Biomedical subjects

M Pi

Publications and source records attributed to M Pi.

At least 19 recordsLinked to original sources

PubMed2003

Bound states of 3He at the edge of a 4He drop on a cesium surface.

We show that small amounts of 3He atoms, added to a 4He drop deposited on a flat cesium surface at zero temperature, populate bound states localized at the contact line. These edge states show up for drops large enough to develop well defined surface and bulk regions together with a contact line, and they are structurally different from the well-known Andreev states that appear at the free surface and at the liquid-solid interface of films. We illustrate the one-body density of 3He in a drop with 1000 4He atoms, and show that for a sufficiently large number of impurities the density profiles spread beyond the edge, coating both the curved drop surface and its flat base and eventually isolating it from the substrate.

Journal Article↗

PubMed2001

Quantized vortices in mixed 3He-4He drops.

Using density functional theory, we investigate the structure of mixed (3)He(N3)-(4)He(N4) droplets with an embedded impurity (Xe atom or HCN molecule) which pins a quantized vortex line. We find that the dopant+vortex+(4)He(N4) complex, which in a previous work [F. Dalfovo et al., Phys. Rev. Lett. 85, 1028 (2000)] was found to be energetically stable below a critical size N(cr), is robust against the addition of 3He. While 3He atoms are distributed along the vortex line and on the surface of the 4He drop, the impurity is mostly coated by 4He atoms. Results for N4 = 500 and a number of 3He atoms ranging from 0 to 100 are presented, and the binding energy of the dopant to the vortex line is determined.

Journal Article↗

PubMed2001

Dissociation of vertical semiconductor diatomic artificial molecules.

We investigate the dissociation of few-electron circular vertical semiconductor double quantum dot artificial molecules at 0 T as a function of interdot distance. A slight mismatch introduced in the fabrication of the artificial molecules from nominally identical constituent quantum wells induces localization by offsetting the energy levels in the quantum dots by up to 2 meV, and this plays a crucial role in the appearance of the addition energy spectra as a function of coupling strength particularly in the weak coupling limit.

Journal Article↗

PubMed2001

Rickets in cation-sensing receptor-deficient mice: an unexpected skeletal phenotype.

The hypothesis that local changes in extracellular calcium may serve a physiological role in regulating osteoblast, osteoclast, and cartilage function through the extracellular cation-sensing receptor, CasR, is gaining widespread support, but lacks definite proof. To examine the effects of CasR deficiency on the skeleton, we performed a detailed analysis of the skeleton in CasR knockout mice (CasR(-/-)) and wild-type littermates (CasR(+/+)). CasR ablation in the parathyroid glands of CasR(-/-) mice resulted in hyperparathyroidism, hypercalcemia, and hypophosphatemia. Except for dwarfism, the expected skeletal manifestations of PTH excess, namely chondrodysplasia and increased mineralized bone formation and resorption, were not the main skeletal features in CasR(-/-) mice. Rather, rickets was the predominant skeletal abnormality in these animals, as evidenced by a widened zone of hypertrophic chondrocytes, impaired growth plate calcification and disorderly deposition of mineral, excessive osteoid accumulation, and prolonged mineralization lag time in metaphyseal bone. CasR transcripts were identified in cartilage and bone marrow of CasR(+/+) mice, but not in mineralized bone containing mature osteoblasts and osteocytes. These findings indicate that a calcium-sensing receptor is present in the skeleton, and its absence results in defective mineralization of cartilage and bone by mechanisms that remain to be elucidated.

Animals↗

PubMed2000

Pinning of quantized vortices in helium drops by dopant atoms and molecules

Using a density functional method, we investigate the properties of liquid 4He droplets doped with atoms (Ne and Xe) and molecules ( SF6 and hydrogen cyanide). We consider the case of droplets having a quantized vortex pinned to the dopant. A liquid-drop formula is proposed that accurately describes the total energy of the complex and allows one to extrapolate the density functional results to large N. For a given impurity, we find that the formation of a dopant+vortex+(4)He(N) complex is energetically favored below a critical size N(cr). Our results support the possibility to observe quantized vortices in helium droplets by means of spectroscopic techniques.

Journal Article↗

PubMed2000

Sensing of extracellular cations in CasR-deficient osteoblasts. Evidence for a novel cation-sensing mechanism.

We isolated osteoblastic cell lines from wild-type (CasR(+/+)) and receptor null (CasR(-/-)) mice to investigate whether CasR is present in osteoblasts and accounts for their responses to extracellular cations. Osteoblasts from both CasR(+/+) and CasR(-/-) mice displayed an initial period of cell replication followed by a culture duration-dependent increase in alkaline phosphatase activity, expression of osteocalcin, and mineralization of extracellular matrix. In addition, a panel of extracellular cations, including aluminum and the CasR agonists gadolinium and calcium, stimulated DNA synthesis, activated a transfected serum response element-luciferase reporter construct, and inhibited agonist-induced cAMP in CasR(-/-) osteoblasts. The functional responses to these cations were identical in CasR(+/+) and CasR(-/-) osteoblasts. Thus, the absence of CasR alters neither the maturational profile of isolated osteoblast cultures nor their in vitro responses to extracellular cations. In addition, CasR transcripts could not be detected by reverse transcription-polymerase chain reaction with mouse specific primers in either CasR(+/+) or CasR(-/-) osteoblasts, and immunoblot analysis with a CasR-specific antibody was negative for CasR protein expression in osteoblasts. The presence of a cation-sensing response in osteoblasts from CasR(-/-) mice indicates the existence of a novel osteoblastic extracellular cation-sensing mechanism.

Amino Acid Sequence↗

PubMed2000

The mitochondrial DNA of Dictyostelium discoideum: complete sequence, gene content and genome organization.

We present an overview of the gene content and organization of the mitochondrial genome of Dictyostelium discoideum. The mitochondria genome consists of 55,564 bp with an A + T content of 72.6%. The identified genes include those for two ribosomal RNAs (rn1 and rns), 18 tRNAs, ten subunits of the NADH dehydrogenase complex (nad1, 2, 3, 4, 4L, 5, 6, 7, 9 and 11), apocytochrome b (cytb), three subunits of the cytochrome oxidase (cox1/2 and 3), four subunits of the ATP synthase complex (atp1, 6, 8 and 9), 15 ribosomal proteins, and five other ORFs, excluding intronic ORFs. Notable features of D. discoideum mtDNA include the following. (1) All genes are encoded on the same strand of the DNA and a universal genetic code is used. (2) The cox1 gene has no termination codon and is fused to the downstream cox2 gene. The 13 genes for ribosomal proteins and four ORF genes form a cluster 15.4 kb long with several gene overlaps. (3) The number of tRNAs encoded in the genome is not sufficient to support the synthesis of mitochondrial protein. (4) In total, five group I introns reside in rnl and cox1/2, and three of those in cox1/2 contain four free-standing ORFs. We compare the genome to other sequenced mitochondrial genomes, particularly that of Acanthamoeba castellanii.

Animals↗

PubMed1999

Aluminum is a weak agonist for the calcium-sensing receptor.

BACKGROUND: Aluminum (Al3+) has diverse biological effects mediated through activation of a putative extracellular cation-sensing receptor. A recently identified calcium-sensing receptor (CaSR), which has been identified in target tissues for Al3+, may transduce some of the biological effects of Al3+. METHODS: To test this possibility, we transfected human embryonic kidney 293 (HEK 293) cells with a cDNA encoding the rat CaSR and evaluated CaSR expression by Western blot analysis and function by measurement of intracellular calcium ([Ca2+]i) levels and inositol monophosphate (IP1) generation following stimulation with Al3+ and a panel of CaSR agonists. RESULTS: The CaSR protein was detected by immunoblot analysis in cells transfected with the CaSR cDNA but not in nontransfected HEK 293 cells. In addition, [Ca2+]i levels and IP1 generation were enhanced in a dose-dependent fashion by additions of the CaSR agonists calcium (Ca2+), magnesium (Mg2+), gadolinium (Gd3+), and neomycin only in cells transfected with CaSR. To determine if Al3+ activated CaSR, we stimulated cells transfected with rat CaSR with 10 microM to 1 mM concentrations of Al3+. Concentrations of Al3+ in the range of 10 microM to 100 microM had no effect on [Ca2+]i levels or IP1 generation. In contrast, 1 mM Al3+ induced small but significant increases in both parameters. Whereas Gd3+ antagonized calcium-mediated activation of CaSR, pretreatment with Al3+ failed to block subsequent activation of rat CaSR by Ca2+, suggesting a distinct mechanism of Al3+ action. CONCLUSION: Al3+ is not a potent agonist for CaSR. Because Al3+ affects a variety of target tissues at micromolar concentrations, it seems unlikely that CaSR mediates these cellular actions of Al3+.

Aluminum↗

PubMed1999

Failure to detect the extracellular calcium-sensing receptor (CasR) in human osteoblast cell lines.

Whether the known calcium-sensing receptor (CasR) is present in osteoblasts is a source of considerable controversy. Prior studies failed to detect CasR in osteoblasts, but more recent investigations purport the detection of CasR in several osteoblast cell lines by immunoblot analysis with polyclonal anti-CasR antisera (4637) and low stringency reverse transcriptase-polymerase chain reaction (RT-PCR). To explain these disparate findings, we performed immunoblot analysis with the 4637 anti-CasR antisera and a highly specific monoclonal antibody to CasR (ADD), and we compared the ability of low and high stringency RT-PCR to amplify CasR transcripts. We found that the ADD antibody detected the anticipated CasR immunoreactive bands, including a approximately 165 kDa and approximately 140 kDa glycosylated doublet and a >250 kDa dimerized receptor, in positive control mouse kidney, human parathyroid, and human embryonic kidney (HEK) 293 cells transfected with rat CasR, but we did not detect these bands in either wild-type HEK 293 cells or Saos2, MG-63, or U-2 OS osteoblast-like cell lines. Standard two-step RT-PCR using CasR-specific primers confirmed these results by detecting CasR transcripts in positive controls but not in negative control HEK 293 cells or osteoblast cell lines. In contrast, the 4637 antisera did not recognize CasR by immunoblot analysis under the conditions studied and our low stringency RT-PCR procedure amplified nonspecific products in wild-type HEK 293 cells and osteoblasts. Since we failed to detect CasR in human osteoblast cell lines using either the highly specific ADD antibody or RT-PCR under standard conditions, it is possible that the cation response in osteoblasts is mediated by a functionally similar but molecularly distinct calcium sensing receptor.

Amino Acid Sequence↗

PubMed1998

The Dictyostelium developmental cDNA project: generation and analysis of expressed sequence tags from the first-finger stage of development.

In an effort to identify and characterize genes expressed during multicellular development ill Dictyostelium, we have undertaken a cDNA sequencing project. Using size-fractionated subsets of cDNA from the first finger stage, two sets of gridded libraries were constructed for cDNA sequencing. One, library S, consisting of 9984 clones, carries relatively short inserts, and the other, library L, which consists of 8448 clones, has longer inserts. We sequenced all the selected clones in library S from their 3'-ends, and this generated 3093 non-redundant, expressed sequence tags (ESTs). Among them, 246 ESTs hit known Dictyostelium genes and 910 showed significant similarity to genes of Dictyostelium and other organisms. For library L, 1132 clones were randomly sequenced and 471 non-redundant ESTs were obtained. In combination, the ESTs from the two libraries represent approximately 40% of genes expressed in late development, assuming that the non-redundant ESTs correspond to independent genes. They will provide a useful resource for investigating the genetic networks that regulate multicellular development of this organism.

Animals↗

PubMed1998

A ribosomal protein gene cluster is encoded in the mitochondrial DNA of Dictyostelium discoideum: UGA termination codons and similarity of gene order to Acanthamoeba castellanii.

We sequenced a region of about 14.5 kb downstream from the ribosomal protein L11 gene (rpl11) in the mitochondrial DNA (54+/-2 kb) of the cellular slime mold Dictyostelium discoideum. Sequence analysis revealed that eleven ribosomal protein genes and six open reading frames (ORFs) formed a cluster arranged in the order: rpl11-orf189-rps12-rps7-rpl2-rps19-+ ++orf425-orf1740-rpl16-rpl14-orf188- rps14-rps8-rpl6-rps13-orf127-orf796. This order was very similar to that of homologous genes in Acanthamoeba castellanii mitochondrial DNA. The N-terminal region of ORF425 and the C-terminal region of ORF1740 had partial similarities to the S3 ribosomal protein of other organisms. The termination codons of rpl16 and orf188 were UGA, which has not hitherto been found in genes encoded in D. discoideum mitochondrial DNA.

Acanthamoeba↗

PubMed1998

Characterization of a novel small RNA encoded by Dictyostelium discoideum mitochondrial DNA.

In this study, we analyzed a mitochondrial small (ms) RNA in Dictyostelium discoideum, which is 129 nucleotides long and has a GC content of only 22.5%. In the mitochondrial DNA, a single-copy gene (msr) for the ms RNA was located downstream of the gene for large-subunit rRNA. The location of msr was similar to that of the 5S rRNA gene in prokaryotes and chloroplasts, but clearly different from that in mitochondria of plants, liverwort and the chlorophycean alga Prototheca wikerhamii, in which small-subunit rRNA and 5S rRNA genes are closely linked. THe primary sequence of ms rRNA showed low homology with mitochondrial 5S rRNA from plants, liverwort and the chlorophycean alga, but the proposed secondary structure of ms RNA was similar to that of cytoplasmic 5S rRNA. In addition, ms RNA showed a highly conserved GAAC sequence in the same loop as in common 5S rRNA. However, ms RNA was detected mainly in the mitochondrial 25,000 x g supernatant fraction which was devoid of ribosomes. It is possible that ms RNA is an evolutionary derivative of mitochondrial 5S rRNA.

Animals↗

PubMed1996