Perceptions of the Agency and Responsibility of the NHS COVID-19 App on Twitter: Critical Discourse Analysis

BACKGROUND

Since September 2020, the National Health Service (NHS) COVID-19 contact-tracing app has been used to mitigate the spread of COVID-19 in the United Kingdom. Since its launch, this app has been a part of the discussion regarding the perceived social agency of decision-making algorithms. On the social media website Twitter, a plethora of views about the app have been found but only analyzed for sentiment and topic trajectories thus far, leaving the perceived social agency of the app underexplored.

OBJECTIVE

We aimed to examine the discussion of social agency in social media public discourse regarding algorithm-operated decisions, particularly when the artificial intelligence agency responsible for specific information systems is not openly disclosed in an example such as the COVID-19 contact-tracing app. To do this, we analyzed the presentation of the NHS COVID-19 App on Twitter, focusing on the portrayal of social agency and the impact of its deployment on society. We also aimed to discover what the presentation of social agents communicates about the perceived responsibility of the app.

METHODS

Using corpus linguistics and critical discourse analysis, underpinned by social actor representation, we used the link between grammatical and social agency and analyzed a corpus of 118,316 tweets from September 2020 to July 2021 to see whether the app was portrayed as a social actor.

RESULTS

We found that active presentations of the app-seen mainly through personalization and agency metaphor-dominated the discourse. The app was presented as a social actor in 96% of the cases considered and grew in proportion to passive presentations over time. These active presentations showed the app to be a social actor in 5 main ways: informing, instructing, providing permission, disrupting, and functioning. We found a small number of occasions on which the app was presented passively through backgrounding and exclusion.

CONCLUSIONS

Twitter users presented the NHS COVID-19 App as an active social actor with a clear sense of social agency. The study also revealed that Twitter users perceived the app as responsible for their welfare, particularly when it provided instructions or permission, and this perception remained consistent throughout the discourse, particularly during significant events. Overall, this study contributes to understanding how social agency is discussed in social media discourse related to algorithmic-operated decisions This research offers valuable insights into public perceptions of decision-making digital contact-tracing health care technologies and their perceptions on the web, which, even in a postpandemic world, may shed light on how the public might respond to forthcoming interventions.

The reception of public health messages during the COVID-19 pandemic

Understanding the reception of public health messages in public-facing communications is of key importance to health agencies in managing crises, pandemics, and other health threats. Established public health communications strategies including self-efficacy messaging, fear appeals, and moralising messaging were all used during the Coronavirus pandemic. We explore the reception of public health messages to understand the efficacy of these established messaging strategies in the COVID-19 context. Taking a community-focussed approach, we combine a corpus linguistic analysis with methods of wider engagement, namely, a public survey and interactions with a Public Involvement Panel to analyse this type of real-world public health discourse.

Our findings indicate that effective health messaging content provides manageable instructions, which inspire public confidence that following the guidance is worthwhile. Messaging that appeals to the audience's morals or fears in order to provide a rationale for compliance can be polarising and divisive, producing a strongly negative emotional response from the public and potentially undermining social cohesion. Provenance of the messaging alongside text-external political factors also have an influence on messaging uptake. In addition, our findings highlight key differences in messaging uptake by audience age, which demonstrates the importance of tailored communications and the need to seek public feedback to test the efficacy of messaging with the relevant demographics. Our study illustrates the value of corpus linguistics to public health agencies and health communications professionals, and we share our recommendations for improving the public health messaging both in the context of the ongoing pandemic and for future novel and re-emerging infectious disease outbreaks.

Molecular modeling approaches for determining gene function: application to a putative poly-A binding protein from Leishmania amazonensis (LaPABP)

The great expansion in the number of genome sequencing projects has revealed the importance of computational methods to speed up the characterization of unknown genes. These studies have been improved by the use of three dimensional information from the predicted proteins generated by molecular modeling techniques. In this work, we disclose the structure-function relationship of a gene product from Leishmania amazonensis by applying molecular modeling and bioinformatics techniques. The analyzed sequence encodes a 159 amino acids polypeptide (estimated 18 kDa) and was denoted LaPABP for its high homology with poly-A binding proteins from trypanosomatids. The domain structure, clustering analysis and a three dimensional model of LaPABP, basically obtained by homology modeling on the structure of the human poly-A binding protein, are described. Based on the analysis of the electrostatic potential mapped on the model's surface and conservation of intramolecular contacts responsible for folding stabilization we hypothesize that this protein may have less avidity to RNA than it's L. major counterpart but still account for a significant functional activity in the parasite. The model obtained will help in the design of mutagenesis experiments aimed to elucidate the mechanism of gene expression in trypanosomatids and serve as a starting point for its exploration as a potential source of targets for a rational chemotherapy.

Heat shock protein 90 homeostasis controls stage differentiation in Leishmania donovani

The differentiation of Leishmania parasites from the insect stage, the promastigote, toward the pathogenic mammalian stage, the amastigote, is triggered primarily by the rise in ambient temperature encountered during the insect-to-mammal transmission. We show here that inactivation of heat shock protein (Hsp) 90, with the use of the drugs geldanamycin or radicicol, mimics transmission and induces the differentiation from the promastigote to the amastigote stage. Geldanamycin also induces a growth arrest of cultured promastigotes that can be forestalled by overexpression of the cytoplasmic Hsp90. Moreover, we demonstrate that Hsp90 serves as a feedback inhibitor of the cellular heat shock response in Leishmania. Our results are consistent with Hsp90 homeostasis serving as cellular thermometer for these primitive eukaryotes, controlling both the heat shock response and morphological differentiation.

The heat shock protein 90 of Leishmania donovani

The 90-kDa heat shock protein (Hsp90) of Leishmania donovani is a highly abundant cytoplasmic protein and is involved in a variety of cellular processes. Pharmacological deactivation of Hsp90 leads to growth arrest and induces the synthesis of heat shock proteins. Moreover, treatment of promastigote parasites with Hsp90 inhibitors induces the synthesis of amastigote-specific marker proteins and a morphological alteration similar to axenic amastigote differentiation. We propose a role for Hsp90 in the feedback control of the cellular stress response and in the control of the parasite's life cycle.

Use of genetic complementation to identify gene(s) which specify species-specific organ tropism of Leishmania

We have employed a genetic complementation screening to identify genetic markers of heat stress tolerance and visceralisation of Leishmania infection. Leishmania major, which has a low thermotolerance and which causes cutaneous lesions, was transfected with a cosmid library of L. donovani DNA. The recombinant parasites were then screened either for thermotolerance or selected by repeated passage in BALB/c mice. Cosmids which conferred selective advantage were isolated. Several strategies were tested to identify the gene(s) within the cosmids responsible for the observed selective advantages. Of the approaches tested, the complete sequence analysis of the cosmids and subsequent screening of defined candidate ORFs proved to be the method of choice. Other approaches, such as creation of sub-libraries or transposon insertion strategies proved to be unsuccessful.

Heat shock protein 100 and the amastigote stage-specific A2 proteins of Leishmania donovani

HSP100 protein in Leishmania spp. plays an important role for the survival and integrity of intracellular amastigotes. The A2 proteins of L. donovani are functionally linked to HSP100. There is evidence for an interdependence between these two proteins, which are both expressed predominantly in the amastigote stage of Leishmania donovani. Mutant strains lacking either of these proteins display very similar phenotypes, i.e. loss of virulence both in vivo and in vitro. Also, both proteins colocalise specifically to small foci within the cytoplasm of amastigotes.

Expression and subcellular localization of cpn60 protein family members in Leishmania donovani

We have identified two diverged members of the cpn60 gene family in Leishmania donovani, causative agent of Indian Kala Azar. One of the genes, cpn60.1, although actively transcribed, is not expressed to detectable levels of protein in cultured L. donovani. The other gene, cpn60.2, which, compared with cpn60.1, shows a higher sequence conservation with the hsp60 genes from Trypanosoma brucei and Trypanosoma cruzi is expressed constitutively in cultured promastigotes. The abundance of the gene product, Cpn60.2, increases by 2.5-fold under heat stress and in axenic amastigotes of L. donovani. Cpn60.2 is also found enriched in mitochondrial cell fractions and localizes to the mitochondrial matrix. We conclude that Cpn60.2 is the major mitochondrial chaperonin in Leishmania.

Uniform distribution of transcription complexes over the entire Leishmania donovani clpB (hsp 100) gene locus

We have analyzed the RNA polymerase density on the Leishmania donovani clpB gene locus. Our results show an even distribution of RNA polymerase over the clpB locus indicating an undiscriminative transcription. We conclude that, unlike the hsp70 genes, the clpB gene is not transcribed individually, but rather as part of a larger, polycistronic transcription unit.

A novel role for 100 kD heat shock proteins in the parasite Leishmania donovani

Heat shock proteins of the 100 kD family have been known to confer general stress tolerance in yeast and plants. Several protozoan parasites possess genes for Hsp100 proteins. In Leishmania species the protein is expressed under heat stress and during the mammalian stage, the amastigote. We show here that replacement of the clpB gene which encodes Hsp100 does not affect thermotolerance or general viability in Leishmania donovani insect stages (promastigotes) nor in axenically cultured mammalian stages (amastigotes). However, its expression is required for normal development of the parasite inside mammalian host cells. Hsp100 appears to function as an antagonist of amastigote-to-promastigote differentiation and a promoter of full amastigote development.

Leishmania donovani heat shock protein 100. Characterization and function in amastigote stage differentiation

We report the cloning and molecular analysis of the Leishmania donovani clpB gene. The protein-coding region is highly conserved compared with its L. major homologue, while 5'- and 3'-flanking DNA sequences display considerable divergence. The encoded mRNA has an unusually long 5'-leader sequence typical for RNAs, which are translated preferentially under heat stress. The gene product, a 100-kDa heat shock protein, Hsp100, becomes abundant only during sustained heat stress, but not under common chemical stresses. Hsp100 associates into trimeric complexes and is found mostly in a cytoplasmic, possibly membrane-associated, localization as determined by immune electron microscopy. Hsp100 shows immediate early expression kinetics during axenic amastigote development. In its absence, expression of at least one amastigote stage-specific protein family is impaired.

Leishmania major Hsp100 is required chiefly in the mammalian stage of the parasite

In Leishmania major a 100-kDa heat shock protein, Hsp100, is abundant in the intracellular amastigote stage which persists in the mammalian host. A replacement of both clpB alleles which encode Hsp100 does not affect promastigote viability under standard culture conditions but impairs thermotolerance in vitro. In experimental infections of BALB/c inbred mice, the lack of Hsp100 in the gene replacement mutants results in a markedly delayed lesion development compared with that in infections with wild-type L. major. Overexpression of exogenous clpB gene copies can partly restore virulence to the gene replacement mutants. Genetic-selection experiments also reveal a strong pressure for Hsp100 expression in the mammalian stage. This requirement for Hsp100 was also observed in in vitro infection experiments with mouse peritoneal macrophages. These experiments indicated a role for Hsp100 during the development from the promastigote to the amastigote stage. Our results suggest an important role for this parasite heat shock protein during the initial stages of a mammalian infection.

Autocrine regulation of apoptosis and bcl-2 expression by nerve growth factor in early differentiating cerebellar granule neurons involves low affinity neurotrophin receptor

Cerebellar granule neurons produce homogenous cultures that provide a unique opportunity for quantifying the apoptosis by propidium iodide- and deoxynucleotidyl transferase-flow cytometry combined analysis and for studying its regulation by neurotrophins. Nerve growth factor (NGF) was found to promote postmitotic survival by preventing apoptosis of newly formed and early differentiated granule neurons. This regulation could be through protein bcl-2, which was underexpressed in apoptotic granule neurons and up-regulated by NGF in a dose-dependent manner. Antibodies against low affinity NGF receptors (p75NTR) mimicked the effects of NGF, suggesting that this receptor, which is transiently expressed at high levels in postmitotic granule neurons, is involved in apoptosis signaling. Since these neurons constitutively produce NGF, this is the first demonstration of an autocrine regulation of apoptosis in the CNS. Preliminary results strongly suggest that neurotrophin-3 (NT-3) and brain derived neurotrophic factor (BDNF) are also involved in the regulation of cell death, by first promoting necrosis and then protecting the remaining cells from apoptosis. In contrast, NGF may protect against two forms of cell death and act preferentially at early stages of granule neuron development. The possibility that these neurotrophins may act in parallel and/or in sequence to regulate survival of developing granule neurons through different mechanisms is discussed in the light of findings on neurotrophin and p75NTR patterns, and p75NTR/high affinity Trk receptor coexpression.

Transcription of the Leishmania major Hsp70-I gene locus does not proceed through the noncoding region

Primary transcripts in kinetoplastid protozoa are generally assumed to be multicistronic. We have analyzed the transcription in the gene locus which encodes the 70-kDa heat shock protein by using nuclear run-on analysis. We find that RNA synthesis in the Hsp70-I gene locus either is terminated or pauses within the intergenic region approximately 250 nt downstream of the polyadenylation site. We therefore propose a discontinuous mode of transcription in the Hsp70 genes of Leishmania major.

Two peptides derived from the nerve growth factor precursor enhance cholinergic enzyme activities in vivo

LIP1, a 29-amino acid (aa) peptide, and LIP2, a 38aa peptide, corresponding to sequences within the nerve growth factor (NGF) precursor that are flanked by basic amino acid processing sites, were shown to be present in the rat intestine and to induce in PC12 cells several early cellular events, such as F-actin rearrangement and tyrosine phosphorylation of the Trk protein. In this report, we provide evidence that the two propeptides can affect cholinergic enzyme activities in vivo. Intracerebroventricular injections of LIP1 or LIP2 in neonatal hypothyroid rats significantly increased choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in forebrain regions with an apparent regional specificity. Moreover, antibodies against LIP1 or LIP2 injected intracerebroventricularly in neonatal rats significantly decreased ChAT and AChE in the same regions of the brain. These data suggest a physiological role for the two propeptides derived from the proNGF in the development of forebrain cholinergic neurons.

cdk5 expression and association with p35nck5a in early stages of rat cerebellum neurogenesis; tyrosine dephosphorylation and activation in post-mitotic neurons

We have examined the expression of cyclin dependent kinase (cdk) 5 protein kinase and p35nck5a, its activator subunit, during postnatal neurogenesis in rat cerebellum, using mono-specific antibodies. Both cdk5 and p35nck5a are present and associated in proliferative stages, although cdk5-p35 kinase activity is barely detectable. Cdk5-p35 activity, but not the expression of either subunit, increases up to 6-fold during neuronal differentiation. Since we observe that cdk5 is phosphorylated on tyrosine in proliferative, but not in post-mitotic stages, we suggest that post-translational regulatory mechanisms control cdk5-p35 protein kinase activity during neurogenesis.

Thyroid hormone promotes BCL-2 expression and prevents apoptosis of early differentiating cerebellar granule neurons

Programmed cell death is a basic cellular process that has aroused much interest in recent years. Like immune cells, cultures of cerebellar granule neurons are very homogeneous and provide a unique opportunity for quantifying by flow cytometry one form of programmed cell death in the CNS, the apoptosis, and for studying its regulation by neurotrophic factors. We found that thyroid hormone promoted postmitotic survival by preventing the apoptosis of newly formed and early differentiated granule neurons in a dose-dependent manner. This regulation could be through the protein bcl-2, which is known to prevent cell death. This protein was present at all stages of granule neuron differentiation and appeared to be developmentally regulated. It was underexpressed in apoptotic granule neurons. The protein content of the cerebellum in hypothyroid rats was drastically reduced. In contrast, thyroid hormone caused a marked dose-dependent increase in the amounts of this protein in granule neuron cultures. The possibility that thyroid hormone may be directly or indirectly required to promote cell survival is discussed, in terms of the hormone control of the local delivery of neurotrophins, such as NGF and NT-3, as well as the expression of their low affinity receptors, gp75. We suggest that thyroid hormone has a permissive action on the developing CNS.

Differences in DNA sequence recognition by the heat-shock factors of Drosophila melanogaster and the parasitic helminth Schistosoma mansoni

It was recently shown that schistosome extracts contain heat-shock factor (HSF) activity that correlates with the pattern of hsp70 mRNA levels at different developmental stages of the parasite (Levy-Holtzman and Schechter (1994) Parasitology 108, 35-42). To extend our understanding of the HSF activity revealed in extracts of Schistosoma mansoni (Sm), it was further analyzed by competition experiments and compared with the well characterized HSF of Drosophila melanogaster (Dm). The interactions of HSF in Sm extracts (SmHSF) and HSF of Dm (DmHSF) with 32P-labeled heat shock element (HSE) probes, with and without unlabeled competitor DNA probes (HSE-related oligos), were analyzed by gel retardation assay. The binding and inhibition studies demonstrated that SmHSF and DmHSF differ in HSE sequence recognition: an array of three nGAAn inverted repeats according to the ideal consensus sequence (nGAAnnTTCnnGAAn) is recognized by DmHSF, but not by SmHSF. In the schistosome, binding is attained only when the third pentamer is a variant, composed of nGTAn instead of nGAAn. The presence of this variant in the promoter of the hsp70 gene of the parasite suggests coevolution of the variant sequence together with the SmHSF which interacts efficiently with the variant, but not with the ideal HSE sequence. Further inhibition studies revealed additional differences between SmHSF and DmHSF in recognition of the first and second nGAAn pentamers of HSE. In analogy to other systems of ligand-protein interactions, we propose that the complementarity between the HSE ligand and the HSF protein is higher in SmHSF, as compared to DmHSF.

High constitutive levels of heat-shock proteins in human-pathogenic parasites of the genus Leishmania

We have analysed the transcription of three heat-shock genes, HSP70, HSP83 and ClpB, in the protozoan parasite Leishmania. All three heat-shock genes are transcribed constitutively and not heat-inducibly. However, we find that two major heat-shock proteins, HSP70 and HSP83, are synthesized at elevated rates during heat stress. We conclude that the cellular stress response in Leishmaniae is regulated exclusively on a post-transcriptional level much in contrast with all other eukaryotes examined so far. The induced synthesis of HSP70 and HSP83, however, does not increase the steady-state level of either protein significantly. This is compensated by high constitutive levels of both proteins: HSP70 and HSP83 make up 2.1% and 2.8%, respectively, of the total protein in unstressed Leishmania promastigotes. Also, HSP70 is a strictly cytoplasmic protein in Leishmania and does not relocate into the nucleus during heat stress, as it does in other eukaryotes examined in the past.

A member of the ClpB family of stress proteins is expressed during heat shock in Leishmania spp

We have identified and isolated the Leishmania major homologue to the bacterial ClpB gene and to the yeast Hsp104 gene. ClpB in Leishmania major is a single-copy gene and encodes a low-abundance mRNA which is induced several-fold during a heat stress. We raised antibodies against the product of the recombinant gene and show that the leishmanial ClpB encodes a predominantly cytoplasmic protein of approx. 100 kDa which is detectable in Leishmania promastigotes of various species after exposure to elevated temperatures. We, therefore, term this protein Hsp100.

Autocrine regulation of proliferation of cerebellar granule neurons by nerve growth factor

Premigratory cerebellar granule neurons, which highly express nerve growth factor (NGF), low (gp75NGFR) and high (gp140trkA) affinity NGF receptors, were used as a physiological model to investigate the effects of NGF on neuronal replication. Studies in vivo and on cultures showed that NGF stimulates DNA synthesis, mitotic activity and related cell acquisition by initiating the entry of cells into the S phase and regulating their time in the G1 and S phases. The NGF-induced effects were blocked in vivo and in vitro by both monoclonal anti-blocked in vivo and in vitro by both monoclonal anti-NGF and anti-gp75NGFR antibodies. These results clearly demonstrate that NGF is essential for the crucial first step of cerebellar ontogenesis and support the idea that low affinity receptors are involved in the biological response, possibly by interacting with gp140trkA. By comparison with a number of well known mitogens, the high affinity form could be the main transducer of the mitogenic signal pathway. The early developing cerebellum appears therefore to be the first autocrine (and/or paracrine) model of NGF action on neurogenesis in the CNS.

pJC20 and pJC40--two high-copy-number vectors for T7 RNA polymerase-dependent expression of recombinant genes in Escherichia coli

We report the construction of two plasmid vectors, pJC20 and pJC40, for the expression of recombinant genes in Escherichia coli under the control of T7 RNA polymerase. Their small sizes of ca. 2.4 kb ease the subcloning of large inserts and the high copy numbers obtained result in satisfactory yields in all plasmid preparations. A multiple-cloning site offers sites for directional cloning and nested deletions. In addition, pJC40 encodes a cleavable amino-terminal histidine tail of 10 residues which is added to the gene product, thus allowing purification by metal chelate chromatography. Observed expression yields are in the range of 10% of total bacterial protein for all genes tested in our laboratory.

Induction temperature of human heat shock factor is reprogrammed in a Drosophila cell environment

Heat shock factor (HSF), the transcriptional activator of eukaryotic heat shock genes, is induced to bind DNA by a monomer to trimer transition involving leucine zipper interactions. Although this mode of regulation is shared among many eukaryotic species, there is variation in the temperature at which HSF binding activity is induced. We investigated the basis of this variation by analysing the response of a human HSF expressed in Drosophila cells and Drosophila HSF expressed in human cells. We report here that the temperature that induces DNA binding and trimerization of human HSF in Drosophila was decreased by approximately 10 degrees C to the induction temperature for the host cell, whereas Drosophila HSF expressed in human cells was constitutively active. The results indicate that the activity of HSF in vivo is not a simple function of the absolute environmental temperature.

Regulation of heat shock factor trimer formation: role of a conserved leucine zipper

The human and Drosophila heat shock transcription factors (HSFs) are multi-zipper proteins with high-affinity binding to DNA that is regulated by heat shock-induced trimerization. Formation of HSF trimers is dependent on hydrophobic heptad repeats located in the amino-terminal region of the protein. Two subregions at the carboxyl-terminal end of human HSF1 were identified that maintain the monomeric form of the protein under normal conditions. One of these contains a leucine zipper motif that is conserved between vertebrate and insect HSFs. These results suggest that the carboxyl-terminal zipper may suppress formation of trimers by the amino-terminal HSF zipper elements by means of intramolecular coiled-coil interactions that are sensitive to heat shock.

Thyroid hormone promotes transient nerve growth factor synthesis in rat cerebellar neuroblasts

Primary cultures of cerebellum from 5-day-old rats indicated that proliferating neuroblasts synthesize and release nerve growth factor (NGF). Since NGF promotes DNA synthesis in these cells, our findings demonstrate that the early developing cerebellum is a suitable physiological model for studying the autocrine mitogenic action of NGF. Thyroid deficiency led to a greater reduction in the NGF content of the cerebellum than of the olfactory bulbs or hippocampus. Cerebellar NGF mRNA was also very sensitive to hormone deprivation. Physiological amounts of thyroid hormone stimulated both the mitotic activity and NGF production of cultured cerebellar neuroblasts. A lack of thyroid hormone is known to markedly alter cell formation in the cerebellum where postnatal neurogenesis is highly significant, in contrast to the olfactory bulbs and hippocampus. Taken together, these results suggest that the hormonal control of cell formation in the cerebellum is, at least partly, mediated by the autocrine mitogenic action of NGF. The thyroid hormone could temporally regulate the transient NGF synthesis by cerebellar neuroblasts directly and/or through its ontogenetic action, and hence all the NGF-dependent trophic effects.

Stress-induced oligomerization and chromosomal relocalization of heat-shock factor

The induction of heat-shock transcription factor (HSF) binding to DNA is accomplished by a heat-induced oligomerization. The transition to the induced state is accompanied by a chromosomal redistribution of HSF to the heat-shock puff sites. Over 150 additional chromosomal sites also accumulate HSF, including developmental loci that are repressed during heat shock. These findings suggest an unforeseen role for HSF as a repressor of normal gene activity during heat stress.

Nerve growth factor enhances DNA synthesis in cultured cerebellar neuroblasts

The cerebellar neuroblasts in primary cultures from five-day-old rats bore NGF receptor immunoreactivity, suggesting a potential responsive to NGF. At low plating density, NGF was found to enhance DNA synthesis in these cells in a dose-dependent manner. As these cells synthesize NGF, one possibility to account for the lack of response of neuroblasts plated at high density is that the amount of endogenous trophic agent produced in this culture condition is sufficient to ensure an optimal effect. The results demonstrate that premitotic neuroblasts in the CNS, as well postmitotic neurons, are responsive to NGF. At the early stage of its development, the cerebellum therefore appears to be a very good autocrine model of NGF action.

Molecular cloning and expression of a human heat shock factor, HSF1

Human cells respond to heat stress by inducing the binding of a preexisting transcriptional activator (heat shock factor, HSF) to DNA. We have isolated recombinant DNA clones for a human HSF (HSF1) by screening cDNA libraries with a human cDNA fragment. The human HSF1 probe was produced by the PCR with primers deduced from conserved amino acids in the Drosophila and yeast HSF sequences. The human HSF1 mRNA is constitutively expressed in HeLa cells under nonshock conditions and encodes a protein with four conserved leucine zipper motifs. Like its counterpart in Drosophila, human HSF1 produced in Escherichia coli in the absence of heat shock is active as a DNA binding transcription factor, suggesting that the intrinsic activity of HSF is under negative control in human cells. Surprisingly, an independently isolated human HSF clone, HSF2, is related to but significantly different from HSF1 [Schuetz, T. J., Gallo, G. J., Sheldon, L., Tempst, P. & Kingston, R. E. (1991) Proc. Natl. Acad. Sci. USA 88, 6911-6915].

FTZ-F1, a steroid hormone receptor-like protein implicated in the activation of fushi tarazu

The Drosophila homeobox segmentation gene fushi tarazu (ftz) is expressed in a seven-stripe pattern during early embryogenesis. This characteristic pattern is largely specified by the zebra element located immediately upstream of the ftz transcriptional start site. The FTZ-F1 protein, one of multiple DNA binding factors that interacts with the zebra element, is implicated in the activation of ftz transcription, especially in stripes 1, 2, 3, and 6. An FTZ-F1 complementary DNA has been cloned by recognition site screening of a Drosophila expression library. The identity of the FTZ-F1 complementary DNA clone was confirmed by immunological cross-reaction with antibodies to FTZ-F1 and by sequence analysis of peptides from purified FTZ-F1 protein. The predicted amino acid sequence of FTZ-F1 revealed that the protein is a member of the nuclear hormone receptor superfamily. This finding raises the possibility that a hormonal ligand affects the expression of a homeobox segmentation gene early in embryonic development.

Biochemical, immunocytochemical and morphological evidence for an interaction between thyroid hormone and nerve growth factor in the developing cerebellum of normal and hypothyroid rats

The effects of treatment with L-thyroxine (T4), 2.5 S nerve growth factor (NGF), monoclonal anti-NGF and monoclonal anti-NGF receptor antibodies, separately or together, on the two main processes of cerebellar histogenesis, the disappearance of the external granular layer (egl) and Purkinje cell (PC) morphogenesis, were studied in 10-day-old (1 day after the last injection) and 15-day-old normal and hypothyroid rats. The results provide the following information. (1) Anti-NGF antibodies given to normal rats alter more markedly the growth of PC soma and dendrite than the developmental pattern of egl. In contrast, anti-NGF receptor antibodies mainly delay the disappearance of egl, with minor changes in PC morphogenesis. This is the first evidence for a physiological role of NGF in neuronal maturation in both pre- and postmigratory phases. (2) The delays in the disappearance of egl and hypotrophy of PC due to hypothyroidism are greater than those induced in normal rats by anti-NGF antibodies, and T4 therapy in hypothyroid rats is more effective than that with NGF. The effects of combined T4/NGF treatment on PC size (including soma and dendrite) were approximately the sum of individual effects, with no apparent positive cooperation. Moreover, the effects of NGF treatment, but not those of T4, disappear over the long term. (3) Thyroid deficiency strongly reduces NGF receptor immunoreactivity. Anti-NGF antibodies given to thyroid-deficient rats partly counteract T4 therapy on the cerebellar growth and cortex layering, whereas they potentiate the action of the T4 on the growth of PC nuclei. The PC somas of thyroid-deficient rats assume a normal shape only after T4/NGF treatment. The perisomatic processes of immature PC in thyroid-deficient rats disappear after T4 therapy whereas they grow after NGF treatment. These results strongly suggest that NGF is complementary to thyroid hormone, and that the T4 action is partly mediated and regulated by NGF. Finally, thyroid hormone appears to have a long-term permissive role, while NGF may be a local and short-term limiting neurotrophic factor. Such a balance is essential for ensuring a normal time course of cerebellar histogenesis.

Molecular cloning and expression of a hexameric Drosophila heat shock factor subject to negative regulation

We report the cloning of the transcriptional activator of heat shock genes, HSF, from Drosophila. The predicted sequence of Drosophila HSF protein is surprisingly divergent from that of yeast HSF, except in regions important for DNA binding and oligomerization. A segment of the DNA binding domain of HSF bears an intriguing similarity to the putative DNA recognition helix of bacterial sigma factors, while the oligomerization domain contains an unusual arrangement of conserved hydrophobic heptad repeats. Drosophila HSF produced in E. coli under nonshock conditions forms a hexamer that binds specifically to DNA with high affinity and activates transcription from a heat shock promoter in vitro. In contrast, when HSF is expressed in Xenopus oocytes, maximal DNA binding affinity is observed only after heat shock induction. These results suggest that Drosophila HSF has an intrinsic affinity for DNA, which is repressed under nonshock conditions in vivo.

Isolation and functional characterization of TIF-IB, a factor that confers promoter specificity to mouse RNA polymerase I

The murine ribosomal gene promoter contains two cis-acting control elements which operate in concert to promote efficient and accurate transcription initiation by RNA polymerase I. The start site proximal core element which is indispensable for promoter recognition by RNA polymerase I (pol I) encompasses sequences from position -39 to -1. An upstream control element (UCE) which is located between nucleotides -142 and -112 stimulates the efficiency of transcription initiation both in vivo and in vitro. Here we report the isolation and functional characterization of a specific rDNA binding protein, the transcription initiation factor TIF-IB, which specifically interacts with the core region of the mouse ribosomal RNA gene promoter. Highly purified TIF-IB complements transcriptional activity in the presence of two other essential initiation factors TIF-IA and TIF-IC. We demonstrate that the binding efficiency of purified TIF-IB to the core promoter is strongly enhanced by the presence in cis of the UCE. This positive effect of upstream sequences on TIF-IB binding is observed throughout the purification procedure suggesting that the synergistic action of the two distant promoter elements is not mediated by a protein different from TIF-IB. Increasing the distance between both control elements still facilitates stable factor binding but eliminates transcriptional activation. The results demonstrate that TIF-IB binding to the rDNA promoter is an essential early step in the assembly of a functional transcription initiation complex. The subsequent interaction of TIF-IB with other auxiliary transcription initiation factors, however, requires the correct spacing between the UCE and the core promoter element.

An interaction between thyroid hormone and nerve growth factor promotes the development of hippocampus, olfactory bulbs and cerebellum: a comparative biochemical study of normal and hypothyroid rats

The effects of treatment with L-thyroxine (T4;20 ng/g body weight, given subcutaneously on days 1, 3, 5, 7 and 9), 2.5 S nerve growth factor (NGF; 2 ng/mg brain weight, given intracerebroventricularly on days 1, 3, 5, 7 and 9), monoclonal anti-NGF (2 ng/mg wet weight, given intracerebroventricularly on days 1, 3, 5, 7 and 9), and monoclonal anti-NGF receptor (192 IgG; 2 ng/mg wet weight, injected daily from day 1 to day 9) antibodies, separately or together, were studied on the biochemical development of hippocampal formation, olfactory bulbs and cerebellum in 10-day-old and 15-day-old normal and hypothyroid rats. The results provide the following information: (1) CNS structures other than the basal forebrain are sensitive to NGF during early development. (2) Both normal and hypothyroid rats are more sensitive to NGF deprivation than NGF supplementation. (3) The effects of anti-NGF antibodies in normal rats are similar to those induced by anti-NGFr antibodies. (4) NGF alone had little or no effect, but interacts with T4 in promoting cell maturation, especially in hypothyroid rats. (5) Hypothyroid rats are more sensitive to T4 and to T4 plus NGF than are normal ones. (6) The synergistic action of both trophic factors, but not that of T4, tend to disappear at long term in hypothyroid rats. (7) The differential sensitivity of the brain areas to T4, NGF, or both trophic factors correlates with their cell acquisition rate, especially in hypothyroid rats. (8) T4 and NGF together act more markedly (but not exclusively) on the cholinergic structures in both normal and hypothyroid rats. (9) RNA appears to be very sensitive to NGF, especially in hypothyroid rats. In close correlation with preliminary morphological observations, the results clearly demonstrate that an interaction between T4 and NGF regulates the ontogeny of a number of neuronal structures in CNS independently of their neurotransmitter phenotype, but with a regional specificity. The possibilities of accounting for this interaction, in particular the major role of thyroxine, are discussed.

A thyroid hormone-vasopressin interaction promotes survival and maturation of hippocampal neurons dissociated postnatally

Hippocampal cells dissociated from 5-day-old rat pups were grown in a suitable chemically defined basal medium, supplemented or not with 3,3',5-triiodo-L-thyronine (T3), [Arg8]-vasopressin (AVP), or both, at different concentrations. Four days after plating, neuron-like cells began to degenerate drastically in the basal medium. Although AVP alone had no effect, T3, and to a greater extent T3 and AVP together, prevented their death. Moreover, T3 and AVP also acted synergically in promoting the maturation of surviving cells, especially AchE-positive neurons, either directly or through glial cells.

Glycogenolytic responsiveness to glucagon, epinephrine, vasopressin and angiotensin II in the liver of developing hypothyroid rats. A comparative study of in vitro hormonal binding and in vivo biological response

Both dose-response curves and time-courses of plasma glucose levels after single maximal doses showed that in vivo glycogenolytic responsiveness to glucagon and epinephrine was significantly higher in developing hypothyroid rats, whereas it remained unchanged after vasopressin and angiotensin II injections. In contrast with the decreased basal activity of phosphorylase(a), the glucagon-stimulated activity increased in hypothyroid rats, whereas it was only slightly modified under vasopressin stimulation. Daily thyroxine treatment abolished these abnormalities. Thus, there is a close correlation between glucose output and enzyme activation. The maximal binding capacity of [3H]vasopressin and [125I]glucagon was significantly decreased in hypothyroid rats, without changes in the apparent dissociation constant of hormone from its specific receptor. Daily thyroxine treatment also abolished this deficit, which moreover appeared to be independent of possible changes in plasma hormone levels. With respect to glucagon action, neither basal nor Gpp(NH)p-stimulated adenylate cyclase activities were affected in hypothyroid rats. Glucagon-sensitive adenylate cyclase activity and the apparent activation constant appeared to be unaffected. The apparent discrepancy between the results obtained from in vivo and in vitro experiments is discussed on the basis of different membrane transducing phenomena and related intracellular mechanisms underlying the biological response to hormonal stimulation.

Developing rat cerebellum--II. Effects of abnormal thyroid states and undernutrition on hyaluronic acid

The early postnatal pattern of hyaluronic acid (HA) deposition in rat cerebellum is affected by thyroid deficiency, thyroxine treatment and undernutrition. The modification of HA ontogenesis apparently reflects the smaller number of cells formed in undernourished rats, or alterations of cell maturation (accelerated in thyroxine-treated and slowed down in thyroid-deficient rats). The developmentally regulated loss of tissue water is also affected in the three conditions; this can be correlated with the roughly simultaneous disappearance of extracellular, but not of total, HA.

Effects of hypothyroidism on high-affinity vasopressin binding sites in developing hippocampal synaptosomes

Binding sites of vasopressin (VP) have been characterized in the hippocampal synaptic plasma membranes of developing normal and hypothyroid rats using a highly specific tritiated VP antagonist, d(CH2)5Tyr(Me)VP (V1 type). This antagonist bound to an apparently homogeneous population of specific sites with an affinity ten times higher than that of VP itself. The total amount of synaptosomal protein in 15-day-old normal rats represented about 50% of the adult value, but the density of binding sites was already maximal and remained constant thereafter, supporting the concept of an early development of an extrahypophyseal vasopressinergic hippocampal system. Thyroid deficiency specifically reduced the amount of synaptosomal protein. However, the binding site density in the synaptsomal fraction appeared to be relatively well preserved from hypothyroidism, although there was a transient decrease in the apparent affinity of the ligand. These data suggest that thyroid hormones are slightly involved in the early development of high-affinity VP receptors.

The cholinergic system in developing cerebellum: comparative study of normal, hypothyroid and underfed rats

To overcome the deficiencies of previous findings, the activities of choline acetyltransferase (ChAT) and acetylcholinesterase (AchE) were studied at very short age intervals to allow a more precise definition of the shape and timing of their developmental curves in normal, hypothyroid and underfed rats. In addition, AchE expression in developing cerebellum was studied histochemically in these three neurological models. When compared with structural findings in the literature, the results provide the following information on the normal and abnormal developing cholinergic system, related or not to cerebellar neurotransmission (1) AchE activity, unlike ChAT, can be considered as a good marker of the developing cholinergic archicerebellum. (2) ChAT and AchE are transiently expressed together in functionally noncholinergic Purkinje cells. In contrast with most regions of the central nervous system, the high ratio of ChAT to AchE activities in the early stage of cerebellar development suggests an enhanced synthesis of acetylcholine (Ach). The level of ChAT activity correlates with Purkinje cell size, supporting the concept of a neurotrophic role of Ach in early maturing macroneurons. (3) The archicerebellar cholinergic network appears to be relatively well preserved from undernutrition and, to an even greater extent, from hypothyroidism, compared to other systems of neurotransmission formed later and more widely distributed throughout the cerebellum. The presynaptic compartment seems to be more affected than the postsynaptic compartment. (4) In disagreement with some data in the literature, the abnormalities induced by both abnormal thyroidal and nutritional states were found to be irreversible.

Developing rat cerebellum--III. Effects of abnormal thyroid states and undernutrition on gangliosides

Alteration of rat postnatal cerebellar development produced by undernutrition, thyroxine treatment and thyroid deficiency also involves ganglioside deposition. The distribution of the different ganglioside types is apparently unaffected but quantitative alterations are present that reflect the reduction of cell number and cell process surface in the adult, and either acceleration or slowing down or reduction of cell formation and maturation occurring during cerebellar development in the three experimental situations.

Developing rat cerebellum--I. Effects of abnormal thyroid states and undernutrition on sulfated glycosaminoglycans

Sulfated glycosaminoglycans deposition during rat postnatal cerebellar developmental is affected by altered thyroid states and undernutrition. These ontogenetic alterations seem not to be specific but to be one aspect of the general acceleration, slowing down and reduction of the cerebellar development occurring in thyroid-deficient, hyperthyroid and undernourished rats, respectively.

The time course of hippocampal cholinergic innervation in the developing hypothyroid rat. A combined histochemical and biochemical study of acetylcholinesterase activity

Development of cholinergic innervation in the hippocampal formation of normal and hypothyroid rats was studied by a combined biochemical and histochemical analysis of acetylcholinesterase (AChE) activity in normal and hypothyroid rats. The normal developmental pattern of cholinergic activity suggests an entrance of septal cholinergic fibers from the fimbria to different zones of the hippocampal formation mainly during the first postnatal week. By 10 days of age, the regional distribution of staining was similar to that in the adult. Thereafter, the intensity of staining increased without major changes in the laminar organization. As shown by closely related histochemical and biochemical findings, hypothyroidism led to a delay in the arrival of cholinergic afferences and a possible subsequent cholinergic hyperinnervation of the hippocampal formation in adulthood. These results are discussed taking into account the time course of structural development in the two synaptic compartments, namely the extrinsic septal neurons and intrinsic pyramidal and granule cells, in comparison with the development of thyroid function.

Comparative study of collecting tubules and vasopressin binding capacity in the renal medulla of developing hypothyroid rat

The effects of congenital hypothyroidism on both the structure and function of the renal medulla were studied by comparing, in 1-month old rats, the structural features of collecting tubules with the capacity of vasopressin to bind membrane preparations and the related adenylate cyclase activation. With the exception of a reduced caliber, hypothyroidism had no effect on the density, total number, distribution of tubules according to epithelial thickness, or on the number of epithelial cells, or their area. The binding capacity of vasopressin and the related adenylate cyclase activation were equally reduced by about 50%, without changes in (i) the basal or guanylyl-imidodiphosphate (Gpp(NH)p)-stimulated adenylate cyclase activities, (ii) the apparent dissociation constant (KD) of labelled vasopressin from its specific receptor or (iii) the apparent activation constant (Kact) of vasopressin for adenylate cyclase. Taken together, these results clearly demonstrate that congenital hypothyroidism exerts a direct influence on the developing responsiveness of the renal medulla, mainly by reducing the density of active hormone receptors per cell, instead of reducing cell number or cell membrane area.

Studies on the 240-kDa Con A-binding glycoprotein of rat cerebellum, a putative marker of synaptic junctions

A Con A-binding glycoprotein of Mr 240,000 was isolated from the remaining residue of rat cerebella after sequential extraction with buffers supplemented with or without neutral detergents. It was further purified by affinity chromatography on Con A-Sepharose in the presence of sodium dodecyl sulfate and preparative gel electrophoresis. This glycoprotein partially resists Triton X-100 extraction and is soluble in N-lauryl sarcosinate. The 240-kDa glycoprotein was not detected in kidney, liver, heart, forebrain and was specifically seen in cerebellar homogenate. The isolated glycoprotein appears to be similar, not necessarily identical with the GPA--a synaptic junction 240-kDa Con A-binding glycoprotein isolated from cerebellum earlier (Groswald and Kelly, J. Neurochem., 42 (1984) 534-546). Monospecific antibodies obtained against the purified 240-kDa protein were used for developmental study in normal and hypothyroid rats. There was observed an increase in the amount of 240-kDa glycoprotein, dependent on the age of the rat and this rise was in correlation with the synapse formation in rat cerebellum. The amount of 240-kDa glycoprotein is considerably reduced in hypothyroid rats.

A comparative study of plasma vasopressin levels and V1 and V2 vasopressin receptor properties in congenital hypothyroid rat under thyroxine or vasopressin therapy

The effects of propylthiouracil (PTU) treatment on the plasma vasopressin level, on the number of hepatic (V1) or renal (V2) vasopressin receptors and on the hormone-sensitive adenylate cyclase activity in the kidney of developing rats were studied in parallel. In addition, we investigated the corrective effects of thyroxine therapy on the plasma vasopressin level and parameters related to the liver, and the effects of vasopressin therapy on the parameters related to the kidney. As already reported in the case of the number of V2 receptors and adenylate cyclase activity in the kidney, the deficient plasma vasopressin level in hypothyroid rats was completely corrected by two daily physiological doses of thyroxine given from birth to the age of sacrifice (1 month). Unlike the V1 receptors, the V2 receptors are known to be highly dependent on their specific circulating ligand. Since, first of all, the deficit was similar in the numbers of V1 and V2 receptors in hypothyroid rats, and, secondly, the treatment of hypothyroid rats by two daily physiological doses of long lasting vasopressin was found ineffective to recover the deficit in the number of V2 receptors, it can be concluded that thyroid deficiency directly alters vasopressin receptor biosynthesis in both liver and kidney, instead of acting via the depressed plasma vasopressin level.