Four Drosophila heat shock genes at 67B: characterization of recombinant plasmids

Small heat shock proteins: big folding machines

The workshop was entitled "The Small HSP World" and had the mission to bring together investigators studying small heat shock proteins (sHSPs). It was held at Le Bonne Entente in Quebec City (Quebec, Canada) from October 2 to October 5 2014. Forty-four scientists from 14 different countries attended this workshop of the Cell Stress Society International (CSSI). The small number of participants stimulated interesting discussions, and the resulting informal atmosphere was appreciated by everybody. This article provides highlights from talks and discussions of the workshop, giving an overview of the latest work on sHSPs.

Transient expression of homologous genes in Drosophila cells

A cloned Drosophila heat shock protein 22 gene was transfected into two independently established Drosophila cell lines. Each line carried a different heat shock protein 22 allele, distinguishable by electrophoresis of the protein. The transfected gene was not expressed at 25 degrees C but could be induced at 36 degrees C. In one line, two heat shock protein 22 electromorphs were synthesized.

Structure, function, property, and role in neurologic diseases and other diseases of the sHsp22

Small heat shock proteins are members of the heat shock proteins family. They share important identical features: 1) they form the conserved structure 'alpha-crystallin domain' with about 80-100 residues in the C-terminal part of the proteins; 2) they have monomeric molecular masses ranging in 12-43 kDa; 3) they associate into large oligomers consisting in many cases of subunits; 4) they increase expression under stress conditions; 5) they exhibit a highly dynamic structure; and 6) they play a chaperone-like role. Hsp22 (also known as HspB8, H11, and E2IG1) retains the structural motif of the 'alpha-crystallin' family of Hsps and is a member of the superfamily of sHsps. Hsp22 displays chaperone activity, autokinase activity, and trigger or block apoptosis activity. It differs from canonical family members existing as a monomer. A decrease in the HspB8 activity may contribute to the development of some neurologic diseases and others.

Co-localization of Polycomb protein and GAGA factor on regulatory elements responsible for the maintenance of homeotic gene expression

The Polycomb group and trithorax group genes of Drosophila are required for maintaining the differential expression state of developmental regulators, such as the homeotic genes, in a stable and heritable manner throughout development. The Polycomb group genes have been suggested to act by regulating higher order chromatin and packaging repressed chromosomal domains in a heterochromatin-like structure. We have mapped, at high resolution, the distribution of Polycomb protein on the bithorax complex of Drosophila tissue culture cells, using an improved formaldehyde cross-linking and immunoprecipitation technique. Polycomb protein is not distributed homogeneously on the regulatory regions of the repressed Ultrabithorax and abdominal-A genes, but is highly enriched at discrete sequence elements, many of which coincide with previously mapped Polycomb group response elements (PREs). Our results further suggest that Polycomb protein spreads locally over a few kilobases of DNA surrounding PREs, perhaps to stabilize silencing complexes. GAGA factor/Trithorax-like, a member of the trithorax group, is also bound at those PREs which contain GAGA consensus-binding sites. Two modes of binding can be distinguished: a high level binding to elements in the regulatory domain of the expressed Abdominal-B gene, and a low level of binding to Polycomb-bound PREs in the inactive domains of the bithorax complex. We propose that GAGA factor binds constitutively to regulatory elements in the bithorax complex, which function both as PREs and as trithorax group response elements.

Stage-specific localization of the small heat shock protein Hsp27 during oogenesis in Drosophila melanogaster

The developmental and heat shock-induced expression of the small heat shock protein Hsp27 was investigated by confocal microscopy of whole-mount immunostained preparations of ovarioles during oogenesis in Drosophila melanogaster. In unstressed flies, Hsp27 was mainly associated with germline nurse cells throughout egg development. A small group of somatic follicle cells also expressed Hsp27 specifically at stages 8 to 10 of oogenesis. Interestingly, this Hsp showed a different intracellular localization depending on the stages of egg chamber development. Thus Hsp27 was localized in the nucleus of nurse cells during the first stages of oogenesis (from germarium to stage 6) whereas it showed a perinuclear and cytoplasmic localization from stage 8. After a heat shock, Hsp27 accumulated in somatic follicle cells surrounding the egg chamber whereas the expression of this small Hsp did not seem to be enhanced in nurse cells. The stage-dependent pattern of intracellular localization of Hsp27 observed in nurse cells of unstressed flies was also observed following heat shock. At late stages of oogenesis, Hsp27 also showed a perinuclear distribution in follicle and nurse cells after heat stress. These observations suggest that different factors may modulate the expression and intracellular distribution of Hsp27. This modulation may be associated with the specific activities occurring in each particular cell type throughout oogenesis during both normal development and under heat shock conditions.

Dual regulation of the Drosophila hsp26 promoter in vitro

Efficient heat shock induction of Drosophila hsp26 gene transcription in vivo requires binding sites for heat shock factor (HSF) and GAGA factor (GAF) close to the TATA box (proximal elements) as well as 350 bp upstream of the start site of transcription (distal elements). We have evaluated the contribution of hsp26 promoter sequences to transcriptional activity in extracts from either heat shocked or unstressed fly embryos. Efficient transcription in either extract was governed by distinct regulatory principles. Transcription in extracts from unstressed embryos relied solely on GAGA elements which efficiently counteracted repression by abundant non-specific DNA-binding proteins. Transcription in extracts from heat shocked embryos depended only a little on GAGA elements, relying mainly on functional HSEs. Constitutively active recombinant HSF or native factor in an extract from heat shocked embryos was able to truly activate transcription essentially via proximal HSEs, but not when bound to distal sites. These two modes of regulation in vitro may correspond to the two functional states of the promoter before and after heat shock in vivo.

Identification of members of the HSP30 small heat shock protein family and characterization of their developmental regulation in heat-shocked Xenopus laevis embryos

In the present study we have characterized the synthesis of members of the HSP30 family during Xenopus laevis development using a polyclonal antipeptide antibody derived from the carboxyl end of HSP30C. Two-dimensional PAGE/immunoblot analysis was unable to detect any heat-inducible small HSPs in cleavage, blastula, gastrula, or neurula stage embryos. However, heat-inducible accumulation of a single protein was first detectable in early tailbud embryos with an additional 5 HSPs at the late tailbud stage and a total of 13 small HSPs at the early tadpole stage. In the Xenopus A6 kidney epithelial cell line, a total of eight heat-inducible small HSPs were detected by this antibody. Comparison of the pattern of protein synthesis in embryos and somatic cells revealed a number of common and unique heat inducible proteins in Xenopus embryos and cultured kidney epithelial cells. To specifically identify the protein product of the HSP30C gene, we made a chimeric gene construct with the Xenopus HSP30C coding sequence under the control of a constitutive promoter. This construct was microinjected into fertilized eggs and resulted in the premature and constitutive synthesis of the HSP30C protein in gastrula stage embryos. Through a series of mixing experiments, we were able to specifically identify the protein encoded by the HSP30C gene in embryos and somatic cells and to conclude that HSP30C synthesis was first head-inducible at the early tailbud stage of development. The differential pattern of heat-inducible accumulation of members of the HSP30 family during Xenopus development suggests that these proteins may have distinct functions at specific embryonic stages during a stress response.

Monoclonal antibody specifically reacting against 73-kilodalton heat shock cognate protein: possible expression on mammalian cell surface

The heat shock proteins (hsp) are regarded as being immunogenic to the animal hosts. Although certain hsp are suggested to be expressed on the cell surface, further evidence for the cell surface expression of these proteins has been required. In this article we report the development of a MAb NT22. This antibody reacted with ATP-binding proteins (which contain a large amount of 70-kDa hsp family) of HeLa cells, and with purified bovine 70-kDa hsp. It did not react with the E. coli lysate, but clearly reacted with the recombinant rat hsc73. However, NT22 failed to react with hsp72. Furthermore, stress treatment of cells also indicated that considerable amounts of NT22-defined antigen translocated into the nucleus from the cell cytoplasm. These results suggest that NT22 is a novel MAb that reacts specifically to the mammalian hsc73. Moreover, this antibody could detect the constitutive and stress-induced cell surface expression of its relevant antigen. It is expressed preferentially on EBV-transformed B cell and certain epithelial cancer cell lines. However, resting B cells did not express this antigen on the cell surface. These data indicate that hsc73 could be expressed on the cell surface of certain cells, and suggest that hsc73 may interact with the host immune system.

Two tightly-linked Drosophila male accessory gland transcripts with the same developmental expression derive from independent transcription units

Acp26Aa and Acp26Ab are Drosophila male accessory gland transcripts that are tightly linked and transcribed from the same DNA strand. Despite their being separated by 20 base pairs, the transcripts show identical responses to several developmental signals. These observations make it important to determine whether the 26A region contains two separable genes with the same developmental expression or a single developmentally regulated transcription unit whose product is processed to yield Acp26Aa and Acp26Ab. We show that Acp26Aa and Acp26Ab are separate mRNAs using a reverse transcription-polymerase chain reaction assay and reporter gene fusions. We also show that the regulatory elements for Acp26Ab lie within a fragment containing the intergenic region and transcribed sequences of Acp26Aa and Acp26Ab.

Analysis of the resistance to heat and hydrogen peroxide stresses in COS cells transiently expressing wild type or deletion mutants of the Drosophila 27-kDa heat-shock protein

The Drosophila melanogaster small heat-shock protein, hsp27 (Dhsp27) belongs to a family of polypeptides which shares a sequence related to alpha-crystallin and which protect cell against heat shock. Dhsp27 accumulates following heat shock and, in absence of stress, in the central nervous system, imaginal discs and the gonads of the developing fly. Two internal and adjacent deletion mutants in the conserved alpha-crystallin domain of Dhsp27 were constructed. Expression vectors containing either the coding sequence of Dhsp27 or that of the two deletion mutants linked to the Simian-Virus-40 late promoter were used to transfect monkey COS cells. The transient expression of Dhsp27 was found to decrease the sensitivity of COS cells to heat and hydrogen-peroxide stresses as judged by Trypan-blue staining and indirect immunofluorescence analysis. Using this rapid test, we observed that a deletion of 62 amino acids, which lies at the 5' end of the conserved alpha-crystallin domain and covers the first 41 amino acids of this region had only a weak effect on the protective activity of Dhsp27. This suggests that the N-terminal half of the conserved alpha-crystallin domain may not be essential for the protective activity of the small hsp. In contrast, Dhsp27 was no more active when the last 42 amino acids of the alpha-crystallin domain were deleted. Biochemical fractionation and indirect immunofluorescence analysis indicated that the protective function of Dhsp27 was localized at the level of the nucleus.

The role of heat-shock proteins in thermotolerance

The role of heat-shock proteins (hsps) in thermotolerance was examined in the budding yeast Saccharomyces cerevisiae and in the fruit fly Drosophila melanogaster. In yeast cells, the major protein responsible for thermotolerance is hsp 100. In cells carrying mutations in the hsp 100 gene, HSP 104, growth is normal at both high and low temperatures, but the ability of cells to survive extreme temperatures is severely impaired. The loss of thermotolerance is apparently due to the absence of the hsp 104 protein itself because, with the exception of the hsp 104 protein, no differences in protein profiles were observed between mutant and wild-type cells. Aggregates found in mutant cells at high temperatures suggest that the cause of death may be the accumulation of denatured proteins. No differences in the rates of protein degradation were observed between mutant and wild-type cells. This, and genetic analysis of cells carrying multiple hsp 70 and hsp 104 mutations, suggests that the primary function of hsp 104 is to rescue proteins from denaturation rather than to degrade them once they have been denatured. Drosophila cells do not produce a protein in the hsp 100 class in response to high temperatures. In this organism, hsp 70 appears to be the primary protein involved in thermotolerance. Thus, the relative importance of different hsps in thermotolerance changes from organism to organism.

hsp23 and hsp26 exhibit distinct spatial and temporal patterns of constitutive expression in Drosophila adults

To determine differences in the patterns of expression of Drosophila small heat shock proteins (shsp) during normal development in the absence of stress, proteins obtained from head, thorax and gonads of young (0-12 h, 3 days), middle-aged (3-6 days) and 15- to 20-day-old adult flies were separated on SDS-PAGE gels and blotted with monoclonal antibodies against hsp23 and hsp26. hsp23 was found in the heads and gonads of young males and females. In contrast, the maximum expression of hsp26 was seen in gonads of young flies, and it was only lightly detected in the brain. The expression of both proteins decreased as flies aged. This age-related decrease was particularly striking for hsp23 in females. The immunoblot results obtained were complemented by immunostaining of thin parasagittal sections of whole fly bodies. Hsp23 was found to be expressed in the brain, thoracic ganglion, fat body and gonads of young (0-12 h) males and females. On the other hand, hsp26 was essentially detected in ovaries and testes of these young flies. The analysis of the tissue expression of both proteins demonstrate that each shsp has a distinct cellular localization. In the central nervous system, hsp23 and hsp26 were present in the neurocytes of the brain and the thoracic ganglion. In addition, hsp23 (but not hsp26) was also detected in the central neuropile of these two organs. In testis, hsp26 was localized in the cytoplasm of spermatocytes and, probably, in the spermatid bundles. In contrast, hsp23 was detected at the periphery of cells (membranes).(ABSTRACT TRUNCATED AT 250 WORDS)

Heat shock response in Drosophila

Major alterations in genetic activity have been observed in every organism after exposure to abnormally high temperatures. This phenomenon, called the heat shock response, was discovered in the fruit fly Drosophila. Studies with this organism led to the discovery of the heat shock proteins, whose genes were among the first eukaryotic genes to be cloned. Several of the most important aspects of the regulation of the heat shock response and of the functions of the heat shock proteins have been unraveled in Drosophila.

Regulatory elements near the Drosophila hsp 22 gene required for ecdysterone and heat shock induction

A transient expression assay was used to localize cis-acting DNA regulatory elements near the Drosophila heat shock protein (hsp) 22 gene, that are involved in heat shock expression and in ecdysterone-induced expression. The results identify a region between positions -320 and -232 that is essential for ecdysterone control, but not for heat-induced expression, and a sequence between -199 and -156, which, when deleted, leads to the loss of heat shock induction. To investigate the function of these DNA sequences, transfection-competition experiments were carried out. The evidence suggests that the DNA regulatory sequences identified by transient expression studies contain binding sites for transacting transcription factors.

Ecdysterone regulatory elements function as both transcriptional activators and repressors

A synthetic, 23-bp ecdysterone regulatory element (EcRE), derived from the upstream region of the Drosophila melanogaster hsp27 gene, was inserted adjacent to the herpes simplex virus thymidine kinase promoter fused to a bacterial gene for chloramphenicol acetyltransferase (CAT). Hybrid constructs were transfected into Drosophila S3 cells and assayed for ecdysterone-inducible CAT expression. In the absence of ecdysterone a tandem pair of EcREs repressed the high constitutive level of CAT activity found after transfection with the parent reporter plasmid alone. After hormone addition very high levels of CAT activity were observed. Insertion of the EcRE pair 3' of the CAT gene also led to high levels of ecdysterone-induced CAT expression, but the repression of high constitutive levels of CAT activity failed to occur. The EcRE-CAT construct was cotransfected with plasmids containing tandem 10-mers or 40-mers of the EcRE but lacking a reporter gene. These additional EcREs led to a reduced level of ecdysterone-induced CAT activity and to an elevation of basal CAT activity in the absence of hormone. The data suggest that the receptor binds to the EcRE in the absence of hormone, blocking basal transcription from a constitutive promoter. In the presence of ecdysterone, receptor-hormone binding to the EcRE leads to greatly enhanced transcription.

Ecdysterone regulatory elements function as both transcriptional activators and repressors

A synthetic, 23-bp ecdysterone regulatory element (EcRE), derived from the upstream region of the Drosophila melanogaster hsp27 gene, was inserted adjacent to the herpes simplex virus thymidine kinase promoter fused to a bacterial gene for chloramphenicol acetyltransferase (CAT). Hybrid constructs were transfected into Drosophila S3 cells and assayed for ecdysterone-inducible CAT expression. In the absence of ecdysterone a tandem pair of EcREs repressed the high constitutive level of CAT activity found after transfection with the parent reporter plasmid alone. After hormone addition very high levels of CAT activity were observed. Insertion of the EcRE pair 3' of the CAT gene also led to high levels of ecdysterone-induced CAT expression, but the repression of high constitutive levels of CAT activity failed to occur. The EcRE-CAT construct was cotransfected with plasmids containing tandem 10-mers or 40-mers of the EcRE but lacking a reporter gene. These additional EcREs led to a reduced level of ecdysterone-induced CAT activity and to an elevation of basal CAT activity in the absence of hormone. The data suggest that the receptor binds to the EcRE in the absence of hormone, blocking basal transcription from a constitutive promoter. In the presence of ecdysterone, receptor-hormone binding to the EcRE leads to greatly enhanced transcription.

Expression of heat shock proteins during development in Drosophila

Studies on the expression of heat shock proteins during development in Drosophila clearly show that individual Hsps accumulate in a tissue- and developmental stage-specific manner. This is in contrast to their coordinate expression in response to stress. Therefore, the Hsps may play at least two roles, one as housekeeping proteins during development and/or differentiation and the second one in restoring cellular functions after environmental stress. Research in the first two decades following the discovery of the heat shock response have focused on a search for functions in stressed cells. The next few years should bring us further understanding on the role of these fascinating proteins during development in Drosophila as well as in other eukaryotes.

Identification of ecdysone response elements by analysis of the Drosophila Eip28/29 gene

We have identified ecdysone-response elements (EcREs) by studying regulation of the steroid-responsive Drosophila Eip28/29 gene. First, functional assays of deletion mutants identified large sequence regions required for the response; then a blotting method using the specifically labeled steroid receptor as probe identified receptor-binding regions. Three short receptor-binding regions near Eip28/29 have been identified: Prox and Dist [521 and 2295 nucleotides, respectively, downstream of the poly(A) site] are probably required for the Eip28/29 response in cell lines; Upstream (-440) is unnecessary for that response. We have also demonstrated that an EcRE-containing region from hsp27 contains a receptor-binding site. Each of these four receptor-binding regions functions as an EcRE when placed upstream of an ecdysone nonresponsive promoter and each contains an imperfect palindrome, suggesting the consensus 5'-RG(GT)TCANTGA(CA)CY-3'. Furthermore, a synthetic 15-bp fragment containing an imperfect palindrome similar to the consensus is a fully functional EcRE. The presence of any of the EcREs leads, in the absence of hormone, to depressed gene expression. When hormone is added, it relieves this repression and causes additional activation. The similarity of the EcRE sequence to response elements for estrogen, thyroid hormone, and retinoic acid receptors suggests that the steroid receptors and their signal transduction mechanisms have been strongly and broadly conserved.

Tissue-specific expression of the heat shock protein HSP27 during Drosophila melanogaster development

The alpha-crystallin-related heat shock (stress) protein hsp27 is expressed in absence of heat shock during Drosophila melanogaster development. Here, we describe the tissue distribution of this protein using an immunoaffinity-purified antibody. In embryos, hsp27 translated from maternal RNA is uniformly distributed, except in the yolk. During the first, second, and early third larval stages, hsp27 expression is restricted to the brain and the gonads. These tissues are characterized by a high level of proliferating cells. In late third instar larvae and early pupae, in addition to the central nervous system and the gonads, all the imaginal discs synthesize hsp27. The disc expression seems restricted to the beginning of their differentiation since it disappears during the second half of the pupal stage: no more hsp27 is observed in the disc-derived adult organs. In adults, hsp27 is still present in some regions of the central nervous system, and is also expressed in the male and female germ lines where it accumulates in mature sperm and oocytes. The transcript and the protein accumulate in oocytes since the onset of vitellogenesis with a uniform distribution similar to that found in embryos. The adult germ lines transcribe hsp27 gene while no transcript is detected in the late pupal and adult brain. These results suggest multiple roles of hsp27 during Drosophila development which may be related to both the proliferative and differentiated states of the tissues.

Genetic analysis of chromosomal region 67A-D of Drosophila melanogaster

In an effort to (1) characterize the 67 interval of chromosome 3 of Drosophila melanogaster genetically and (2) isolate mutations of the 67B1 small heat shock protein (hsp) gene cluster specifically, we undertook a mutational analysis of the 67A-D subinterval. Using a deficiency of the 67A2 to 67D11-13 region, Df(3L)AC1, we screened 8700 diepoxybutane-treated chromosomes and 7800 ethyl methanesulfonate-treated chromosomes for visible and lethal mutations throughout this interval and recovered 74 independent recessive lethal mutations, but no visible mutations. One of the lethal mutations, d29A6, was identified as an overlapping deficiency extending from 66F3 to 67B1. An additional 6000 diepoxybutane-treated chromosomes were screened for lethality over d29A6, yielding another four lethal mutations within the 67A2-B1 subinterval. These 78 lethal mutations, along with two others isolated in other laboratories, define 23 essential loci--6 within the 67A2-B1 subinterval and 17 within the 67A2 to D11-13 subinterval. Many of these loci appear to be required for imaginal development only, exhibiting late larval to pharate adult lethal phases. Examination of the 67A2-B1 lethal complementation groups for (1) earlier onset of lethality following a heat shock, (2) missing or altered small hsps on two-dimensional protein gels, and (3) restoration of viability by transformed wild-type copies of the small hsp genes indicates that none of these mutations affect the small hsps. On the basis of this analysis and the known homology of the genes, we conclude that the small hsps are functionally equivalent.

The Caenorhabditis elegans hsp70 gene family: a molecular genetic characterization

We have isolated genomic clones representing six distinct members of the Caenorhabditis elegans 70-kDa heat-shock protein gene (hsp70) family. Each member exists as a single copy element in the C. elegans genome. Transcripts of four of the hsp70 genes have been detected by Northern-blot analysis. One member, hsp70C, appears to be a heat-shock-cognate hsp70 gene (hsc70) since its transcription is developmentally regulated and is not increased in response to heat shock. Transcripts of another gene, hsp70A, are abundant in control worms and are also increased (two- to six-fold) upon heat shock. Nucleotide sequencing of genomic and cDNA clones of hsp70A reveals that it is highly homologous to Drosophila and yeast heat-shock-inducible and heat-shock-cognate hsp70 genes. Three DNA elements homologous to the heat-shock promoter, 5'-C--GAA--TTC--G-3' are located upstream from the Hsp70A-coding region. We find that hsp70A contains three introns, one of which is in a similar position with an intron in the Drosophila hsc1 and hsc2 genes. Finally, utilizing strain-specific restriction fragment length differences, we have mapped the chromosomal position of hsp70A to the far right of chromosome IV.

An unusual split Drosophila heat shock gene expressed during embryogenesis, pupation and in testis

Gene 2, one of the seven heat shock genes from locus 67B of Drosophila melanogaster, is transcribed into two polyadenylated RNAs having different developmental profiles of expression. The smaller transcript, of about 560 nucleotides, is expressed from mid-embryogenesis to the first two larval stages and again at the beginning of pupation. The larger transcript, 780 nucleotides, contains an additional 5' exon, accounting for its larger size. It is detected in pupae and adults, is male-specific and is localized in the testes. Heat shock does not affect the abundance of these two transcripts but induces the accumulation of a third RNA species of about 2000 nucleotides. This heat-shock RNA has the same cap site as the embryonic transcript, while its 3' portion entirely includes the neighbouring hsp22 gene. It appears, therefore, that in this case, heat shock alters the normal transcription termination process. By contrast to most heat shock genes, gene 2 contains several micro introns. One long open reading frame common to the three transcripts encodes a putative polypeptide of 111 amino acid residues. No homology was found with the other small heat shock genes of locus 67B.

Characterization of HSP27 and three immunologically related polypeptides during Drosophila development

The low-molecular-weight heat-shock protein HSP27 is made in the absence of heat shock during Drosophila melanogaster development. An analysis of the accumulation of HSP27 during specific stages of development is presented using an antiserum recognizing this protein. Whereas HSP27 is abundant during embryogenesis, the level of this protein begins to decrease in the 20-h old embryo and is no longer detectable in second instar larvae. A high level of HSP27 is again observed in third instar larvae and reaches a maximal level in late pupae. While still abundant in young adult flies of both sexes, a greater amount of HSP27 is found in females with the protein being highly concentrated within the ovaries. Following lysis of whole pupae, about 60% of HSP27 is found in the soluble lysate fraction in a form which sediments between 5 and 20 S. Anti-HSP27 serum also recognizes three other developmentally regulated polypeptides with apparent MW of 33, 85 and 120 kDa. The 33 kDa protein accumulates in pupae while those of 85 and 120 kDa are more abundant in third instar larvae. Unlike HSP27, these proteins are not detected in embryos or ovaries. Immunoblot analysis of V8 proteolytic fragments suggests that HSP 27 and 33 kDa are related polypeptides. Exposure of the developing insect to heat-shock treatment results in increased level of HSP27. In larvae, a small amount of the 33 kDa protein accumulates following heat shock, while in pupae and adult flies a decrease in the concentration of this protein is observed after heat shock. Finally, different cellular localizations and distributions within the pupal body have been found for these developmentally regulated polypeptides.

A Drosophila heat shock gene from locus 67B is expressed during embryogenesis and pupation

We present a detailed characterization of the structure and expression of gene 3 from the 67B locus of Drosophila melanogaster. Northern blot analysis reveals a major poly(A)+ transcript during two stages of development: mid-embryogenesis and beginning of pupation. After heat shock, the abundance of this mRNA is increased and small amounts of larger RNAs representing alternate terminations of the major transcript appear. In Schneider 3 tissue culture cells, beside the major transcript, we also observe small amounts of the larger RNAs after a heat shock. The sequencing of cDNA and genomic clones shows an intronless transcription unit with one long open reading frame. The deduced polypeptide has 169 amino acids. It shares a strong homology with the four small heat shock proteins in the region also conserved in the mammalian alpha-crystalline B2 chain. In gene 3, this homology is restricted to the first 50 residues along the conserved 83 amino acid stretch. Two heat shock regulatory elements are localized upstream from the gene.

Localization of specific topoisomerase I interactions within the transcribed region of active heat shock genes by using the inhibitor camptothecin

Camptothecin stabilizes the topoisomerase I-DNA covalent intermediate that forms during the relaxation of torsionally strained DNA. By mapping the position of the resultant DNA nicks, we analyzed the distribution of the covalent intermediates formed on heat shock genes in cultured Drosophila melanogaster cells. Topoisomerase I was found to interact with the transcriptionally active genes hsp22, hsp23, hsp26, and hsp28 after heat shock but not with the inactive genes before heat shock. The interaction occurred predominantly within the transcribed region, with specific sites occurring on both the transcribed and nontranscribed strands of the DNA. Little interaction was seen with nontranscribed flanking sequences. Camptothecin only partially inhibited transcription of the hsp28 gene during heat shock, causing a reduced level of transcripts which were nonetheless full length. Topoisomerase I also interacted with the DNA throughout the transcriptionally active hsp83 gene, including an intron, in both heat-shocked and non-heat-shocked cells. The results point to a dynamic set of interactions at the active locus.

Expression and localization of Drosophila melanogaster hsp70 cognate proteins

Monoclonal antibodies have been used to identify three proteins in Drosophila melanogaster that share antigenic determinants with the major heat shock proteins hsp70 and hsp68. While two of the proteins are major proteins at all developmental stages, one heat shock cognate protein, hsc70, is especially enriched in embryos. hsc70 is shown to be the product of a previously identified gene, Hsc4. We have examined the levels of hsp70-related proteins in adult flies and larvae during heat shock and recovery. At maximal induction in vivo, hsp70 and hsp68 never reach the basal levels of the major heat shock cognate proteins. Monoclonal antibodies to hsc70 have been used to localize it to a meshwork of cytoplasmic fibers that are heavily concentrated around the nucleus.

Heat-shock proteins and development

At the simplest level there is little doubt that the heat shock response is homeostatic, to protect the cell against the ravages of the environmental insult and ensure that the cell can continue its normal life after the crisis has passed.

Localization of specific topoisomerase I interactions within the transcribed region of active heat shock genes by using the inhibitor camptothecin

Camptothecin stabilizes the topoisomerase I-DNA covalent intermediate that forms during the relaxation of torsionally strained DNA. By mapping the position of the resultant DNA nicks, we analyzed the distribution of the covalent intermediates formed on heat shock genes in cultured Drosophila melanogaster cells. Topoisomerase I was found to interact with the transcriptionally active genes hsp22, hsp23, hsp26, and hsp28 after heat shock but not with the inactive genes before heat shock. The interaction occurred predominantly within the transcribed region, with specific sites occurring on both the transcribed and nontranscribed strands of the DNA. Little interaction was seen with nontranscribed flanking sequences. Camptothecin only partially inhibited transcription of the hsp28 gene during heat shock, causing a reduced level of transcripts which were nonetheless full length. Topoisomerase I also interacted with the DNA throughout the transcriptionally active hsp83 gene, including an intron, in both heat-shocked and non-heat-shocked cells. The results point to a dynamic set of interactions at the active locus.

Terminal structure of hypovirulence-associated dsRNAs in the chestnut blight fungus Endothia parasitica

The 3'- and 5'-terminal sequences of the five large double-stranded RNA species (L-dsRNA; 4.5-6.0 X 10(6) daltons) of EP713, a hypovirulent strain of Endothia parasitica, were determined by mobility-shift and enzymatic methods. All the L-dsRNAs appeared to have identical terminal sequences. A heteropolymer sequence was found at one 3'-terminus and a poly(A) sequence of variable length at the other. It was possible to label only one 5'-terminus using polynucleotide kinase and [gamma-32P]ATP, and this was shown to be a poly(U) sequence of variable length. We propose that the dsRNAs have the following structure, where X represents a blocking group: (Formula: see text). A recombinant plasmid containing dsRNA-related sequences was constructed. Hybridization analysis using the recombinant probe indicated that the sequence homology among the L-dsRNAs extended beyond these terminal regions and was also shared by small dsRNAs (0.3-0.45 X 10(6) daltons).

Nucleosomal instability and induction of new upstream protein-DNA associations accompany activation of four small heat shock protein genes in Drosophila melanogaster

We investigated in detail the structural changes that occur in nuclear chromatin upon activation of the four small heat shock protein genes in D. melanogaster. Both the chemical cleavage reagent methidiumpropyl-EDTA X iron(II) [MPE X Fe(II)] and the nuclease DNase I revealed a complex pattern of four or five hypersensitive sites upstream of each gene before activation. In addition, MPE X Fe(II) detected a short positioned array of nucleosomes located on each coding region. Upon heat shock activation a number of changes in the patterns occurred. For each gene, at least one of the upstream hypersensitive regions was eliminated or substantially shifted in position. Regions were established which became highly refractile to digestion by either MPE X Fe(II) or DNase I and, as such, appeared as small "footprints" in the pattern. The location of these refractile regions relative to the cap site varied for each gene examined. The coding regions themselves became highly accessible to DNase I. The nucleosomal arrays detected by MPE X Fe(II) were characterized by a considerable loss of detail and significantly enhanced accessibility, the extent of which probably reflected the relative transcription rate of each gene. Careful mapping of the location and extent of each upstream footprint and comparison with the DNA sequence revealed the presence at each location of two (or more) contiguous or overlapping segments that bear high homology to the heat shock consensus sequence C-T-N-G-A-A-N-N-T-T-C-N-A-G. A specific protein factor (or factors) is most likely bound at or near these sequence in heat-shocked Drosophila cells.

Ecdysteroid-regulated heat-shock gene expression during Drosophila melanogaster development

Peaks in hsp 26, 28, and 83 RNA levels are correlated with peaks in ecdysteroid titers during mid-embryogenesis, pupariation, and mid-pupation, and with a peak in the level of RNA from the 74EF ecdysone puff at pupariation. Inhibition of the ecdysteroid peak at pupariation by temperature shift of the conditionally ecdysteroid-deficient strain ecd-1 was followed by a disappearance of hsp 26 RNA and a decline in hsp 83 RNA level; subsequent addition of exogeneous 20-OH-ecdysone to the temperature-shifted strain resulted in a severalfold increase in hsp 83 RNA level, and a dramatic increase in that of hsp 26. These results are consistent with the induction of the hsp 83, 28, and 26 genes by ecdysteroid at several developmental stages.

Sequence and organization of genes encoding the human 27 kDa heat shock protein

The 27 kDa human heat shock protein (hsp27) is encoded by a gene family of 4 members. Two genomic fragments hybridizing to cDNA encoding hsp27 have been isolated, characterized, and sequenced. One clone is a member of a cluster of three genes linked within a 14-18 kb region of the genome and encodes a transcript interrupted by two intervening sequences. A single open reading frame encodes a polypeptide of 22,300 deduced molecular weight. The 5' flanking region contains two transcription start sites and sequences homologous to the Drosophila consensus heat inducible control element. Induction of both potential transcripts follows heat shock in vivo. Accurate heat inducible transcription occurs at both start sites after injection into Xenopus oocytes. The second genomic clone is a processed pseudogene lacking promoter elements and is unlinked with the other members of the hsp27 gene family. The amino acid sequence of human hsp27 shows striking homology with mammalian alpha crystallin, and contains a region towards the carboxy terminus which shares homology with the small hsp of Drosophila and other organisms.

Expression and localization of Drosophila melanogaster hsp70 cognate proteins

Monoclonal antibodies have been used to identify three proteins in Drosophila melanogaster that share antigenic determinants with the major heat shock proteins hsp70 and hsp68. While two of the proteins are major proteins at all developmental stages, one heat shock cognate protein, hsc70, is especially enriched in embryos. hsc70 is shown to be the product of a previously identified gene, Hsc4. We have examined the levels of hsp70-related proteins in adult flies and larvae during heat shock and recovery. At maximal induction in vivo, hsp70 and hsp68 never reach the basal levels of the major heat shock cognate proteins. Monoclonal antibodies to hsc70 have been used to localize it to a meshwork of cytoplasmic fibers that are heavily concentrated around the nucleus.

Nucleosomal instability and induction of new upstream protein-DNA associations accompany activation of four small heat shock protein genes in Drosophila melanogaster

We investigated in detail the structural changes that occur in nuclear chromatin upon activation of the four small heat shock protein genes in D. melanogaster. Both the chemical cleavage reagent methidiumpropyl-EDTA X iron(II) [MPE X Fe(II)] and the nuclease DNase I revealed a complex pattern of four or five hypersensitive sites upstream of each gene before activation. In addition, MPE X Fe(II) detected a short positioned array of nucleosomes located on each coding region. Upon heat shock activation a number of changes in the patterns occurred. For each gene, at least one of the upstream hypersensitive regions was eliminated or substantially shifted in position. Regions were established which became highly refractile to digestion by either MPE X Fe(II) or DNase I and, as such, appeared as small "footprints" in the pattern. The location of these refractile regions relative to the cap site varied for each gene examined. The coding regions themselves became highly accessible to DNase I. The nucleosomal arrays detected by MPE X Fe(II) were characterized by a considerable loss of detail and significantly enhanced accessibility, the extent of which probably reflected the relative transcription rate of each gene. Careful mapping of the location and extent of each upstream footprint and comparison with the DNA sequence revealed the presence at each location of two (or more) contiguous or overlapping segments that bear high homology to the heat shock consensus sequence C-T-N-G-A-A-N-N-T-T-C-N-A-G. A specific protein factor (or factors) is most likely bound at or near these sequence in heat-shocked Drosophila cells.

Developmental effects of chemicals and the heat shock response in Drosophila cells

Exposure of prokaryotic and eukaryotic cells to heat shock (hyperthermia) or to a number of diverse environmental stresses such as teratogens, anoxia, and inhibitors of oxidative phosphorylation results in the enhanced synthesis of a number of proteins which have been previously referred to as heat shock proteins (hsps). More recently, in view of the diverse types of agents that can induce these proteins, they have also been referred to as stress proteins. This phenomenon is one of the most basic regulatory mechanisms in living organisms. Exposure of Drosophila embryos, larvae, or pupae to these types of stresses also results in a variety of developmental abnormalities in the ensuing adult. Although the function(s) of these heat shock proteins has yet to be determined, they are widely thought to play an important role in cell survival and protection following some types of environmental stress. In our laboratory, we have developed an in vitro assay for detecting agents that act as teratogens, utilizing Drosophila embryonic cultures. Drosophila embryonic cells differentiate in vitro to a number of functional cell types including myotubes and ganglia. A number of drugs that have been shown to act as teratogens in mammals have also been found to inhibit muscle and/or neuron differentiation in Drosophila embryonic cultures. We have examined, by two-dimensional gel electrophoresis, the effects of such teratogens on protein synthesis in Drosophila embryonic cells. Inhibition of muscle and/or neuron differentiation correlates well with the induction of two proteins of about 20 kilodaltons. These are identical to two of the heat shock proteins (hsp 23, 22) as shown by electrophoretic mobilities and peptide mapping by partial proteolysis. Heat shock and other treatments such as exposure to some of the metal ions and ether induces the entire set of seven major heat shock proteins in the Drosophila embryonic cells. Dose-response studies of several teratogens show a correlation between the degree of inhibition of differentiation and the level of induction of hsps. Since heat shock proteins have been suggested as possibly serving a protecting role, our present studies are aimed at identifying the role of hsps in teratogenesis and investigating the differential regulation of heat shock genes in response to different external stimuli.

Hydrogen peroxide toxicity may be enhanced by heat shock gene induction in Drosophila

Recent evidence suggests that low dose exposure of cells to hydrogen peroxide and/or induction of heat shock protein (HSP) synthesis will render cells resistant to the lethal effects of a subsequent high dose hydrogen peroxide stress. We explored this possibility in the Drosophila melanogaster Schneider tissue culture line 2. It was found that chronic low dose exposure (1 mM H2O2 for 3 days) resulted in marked potentiation of the toxic effects of a subsequent high dose exposure (50 mM H2O2 for 1 h), as assessed by impairment of uridine incorporation and cell proliferation. Cells preexposed to low dose H2O2 exhibited enhanced heat shock gene transcription upon exposure to high dose H2O2, as compared to cells that did not receive low dose preexposure. Transcriptional induction of the heat shock genes by a mild non-toxic heat shock resulted in marked enhancement of the anti-proliferative effects of a subsequent H2O2 exposure. Thus, low dose hydrogen peroxide exposure or mild heating results in subsequent enhancement of high dose hydrogen peroxide toxicity; this effect correlates with enhanced heat shock gene expression. Possible mechanisms are discussed.

Transcript length heterogeneity at the small heat shock protein genes of Drosophila

Expression of the small heat shock protein (hsp) genes can be induced in cultured Drosophila cells by high temperature shock and by exposure to physiological doses of the insect molting hormone ecdysterone. Northern blot analysis was performed in order to compare the size of small hsp transcripts synthesized in response to these two stimuli. Transcripts from several other genes were also examined. Two types of length heterogeneity were observed for the small hsp gene transcripts. One involved the synthesis of what are designated as long form transcripts during heat shock; small hsp messenger RNAs extended at the 3' end by some 1.5 X 10(3) base-pairs. The second type of size heterogeneity observed is based on differences in the length of the poly(A) tail. The results of S1 nuclease protection analysis provided evidence that different initiation sites are not used for hsp 22 mRNA transcription in response to the two stimuli.

Family of developmentally regulated, maternally expressed Drosophila RNA species detected by a v-myc probe

Drosophila melanogaster genomic sequences that hybridize with v-myc have been reported (B.-Z. Shilo and R. A. Weinberg, Proc. Natl. Acad. Sci. U.S.A. 78:6789-6792, 1981). We have detected Drosophila RNA sequences that also hybridize with v-myc. In an attempt to characterize these RNA sequences, we used v-myc hybridization probes to isolate Drosophila genomic segments. None of the Drosophila genomic or cDNA clones that we have isolated hybridize with the 3' exon of v-myc. Preliminary nucleotide sequence analyses have revealed sufficient homology to account for the observed hybridization between v-myc and the Drosophila clones but have failed to detect significant amino acid sequence homology. Thus is seems unlikely that the mRNA sequences or the genomic sequences that we have isolated by hybridization with v-myc represent homologs of the vertebrate myc gene. Despite the lack of structural homology between the cloned Drosophila sequences and v-myc, we have investigated the pattern of expression of those RNA species that hybridize with v-myc. Polyadenylic acid-containing transcripts of 2.7, 2.2, and 1.7 kilobases (kb) in embryos, pupae, adults, and Kc cells and an additional 1.4-kb transcript in adults were complementary to the Drosophila genomic clones and to v-myc. The 1.7- and 2.2-kb transcripts were localized on polyribosomes in Kc cells. The 1.7- and 2.2-kb transcripts were present after 45 min, 2 h, and 4 h of embryonic development, but by 16 h of development their levels had decreased by more than sixfold. During metamorphosis, two peaks of expression of the 1.7- and 2.2-kb transcripts were observed, at 6 and 72 h postpupariation. The 1.4-kb RNA species was first detected at 72 h postpupariation. In adults, the 1.7- and 2.2-kb transcripts were detected only in ovaries in females, whereas the 1.4-kb transcript was present in female nonovarian RNA and in males. These results suggest that the transcripts in early embryos are of maternal origin.

Determinants of heat shock-induced chromosome puffing

Modified Drosophila heat shock genes were introduced into the germ line by P element transformation. The genes were altered such that several factors could be tested for their influence upon chromosome puffing. Deletion of promoter sequences upstream of position -73 of an hsp70-IacZ hybrid gene was sufficient to abolish puffing. Analysis of progressive 5' deletions defines a 16 bp interval that contains sequences required for both heat-induced puffing and gene expression. An internal deletion of the hsp70-IacZ gene that reduces the transcript size from 9 kb to 0.8 kb results in a dramatic reduction in puff size. The chromosomal insertion sites of 26 variant hsp70 or hsp26 genes fail to influence puffing greatly with one marked exception. This transformant possesses an insert that fails to puff and exhibits a tissue-restricted pattern of expression. These results indicate that variation in either promoter strength or transcript length have profound effects on puffing.

Family of developmentally regulated, maternally expressed Drosophila RNA species detected by a v-myc probe

Drosophila melanogaster genomic sequences that hybridize with v-myc have been reported (B.-Z. Shilo and R. A. Weinberg, Proc. Natl. Acad. Sci. U.S.A. 78:6789-6792, 1981). We have detected Drosophila RNA sequences that also hybridize with v-myc. In an attempt to characterize these RNA sequences, we used v-myc hybridization probes to isolate Drosophila genomic segments. None of the Drosophila genomic or cDNA clones that we have isolated hybridize with the 3' exon of v-myc. Preliminary nucleotide sequence analyses have revealed sufficient homology to account for the observed hybridization between v-myc and the Drosophila clones but have failed to detect significant amino acid sequence homology. Thus is seems unlikely that the mRNA sequences or the genomic sequences that we have isolated by hybridization with v-myc represent homologs of the vertebrate myc gene. Despite the lack of structural homology between the cloned Drosophila sequences and v-myc, we have investigated the pattern of expression of those RNA species that hybridize with v-myc. Polyadenylic acid-containing transcripts of 2.7, 2.2, and 1.7 kilobases (kb) in embryos, pupae, adults, and Kc cells and an additional 1.4-kb transcript in adults were complementary to the Drosophila genomic clones and to v-myc. The 1.7- and 2.2-kb transcripts were localized on polyribosomes in Kc cells. The 1.7- and 2.2-kb transcripts were present after 45 min, 2 h, and 4 h of embryonic development, but by 16 h of development their levels had decreased by more than sixfold. During metamorphosis, two peaks of expression of the 1.7- and 2.2-kb transcripts were observed, at 6 and 72 h postpupariation. The 1.4-kb RNA species was first detected at 72 h postpupariation. In adults, the 1.7- and 2.2-kb transcripts were detected only in ovaries in females, whereas the 1.4-kb transcript was present in female nonovarian RNA and in males. These results suggest that the transcripts in early embryos are of maternal origin.

The heat shock response

The response of cells to a heat shock or other stresses is the activation of a small number of genes which were previously inactive or transcribed at low levels. This response has been observed in a wide variety of bacterial, plant, and animal species. Evidence is accumulating that at least some of the proteins found in diverse species are similar, indicating a conservation of the response and the proteins in evolution. In a number of organisms a strong positive correlation has been found between the presence of heat shock proteins and ability of the organism to withstand thermal stress. This review attempts to assess the available data concerning the homology of proteins in different species, the localization of the proteins in cells, and the relationship between heat shock proteins and thermoresistance.

Electron microscopical analysis of Drosophila polytene chromosomes. II. Development of complex puffs

Data are presented of electron microscopic (EM) analysis of consecutive developmental stages of Drosophila melanogaster complex puffs, formed as a result of simultaneous decondensation of several bands. EM mapping principles proposed by us permitted more exact determination of the banding patterns of 19 regions in which 31 puffs develop. It is shown that 20 of them develop as a result of synchronous decondensation of two bands, 7 of three and 4 of one band. Three cases of two-band puff formation when one or both bands undergo partial decondensation are described. In the 50CF, 62CE, 63F and 71CF regions puffing zones are located closely adjacent to each other but the decondensation of separate band groups occurs at different puff stages (PS). These data are interpreted as activation of independently regulated DNA sequences. The decondensation of two or three adjacent bands during formation of the majority of the puffs occurs simultaneously in the very first stages of their development. It demonstrates synchronous activation of the material of several bands presumably affected by a common inductor. Bands adjacent to puffing centres also lose their clarity as the puff develops, probably due to "passive" decondensation connected with puff growth. The morphological data obtained suggest a complex genetic organisation of many puffs.

High-resolution mapping of DNase I-hypersensitive sites of Drosophila heat shock genes in Drosophila melanogaster and Saccharomyces cerevisiae

High-resolution analysis of the chromatin structure of the promoter regions of five Drosophila heat shock genes showed a similar location for the hypersensitive sequences relative to the start of transcription. For each of the five genes examined--those coding for hsp27, hsp26, hsp23, hsp70, and hsp83--the DNase I-hypersensitive sites in Drosophila melanogaster nuclei mapped to two regions upstream of the coding region. These sites occurred on the average, 115 and 17 base pairs upstream from the start of transcription of the five heat shock genes examined. This latter site corresponded to sequences at or near the TATA consensus sequence. Sites even further upstream of the hsp27, hsp26, and hsp83 genes were also evident. Additionally, for the two genes examined--hsp70 and hsp83--the DNase I-hypersensitive sites were preserved, at least within this level of resolution (+/- 10 base pairs), when the Drosophila genes were integrated into the Saccharomyces cerevisiae genome. This result indicates that the signals responsible for generating these hypersensitive sites are inherent in the DNA sequences and, in this case, are not highly species specific.

Drosophila cells and ecdysterone: a model system for gene regulation

When Drosophila cell lines are exposed to physiological doses of the steroid molting hormone, ecdysterone, they enter mitotic arrest and differentiate morphologically. These responses are accompanied by specific changes in gene expression. Several enzyme activities (acetylcholinesterase, beta-galactosidase, dopa decarboxylase, and catalase) are induced and the synthesis of a cytoplasmic actin and the four small heat-shock proteins is initiated. Several of these ecdysterone inducible genes have been physically isolated and characterized, in several cases by DNA sequencing. Current studies focus on introducing cloned ecdysterone inducible genes into responsive cells by DNA mediated transfection. Once it is clear that these introduced genes acquire the normal pattern of hormone-regulated gene expression in the cell, in vitro mutagenesis can be used before transfection to modify their structure. Transient expression, then, can become a functional assay to define regions of DNA flanking the coding region of inducible genes that are needed for proper gene expression and regulation in cultured cells.

Differential regulation of the 70K heat shock gene and related genes in Saccharomyces cerevisiae

Saccharomyces cerevisiae contains a family of genes related to Hsp70, the major heat shock gene of Drosophila melanogaster. The transcription of three of these genes, which show no conservation of sequences 5' to the protein-coding region, was analyzed. The 5' flanking regions from the three genes were fused to the Escherichia coli beta-galactosidase structural gene and introduced into yeasts on multicopy plasmids, putting the beta-galactosidase production under yeast promoter control. Analysis of beta-galactosidase mRNA and protein production in these transformed strains revealed that transcription from the three promoters is differentially regulated. The number of transcripts from one promoter is vastly increased for a brief period after heat shock, whereas mRNA from another declines. Transcripts from a third gene are slightly enhanced upon heat shock; however, multiple 5' ends of the mRNA are found, and a minor species increases in amount after heat shock. Transcription of these promoters in their native state on the chromosome appears to be modulated in the same manner.