Recombinant expression of perchloric acid-soluble protein reduces cell proliferation

Perchloric acid-soluble protein (PSP) may play an important role in the regulation of cellular physiological functions because it has been highly conserved throughout evolution; however, this role has not been well elucidated. In previous reports, we suggested that PSP regulates cell proliferation. In this study, we examined the effect of PSP expression on proliferation of the normal rat kidney cell line NRK-52E, the rat hepatocyte cell line RLN-10, and the rat hepatoma cell line dRLh-84. Cells transfected with pcDNA-sense-PSP (pcDNA-S-PSP) over-expressed PSP mRNA and protein, and cell proliferation of the transfected cells was suppressed compared with that of cells transfected with pcDNA-empty (pcDNA-E). Cell viability of pcDNA-S-PSP-transfected cells was similar to that of pcDNA-E-transfected cells. Thus, over-expression of PSP suppresses cell proliferation without any influence on cell viability. These findings are the first to report an inhibitory activity of PSP on cell proliferation. Received 27 April 2001; received after revision 8 June 2001; accepted 8 June 2001     

Telomere dysfunction and evolution of intestinal carcinoma in mice and humans

Telomerase activation is a common feature of advanced human cancers and facilitates the malignant transformation of cultured human cells and in mice. These experimental observations are in accord with the presence of robust telomerase activity in more advanced stages of human colorectal carcinogenesis. However, the occurrence of colon carcinomas in telomerase RNA (Terc)-null, p53-mutant mice has revealed complex interactions between telomere dynamics, checkpoint responses and carcinogenesis. We therefore sought to determine whether telomere dysfunction exerts differential effects on cancer initiation versus progression of mouse and human intestinal neoplasia. In successive generations of ApcMin Terc-/- mice, progressive telomere dysfunction led to an increase in initiated lesions (microscopic adenomas), yet a significant decline in the multiplicity and size of macroscopic adenomas. That telomere dysfunction also contributes to human colorectal carcinogenesis is supported by the appearance of anaphase bridges (a correlate of telomere dysfunction) at the adenoma-early carcinoma transition, a transition recognized for marked chromosomal instability. Together, these data are consistent with a model in which telomere dysfunction promotes the chromosomal instability that drives early carcinogenesis, while telomerase activation restores genomic stability to a level permissive for tumor progression. We propose that early and transient telomere dysfunction is a major mechanism underlying chromosomal instability of human cancer.     

High frequency of homoplasmic mitochondrial DNA mutations in human tumors can be explained without selection

Researchers in several laboratories have reported a high frequency of homoplasmic mitochondrial DNA (mtDNA) mutations in human tumors. This observation has been interpreted to reflect a replicative advantage for mutated mtDNA copies, a growth advantage for a cell containing certain mtDNA mutations, and/or tumorigenic properties of mtDNA mutations. We consider another possibility-that the observed homoplasmy arose entirely by chance in tumor progenitor cells, without any physiological advantage or tumorigenic requirement. Through extensive computer modeling, we demonstrate that there is sufficient opportunity for a tumor progenitor cell to achieve homoplasmy through unbiased mtDNA replication and sorting during cell division. To test our model in vivo, we analyzed mtDNA homoplasmy in healthy human epithelial tissues and discovered that the model correctly predicts the considerable observed frequency of homoplasmic cells. Based on the available data on mitochondrial mutant fractions and cell division kinetics, we show that the predicted frequency of homoplasmy in tumor progenitor cells in the absence of selection is similar to the reported frequency of homoplasmic mutations in tumors. Although a role for other mechanisms is not excluded, random processes are sufficient to explain the incidence of homoplasmic mtDNA mutations in human tumors.     

Failure to confirm NOTCH4 association with schizophrenia in a large population-based sample from Scotland

The NOTCH4 gene was recently reported to be associated with schizophrenia based on TDT analysis of 80 British trios. The strongest evidence for association derived from two microsatellites. We genotyped both loci in a large sample of unrelated Scottish schizophrenics and controls, but failed to replicate the reported association, finding instead that each putative schizophrenia-associated allele had a somewhat lower frequency in schizophrenics than in controls.     

A 5-bp deletion in ELOVL4 is associated with two related forms of autosomal dominant macular dystrophy

Stargardt-like macular dystrophy (STGD3, MIM 600110) and autosomal dominant macular dystrophy (adMD) are inherited forms of macular degeneration characterized by decreased visual acuity, macular atrophy and extensive fundus flecks. Genetic mapping data suggest that mutations in a single gene may be responsible for both conditions, already known to bear clinical resemblance. Here we limit the minimum genetic region for STGD3 and adMD to a 0.6-cM interval by recombination breakpoint mapping and identify a single 5-bp deletion within the protein-coding region of a new retinal photoreceptor-specific gene, ELOVL4, in all affected members of STGD3 and adMD families. Bioinformatic analysis of ELOVL4 revealed that it has homology to a group of yeast proteins that function in the biosynthesis of very long chain fatty acids. Our results are therefore the first to implicate the biosynthesis of fatty acids in the pathogenesis of inherited macular degeneration.     

Porcine factor V: cDNA cloning, gene mapping, three-dimensional protein modeling of membrane binding sites and comparative anatomy of domains

Factor V is a plasma protein essential for blood coagulation. This protein is involved in activated protein C resistance, the most common inherited thrombotic disorder known. We utilized the polymerase chain reaction to clone the porcine factor V gene by generating overlapping clones amplified with primers chosen by comparison with known nucleotide sequences. The porcine factor V cDNA contig encodes a predicted 2258-amino acid protein, making it the largest in comparison to the bovine, human, and murine proteins. Porcine factor V has the highest level of homology with bovine factor V, but also has high levels of conservation of important residues with all the species. Radiation hybrid mapping assigned the porcine factor V gene to chromosome 4. Three-dimensional models of factor V were generated and used to analyze membrane-binding sites in terms of conserved, and therefore likely important residues. Received 3 October 2000; revised 23 November 2000; accepted 6 December 2000     

The prolactin releasing peptides: RF-amide peptides

Although dopamine is considered the major hypothalamic controller of prolactin release from the anterior pituitary gland, there is evidence that a yet to be discovered prolactin releasing factor (PRF) also exists in brain. Recently, two peptides were isolated, products of the same prohormone, that were reported to have significant prolactin-releasing activity. These peptides, called prolactin releasing peptides, are not accepted by all investigators to be in fact PRFs. Instead, it appears that their widespread distribution in brain and the presence of receptors for the peptides in sites unrelated to neuroendocrine function are the basis for a variety of central nervous system action including activation of the autonomic nervous system. Thus, these peptides may not be PRFs, but instead neuroactive agents that are involved in many brain circuits with divergent functions.     

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

The discovery of superconductivity at 39 K in magnesium diboride, MgB2, raises many issues, a critical one being whether this material resembles a high-temperature copper oxide superconductor or a low-temperature metallic superconductor in terms of its behaviour in strong magnetic fields. Although the copper oxides exhibit very high transition temperatures, their in-field performance is compromized by their large anisotropy, the result of which is to restrict high bulk current densities to a region much less than the full magnetic-field-temperature (H-T) space over which superconductivity is found. Moreover, the weak coupling across grain boundaries makes transport current densities in untextured polycrystalline samples low and strongly sensitive to magnetic field. Here we report that, despite the multiphase, untextured, microscale, subdivided nature of our MgB2 samples, supercurrents flow throughout the material without exhibiting strong sensitivity to weak magnetic fields. Our combined magnetization, magneto-optical, microscopy and X-ray investigations show that the supercurrent density is mostly determined by flux pinning, rather than by the grain boundary connectivity. Our results therefore suggest that this new superconductor class is not compromized by weak-link problems, a conclusion of significance for practical applications if higher temperature analogues of this compound can be discovered.     

Late Jurassic salamanders from northern China

With ten extant families, salamanders (urodeles) are one of the three major groups of modern amphibians (lissamphibians). Extant salamanders are often used as a model system to assess fundamental issues of developmental, morphological and biogeographical evolution. Unfortunately, our understanding of these issues has been hampered by the paucity of fossil evidence available to assess the early history of the group. Here we report the discovery of an extraordinary sample of salamander fossils, some with rare soft-tissue impressions, from the Upper Jurassic of China. With over 500 articulated specimens, this assemblage documents the morphological diversity of early urodeles and includes larvae and adults of both neotenic and metamorphosed taxa. Phylogenetic analysis confirms that these salamanders are primitive, and reveals that all basal salamander clades have Asian distributions. This is compelling evidence for an Asian origin of Recent salamanders, as well as for an extensive and early radiation of several major lineages. These discoveries show that the evolution of salamanders has involved phylogenetic and ecological diversification around a body plan that has remained fundamentally stable for over 150 million years.