Double Superconducting Dome and Triple Enhancement of T_{c} in the Kagome Superconductor CsV_{3}Sb_{5} under High Pressure.

CsV_{3}Sb_{5} is a newly discovered Z_{2} topological kagome metal showing the coexistence of a charge-density-wave (CDW)-like order at T^{*}=94 K and superconductivity (SC) at T_{c}=2.5 K at ambient pressure. Here, we study the interplay between CDW and SC in CsV_{3}Sb_{5} via measurements of resistivity, dc and ac magnetic susceptibility under various pressures up to 6.6 GPa. We find that the CDW transition decreases with pressure and experience a subtle modification at P_{c1}≈0.6-0.9 GPa before it vanishes completely at P_{c2}≈2 GPa. Correspondingly, T_{c}(P) displays an unusual M-shaped double dome with two maxima around P_{c1} and P_{c2}, respectively, leading to a tripled enhancement of T_{c} to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram resembles those of unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range P_{c1}≤P≤P_{c2} as evidenced by the broad superconducting transition and reduced superconducting volume fraction. The modification of CDW order around P_{c1} has been discussed based on the band structure calculations. This work not only demonstrates the potential to raise T_{c} of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electron correlations in this novel family of topological kagome metals.

Rhizosphere bacterial communities associated with long-lived perennial prairie plants vary in diversity, composition, and structure.

The goal of this research was to investigate the variation in rhizosphere microbial community composition, diversity, and structure among individual Andropogon gerardii Vitman (big bluestem) and Lespedeza capitata Michx. (bush clover). Bacterial communities from the rhizosphere of 10 plants of each species (n = 20 plants total) were explored using a culture-independent pipeline. Microbial communities associated with both host plants had high bacterial diversity within individual plant rhizosphere and taxa unique to individual rhizospheres. Bacterial communities associated with the rhizosphere of A. gerardii were consistently more diverse than those associated with L. capitata, and there were significant differences between plant species in rhizosphere bacterial community composition. Differences included microbial taxa with no known functional relationship with their preferred host species, including sulfide-methylating obligate anaerobes (Holophaga), complete denitrifiers (Rhodoplanes), sludge inhabitants (Ktedonobacter), and nitrate oxidizers (Nitrospira). These results suggest the potential for plant species to have significant impacts on a broad array of ecosystem functions (e.g., cycling of carbon, nitrogen sulfurs, metals, and trace elements) via their selective impacts on soil microbes. However, sequence-based community analysis and the corresponding lack of intact microbial cultures limits understanding of the potential influences of enriched microbial taxa on plant hosts and their roles in ecosystem functioning.

Discovery of conjoined charge density waves in the kagome superconductor CsV3Sb5.

The electronic instabilities in CsV3Sb5 are believed to originate from the V 3d-electrons on the kagome plane, however the role of Sb 5p-electrons for 3-dimensional orders is largely unexplored. Here, using resonant tender X-ray scattering and high-pressure X-ray scattering, we report a rare realization of conjoined charge density waves (CDWs) in CsV3Sb5, where a 2 × 2 × 1 CDW in the kagome sublattice and a Sb 5p-electron assisted 2 × 2 × 2 CDW coexist. At ambient pressure, we discover a resonant enhancement on Sb L1-edge (2s→5p) at the 2 × 2 × 2 CDW wavevectors. The resonance, however, is absent at the 2 × 2 × 1 CDW wavevectors. Applying hydrostatic pressure, CDW transition temperatures are separated, where the 2 × 2 × 2 CDW emerges 4 K above the 2 × 2 × 1 CDW at 1 GPa. These observations demonstrate that symmetry-breaking phases in CsV3Sb5 go beyond the minimal framework of kagome electronic bands near van Hove filling.

Direct modulation of tumor suppressor connexin 26 gene by human chorionic gonadotropin in rat mammary glands.

Human chorionic gonadotropin (hCG) has been shown to reduce the incidence of carcinogen-induced rat mammary tumors. Because connexin 26 (Cx26), a tumor suppressor gene candidate, can be up-regulated in mammary epithelial cells during lactation, we examined the in vivo and ex vivo effects of hCG on Cx26 expression in rat mammary tissues and used its effect on the expressions of beta-casein and Cx43 as controls. The Cx26 mRNA and protein expressions were up-regulated by daily administrations of 100 units of hCG, starting on day 5 and reaching a 14-fold maximum increment on days 16 through 21. It remained elevated above the basal level even 20 days after hCG withdrawal. The changes in beta-casein expression ran parallel to that of Cx26, whereas the expression of Cx43 was down-regulated. There was no correlation between steroidal hormone levels and Cx26 expression, except for the first 5 days of hCG treatment. In the ex vivo organ culture system, exposure of mammary glands to 10 units/ml hCG for 5 days up-regulated Cx26 but had no effect on beta-casein expression. These results imply a direct induction of the tumor suppressor Cx26 gene by hCG in mammary epithelial cells, a mechanism unrelated to lactation.

Mapping and characterization of the basal promoter of the human connexin26 gene.

Connexin26 (Cx26) is a major gap junction protein expressed in mammary and endometrial epithelial cells. Previously, we have cloned the genomic upstream sequence of the human connexin26 gene. In this paper, we studied the structure and function of its basal promoter. Various 5'-flanking regions of the human Cx26 gene were inserted upstream of the bacterial chloramphenicol acetyltransferase (CAT) reporter gene and transfected into human immortalized mammary MCF-10A and MCF-12A cell lines and endometrial RL95-2 cancer cell line. Through CAT reporter gene analysis, we identified the basal promoter of human Cx26 gene in the proximal 5'-flanking region from -128 to +2 (relative to the transcription initiation site). Further deletion analyses suggested that the critical regulatory area was located within a 29 bp region (from -97 to -69), where two GC consensus boxes (CCGCCC) resided, one at -93 and the other at -81. Labeled oligonucleotides encompassing these two GC box DNA sequences could bind the nuclear extracts from MCF-12A and RL95-2 cells in the electrophoretic mobility shift assay. These binding complexes could be competitively reduced by non-labeled self or Sp1 consensus oligonucleotide, and supershifted by antibodies against either Sp1 or Sp3. Mutations in the core sequence of these two GC boxes from CCGCCC to CCGAAC caused a loss of competitive ability and also produced a drastic reduction of basal promoter activity when integrated into promoter/reporter constructs. Furthermore, co-transfection of Sp1 and/or Sp3 expressing plasmids could trans-activate the expression of human Cx26 promoter/reporter constructs in Drosophila Schneider line 2 (SL2) cells. Taken together, these data indicated that the two GC boxes in the proximal promoter region play an important role in the control of human Cx26 gene expression.

Differential up-regulation of gap junction connexin 26 gene in mammary and uterine tissues: the role of Sp transcription factors.

The mRNA and protein expressions of connexin 26 (Cx26) in rat mammary gland and uterus can be up-regulated during pregnancy as well as by the administration of human CG (hCG). In the present study, we found that the time course and magnitude of Cx26 induction by hCG was different in these two tissues. The molecular mechanism underscoring this difference was therefore investigated. We had previously demonstrated that both Sp1 and Sp3 transcription factors play a functional role in Cx26 expression. By the electrophoretic mobility shift assay, nuclear extracts from both virgin mammary gland and uterus were capable of binding to a labeled oligonucleotide probe that contained the proximal GC box and formed three protein-DNA complexes (C1, C2, and C3). In the mammary gland, pregnancy enhanced the intensity of all three complexes, whereas in the uterine tissue there was a decrease in the C2 and C3 complexes and an emergence of a new major component, C4 complex. In the supershift study, the C1 complex could be supershifted only by an antibody against Sp1, whereas C2, C3, and C4 could all be supershifted by an antibody against Sp3, suggesting a potential presence of Sp3 isoforms of various sizes. We therefore conclude that the basal Sp profiles in virgin mammary gland and uterine tissue are similar. However, in response to pregnancy, the changes in Sp profile are tissue specific and may account for the temporal and quantitative differences between these two tissues in Cx26 induction.

Upstream genomic sequence of the human connexin26 gene.

Human connexin 26 (Cx26) has been considered to be a candidate suppressor gene in mammary epithelial cells. To gain insight into the transcriptional regulation of this gene, we have cloned and sequenced the 5' portion of the gene, which extends 4.8 kb upstream from the ATG translation start site. The 3' end of the non-coding exon 1 (160 bp) is located at 3149 bp upstream from the 5' end of exon 2. Comparison between the human Cx26 gene and the mouse gene reveals a highly conserved promoter region with 81% homology. In addition to six GC boxes and two GT boxes, a TTAAAA box is located at -24 to -19 bp upstream of the transcription start point. Analogous to the mouse beta-casein gene, the promoter region of the human Cx26 gene also contains a YY1-like binding site and a consensus mammary gland factor binding site.

Gap junction Cx26 gene modulation by phorbol esters in benign and malignant human mammary cells.

Connexin (Cx) 26, a major gap junction protein expressed in mammary epithelial cells, has been considered to be a tumor suppressor gene candidate. This study investigated the molecular mechanism of transcriptional up-regulation of Cx26 by phorbol ester (TPA) in human immortalized MCF-10 mammary epithelial cells and MDA-MB-231 mammary cancer cells. Such up-regulation was mediated through the protein kinase C pathway and could be blocked by the PKC inhibitor, calphostin C. Based on the results of the nuclear run-on assay, there was a TPA-induced increase in the rate of transcriptional initiation. We identified a TPA-induced DNase I hypersensitivity (DH) region approximately 1 kb 5' upstream of the ATG translation starting site. Sequence analysis revealed that this DH region was located in intron 1 and contained two TRE-like TGAT/ATCA elements, two 5'TTCA3' motifs and a 5'AGGAAG3' PEA3 motif. Both TRE-like elements were capable of binding AP1. TPA inducibility of this DH region was seen by the CAT reporter assay and appeared to be direction-dependent suggesting a functional cooperation between PEA3/TTCA and TRE.

Isoproterenol/tannin-dependent R15 expression in transgenic mice is mediated by an upstream parotid control region.

Transgenic mice were used to locate the cis-acting DNA elements that are essential for tissue-specific and inducible expression of the rat proline-rich protein gene, R15. Chimeric genes with up to 10 kb of R15 5'-flanking region fused to chloramphenicol acetyltransferase (CAT) or polyomaviral large T-antigen (PyLT) reporter genes were tested. Our results demonstrate that (1) the isoproterenol/tannin-inducible, parotid-specific transgene expression requires an upstream cis-regulatory domain, namely the parotid control region, which extends from -6 to -1.7 kb of the R15 gene; (2) this parotid control region functions with a heterologous promoter and is indispensable for achieving a reproducible chromosomal position-independent transgene expression; (3) deletion of the R15 5'-flanking region up to -1.7 kb results in a pleiotropic effect on the transgene expression, which includes ectopic (nonsalivary) reporter expression and lack of inducibility by either the beta-agonist isoproterenol or dietary tannin stimulation; (4) when the -10 to -6 kb region from the R15 gene is deleted in the construct, the inducible expression in the parotid glands of the transgenic mice decreases by over 30-fold, but position-independent and tissue-specific transgene expression is retained. Moreover, the mechanism of induction by either catecholamine isoproterenol or dietary tannin appears to be through a beta 1-adrenergic receptor-mediated pathway for both normal (non-transgenic) and transgenic animals.

Modulation of the connexin26 tumor suppressor gene expression through methylation in human mammary epithelial cell lines.

BACKGROUND: Normal mammary epithelial cells express mainly gap junction connexin 26 (Cx26) that is either reduced or absent in breast cancers. Since connexin gene mutations are rare we examined if Cx26 gene repression is related to hypermethylation. MATERIALS AND METHODS: Five breast epithelial cell lines were examined for Cx26 mRNA expression and hypermethylation. Treatment with a DNA methyltransferase inhibitor, 5-Aza-2'-deoxycytidine (5-Aza-CdR), was carried out to determine if Cx26 gene expression could be upregulated. RESULTS: Cx26 expression was easily detectable in an immortalized human mammary epithelial cell line (MCF-10) and markedly diminished (MDA-MB231) or undetectable in (MCF-7, BT-20, T47-D) breast cancer cell lines. Hypermethylation of the Cx26 5' region was observed in MCF-10 and MCF-7 cells. Treatment with 5-Aza-CdR resulted in slight or no induction in Cx26 expression in breast cancer cell lines. CONCLUSIONS: Hypermethylation is unlikely to be a major mechanism for Cx26 gene repression in human mammary cancer cell lines.

Involvement of nuclear orphan receptor NGFI-B in transcriptional activation of salivary-specific R15 gene by cAMP.

Proline-rich proteins (PRPs) are selectively expressed in the acinar cells of the salivary glands and are inducible by beta-agonist isoproterenol and dietary tannins. In the previous studies of rat PRP gene, R15, the 5'-flanking region up to -1.7 kilobase pairs (kb), which was thought to contain the necessary proximal regulatory elements, failed to confer the catecholamine isoproterenol and dietary tannin inducibility to the transgene expression in the salivary glands of transgenic mice. Here we analyzed distal 5'-flanking region of R15 in order to understand the mechanisms of tissue-specific and inducible gene regulation. An upstream regulatory region located between -2.4 and -1.7 kb of the R15 5'-flanking region is demonstrated to be indispensable for the salivary-specific and inducible reporter gene expression in vivo, by transgenic approach. Element(s) within the 0.7-kb (-2.4 to -1.7) region that is able to cis-activate the expression of a heterologous reporter gene expression is further elucidated by transient transfection assays in vitro. Three distinct nuclear orphan receptor NGFI-B regulatory sequences are identified within a 184-base pair (bp) minimal control region extended from -1995 to -1812 nucleotides relative to the transcription start site. When reporter gene containing this 184-bp control region and heterologous promoter was cotransfected with the NGFI-B expression construct, a transactivation that mimics the effect of cAMP is observed in the parotid cells. Finally, mutations on all three identified NGFI-B binding sites and coexpression of a dominant negative mutant construct, pCMV-NGFI-B(Delta25-195), abolish this transactivation mediated by NGFI-B. In summary, these data suggest that the inducible nuclear orphan receptor NGFI-B may participate in the regulation of salivary acinar cell-specific and inducible expression of the rat R15 gene via three distinct distal NGFI-B sites.

Characterization of the statin-like S1 and rat elongation factor 1 alpha as two distinctly expressed messages in rat.

Previously, we reported a rat S1 protein that is antigenically related to statin, a nonproliferating cell-specific marker; however, it shares high homology with the known human elongation factor-1 alpha (EF-1 alpha). To differentiate S1 from rat EF-1 alpha and to study their respective regulation for expression, a rat EF-1 alpha cDNA clone was isolated and characterized. The nucleotide and deduced amino acid sequences of this partial rat EF-1 alpha cDNA are compared with that of human and mouse as well as with rat S1. Both their messages were detected in rat brain by EF-1 alpha- or S1-specific probes. However, the mRNA encoding EF-1 alpha is more abundant than that encoding S1. S1 and EF-1 alpha expression were investigated in the parotid and submandibular glands of untreated rats and those treated with isoproterenol, a proliferation-inducing catecholamine. Quantitative solution hybridization demonstrated a dramatic reduction (approximately 68%) in the S1 mRNA following isoproterenol injection in proliferation-responsive parotid glands and a mild reduction (approximately 20%) of S1 steady-state messages in the proliferation-refractile submandibular glands. A slight increase or no changes of EF-1 alpha levels in both parotid and submandibular glands following isoproterenol treatment are also observed. Therefore, the EF-1 alpha and S1 genes are different genes, both expressed and regulated in vivo, but in differential quantitative and qualitative patterns.

Involving AP-2 transcription factor in connexin 26 up-regulation during pregnancy and lactation.

Gap junction connexin 26 (Cx26) is up-regulated in mammary epithelial cells during pregnancy and lactation. To understand the transcriptional regulation of Cx26, we identified a protected DNase I footprint region (-140 to -113) in the rat Cx26 promoter. This rCx26 Promoter Footprinting Region, or CPFR, contains an Sp binding site (CCGCCC) overlapping with an AP-2 binding site (GCCCGCGGC), and is evolutionarily conserved. Nuclear extracts from rat mammary glands and human MCF-10 mammary epithelial cells formed protein-DNA complexes with the labeled CPFR probe in the electrophoretic mobility shift assay (EMSA), and these complexes were markedly enhanced during pregnancy and lactation. Antibody supershift analysis further identified the presence of Sp1, Sp3, and AP-2 in these binding complexes. Human mammary epithelial MCF-10A and MCF-12A cells were transiently transfected with chimeric mutant rCx26 promoter/luciferase reporter constructs, and luciferase activities measured. Mutations along the CPFR fragment drastically reduced the promoter activity, specially at the Sp/AP-2 overlapping site. Cotransfection of AP-2 with rCx26 promoter/reporter constructs into MCF-10 cells markedly induced the reporter activity. These data infer that AP-2, along with previously reported Sp transcription factors, is involved in the up-regulation of Cx26 gene during pregnancy and lactation.