Håkan Persson

Coexpression of the sis and myc proto-oncogenes in developing human placenta suggests autocrine control of trophoblast growth

First trimester human placentas actively express the sis proto-oncogene, the structural gene for the B chain of platelet-derived growth factor (PDGF). Using the in situ hybridization technique, the 4.2 kb c-sis transcript has been localized to the cytotrophoblastic component, especially the highly proliferative and invasive cytotrophoblastic shell, paralleling the distribution of c-myc transcripts in early placenta. Explants of first trimester placenta release significant levels of PDGF-like activity into the medium under apparent developmental control. Moreover, cultured trophoblasts display abundant high-affinity PDGF receptors and respond to exogenous authentic PDGF by an activation of the c-myc gene and DNA synthesis. The developing human placenta may therefore represent a case of autocrine growth regulation in a normal tissue, in which cells bearing receptors for a growth factor can also synthesize and respond to that factor.

On the interaction between polysaccharides and other macromolecules: II. The transport of globular particles through hyaluronic acid solutions☆

Abstract A study of the diffusion behaviour of albumin, α-crystallin, fribrinogen, and turnip yellow mosaic virus in hyaluronic acid media has shown that the diffusion rates of these substances are markedly decreased by the presence of the polysaccharide. The relative decrease in the same as the corresponding effect observed on the sedimentation rates of these substances. Investigation of eleven globular particles with diameters of 47–3650 A established that the relative decrease of the sedimentation rate of a particle in the presence of hyaluronic acid was essentially a function of the diameter of the particle and the concentration of the polysaccharide and that the effect could be expressed by a simple exponential relationship. The results observed have been interpreted as a macromolecular-sieving effect of the polysaccharide.

Decreased level of nerve growth factor (NGF) and its messenger RNA in the aged rat brain

Trophic factors such as nerve growth factor (NGF) are thought to support survival, differentiation and maintenance of neurons. Recent results indicate that NGF produced in cortical and hippocampal areas is required for the function of cholinergic neurons in the basal forebrain. With the use of enzyme immunoassay and RNA blot hybridization we studied the NGF protein and NGF mRNA, respectively, in regions of the brain innervated by basal forebrain cholinergic neurons in adult and aged rats. Levels of NGF protein were decreased by 40% in hippocampus of aged (28 months) Fischer 344 rats compared with adults (6 months), whereas no alterations were observed in cerebral cortex. Moreover, a reduction by 50% in the NGF mRNA was found in samples of the aged forebrain (cerebral cortex, hippocampus, basal forebrain and hypothalamus) compared to the adult. NGF deficiencies may thus account for the loss of cholinergic neurons in the basal forebrain generally found to accompany normal aging and resulting in altered cognitive functions.

Synthesis of a structural adenovirus polypeptide in the absence of viral DNA replication.

HeLa cells were pulse labeled with [35S]methionine at different times after infection with adenovirus type 2 to follow the kinetics of viral polypeptide synthesis. Cell lysates were prepared and viral proteins were analyzed by immunoprecipitation with antisera directed against “early” polypeptides or selected structural proteins of the adenovirus particle. The results showed that polypeptide IX, a structural component of the virion, is synthesized earlier than other structural polypeptides. Polypeptide IX is further distinguished from other components of the virion in that it is synthesized in the presence of cytosine arabinoside, a drug which blocks viral DNA replication. Cycloheximide, another drug which blocks viral replication and the onset of “late” viral transcription, also fails to prevent the accumulation of the messenger RNA coding for polypeptide IX, although mRNAs corresponding to the other structural viral components remain undetectable. Size fractionation of infected cell RNA showed that, like its “late” counterpart, the “early” messenger RNA for polypeptide IX sediments at 9 S. These results indicate that the regulation of the gene for polypeptide IX differs from that of other genes for structural adenovirus polypeptides.

Chapter 3 Developmental appearance of nerve growth factor in the rat brain: significant deficits in the aged forebrain

Publisher Summary Nerve growth factor (NGF) deficiencies may account for the loss of cholinergic neurons in the basal forebrain generally found to accompany aging, and subsequently result in altered cognitive functions. This chapter describes the time course of appearance of NGF in the rat brain during development, adulthood, and aging. Cholinergic systems in the basal forebrain play a role in cognitive functions and a correlation exists between cholinergic deficits and memory dysfunction in aging and in neurodegenerative diseases. During normal aging, a substantial loss of cholinergic afferents in hippocampus and neocortex occurs. The present study shows that the level of NGF protein increases in brain during development, reaching a maximum three weeks postnatally that coincides with the final maturation of the cholinergic projections from the basal forebrain. During aging, a significant decrease in NGF level in hippocampus of Fischer 344 and Brown Norwegian rats has been seen. The loss of neurons during aging and neurodegenerative diseases might occur because of lack of trophic agents produced by the target areas. Whether, neuronal substitution that involves replacement of the damaged neurons with surrogate populations of cells, or infusion of exogenous NGF could counteract the cholinergic neuron death, which occurs during aging and in some neurodegenerative diseases remains to be examined.

Control of adenovirus early gene expression: posttranscriptional control mediated by both viral and cellular gene products.

An adenovirus type 5 host range mutant (hr-1) located in region E1A and phenotypically defective in expressing viral messenger ribonucleic acid (RNA) from other early regions (Berk et al., Cell 17:935-944, 1979) was analyzed for accumulation of viral RNA in the presence of protein synthesis inhibitors. Nuclear RNA was transcribed from all early regions at the same rate, regardless of whether the drug was present or absent. As expected, low or undetectable levels of RNA were found in the cytoplasm of hr-1-infected cells compared with the wild-type adenovirus type 5 in the absence of drug. When anisomycin was added 30 min before hr-1 infection, cytoplasmic RNA was abundant from early regions E3 and E4 when assayed by filter hybridization. In accordance, early regions E3 and E4 viral messenger RNA species were detected by the S1 endonuclease mapping technique only in hr-1-infected cells that were treated with the drug. Similar results were obtained by in vitro translation studies. Together, these results suggest that this adenovirus type 5 mutant lacks a viral gene product necessary for accumulation of viral messenger RNA, but not for transcription. It is proposed that a cellular gene product serves as a negative regulator of viral messenger RNA accumulation at the posttranscriptional level.

The interaction between polysaccharides and other macromolecules VII. The effects of various polymers on the sedimentation rates of serum albumin and α-crystallin

The sedimentation behaviour of two globular proteins of different size has been studied in solutions of polymers of varied structure. That the movement of the larger protein was in all instances retarded to a greater extent than that of the smaller indicated that the polymers investigated had a sieving effect. The ability of a polymer to inhibit the migration of another substance was demonstrated to increase with its degree of polymerization and decrease with branching. Charged substituents in a polymer were found to augment materially its effectiveness in restricting transport.

Production and characterization of biologically active recombinant beta nerve growth factor

DNA fragments encoding either rat or chicken beta nerve growth factor (NGF) were inserted in the expression vector p91023(B) for transient expression in COS cells. The two NGF constructs produced RNA transcripts and proteins of the predicted sizes. Conditioned media from the transfected cells stimulated neurite outgrowth from cultured chicken embryo sympathetic ganglia. The results show that the rat or chicken NGF gene can direct the synthesis of a biologically active NGF protein after transfection of COS cells.

Detection of nerve growth factor and its mRNA by separate and combined immunohistochemistry andin situ hybridization in mouse salivary glands

SummaryIntense labelling of secretory cells in the male mouse submandibular gland was observed afterin situ hybridization using mouse nerve growth factor (NGF) cDNA probes. Under the same conditions, sparse less intensely labelled cells were also found in the sublingual gland. Hybridization to a chicken NGF cDNA probe gave weak labelling on the glands in accordance with a weak cross-hybridization between mouse NGF mRNA and chicken NGF cDNA probes, whereas no labelling was seen using pUC9 DNA as a hybridization probe. A combination ofin situ hybridization and immunohistochemistry was also carried out on the same sections of submandibular gland. A good correlation was seen between actively synthesizing and intensely immunoreactive cells in the gland. The technique described here allows the detection of individual cells synthesizing relatively low levels of NGF. The combination ofin situ hybridization and immunocytochemistry on the same section should be particularly useful in cases where NGF is transported away from its site of synthesis.

On the interaction between polysaccharides and other macromolecules: III. The use of hyaluronic acid for the separation of macromolecules in the ultacentrifuge

Abstract Advantage has been taken of the macromoleculer-sieve effect of hyaluronic acid to increase resolution in the ultracentrifuge. Substances, which normally sediment at the same rate in salt solutions because of a similarity in their sedimentation coefficients can be separated in hyaluronic acid media if they differ in size and shape. By selecting suitable concentrations of hyaluronic acid it has proved possible to separate fibrinogen from γ-globulin; albumin from dextran; and a colloidal silica from a polystyrene latex. Like procedures revealed and unsuspected inhomogeneity in a dextran preparation and served to resolve the polyglucose into two fractions.