Heat shock regulatory elements are present in telomeric repeats of Chironomus thummi

Clinical and laboratory results in vaginal wall restoration using a fractional-pixel-CO2 laser: histological findings and changes in the Ki67 protein and telomere length

Thermal deposition of laser energy in the vaginal epithelium in genitourinary syndrome of menopause (GSM) results in clinical and biological effects, but many cellular and molecular changes indicating cell proliferation or senescence inhibition are unknown. The aim of this study is to evaluate the clinical efficacy of the fractional-pixel-CO2 laser in the possible improvement of GMS signs and symptoms that can be correlated with histological changes or with cellular or molecular indicators of restoration. A detailed prospective study was designed to assess 17 women diagnosed with GSM who were treated intravaginally with two laser sessions. Seven non-treated women diagnosed with GSM were used as controls. Three validated outcome questionnaires for assessment of quality of sexual life and urinary incontinence were performed. Vaginal biopsies were collected before the first laser treatment and 4 months following the second session. Histological status, elastin, collagen, and hyaluronic acid content of the biopsies were also evaluated. Cell proliferation was assessed by Ki67 staining. Telomere length (TL) was measured by qPCR. The results show an improvement of the clinical symptoms of GSM (p < 0.05), vaginal epithelium recovery and enhancement of collagen (p < 0.05), elastic fibers (p < 0.005), and hyaluronic acid (p < 0.0005) content in the lamina propria after fractional-pixel-CO2 laser treatment. The laser treatment induced a significant rise on the TL of vaginal epithelial cells (VECs), and a positive correlation was found between the improvements of the collagen and hyaluronic acid content and TL changes (r = 0.82, p < 0.05; r = 0.38, p < 0.05). The percentage of proliferative Ki67-positive VECs was increased in patients whose vaginal TL lengthened after laser treatment (p < 0.05). In conclusion, the results indicate that laser treatment may induce restoration of the vaginal epithelium which is associated to increased TL and proliferation in the VECs. Performing a TL assay could be a suitable tool to evaluate the efficacy of vaginal laser treatment.

CriTER-A: A Novel Temperature-Dependent Noncoding RNA Switch in the Telomeric Transcriptome of Chironomus riparius

The telomeric transcriptome of Chironomus riparius has been involved in thermal stress response. One of the telomeric transcripts, the so-called CriTER-A variant, is highly overexpressed upon heat shock. On the other hand, its homologous variant CriTER-B, which is the most frequently encoded noncoding RNA in the telomeres of C. riparius, is only slightly affected by thermal stress. Interestingly, both transcripts show high sequence homology, but less is known about their folding and how this could influence their differential behaviour. Our study suggests that CriTER-A folds as two different conformers, whose relative proportion is influenced by temperature conditions. Meanwhile, the CriTER-B variant shows only one dominant conformer. Thus, a temperature-dependent conformational equilibrium can be established for CriTER-A, suggesting a putative functional role of the telomeric transcriptome in relation to thermal stress that could rely on the structure-function relationship of the CriTER-A transcripts.

lncRNAs in Stress Response

All living organisms sense and respond to harmful changes in their intracellular and extracellular environment through complex signaling pathways that lead to changes in gene expression and cellular function in order to maintain homeostasis. Long non-coding RNAs (lncRNAs), a large and heterogeneous group of functional RNAs, play important roles in cellular response to stressful conditions. lncRNAs constitute a significant fraction of the genes differentially expressed in response to diverse stressful stimuli and, once induced, contribute to the regulation of downstream cellular processes, including feedback regulation of key stress response proteins. While many lncRNAs seem to be induced in response to a specific stress, there is significant overlap between lncRNAs induced in response to different stressful stimuli. In addition to stress-induced RNAs, several constitutively expressed lncRNAs also exert a strong regulatory impact on the stress response. Although our understanding of the contribution of lncRNAs to the cellular stress response is still highly rudimentary, the existing data point to the presence of a complex network of lncRNAs, miRNAs, and proteins in regulation of the cellular response to stress.

Telomeric transcriptome from Chironomus riparius (Diptera), a species with noncanonical telomeres

Although there are alternative telomere structures, most telomeres contain DNA arrays of short repeats (6-26 bp) maintained by telomerase. Like other diptera, Chironomus riparius has noncanonical telomeres and three subfamilies, TsA, TsB and TsC, of longer sequences (176 bp) are found at their chromosomal ends. Reverse transcription PCR was used to show that different RNAs are transcribed from these sequences. Only one strand from TsA sequences seems to render a noncoding RNA (named CriTER-A); transcripts from both TsB strands were found (CriTER-B and αCriTER-B) but no TsC transcripts were detected. Interestingly, these sequences showed a differential transcriptional response upon heat shock, and they were also differentially affected by inhibitors of RNA polymerase II and RNA polymerase III. A computer search for transcription factor binding sites revealed putative regulatory cis-elements within the transcribed sequence, reinforcing the experimental evidence which suggests that the telomeric repeat might function as a promoter. This work describes the telomeric transcriptome of an insect with non-telomerase telomeres, confirming the evolutionary conservation of telomere transcription. Our data reveal differences in the regulation of telomeric transcripts between control and stressful environmental conditions, supporting the idea that telomeric RNAs could have a relevant role in cellular metabolism in insect cells.

Overexpression of long non-coding RNAs following exposure to xenobiotics in the aquatic midge Chironomus riparius

Non-coding RNAs (ncRNAs) represent an important transcriptional output of eukaryotic genomes. In addition to their functional relevance as housekeeping and regulatory elements, recent studies have suggested their involvement in rather unexpected cellular functions. The aim of this work was to analyse the transcriptional behaviour of non-coding RNAs in the toxic response to pollutants in Chironomus riparius, a reference organism in aquatic toxicology. Three well-characterized long non-coding sequences were studied: telomeric repeats, Cla repetitive elements and the SINE CTRT1. Transcription levels were evaluated by RT-PCR after 24-h exposures to three current aquatic contaminants: bisphenol A (BPA), benzyl butyl phthalate (BBP) and the heavy metal cadmium (Cd). Upregulation of telomeric transcripts was found after BPA treatments. Moreover, BPA significantly activated Cla transcription, which also appeared to be increased by cadmium, whereas BBP did not affect the transcription levels of these sequences. Transcription of SINE CTRT1 was not altered by any of the chemicals tested. These data are discussed in the light of previous studies that have shown a response by long ncRNAS (lncRNAs) to cellular stressors, indicating a relationship with environmental stimuli. Our results demonstrated for the first time the ability of bisphenol A to activate non-coding sequences mainly located at telomeres and centromeres. Overall, this study provides evidence that xenobiotics can induce specific responses in ncRNAs derived from repetitive sequences that could be relevant in the toxic response, and also suggests that ncRNAs could represent a novel class of potential biomarkers in toxicological assessment.

Transcription and activation under environmental stress of the complex telomeric repeats of Chironomus thummi

In contrast to their traditional role, telomeres seem to behave as transcriptionally active regions. RNAs complementary to the short DNA repeats characteristic of telomerase-maintained telomeres have recently been identified in various mammalian cell lines, representing a new and unexpected element in telomere architecture. Here, we report the existence of transcripts complementary to telomeric sequences characteristic of Chironomus thummi telomeres. As in other Diptera, the non-canonical telomeres of chironomids lack the simple telomerase repeats and have instead more complex repetitive sequences. Northern blots of total RNA hybridized with telomere probes and RT-PCR with telomere-specific tailed primers confirm the existence of small non-coding RNAs of around 200 bp, the size of the DNA repeated telomeric unit. Telomere transcripts are heterogeneous in length, and they appear as a ladder pattern that probably corresponds to multimers of the repeat. Moreover, telomeres are activated under conditions of environmental stress, such as heat shock, appearing highly decondensed and densely labelled with acetylated H4 histone, as well as with RNA polymerase II antibodies, both marks of transcriptional activity. Changes in the expression levels of telomeric RNA were detected after heat shock. These findings provide evidence that transcriptional activity of the repetitive telomere sequences is an evolutionarily conserved feature, not limited to telomerase telomeres. The functional significance of this non-coding RNA as a new additional element in the context of telomere biology remains to be explained.

Characterization and expression during development and under environmental stress of the genes encoding ribosomal proteins L11 and L13 in Chironomus riparius

The Chironomus riparius gene sequences encoding ribosomal proteins L11 and L13 were characterized and their expression analysed during development, and under different types of cellular stress. A comparative and phylogenetic study among different orders of insects was carried out by analysis of sequence databases. L11 is highly conserved, both at the level of DNA and protein, and it shares over 90% amino acid identity with homologous sequences from other insects. Interestingly, the changes are mainly concentrated in the C-terminal domain of the protein. Conversely, L13 shows a lower degree of homology, around 60% amino acid identity, and the changes were dispersed throughout the length of the polypeptide. Surprisingly, when comparing L13 nucleotide sequences, only a very low or no homology was found even among diptera. These results are helpful for defining the structural and, therefore, evolutionary constraints of these proteins. Studies of gene expression by RT-PCR showed that they are differentially expressed in distinct stages of development. Both L11 and L13 were significantly upregulated during embryogenesis. The expression profiles of the transcripts were also analysed after a general stress, such as heat shock, as well as after a specific stress, such as acute cadmium treatment. In both conditions, no significant differences to controls were detected in L11 and L13 transcripts, in spite of the drastic changes observed in the stress-induced gene HSP70, and the inhibitory effect on rRNA transcription. These data confirm that both genes are equally robust against harmful environmental conditions, suggesting that they could be used as a control for environmentally responsive genes in Chironomus. Overall, our results show a coordinated expression of both the L11 and the L13 genes, but not a coordinated regulation of rRNA and ribosomal protein production.

Ribosomal genes as early targets of cadmium-induced toxicity in Chironomus riparius larvae

Cadmium is a widespread environmental pollutant that causes severe impacts in organisms. Although the effects of cadmium on aquatic insects have been studied in terms of their toxicity and changes in developmental parameters, little is known about its molecular and genetic effects. We have investigated the alterations in the pattern of gene expression provoked by acute exposure to cadmium in Chironomus riparius Mg. (Diptera, Chironomidae), a sentinel organism widely used in aquatic toxicity testing. The early cytotoxic effects were evaluated using immunocytochemistry and specific fluorescent probes in fourth instar larvae after 12 h of 10 mM cadmium treatments; under these conditions no significant effect on larvae mortality was detected until after 36 h of exposure. The changes in the pattern of gene expression were analysed by means of DNA/RNA hybrid antibodies in the polytene chromosomes from salivary gland cells. A decrease in the activity of the nucleolus is especially remarkable, accompanied by a significant reduction in size and the modification in nucleolar architecture, as shown by FISH. The inhibition of rDNA transcription was further evaluated by Northern blot analysis, which showed a marked decrease in the level of preribosomal rRNA (54% 45S 12 h). However, the BR genes, whose products are the giant polypeptides that constitute the silk-like secretion for constructing housing tubes, remain active. Simultaneously, decondensation and activation take place at some chromosomal regions, especially at the centromeres. The changes observed in the pattern of gene expression do not resemble those found after heat shock or other cell stressors. These data provide the first evidence that cadmium interacts with ribosomal genes and results in a drastic impairment of the functional activity of the nucleolus, an essential organelle for cellular survival. Therefore, the depletion of ribosomes would be a long-term effect of Cd-induced cellular damage. These findings may have important implications for understanding the adverse biological effects of cadmium and its toxic mechanism, as yet not clearly defined, and provide a sensitive biomarker of cadmium exposure.

The effects of temperature shock on transcription and replication in Rhynchosciara americana (Diptera: Sciaridae)

The chromosomal response to temperature shock in Rhynchosciara americana is similar to that observed in other Diptera. After a 33 degrees C/90 min or a 36 degrees C/30 min shock the reaction for RNA polymerase II (RpII) is enhanced at five loci. The most prominent of these was identified by in situ hybridization as the site of the hsp70 gene. At 33 degrees C, an accumulation of heat shock factor (HSF) and an increase in the level of RpII was observed at some heat shock loci after 5 min and reached a maximum after 15 min at most loci. The pattern of accumulation of HSF and RpII at individual heat shock loci was similar and their increases were generally coordinated among the loci. RpII gradually decreased at sites active prior to shock, the rate of decrease varying with the site. The B2 DNA puff retained RpII for a significant length of time while the histone locus still contained RpII after a shock of 90 min. With a 36 degrees C/30 min shock, the size of the heat shock puffs and the intensities of HSF and RpII peaked at 1-4 h post stress. The level of HSF declined rapidly after 1 h while the level of RpII remained high for an additional 4 h. The reaction of the DNA puffs to heat shock varied. Usually they did not regress completely and retained traces of RpII. BrdU incorporation continued at both amplifying and non-amplifying bands after shock but on average it appeared depressed for about 24 h post stress.

Nucleolar localization of a reverse transcriptase related to telomere maintenance in Chironomus (Diptera)

A growing number of cellular processes originally thought not to involve the nucleolus now seem to be associated with this organelle. In recent years, a variety of RNAs and proteins with no apparent function in ribosome genesis have been discovered in this nuclear compartment. This paper reports the presence in the nucleolus of a reverse transcriptase (RT) previously found to be associated with telomeres in Chironomus. Immunofluorescence detection using a specific antibody against conserved domains shared by RTs showed a distinct pattern of staining in the giant nucleoli of polytenized cells. This nucleolar localization was confirmed in a number of larval tissues and embryonic cells of Chironomus thummi and C. pallidivitatus; its distribution showed a definite necklace pattern that did not completely colocalize with fibrillarin or nucleolin and appeared to be different to that of typical nucleolar components. There is evidence that both telomerase RT and RNA template subunits are present in the nucleoli of mammalian and yeast cells. However, chironomids do not have typical telomeres or telomerase. As in other Diptera, telomeres lack the short, simple repeats maintained by telomerase and instead have more complex sequences in the range of hundreds of nucleotides. It has been suggested that the RT associated with these telomeres might be involved in their maintenance, perhaps involving a mechanism similar to that of telomerase retrotranscription and retrotransposition in Drosophila. The present results indicate that the putative Chironomus telomere elongation machinery and telomerase share a nucleolar localization. This reinforces the idea that nucleoli are functionally linked to telomere maintenance irrespective of the differences in their molecular organization and therefore in the strategy adopted for their elongation.

Role of HSPs and telomerase in radiotherapy

The inability of radiotherapy to control tumour growth is still a daunting clinical problem leading to failure of the overall treatment regimens. The fundamental question is; could tumour cells be specifically sensitized to ionizing radiation (IR) by heat or factors exclusively expressed in tumour cells? One such factor, expressed in most tumours and silent in somatic cells, is telomerase. Biochemical and genetic studies have established an association between telomere maintenance and extended life span of human cells mediated through the expression of the catalytic sub-unit of telomerase (hTERT). Because of this, telomerase is an attractive target for inhibition in anti-cancer therapy. Telomeres are maintained by telomerase and hTERT interacts with heat shock protein (HSP) chaperones. This review will focus on the possible role of HSPs and telomerase in sensitizing tumour cells and, thus, enhancing the potential of targeted radiotherapy.

Reverse transcriptase-related proteins in telomeres and in certain chromosomal loci of Rhynchosciara (Diptera: Sciaridae)

The localization of reverse transcriptase-related proteins in polytene chromosomes of dipterans was investigated using previously characterized antibodies to a recombinant polypeptide containing conserved motifs of insect reverse transcriptases. The immunoreactions were carried out with polytene chromosome squashes of eight sciarids, one chironomid and three Drosophila species. Telomeric staining was regularly observed on chromosomes of the sciarid Rhynchosciara americana under normal growth conditions. Five of eight chromosomal tips were labelled except for the heterochromatic ends that are occasionally found associated forming a chromocentre in the salivary gland. Reverse transcriptase-related proteins were detected at chromosomal tips of young larvae and remained bound to the telomeres throughout larval development. As in salivary gland chromosomes, five non-telocentric ends of the chromosomes from Malpighian tubules of R. americana appeared clearly stained with anti-reverse transcriptase. The occurrence of telomeric reverse transcriptase in R. americana correlates with the presence of RNA in addition to an unusual enrichment with homopolymeric dA/dT DNA associated with the telomeric heterochromatin. The antibodies also reacted with a few interstitial sites in chromosomes of four Rhynchosciara species, one band overlapping the histone gene locus of three species in the americana -like group. The results provide evidence for a reverse transcriptase-related protein as a constitutive component in telomeres of R. americana and also in certain interstitial loci of Rhynchosciara species in which RNA was immunologically detected in the form of RNA:DNA hybrids.

In vivo binding of active heat shock transcription factor 1 to human chromosome 9 heterochromatin during stress

Activation of the mammalian heat shock transcription factor (HSF)1 by stress is a multistep process resulting in the transcription of heat shock genes. Coincident with these events is the rapid and reversible redistribution of HSF1 to discrete nuclear structures termed HSF1 granules, whose function is still unknown. Key features are that the number of granules correlates with cell ploidy, suggesting the existence of a chromosomal target. Here we show that in humans, HSF1 granules localize to the 9q11-q12 heterochromatic region. Within this locus, HSF1 binds through direct DNA-protein interaction with a nucleosome-containing subclass of satellite III repeats. HSF1 granule formation only requires the DNA binding competence and the trimerization of the factor. This is the first example of a transcriptional activator that accumulates transiently and reversibly on a chromosome-specific heterochromatic locus.