“Unblocking” Serum Activity <Emphasis Type="Italic">in vitro</Emphasis> in the Polyoma System may Correlate with Antitumour Effects of Antiserum <Emphasis Type="Italic">in vivo</Emphasis>

In a variety of tumour systems, individuals carrying progressively growing neoplasms have lymphoid cells with a specific cytotoxic effect on cultured tumour cells from the same individual^1–4. Since the sera of tumour-bearing individuals have been shown to prevent tumour cell destruction by immune lymphocytes in vitro^2,5–8 and since this serum blocking activity appears early in primary and transplant tumour development^5,7, it has been suggested that the appearance of this serum blocking activity might be responsible for the progressive growth of tumours in individuals having cytotoxic lymphocytes. Counteraction of this blocking activity would thus be of primary importance in facilitating the function of an already existing or bolstered cell-mediated immunity. The serum blocking activity might be inhibited in various ways, by preventing the formation of blocking antibody or by interfering with its action (“unblocking”), as demonstrated in Moloney sarcoma regressor sera⁹. This type of serum also has a therapeutic effect on Moloney sarcomas in vivo^10,11, which has been tentatively attributed to its unblocking activity^8,9 or, possibly, to a complement-dependent cytotoxicity¹⁰. Tumour growth in the Moloney sarcoma system, however, might be due in part to continuous recruitment of neoplastic cells by virus-induced transformation and so the therapeutic effect could be due to a virus-neutralizing serum activity^9,10.     

On the mechanism of ATP-induced shape changes in the human erythrocyte membranes: the role of ATP

In the preceding paper (Sheetz, M. and S.J. Singer. 1977. J Cell Biol. 73:638-646) it was shown that erythrocyte ghosts undergo pronounced shape changes in the presence of mg-ATP. The biochemical effects of the action of ATP are herein examined. The biochemical effects of the action of ATP are herein examined. Phosphorylation by ATP of spectrin component 2 of the erythrocyte membrane is known to occur. We have shown that it is only membrane protein that is significantly phosphorylated under the conditions where the shape changes are produced. The extent of this phosphorylation rises with increasing ATP concentration, reaching nearly 1 mol phosphoryle group per mole of component 2 at 8mM ATP. Most of this phosphorylation appears to occur at a single site on the protein molecule, according to cyanogen bromide peptide cleavage experiments. The degree of phosphorylation of component 2 is apparently also regulated by a membrane-bound protein phosphatase. This activity can be demonstrated in erythrocyte ghosts prepared from intact cells prelabeled with [(32)P]phosphate. In addition to the phosphorylation of component 2, some phosphorylation of lipids, mainly of phosphatidylinositol, is also known to occur. The ghost shape changes are, however, shown to be correlated with the degree of phosphorylation of component 2. In such experiment, the incorporation of exogenous phosphatases into ghosts reversed the shape changes produced by ATP, or by the membrane-intercalating drug chlorpromazine. The results obtained in this and the preceding paper are consistent with the proposal that the erythrocyte membrane possesses kinase and phosphates activities which produce phosphorylation and dephosphorylation of a specific site on spectrin component 2 molecules; the steady-state level of this phosphorylation regulates the structural state of the spectrin complex on the cytoplasmic surface of the membrane, which in turn exerts an important control on the shape of the cell.     

Selective inhibition of prostaglandin biosynthesis by gold salts and phenylbutazone

Gold salts and phenylbutazone selectively inhibit the synthesis of PGF_2α and PGE₂ respectively. Lowered production of one prostaglandin species is accompanied by an increased production of the other. Selective inhibition by these drugs was observed in the presence of adrenaline, reduced glutathione and copper sulphate under conditions when most anti-inflammatory compounds inhibited PGE₂ and PGF_2α syntheses equally. It is postulated that selective inhibitors may have a different mode of action and beneficial effects may be related to the endogenous ratio of PGE to PGF required for normal function.     

A dynamic spatiotemporal extracellular matrix facilitates epicardial-mediated vertebrate heart regeneration

Unlike humans, certain adult vertebrates such as newts and zebrafish possess extraordinary abilities to functionally regenerate lost appendages and injured organs, including cardiac muscle. Here, we present new evidence that a remodeled extracellular matrix (ECM) directs cell activities essential for cardiac muscle regeneration. Comprehensive mining of DNA microarrays and Gene Ontology term enrichment analyses for regenerating newt and zebrafish hearts revealed that distinct ECM components and ECM-modifying proteases are among the most significantly enriched genes in response to local injury. In contrast, data analyses for mammalian cardiac injury models indicated that inflammation and metabolic processes are the most significantly activated gene groups. In the regenerating newt heart, we show dynamic spatial and temporal changes in tenascin-C, hyaluronic acid, and fibronectin ECM distribution as early as 3 days postamputation. Linked to distinct matrix remodeling, we demonstrate a myocardium-wide proliferative response and radial migration of progenitor cells. In particular, we report dramatic upregulation of a regeneration-specific matrix in the epicardium that precedes the accumulation and migration of progenitor cells. For the first time, we show that the regenerative ECM component tenascin-C significantly increases newt cardiomyocyte cell cycle reentry in vitro. Thus, the engineering of nature-tested extracellular matrices may provide new strategic opportunities for the enhancement of regenerative responses in mammals.     

Dedifferentiation of mammalian myotubes induced by msx1

The process of cellular differentiation culminating in terminally differentiated mammalian cells is thought to be irreversible. Here, we present evidence that terminally differentiated murine myotubes can be induced to dedifferentiate. Ectopic expression of msx1 in C2C12 myotubes reduced the nuclear muscle proteins MyoD, myogenin, MRF4, and p21 to undetectable levels in 20%-50% of the myotubes. Approximately 9% of the myotubes cleave to produce either smaller multinucleated myotubes or proliferating, mononucleated cells. Finally, clonal populations of the myotube-derived mononucleated cells can be induced to redifferentiate into cells expressing chondrogenic, adipogenic, myogenic, and osteogenic markers. These results suggest that terminally differentiated mammalian myotubes can dedifferentiate when stimulated with the appropriate signals and that msx1 can contribute to the dedifferentiation process.     

A web server to locate periodicities in a sequence

Summary : FT is a tool written in C++, which implements the Fourier analysis method to locate periodicities in aminoacid or DNA sequences. It is provided for free public use on a WWW server with a Java interface. Availability : The server address is http://o2.db. uoa.gr/FT Contact : shamodr@atlas.uoa.gr      

Cellular electroporation induces dedifferentiation in intact newt limbs

Newts have the remarkable ability to regenerate lost appendages including their forelimbs, hindlimbs, and tails. Following amputation of an appendage, the wound is rapidly closed by the migration of epithelial cells from the proximal epidermis. Internal cells just proximal to the amputation plane begin to dedifferentiate to form a pool of proliferating progenitor cells known as the regeneration blastema. We show that dedifferentiation of internal appendage cells can be initiated in the absence of amputation by applying an electric field sufficient to induce cellular electroporation, but not necrosis or apoptosis. The time course for dedifferentiation following electroporation is similar to that observed following amputation with evidence of dedifferentiation beginning at about 5 days postelectroporation and continuing for 2 to 3 weeks. Microarray analyses, real-time RT-PCR, and in situ hybridization show that changes in early gene expression are similar following amputation or electroporation. We conclude that the application of an electric field sufficient to induce transient electroporation of cell membranes induces a dedifferentiation response that is virtually indistinguishable from the response that occurs following amputation of newt appendages. This discovery allows dedifferentiation to be studied in the absence of wound healing and may aid in identifying genes required for cellular plasticity.     

Multi-Tissue Microarray Analysis Identifies a Molecular Signature of Regeneration

The inability to functionally repair tissues that are lost as a consequence of disease or injury remains a significant challenge for regenerative medicine. The molecular and cellular processes involved in complete restoration of tissue architecture and function are expected to be complex and remain largely unknown. Unlike humans, certain salamanders can completely regenerate injured tissues and lost appendages without scar formation. A parsimonious hypothesis would predict that all of these regenerative activities are regulated, at least in part, by a common set of genes. To test this hypothesis and identify genes that might control conserved regenerative processes, we performed a comprehensive microarray analysis of the early regenerative response in five regeneration-competent tissues from the newt Notophthalmus viridescens. Consistent with this hypothesis, we established a molecular signature for regeneration that consists of common genes or gene family members that exhibit dynamic differential regulation during regeneration in multiple tissue types. These genes include members of the matrix metalloproteinase family and its regulators, extracellular matrix components, genes involved in controlling cytoskeleton dynamics, and a variety of immune response factors. Gene Ontology term enrichment analysis validated and supported their functional activities in conserved regenerative processes. Surprisingly, dendrogram clustering and RadViz classification also revealed that each regenerative tissue had its own unique temporal expression profile, pointing to an inherent tissue-specific regenerative gene program. These new findings demand a reconsideration of how we conceptualize regenerative processes and how we devise new strategies for regenerative medicine.