Clinical and Genetic Insights into Desbuquois Dysplasia: Review of 111 Case Reports

Skeletal disorders encompass a wide array of conditions, many of which are associated with short stature. Among these, Desbuquois dysplasia is a rare but severe condition characterized by profound dwarfism, distinct facial features, joint hypermobility with multiple dislocations, and unique vertebral and metaphyseal anomalies. Desbuquois dysplasia is inherited in an autosomal recessive manner, with both the DBQD1 (MIM 251450) and DBQD2 (MIM 615777) forms resulting from biallelic mutations. Specifically, DBQD1 is associated with homozygous or compound heterozygous mutations in the CANT1 gene, while DBQD2 can result from mutations in either the CANT1 or XYLT1 genes. This review synthesizes the findings of 111 published case reports, including 54 cases of DBQD1, 39 cases of DBQD2, and 14 cases of the Kim variant (DDKV). Patients in this cohort had a median birth weight of 2505 g, a median length of 40 cm, and a median occipitofrontal circumference of 33 cm. The review highlights the phenotypic variations across Desbuquois dysplasia subtypes, particularly in facial characteristics, joint dislocations, and bone deformities. Genetic analyses revealed a considerable diversity in mutations, with over 35% of cases involving missense mutations, primarily affecting the CANT1 gene. Additionally, approximately 60% of patients had a history of parental consanguinity, indicating a potential genetic predisposition in certain populations. The identified mutations included deletions, insertions, and nucleotide substitutions, many of which resulted in premature stop codons and the production of truncated, likely nonfunctional proteins. These findings underscore the genetic and clinical complexity of Desbuquois dysplasia, highlighting the importance of early diagnosis and the potential for personalized therapeutic approaches. Continued research is essential to uncover the underlying mechanisms of this disorder and improve outcomes for affected individuals through targeted treatments.

Pan-cancer analysis predicts CANT1 as a potential prognostic, immunologic biomarker

BACKGROUND

CANT1, calcium-activated nucleotidase 1, was reported to be upregulated in certain tumors. However, the function mechanism of CANT1 in pan-cancer is still unclear.

METHODS

We utilized the Cancer Genome Atlas Program (TCGA) and UALCAN databases to analyze CANT1 expression at the level of mRNA, protein, and promoter methylation in pan-cancer, and the cBioportal database to study the frequency of gene changes for CANT1. Wilcoxon test was applied to discuss the correlation between CANT1 and clinicopathological features in different tumor types. The prognosis of CANT1 in pan-cancer was discussed by Cox regression. Spearman analysis was applied to discuss the relationship of CANT1 with tumor mutation burden(TMB), microsatellite instability(MSI), immune cell infiltration, and immune checkpoints. The association between CANT1 expression and drug sensitivity for pan-cancer was investigated by the GSCALite database. In addition, we collected 40 cases of lung adenocarcinoma (LUAD) and adjacent normal tissues for immunohistochemical staining and investigated the relationship between CANT1 and clinicopathology and prognosis in LUAD. Finally, the molecular pathways involved in CANT1-related genes in LUAD were analyzed by gene set enrichment analysis(GSEA).

RESULTS

The CANT1 mRNA level was significant higher in 14 tumors, and CANT1 protein level was significant higher in 7 tumors compared with normal tissues. CANT1 expression was linked with the T stage, N stage, and pathological stage in some tumors, and overexpression CANT1 was associated with adverse overall survival(OS) and disease-specific survival(DSS) in kidney renal papillary cell carcinoma(KIRP), brain lower grade glioma(LGG), and LUAD. By Spearman correlation analysis, the results showed that CANT1 had a positive correlation with TMB and MSI in bladder urothelial carcinoma(BLCA), breast invasive carcinoma(BRCA), esophageal carcinoma(ESCA), LGG, and sarcoma(SARC). Furthermore, CANT1 was related to immune cell infiltration and immune checkpoints in several cancers. Drug sensitivity analysis suggested that CANT1 was inversely linked with three drugs. Immunohistochemical staining analysis showed that CANT1 expression was higher in LUAD than in normal tissues, and was related to N stage and pathological stage. Survival curves showed that CANT1 overexpression had poor OS and DSS. Time-dependent ROC curves revealed that the 1-year, 5-year, and 10-year OS and DSS in LUAD were above 0.5. CANT1-related genes in LUAD mainly participated in the pathway of dorso ventral axis formation, small cell lung cancer, DNA replication, O-glycan biosynthesis, and cell cycle.

CONCLUSION

CANT1 is considered a potential marker for prognosis in several tumors, and a promising target for tumor immunological treatment.

Upregulated CANT1 is correlated with poor prognosis in hepatocellular carcinoma

BACKGROUND

CANT1, as calcium-activated protein nucleotidase 1, is a kind of phosphatase. It is overexpressed in some tumors and related to poor prognosis, but few studies explore its function and carcinogenic mechanism in hepatocellular carcinoma (HCC).

METHODS

The expression of CANT1 mRNA and protein was analyzed by the Cancer Genome Atlas (TCGA) database and immunohistochemistry(IHC) staining. The relationship between CANT1 expression and clinicopathology was evaluated by various public databases. The receiver operating characteristic (ROC) curve was used to assess the diagnostic accuracy of CANT1 by the area under curve (AUC). Univariate, multivariate Cox regression and Kaplan-Meier curves were applied to evaluate the predictive value of CANT1 on the prognosis of HCC. Methsurv was used to analyze gene changes and DNA methylation, and its impact on prognosis. The enrichment analysis of DEGs associated with CANT1 revealed the biological process of CANT1 based on Gene Set Enrichment Analysis (GSEA). The relationship between immune cell infiltration level and CANT1 expression in HCC was investigated using the single-sample GSEA (ssGSEA) method and the Tumor Immune Estimation Resource (TIMER) database. Finally, the association between CANT1 and immune checkpoints and drug sensitivity was also analyzed.

RESULTS

CANT1 was highly expressed in 22 cancers, including HCC, and CANT1 overexpression in HCC was confirmed by IHC. The expression of CANT1 was correlated with clinical features, such as histologic grade. Highly expressed CANT1 caused poor overall survival (OS) of HCC patients. Univariate and multivariate regression analysis suggested that CANT1 was an independent prognostic marker. Of the 31 DNA methylation at CpG sites, three CpG sites were associated with the prognosis of HCC. GSEA indicated that CANT1 was mainly involved in the cell cycle, DNA replication, and etc. Moreover, CANT1 expression was correlated with immune cell infiltration and independently associated with the prognosis of HCC patients. Finally, CANT1 expression was correlated with most immune checkpoints and drug sensitivity.

CONCLUSION

CANT1 may be a latent oncogene of HCC, and associated with immune cells and immune checkpoints, which may assist in HCC treatment.

Circ_0001715 accelerated lung adenocarcinoma process by the miR-1322/CANT1 axis

Lung adenocarcinoma (LUAD) is a type of lung cancer, which belongs to non-small cell lung cancer and has seriously endangered the physical and mental health of people. The study of circRNAs (circRNAs) has been increasingly hot in recent years, in which circRNAs also play an important regulatory role in cancer. The aim of this study was to investigate the biological molecular mechanisms of circ_0001715 in the progression of LUAD. The expression of circ_0001715, miR-1322 and calcium-activated nucleotidase 1 (CANT1) in LUAD tissues and cell lines was assessed by quantitative reverse transcription PCR (RT-qPCR) and western bot assay. Clone formation assay, 5-Ethynyl-2'-Deoxyuridine (EDU) assay and wound healing assay were used to verify the proliferation ability of cells. Dual-luciferase reporter assay and RNA pull-down assay were performed to characterize the interactions between the three factors. Finally, a mouse tumor model was constructed to assess the tumorigenicity of circ_0001715. RT-qPCR assay results showed that circ_0001715 expression was significantly increased in LUAD tissues and cell lines. Finally, knockdown of circ_0001715 could inhibit tumor growth in vivo. Circ_0001715 regulated the progression of LUAD through the miR-1322/CANT1 axis. The results of this study provided ideas for understanding the molecular mechanisms of circ_0001715 in LUAD.

CD73, a Promising Therapeutic Target of Diclofenac, Promotes Metastasis of Pancreatic Cancer through a Nucleotidase Independent Mechanism

CD73, a cell surface-bound nucleotidase, facilitates extracellular adenosine formation by hydrolyzing 5'-AMP to adenosine. Several studies have shown that CD73 plays an essential role in immune escape, cell proliferation and tumor angiogenesis, making it an attractive target for cancer therapies. However, there are limited clinical benefits associated with the mainstream enzymatic inhibitors of CD73, suggesting that the mechanism underlying the role of CD73 in tumor progression is more complex than anticipated, and further investigation is necessary. In this study, CD73 is found to overexpress in the cytoplasm of pancreatic ductal adenocarcinoma (PDAC) cells and promotes metastasis in a nucleotidase-independent manner, which cannot be restrained by the CD73 monoclonal antibodies or small-molecule enzymatic inhibitors. Furthermore, CD73 promotes the metastasis of PDAC by binding to the E3 ligase TRIM21, competing with the Snail for its binding site. Additionally, a CD73 transcriptional inhibitor, diclofenac, a non-steroidal anti-inflammatory drug, is more effective than the CD73 blocking antibody for the treatment of PDAC metastasis. Diclofenac also enhances the therapeutic efficacy of gemcitabine in the spontaneous KPC (LSL-Kras^G12D/+ , LSL-Trp53^R172H/+ , and Pdx-1-Cre) pancreatic cancer model. Therefore, diclofenac may be an effective anti-CD73 therapy, when used alone or in combination with gemcitabine-based chemotherapy regimen, for metastatic PDAC.

Effects of physical exercise on the functionality of human nucleotidases: A systematic review

Nucleotidases contribute to the regulation of inflammation, coagulation, and cardiovascular activity. Exercise promotes biological adaptations, but its effects on nucleotidase activities and expression are unclear. The objective of this study was to review systematically the effects of exercise on nucleotidase functionality in healthy and unhealthy subjects. The MEDLINE, EMBASE, Cochrane Library, and Web of Science databases were searched to identify, randomized clinical trials, non-randomized clinical trials, uncontrolled clinical trials, quasi-experimental, pre-, and post-interventional studies that evaluated the effects of exercise on nucleotidases in humans, and was not limited by language and date. Two independent reviewers performed the study selection, data extraction, and assessment of risk of bias. Of the 203 articles identified, 12 were included in this review. Eight studies reported that acute exercise, in healthy and unhealthy subjects, elevated the activities or expression of nucleotidases. Four studies evaluated the effects of chronic training on nucleotidase activities in the platelets and lymphocytes of patients with metabolic syndrome, chronic kidney disease, and hypertension and found a decrease in nucleotidase activities in these conditions. Acute and chronic exercise was able to modify the blood plasma and serum levels of nucleotides and nucleosides. Our results suggest that short- and long-term exercise modulate nucleotidase functionality. As such, purinergic signaling may represent a novel molecular adaptation in inflammatory, thrombotic, and vascular responses to exercise.

Tissue-nonspecific alkaline phosphatase is an anti-inflammatory nucleotidase

Tissue-nonspecific alkaline phosphatase (TNAP) is necessary for skeletal mineralization by its ability to hydrolyze the mineralization inhibitor inorganic pyrophosphate (PP_i), which is mainly generated from extracellular ATP by ectonucleotide pyrophosphatase phosphodiesterase 1 (NPP1). Since children with TNAP deficiency develop bone metaphyseal auto-inflammations in addition to rickets, we hypothesized that TNAP also exerts anti-inflammatory effects relying on the hydrolysis of pro-inflammatory adenosine nucleotides into the anti-inflammatory adenosine. We explored this hypothesis in bone metaphyses of 7-day-old Alpl^+/- mice (encoding TNAP), in mineralizing hypertrophic chondrocytes and osteoblasts, and non-mineralizing mesenchymal stem cells (MSCs) and neutrophils, which express TNAP and are present, or can be recruited in the metaphysis. Bone metaphyses of 7-day-old Alpl^+/- mice had significantly increased levels of Il-1β and Il-6 and decreased levels of the anti-inflammatory Il-10 cytokine as compared with Alpl^+/+ mice. In bone metaphyses, murine hypertrophic chondrocytes and osteoblasts, Alpl mRNA levels were much higher than those of the adenosine nucleotidases Npp1, Cd39 and Cd73. In hypertrophic chondrocytes, inhibition of TNAP with 25 μM of MLS-0038949 decreased the hydrolysis of AMP and ATP. However, TNAP inhibition did not significantly modulate ATP- and adenosine-associated effects in these cells. We observed that part of TNAP proteins in hypertrophic chondrocytes was sent from the cell membrane to matrix vesicles, which may explain why TNAP participated in the hydrolysis of ATP but did not significantly modulate its autocrine pro-inflammatory effects. In MSCs, TNAP did not participate in ATP hydrolysis nor in secretion of inflammatory mediators. In contrast, in neutrophils, TNAP inhibition with MLS-0038949 significantly exacerbated ATP-associated activation and secretion of IL-1β, and extended cell survival. Collectively, these results demonstrate that TNAP is a nucleotidase in both hypertrophic chondrocytes and neutrophils, and that this nucleotidase function is associated with autocrine effects on inflammation only in neutrophils.

Discovery profiling and bioinformatics analysis of serum microRNA in Mitochondrial NeuroGastroIntestinal Encephalomyopathy (MNGIE)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare and fatal inherited metabolic disorder due to mutations in the nuclear TYMP gene and leads to a deficiency in the enzyme thymidine phosphorylase. This results in an accumulation of the deoxynucleosides, thymidine and deoxyuridine in the cellular and extracellular compartments, ultimately leading to mitochondrial failure. The understanding of the precise molecular mechanisms that underlie the disease pathology is limited, being hampered by the rarity of the disorder. Expression profiling of serum based mircoRNAs and subsequent bioinformatical analyses provide an approach to facilitate the identity of dysregulated genes and signalling pathways potentially involved in the pathogenesis of MNGIE.

HISTOCHEMICAL LOCALIZATION OF ENZYME ACTIVITY IN THE KIDNEYS OF THREE MAMMALIAN SPECIES DURING THEIR POSTNATAL DEVELOPMENT

The activities of various enzymes were studied histochemically in two species which at birth have a kidney with an active nephrogenic zone, the rat and rabbit, and one (the guinea pig) in which this organ is at this time apparently fully matured. The histochemical reactions, in general, reflect the degree of maturity found in kidneys of newborn and growing animals. Immature proximal convoluted tubules lack enzymatic activity or show only minimal amounts. As these tubules mature, the adult pattern is noted at about the 14th to 16th day after birth in rat, and after 21 to 28 days in rabbit. Within this general pattern, however, considerable variations are noted. Glucose-6-phosphatase, e.g., is less active at birth, even in mature tubules, while acid phosphatase localized in granular "lysosomal" bodies is as prominent in newborn kidney as in adult. Newborn guinea pig kidney lacks glomerular adenosine triphosphatase activity in spite of its general enzymatic maturity, while rat kidney at birth has no tubular adenosine triphosphatase activity, even in more mature proximal convolutions.

Oxidative enzymes, particularly succinic dehydrogenase, and acid phosphatase are active in tubules of the inner portion of medulla in rat and rabbit at birth. This appears to be an expression of the immaturity of newborn kidney. With the progress of zonal differentiation, this enzyme activity is no longer found in the papillary portion of medulla where thin limbs of Henle's loop are now located. In rat kidney, best seen in cryostat sections briefly postfixed in very cold neutral formalin, single cells are found in the collecting ducts with striking 5-nucleotidase activity. The number of these cells is greater in neonatal kidney than in adult kidney. The physiological significance of many of the findings described in this report has still to be clarified.

Association of Myxoviruses with an Adenosine Diphosphatase / Adenosine Triphosphatase / as Revealed by Chromatography on DEAE-Cellulose and by Density Gradient Centrifugation

Die Assoziation von einem, schon früher beschriebenen Adenosindiphosphat spaltenden Enzym mit den Teilchen von Myxoviren wurde mittels Chromatographie an DEAE-Cellulose und Dichte-Gradient-Zentrifugation von vorgereinigten Präparaten von Newcastle Disease, Sendai und A 2- Influenza-Viren sowie von dem gewebseigenen Enzym bestätigt. Das Enzym ist fähig, auch Adenosintriphosphat zu spalten.

Functional characterization of the C-terminal domain of mouse capping enzyme

Mouse capping enzyme (Mce1) consists of two functional domains: the amino-terminal triphosphatase domain and the carboxyl-terminal guanylyltransferase (GTase) domain. The bifunctional Mce1 gene encodes 597 a.a. with a molecular weight approximately 68 kDa. Mce1 cDNA is located on chromosome 4A4 approximately 4A5 and is composed of 17 exons. To functionally characterize the C-terminus of Mce1, we generated four truncated proteins with 12, 30, 37, or 60 a.a. deletions from the C-terminus of either the wild type (Mce1) or the isolated GTase domain (211-597), respectively. Plasmid shuffling experiment with Saccharomyces cerevisiae GTase subunit gene CEG1 null mutant demonstrated that deletion mutants 211-567 and 211-585 were able to support cell viability in the presence of 5-fluoroorotic acid, whereas 211-537 and 211-560 were not. Consistent with the yeast genetic study, both 211-567 and 211-585 had significant GTase activity in vitro, while 211-537 and 211-560 that were only detected in the insoluble fraction in the bacterial expression system, were completely inactive. Overall, both in vivo and in vitro studies indicate that the functional domain of Mce1 is between a.a. 211 and 567, and the heptapeptide sequence between 561 and 567 may play an important role in the enzyme activity.

Ecto-nucleotidases of the CD39/NTPDase family modulate platelet activation and thrombus formation: Potential as therapeutic targets

Extracellular nucleotide P2-receptor-mediated effects on platelets, leukocytes and endothelium are modulated by ecto-nucleotidases. These ecto-enzymes hydrolyze extracellular nucleotides to the respective nucleosides. The dominant ecto-nucleotidase expressed by the endothelium, by monocytes and vascular smooth muscle cells is CD39/NTPDase1. Ecto-nucleotidase biochemical activity of CD39 is lost at sites of acute vascular injury, such as in ischemia reperfusion and immune graft rejection. CD39L(Like)1/NTPDase2, a related protein, is associated with the basolateral surface of endothelium, the adventitia of vessels and microvascular pericytes. CD39/NTPDase1 hydrolyzes both tri- and diphosphonucleosides and blocks platelet aggregation responses to ADP. In contrast, CD39L1/NTPDase2, a preferential nucleoside triphosphatase, activates platelets by preferentially converting ATP to ADP, the major agonist of platelet P2 receptors. Spatial and temporal expression of NTPDases in the vasculature appears to control platelet activation, thrombus size and stability by regulating phosphohydrolytic activity and consequent P2 receptor signaling. Constitutively circulating microparticles appear to be associated with functional NTPDases, and accumulation of these at sites of vascular injury might influence local thrombus formation and evolution. The phenotype of the cd39-null mouse is in keeping with disordered thromboregulation with heightened susceptibility to inflammatory vasculary reactions, increased permeability and high levels of tissue fibrin. Paradoxically, these mutant mice also exhibit a bleeding phenotype with differential platelet P2Y1 desensitization. Over-expression of CD39 at sites of vascular injury and inflammation by adenoviral vectors, by transgenesis or by the use of pharmacological modalities with soluble derivatives has been shown to have major potential in several animal models tested to date. Future clinical applications will involve the development of new therapeutic strategies to various inflammatory vascular diseases and in transplantation.

Effects of single or combined histamine H1-receptor and leukotriene CysLT1-receptor antagonism on nasal adenosine monophosphate challenge in persistent allergic rhinitis

BACKGROUND

The effects of single or combined histamine H(1)-receptor and leukotriene CysLT(1)-receptor antagonism on nasal adenosine monophosphate (AMP) challenge in allergic rhinitis are unknown.

OBJECTIVE

We elected to study the effects of usual clinically recommended doses of fexofenadine (FEX), montelukast (ML) and FEX + ML combination, compared with placebo (PL), on nasal AMP challenge in patients with persistent allergic rhinitis.

METHODS

Twelve patients with persistent allergic rhinitis (all skin prick positive to house dust mite) were randomized in a double-blind cross-over fashion to receive for 1 week either FEX 180 mg, ML 10 mg, FEX 180 mg + ML 10 mg combination, or PL, with nasal AMP challenge performed 12 h after dosing. There was a 1-week washout period between each randomized treatment. The primary outcome measure was the maximum percentage peak nasal inspiratory flow (PNIF) fall from baseline over a 60-min period after nasal challenge with a single 400 mg ml(-1) dose of AMP. The area under the 60-min time-response curve (AUC) and nasal symptoms were measured as secondary outcomes.

RESULTS

There was significant attenuation (P < 0.05) of the mean maximum percentage PNIF fall from baseline after nasal AMP challenge vs. PL, 48; with FEX, 37; 95% confidence interval for difference 2, 20; ML, 35 (4, 22); and FEX + ML, 32 (7, 24). The AUC (%.min) was also significantly attenuated (P < 0.05) vs. PL, 1893; with FEX, 1306 (30, 1143); ML, 1246 (214, 1078); and FEX + ML, 1153 (251, 1227). There were no significant differences for FEX vs. ML vs. FEX + ML comparing either the maximum or AUC response. The total nasal symptom score (out of 12) was also significantly improved (P < 0.05) vs. PL, 3.3; with FEX, 2.1 (0.3, 2.0); ML, 2.0 (0.5, 1.9); and FEX + ML, 2.5 (0.1, 1.4).

CONCLUSION

FEX and ML as monotherapy significantly attenuated the response to nasal AMP challenge and improved nasal symptoms compared with PL, while combination therapy conferred no additional benefit.

Overexpression of a soybean cytosolic glutamine synthetase gene linked to organ-specific promoters in pea plants grown in different concentrations of nitrate

A glutamine synthetase gene ( GS15) coding for soybean cytosolic glutamine synthetase (GS1) fused to a constitutive promoter (CaMV 35S), a putative nodule-specific promoter (LBC(3)) and a putative root-specific promoter (rolD) was transformed into Pisum sativum L. cv. Greenfeast. Four lines with single copies of GS15 (one 35S-GS15 line, one LBC (3) -GS15 line, and two rolD-GS15 lines) were tested for the expression of GS15, levels of GS1, GS activity, N accumulation, N(2) fixation, and plant growth at different levels of nitrate. Enhanced levels of GS1 were detected in leaves of three transformed lines (the 35S-GS15 and rolD-GS15 transformants), in nodules of three lines (the LBC (3) -GS15 and rolD-GS15 transformants), and in roots of all four transformants. Despite increased levels of GS1 in leaves and nodules, there were no differences in GS activity in these tissues or in whole-plant N content, N(2) fixation, or biomass accumulation among all the transgenic lines and the wild-type control. However, the rolD-GS15 transformants, which displayed the highest levels of GS1 in the roots of all the transformants, had significantly higher GS activity in roots than the wild type. In one of the rolD-GS15 transformed lines (Line 8), increased root GS activity resulted in a lower N content and biomass accumulation, supporting the findings of earlier studies with Lotus japonicus (Limami et al. 1999 ). However, N content and biomass accumulation was not negatively affected in the other rolD-GS15 transformant (Line 9) and, in fact, these parameters were positively affected in the 0.1 mM treatment. These findings indicate that overexpression of GS15 in various tissues of pea does not consistently result in increases in GS activity. The current study also indicates that the increase in root GS activity is not always consistent with decreases in plant N and biomass accumulation and that further investigation of the relationship between root GS activity and growth responses is warranted.

SDT1/SSM1, a multicopy suppressor of S-II null mutant, encodes a novel pyrimidine 5'-nucleotidase

SDT1 (suppressor of disruption of TFIIS 1, YGL224c, also known as SSM1, suppressor of S-II null mutant 1) is Saccharomyces cerevisiae gene identified as a multicopy suppressor of 6-azauracil sensitivity in a null mutant of the transcription elongation factor S-II. We found that overproduction of SDT1 caused hyposensitivity to not only 6-azauracil but also 5-fluorouracil and 5-fluorocytosine. This hyposensitivity was limited to pyrimidine derivatives, and no effect was observed for non-pyrimidine drugs including such clinically used anti-fungal drugs as amphotericin B and fluconazole. Purified recombinant SDT1 protein specifically dephosphorylated 5'-UMP and 5'-CMP. These results suggested that SDT1 conferred pyrimidine-specific hyposensitivity by dephosphorylating active metabolites of 6- or 5-modified pyrimidines, i.e. 6- or 5-modified UMP. This is the first description of a highly specific pyrimidine 5'-nucleotidase in S. cerevisiae.

Transcription elongation factor S-II confers yeast resistance to 6-azauracil by enhancing expression of the SSM1 gene

Loss of function of S-II makes yeast sensitive to 6-azauracil. Here, we identified a multi-copy suppressor gene of this phenotype, termed SSM1 (suppressor of 6-azauracil sensitivity of the S-II null mutant 1), that encodes a novel protein consisting of 280 amino acid residues. Although both the SSM1 null mutant and the S-II/SSM1 double null mutant were viable under normal growth conditions, they resembled the S-II null mutant in being sensitive to 6-azauracil. Expression of the SSM1 gene was found to be repressed in the S-II null mutant but was restored by overexpression of chimeric S-II molecules that were able to stimulate transcription elongation by RNA polymerase II in vitro. Furthermore, we identified two transcription arrest sites within the transcription unit of the SSM1 gene in vitro that could be relieved by S-II. These results indicate that S-II confers yeast resistance to 6-azauracil by stimulating transcription elongation of the SSM1 gene.

Adenosinetriphosphatase and 5-nucleotidase activities in the plasma membrane of liver cells as revealed by electron microscopy

The sites of reaction product resulting from ATPase and 5-nucleotidase activities remaining in parenchymatous cells of osmium-fixed rat liver were studied by electron microscopy of thin sections. These indicate that both ATPase and 5-nucleotidase activities are localized in the plasma membrane where it folds to form the microvilli of the bile canaliculus, and that 5-nucleotidase activity is also present in the microvilli at the sinusoidal aspects of the cells. It is suggested that these enzymes, particularly ATPase, may play a role in molecular transport or in some kind of membrane activity at the cell surface. Of special interest is the apparent differential localization of these enzymes at the absorptive and secretory regions of the plasma membrane of the cell. It may be of interest to study changes in these enzyme localizations in pathologic states, as a sign of changed cell function. Some of the difficulties in the interpretation of enzyme reaction products seen in electron micrographs are discussed.

ATP enhances repair of hair bundles in sea anemones

Hair bundle mechanoreceptors of sea anemones are similar to those of the acousticolateralis system of vertebrates (Watson, Mire and Hudson, 1997, Hear. Res. 107, 53-63). Anemone hair bundles are repaired by 'repair proteins' secreted following a complete loss of structural integrity and loss of function caused by 1 h exposure to calcium free seawater. Exogenously supplied repair proteins (RP) restore structural integrity to hair bundles and restore vibration sensitivity in 7-8 min (Watson, Mire and Hudson, 1998, Hear. Res. 115, 119-128). We here report that exogenously supplied ATP enhances the rate by which RP restore vibration sensitivity. A bimodal dose response to ATP indicates maximal enhancement at picomolar and micromolar concentrations of ATP. At these concentrations of ATP, vibration sensitivity is restored in 2 min. These data suggest that at least two ATPases exhibiting different binding affinities for ATP are involved in the repair process. Whereas the higher affinity site is specific for ATP, the lower affinity site does not discriminate between ATP and ADP. Nucleotidase cytochemistry localizes ATPase activity in isolated repair proteins. In the absence of exogenously added RP, sea anemones secrete and consume ATP during the 4 h recovery period after 1 h exposure to calcium free seawater. In the presence of exogenously added RP, ATP is secreted and then consumed within 10 min. Quinacrine cytochemistry localizes possible stores of ATP in the apical cytoplasm of sensory neurons located at the center of the hair bundle. According to our model, ATP is secreted by the sensory neuron after its hair bundle loses structural integrity. Hydrolysis of ATP by repair proteins is essential to the repair process.

The fine localization of nucleoside triphosphatase activity in the retina of the frog

Nucleoside triphosphatase (NTPase) activity was demonstrated at the submicroscopic level in the frog retina by the Wachstein-Meisel method utilizing various purine and pyrimidine nucleosides. Under the electron microscope magnesium-activated NTPase was localized in the outer and inner segments, and in the plexiform layers. NTPase active sites in the cones were localized diffusely in the 70 to 80 A interspaces between the double membranes of the stacked lamellae and in the investing cytoplasm. In the rods, on the other hand, sites of activity were observed at the periphery of the stacked lamellae as discrete electron opaque deposits measuring 1000 to 1500 A which interdigitated between the lamellae for short distances. Deposits of reaction product appeared more numerous in rods of dark-adapted frogs stimulated with monochromatic light with a wave length of 510 mmicro. Enzyme activity was also observed in mitochondria of the rod and cone ellipsoids. In the outer and inner plexiform layers NTPase active sites were present on and between the membranes of axons and the plasma membranes of some of the neurons.