anhydrobiotic stage were significantly upregulated. A high gene expression (778.6-fold) was found for the small alpha-crystallin heat-shock protein gene Mt-sHsp17.2 after heat shock. We discuss the limited role of the stress-gene expression in the transitional stages between the active and anhydrobiotic tardigrades and other mechanisms which allow tardigrades to survive desiccation.

Identification of genes that are preferentially expressed in conidiogenous cell development of Metarhizium anisopliae by suppression subtractive hybridization

The insect pathogenic fungus Metarhizium anisopliae is widely used as an insect biocontrol agent. The M. anisopliae conidium plays an important role in pathogenesis and disease transmission. The aim of this study was to identify genes whose expression is up-regulated during conidiogenous cell development. This is a powerful strategy for obtaining insight into the molecular events that regulate conidiation. We isolated genes that are preferentially expressed in the developing conidiophores of the common fungal locust pathogen M. anisopliae CQMa102 using suppression subtractive hybridization. Based on the results of cDNA array dot blotting, we identified 109 unique expressed sequence tags (ESTs) that were up-regulated more than fivefold during conidiophore formation. Among these 109 ESTs were 45 (41.3%) with significant similarity to NCBI annotated hypothetical proteins, 35 (32.1%) with low similarity to known or predicted genes that might represent novel genes, and 29 (26.6%) with significant similarity to known proteins involved in various cell and molecular processes, such as ell structure and function, cell metabolism, protein metabolism, stress response, nucleic acid metabolism, and cell cycle and growth. We confirmed the up-regulation of 11 randomly selected genes with real-time reverse transcriptase-PCR analysis. The results of this study provide a preliminary description of genes that may be involved in the molecular regulation of fungal conidiogenesis.

Differential expression of two small Hsps during diapause in the corn stalk borer Sesamia nonagrioides (Lef.)

We isolated and characterized two members of the alpha-crystallin/sHsp family, SnoHsp19.5 and SnoHsp20.8 from Sesamia nonagrioides (Lepidoptera: Noctuidae). The cDNAs encoded proteins of 174 and 185 amino acids, with calculated molecular weights of 19.5 and 20.8 kDa, respectively. The deduced amino acid sequences of SnoHsp19.5 and SnoHsp20.8 showed highest homology to Hsp19.7 of Mamestra brassicae and to Bombyx mori Hsp20.4, respectively. Expression patterns of SnoHsp19.5 and SnoHsp20.8 in non-diapausing individuals under different environmental conditions (heat or cold) showed different accumulation profiles for the two genes after heat and cold treatment. SnoHsp19.5 was consistently expressed, while SnoHsp20.8 gene was down-regulated in deep diapause and was up-regulated at the termination of diapause. Our results suggest that these two genes play distinctive roles in the regulation of diapause.

Transcriptome analysis in response to heat shock and cadmium in the aquatic fungus Blastocladiella emersonii

The global transcriptional response of the chytridiomycete Blastocladiella emersonii to environmental stress conditions was explored by sequencing a large number of expressed sequence tags (ESTs) from three distinct cDNA libraries, constructed with mRNA extracted from cells exposed to heat shock and different concentrations of cadmium chloride. A total of 6,350 high-quality EST sequences were obtained and assembled into 2,326 putative unigenes, 51% of them not previously described in B. emersonii. To approximately 59% of the unigenes it was possible to assign an orthologue in another organism, whereas 41% of them remained without a putative identification, with transcripts related to protein folding and antioxidant activity being highly enriched in the stress libraries. A microarray chip was constructed encompassing 3,773 distinct ESTs from the B. emersonii transcriptome presently available, which correspond to a wide range of biological processes. Global gene expression analysis of B. emersonii cells exposed to stress conditions revealed a large number of differentially expressed genes: 122 up- and 60 downregulated genes during heat shock and 189 up- and 110 downregulated genes during exposure to cadmium. The main functional categories represented among the upregulated genes were protein folding and proteolysis, proteins with antioxidant properties, and cellular transport. Interestingly, in response to cadmium stress, B. emersonii cells induced genes encoding six different glutathione S-transferases and six distinct metacaspases, as well as genes coding for several proteins of sulfur amino acid metabolism, indicating that cadmium causes oxidative stress and apoptosis in this fungus. All sequences described in this study have been submitted to the GenBank EST section with the accession numbers EE 730389 to EE 736848.

Comparative expression analysis of members of the Hsp70 family in the chytridiomycete Blastocladiella emersonii

Sequencing of a large number of expressed sequence tags from Blastocladiella emersonii revealed the presence of ten distinct putative members of the 70 kDa-heat shock protein (Hsp70) family in this fungus. The amino acid sequence deduced from eight of these cDNAs showed significant similarity to members of the Saccharomyces cerevisiae Hsp70 family, and the remaining displayed high sequence homology with hsp70 gene products from other organisms. The hsp70-3 gene was the most highly expressed at normal temperatures and was poorly induced during heat shock. Except for hsp70-4 and hsp70-6, all other hsp70 genes were induced to different degrees upon exposure of B. emersonii cells to heat shock, with hsp70-1 gene presenting the highest transcript levels. Phylogenetic analysis of complete B. emersonii putative Hsp70 protein sequences indicated that Hsp70-1 and Hsp70-3 corresponded to cytosolic proteins, whereas Hsp70-7 and Hsp70-9 are probably localized in the endoplasmic reticulum and mitochondria, respectively.

Gene expression of heat-shock proteins (Hsp23, Hsp70 and Hsp90) during and after larval diapause in the blow fly Lucilia sericata

Genes encoding heat-shock protein 23 (Hsp23), Hsp70 and Hsp90 were cloned from Lucilia sericata to examine whether their expression is related to the regulation of its larval diapause. The level of all three Hsps mRNAs was consistently low irrespective of diapause status. These results indicate that expression of Hsp23, Hsp70 and Hsp90 is not regulated in response to diapause, in contrast to the flesh fly Sarcophaga crassipalpis that shows upregulation of Hsp23 and Hsp70 and downregulation of Hsp90 during its pupal diapause. On the other hand, Hsp90 transcripts were regulated developmentally in nondiapause larvae of L. sericata, i.e., they were at low levels after cessation of feeding but were considerably upregulated a day before pupariation, suggesting that Hsp90 is involved in a developmental process that occurs between the cessation of feeding and pupariation. When diapause larvae were transferred to all of the conditions that terminate diapause and allow postdiapause development, Hsp90 transcripts were promptly upregulated. These results indicate that Hsp90 may serve as an early marker to predict diapause termination in this species.

Differential regulation of spontaneous and heat-induced HSP 70 expression in developing zebrafish (Danio rerio)

A spontaneous high expression of heat shock protein 70 (HSP 70) was found to arise in zebrafish (Danio rerio) at the larval stage (84 hr after fertilization). The level of HSP 70 in 84-hr-old larvae was estimated to be six- to eightfold that of 12-hr-old embryos. As heat-induced HSP 70 synthesis in many eukaryotic organisms is known to be mediated by a transcriptional-dependent pathway activated by heat shock factor 1 (HSF-1), we then examined if the spontaneous and heat-induced HSP 70 synthesis in zebrafish were controlled by the same mechanism. Although the transient increase of a 62-kDa HSF-1-like polypeptide in 72- to 96-hr-old larvae seemed to correlate with the onset of the spontaneous HSP 70 production, an anti-HSF-1 antibody cocktail supershifted the heat shock element (HSE) binding complex induced by stressed but not by unstressed zebrafish extracts. Northern blot and quantitative RT-PCR analysis demonstrated the predominant presence of the cognate form of hsp 70 mRNA (hsc 70 mRNA) in developing zebrafish. The extent of heat-induced HSP 70 production in 84-hr-old larvae matched well with a dramatic increase in hsp 70 mRNA accumulation, while no apparent increase in total hsp 70 mRNA could be detected in 72- to 84-hr-old unstressed larvae by northern blot analysis. The stable expression of hsc 70 mRNA specific to beta-actin mRNA in normal zebrafish was confirmed by RT-PCR analysis. Hence, the spontaneous high expression of HSP 70 in zebrafish is believed to be controlled by a mechanism different from the HSF-1-dependent transcriptional activation of hsp 70 under heat stress. J. Exp. Zool. 293:349-359, 2002.

Regulation of diapause

Environmental and hormonal regulators of diapause have been reasonably well defined, but our understanding of the molecular regulation of diapause remains in its infancy. Though many genes are shut down during diapause, others are specifically expressed at this time. Classes of diapause-upregulated genes can be distinguished based on their expression patterns: Some are upregulated throughout diapause, and others are expressed only in early diapause, late diapause, or intermittently throughout diapause. The termination of diapause is accompanied by a rapid decline in expression of the diapause-upregulated genes and, conversely, an elevation in expression of many genes that were downregulated during diapause. A comparison of insect diapause with other forms of dormancy in plants and animals suggests that upregulation of a subset of heat shock protein genes may be one feature common to different types of dormancies.

Differential expression of an hsp70 gene during transition from the mycelial to the infective yeast form of the human pathogenic fungus Paracoccidioides brasiliensis

We have isolated and characterized cDNA and genomic clones that encode a 70 kDa heat shock protein (Hsp70) from the dimorphic human pathogenic fungus Paracoccidioides brasiliensis. The gene encodes a 649-amino-acid protein showing high identity with other members of the hsp70 gene family. The hsp70 gene is induced during both heat shock of yeast cells at 42 degrees C and the mycelial to yeast transition. A differential expression of this gene can be observed between mycelial and yeast forms, with a much higher level of expression in the yeast. We found two introns of 178 and 72 nucleotides in the P. brasiliensis hsp70 gene. Splicing of these introns is regulated during the heat shock process and possibly during infection. In order to analyse the differential accumulation of unspliced mRNA following cellular differentiation and/or heat shock, reverse transcriptase-polymerase chain reaction (RT-PCR) experiments were carried out. The temperature-induced mycelial to yeast transition results in the transient accumulation of unspliced hsp70 mRNA transcripts. Yeast cells, after adaptation at 36 degrees C, seem to be more proficient at splicing, at least with respect to hsp70 mRNA because, during a severe heat shock (42 degrees C), the unspliced form of this mRNA does not accumulate. The mycelial to yeast differentiation will have the adaptational effect of increasing the resistance of the organism to environmental stress, which may be necessary for parasite survival in the mammalian host.

Differential stress gene expression during the development of Neurospora crassa and other fungi

Stress genes are differentially expressed during the development of Neurospora crassa and other fungi. Large amounts of constitutive heat shock protein 70 (HSC70) are found in dormant conidia of N. crassa, whereas little mRNA of the related glucose-regulated protein (grp78) is detected. It is, however, not generally clear whether heat shock protein or mRNA is preferentially stored in dormant spores. Germinating spores of N. crassa increase the level of grp mRNA. During this developmental stage, the induction of inducible heat shock protein (hsp) genes can be elicited by heat shock only at certain times after the beginning of germination. Exponential growth (proliferation) is paralleled by increased levels of HSCs. The stationary state is characterized by decreased levels of some HSCs and increased levels of others. Conidiation in N. crassa is accompanied by a strong enhancement of the synthesis and levels of HSCs but also of HSPs after heat shock. This increase may serve a need for additional rounds of replication, for the expression and transport of sporulation-specific proteins or for stabilization of macromolecules in the spores and their preservation for germination. The control mechanisms involved in the differential expression of hsc genes are currently not known.

Differential expression of glucose-regulated (grp78) and heat-shock-inducible (hsp70) genes during asexual development of Neurospora crassa

The expression of a glucose-regulated gene (grp78) changes significantly during the vegetative life cycle of Neurospora crassa: the amounts of grp78 mRNA are low in dormant conidia, increase during germination and exponential growth, decline in young aerial hyphae and reach a maximum in late (15-18 h) aerial hyphae. Heat shock (30 min at 45 degrees C) elevated the mRNA level of this gene especially in early aerial hyphae, whereas no increase above the high constitutive amount was found after heat treatment of late aerial hyphae. The expression of the inducible hsp70 gene after heat shock also varied with the state of development and showed the highest inducibility in late aerial hyphae. Surface mycelium, from which aerial hyphae emerge, showed a similar increase in the amounts of both mRNA species. A developmental mutant (acon-2), which is defective in minor constriction budding of aerial hyphae, showed lower levels of con-2 mRNA as well as of grp78 and hsp70 mRNA (after heat shock) in late aerial hyphae. The acon-2 mutant did not form conidia at this stage. It is concluded that the high constitutive and inducible expression of stress genes in late aerial hyphae is due to a developmental activation of their transcription or, alternatively, to a lower degradation rate of their mRNA during this stage.

Differential HSC70 expression during asexual development of Neurospora crassa

The constitutive and the heat-shock-induced expression of members of heat-shock protein families changed during vegetative development and conidiation of Neurospora crassa as determined by two-dimensional gel electrophoresis. Western blot and ELISA analyses revealed the highest amounts of the constitutive heat-shock protein 70 (HSC70) in conidiating aerial hyphae and dormant conidia. During conidial germination the amount of HSC70 decreased and subsequently increased during vegetative growth. Stationary mycelia and young aerial hyphae exhibited the lowest HSC70 level. The stationary-phase-dependent decrease in HSC70 was accompanied by a concomitant increase in its nuclear localization, whereas no significant changes in the amount of nuclear HSC70 were found during aerial hyphae development. The cAMP content during aerial hyphae development was inversely correlated with that of HSC70. To examine possible causal relations between HSC70 expression and cAMP content, the adenylate-cyclase-deficient mutant crisp (cr-1) was analysed, which exhibits low concentrations of endogenous cAMP. This mutant, however, showed a lower constitutive HSC70 level, compared to the bdA strain. Treatment of the bd strain and cr-1 mutant with 20 microM 8-bromo-cAMP did not result in significant changes of the constitutive HSC70 level, but in the level of heat-induced HSC/HSP70. In a developmental mutant (acon-2) which is defective in a differentiation step toward conidiation, the expression of HSC70 in aerial hyphae was delayed until the first proconidial chains were observed. It is concluded that the differential expression of HSC/HSP70 does not depend on different nuclear levels of HSC70 or on changes in cAMP concentrations, but rather on developmental genes controlling conidiation.

Heat-shock response of the entomopathogenic fungus Beauveria brongniartii

The heat-shock response of five strains of the entomopathogenic fungus Beauveria brongniartii was studied using two-dimensional (2D) gel electrophoresis. The fungal cells were heat shocked at 45 °C for 1 h and the total cellular protein was subjected to 2D gel electrophoresis. Proteins were separated in the first dimension using isoelectric focusing (pH range of 3.0–10) and in the second dimension by sodium dodecyl sulphate – polyacrylamide gel electrophoresis. More than 150 polypeptides for each strain were visualized by silver staining and have been assigned individual numbers as polypeptide coordinates. Analysis of the polypeptide map obtained by 2D gels indicated three patterns; several unique heat-shock proteins (HSPs) were (i) induced, (ii) enhanced, or (iii) repressed. Some of the HSPs induced by 45 °C were unique for each of the strains tested. Identification of heat-inducible protein synthesis or repression has ramifications for field survival and performance of entomopathogenic fungi. As well, the HSPs can be used as "signature proteins" for identification pruposes and this raises the possibility of using HSPs as a diagnostic tool applicable to other pest control fungi.Key words: heat-shock proteins, heat-shock response, two-dimensional electrophoresis, entomopathogenic fungi, Beauveria brongniartii.

A unique intron-containing hsp70 gene induced by heat shock and during sporulation in the aquatic fungus Blastocladiella emersonii

We have isolated and characterized cDNA and genomic DNA clones encoding the 70-kDa heat-shock protein (Hsp70) from the aquatic fungus Blastocladiella emersonii (Be). Nucleotide (nt) sequence analysis predicts an acidic protein containing 650 amino acids, with a calculated molecular mass of 70.8 kDa. The Be hsp70 gene is induced by heat shock (HS), as well as during sporulation of the fungus, and its coding region is interrupted by a single intron. All the evidence seems to indicate that this is the only hsp70 in Be. S1 nuclease protection assays revealed that splicing of the hsp70 intron is highly thermoresistant; at the lethal temperature of 42 degrees C, only 30% of the hsp70 mRNAs have not been processed. A single transcription start point (tsp), localized about 30 nt downstream from a putative TATA box, was determined both during HS and at normal temperatures. The promoter region presented several NGAAN repeats (where N is any nucleotide) characteristic of HS elements, as well as putative binding sites for ATF, Sp1 and two metal-responsive elements.

Isolation and nucleotide sequence analysis of the rat testis-specific major heat-shock protein (HSP70)-related gene

The isolation of a rat hsp 70-related gene which is specifically and highly expressed in testis is described together with the complete nucleotide sequence of the transcription unit (2947 bp), 5' flanking (about 1 kbp) and 3' flanking (about 0.3 kbp) regions. The sequence analysis and nuclease S1 mapping revealed that the isolated gene (referred to as the hst70 gene) represents a novel, distinct member of the hsp70 multigene family. Its transcription unit lacks introns and a single open reading frame encodes a protein of 69.5 kDa. The predicted amino acid sequence of this protein is highly similar (only four out of 633 amino acids are different) to that encoded by the mouse testis-specific hsp70.2 gene (Zakeri, Z.F., Wolgemuth, D.J. and Hunt, C.R. (1988) Mol. Cell. Biol. 8, 2925-2932). The functional significance of multiple potentially regulatory sequences (e.g. TATA-boxes, heat-shock element and estrogen receptor binding site) present in the 5' flanking region of the rat hst70 gene is discussed.

Microbial stress proteins

There is general agreement that a function, perhaps the major function, of stress proteins under normal physiological conditions is to help assembly and disassembly of protein complexes and to catalyse protein-translocation processes. It remains unclear, however, as to what role these processes play in stressed cells. It could be that cells under stress produce abnormal, misfolded or otherwise damaged proteins and that increased synthesis of stress proteins is required to counter protein modifications. A role for stress proteins in recovery of cells from stress, as opposed to a role in helping cells to withstand a lethal stress, is thus suggested. The intracellular location of stress proteins, in the unstressed and stressed cell, is worthy of further studies. Members of the hsp70 family are associated with the cytosol, mitochondria and endoplasmic reticulum. There is evidence, particularly from studies on mammalian cells (Tanguay, 1985; Welch and Mizzen, 1988; Arrigo et al., 1988), that following stress hsps migrate to various cellular compartments and subsequently delocalize after stress. However, there is little comparable data from microbial systems for this phenomenon (e.g. Rossi and Lindquist, 1989). The question as to the role of stress proteins in the transient acquisition of thermotolerance remains to be answered. It is insufficient to equate the kinetics of stress-protein synthesis with acquisition of thermotolerance. Quantitative data on the amount of stress protein present at various times, including the recovery period, is required. The demonstration that microbial stress proteins are important antigenic determinants of micro-organisms causing major debilitating diseases in the world is an exciting observation. Studies on the interplay of pathogen and host, both carrying similar antigenic hsp determinants, will be a challenging area for future research. It is likely that E. coli and Sacch. cerevisiae, with their well-established biochemical and genetic properties, will continue to be the experimental systems of choice for studies on stress proteins. On the other hand, it is encouraging that studies on other micro-organisms have expanded in the past few years and have made substantial contributions towards our understanding of the stress response. The ubiquitous nature of the stress response and the remarkable evolutionary conservation of the stress proteins continue to be attractive areas for research.

An analysis of developmental timing in Blastocladiella emersonii sporulation

We propose a model of time regulation for the expression of the Blastocladiella emersonii sporulation phenotypes based on new methods (Soll, 1986) which analyse the effect of temperature on the rate limiting processes, i.e., "timers" of certain events during development. By using reciprocal shift experiments (transferring sporulating cells from 22 to 27 degrees C and vice versa) we characterized the timers of the phenotypes: septate zoosporangium, papillate zoosporangium, cleavage zoosporangium, and empty zoosporangium, considering the number of the components, sensitivity, duration, and the mutual dependency of each limiting factor. The timers for the first three phenotypes started at zero time of sporulation induction and acted in parallel. The fourth phenotype, empty zoosporangium, has a timer which appears to act sequentially to that of the papillate zoosporangium. We also studied the effects of polyoxin D, calcofluor white, and congo red on sporulation. The first drug prevents the appearance of the septate zoosporangium and the other two prevent the expression of the papillate zoosporangium. In spite of the morphological blockage, the zoosporogenesis proceeds, resulting in the formation of normal zoospores. These results are interpreted as additional evidence for the parallel model of control proposed here.

Effect of heat shock on S6 phosphorylation during the development of Blastocladiella emersonii

Changes in phosphorylation of ribosomal protein S6 during heat shock, induction of thermotolerance and recovery from heat shock at different stages of Blastocladiella emersonii development were investigated. Independently of the initial state of S6 phosphorylation (maximal or intermediate), a rapid and complete dephosphorylation of S6 is induced by heat shock and S6 remains unphosphorylated during the acquired thermotolerance. During recovery from heat shock rephosphorylation of S6 occurs always to the levels characteristic of that particular stage, coincidently with the turn off of heat shock protein synthesis.