Wilhelm Engström

Spider Silk Proteins – Mechanical Property and Gene Sequence

Abstract Spiders spin up to seven different types of silk and each type possesses different mechanical properties. The reports on base sequences of spider silk protein genes have gained importance as the mechanical properties of silk fibers have been revealed. This review aims to link recent molecular data, often translated into amino acid sequences and predicted three dimensional structural motifs, to known mechanical properties.

Insulin-Like Growth Factor 2 in Development and Disease: A Mini-Review

Background: Insulin-like growth factor 2 (IGF2) is a protein hormone known to regulate cell proliferation, growth, migration, differentiation and survival. The gene is parentally imprinted in the sense that transcripts are almost exclusively derived from the paternal allele. Loss of imprinting of the IGF2 gene is a recurrent observation in growth disorders that combine overgrowth with a variety of malignant tumours. Moreover, IGF2 has been proposed to play a role in the development of a variety of seemingly unrelated cancers that play an important role in geriatric medicine, e.g. breast cancer, colon cancer and lung cancer. Finally, IGF2 has been implicated in cardiovascular disease, since, for example, IGF2 has been shown to influence the size of atherosclerotic lesions. Objective: To summarize current knowledge about IGF2, its interactions with binding proteins and receptors and connections with key diseases. Methods: The contents of this paper were based on reviews of existing literature within the field. Results: There is a substantial amount of research linking IGF2 to growth disorders, cancer and to a much lesser degree cardiovascular disease. Some of the studies on IGF2 and tumour growth have yielded conflicting results, for instance regarding its effect on apoptosis. Conclusion: Today, our knowledge on how IGF2 is composed and interacts with receptors has come a long way. However, there is comparatively little information on how IGF2 affects tumour growth and cardiovascular diseases such as atherosclerosis. Thus, further research will be needed to elucidate the impact of IGF2 on key diseases.

Epigenetic regulation of the Igf2/H19 gene cluster

Igf2 (insulin‐like growth factor 2) and H19 genes are imprinted in mammals; they are expressed unevenly from the two parental alleles. Igf2 is a growth factor expressed in most normal tissues, solely from the paternal allele. H19 gene is transcribed (but not translated to a protein) from the maternal allele. Igf2 protein is a growth factor particularly important during pregnancy, where it promotes both foetal and placental growth and also nutrient transfer from mother to offspring via the placenta. This article reviews epigenetic regulation of the Igf2/H19 gene‐cluster that leads to parent‐specific expression, with current models including parental allele‐specific DNA methylation and chromatin modifications, DNA‐binding of insulator proteins (CTCFs) and three‐dimensional partitioning of DNA in the nucleus. It is emphasized that key genomic features are conserved among mammals and have been functionally tested in mouse. ‘The enhancer competition model’, ‘the boundary model’ and ‘the chromatin‐loop model’ are three models based on differential methylation as the epigenetic mark responsible for the imprinted expression pattern. Pathways are discussed that can account for allelic methylation differences; there is a recent study that contradicts the previously accepted fact that biallelic expression is accompanied with loss of differential methylation pattern.

Pathbase: a database of mutant mouse pathology.

Pathbase is a database that stores images of the abnormal histology associated with spontaneous and induced mutations of both embryonic and adult mice including those produced by transgenesis, targeted mutagenesis and chemical mutagenesis. Images of normal mouse histology and strain-dependent background lesions are also available. The database and the images are publicly accessible (http://www.pathbase.net) and linked by anatomical site, gene and other identifiers to relevant databases; there are also facilities for public comment and record annotation. The database is structured around a novel ontology of mouse disorders (MPATH) and provides high-resolution downloadable images of normal and diseased tissues that are searchable through orthogonal ontologies for pathology, developmental stage, anatomy and gene attributes (GO terms), together with controlled vocabularies for type of genetic manipulation or mutation, genotype and free text annotation for mouse strain and additional attributes. The database is actively curated and data records assessed by pathologists in the Pathbase Consortium before publication. The database interface is designed to have optimal browser and platform compatibility and to interact directly with other web-based mouse genetic resources.

The role of scaffold proteins in JNK signalling

This paper summarises how scaffold proteins affects and regulate the JNK signalling pathway. We believe that some of these scaffold proteins, by virtue of their anchoring and catalytic properties contribute to a high degree of specificity of intra cellular signalling pathways that regulate the progression through the cell cycle.

Major ampullate spidroins from Euprosthenops australis: multiplicity at protein, mRNA and gene levels

Spider dragline silk possesses extraordinary mechanical properties. It consists of large fibrous proteins called spidroins that display modular structures. It is known to consist of two proteins: the major ampullate spidroin (MaSp) 1 and MaSp2. This study analyses MaSp sequences from the nursery‐web spider Euprosthenops australis. We have identified a previously uncharacterized MaSp2 sequence and a new MaSp‐like spidroin, which display distinct homogenous submotifs within their respective Gly‐rich repeats. Furthermore, a group of MaSp1 cDNA clones show unexpected heterogeneity. Genomic PCR identified several MaSp1 gene variants within individual spiders, which suggests the presence of a gene cluster in E. australis. Finally, the evolution of spidroin genes is discussed in relation to phylogenetic analysis of nonrepetitive C‐terminal domains from diverse species.

Induction of DNA synthesis and mitosis in the absence of cellular enlargement

Swiss 3T3 cells, starved to quiescence in low serum concentration, initiate DNA synthesis and undergo mitosis in low serum concentration (less than 0.1%) after a short exposure (2-10 min) to alkaline medium (pH 8.5-10). This study shows that initiation of DNA synthesis and mitosis can be dissociated from growth in cell size. Alkaline-stimulated cells do not increase in size before mitosis (unbalanced growth) in contrast to quiescent cells stimulated by 10% serum, which approximately double their protein content before mitosis (balanced growth). The exposure to the alkaline medium per se does not render the cells incapable of growing in size, since alkaline-treated cells, which are subsequently cultured in 10% serum, undergo balanced growth to the same extent as cells only stimulated by 10% serum without alkaline pretreatment. This study also shows that the small proportion of cells undergoing background proliferation in low serum concentration (less than 0.1%) do not increase in size before mitosis. The extent to which alkaline-stimulated cells, as well as cells undergoing background proliferation, grow in size before mitosis, is correlated to the serum concentration in the culture medium (DMEM). In 0.1% serum or less the cells do not grow in size. In 0.5% serum the cells increase in size by 30% before mitosis and complete balanced growth is achieved in medium containing 2% serum or more. These findings indicate that some macromolecular factor or factors in serum are required for growth in cell size before mitosis.

Transcriptional regulation and biological significance of the insulin like growth factor II gene

Abstract. The insulin like growth factors I and II are the most ubiquitous in the mammalian embryo. Moreover they play a pivotal role in the development and growth of tumours. The bioavailability of these growth factors is regulated on a transcriptional as well as on a posttranslational level. The expression of non‐signalling receptors as well as binding proteins does further tune the local concentration of IGFs. This paper aims at reviewing how the transcription of the IGF genes is regulated. The biological significance of these control mechanisms will be discussed.

GROWTH ACTIVATION OF RESTING CELLS: INDUCTION OF BALANCED AND IMBALANCED GROWTH*

Little is known about how mitogenic factors generate growth regulatory signals and how these are mediated within the cell. We have developed three different types of mitogenic stimuli in order to identify the possible existence of common denominators in a complex and perhaps pleiotypic signal-response system. 3T3 cells, starved to quiescence by reducing the serum content of the culture medium 100-fold, can be irreversibly committed to undergo DNA replication and mitosis in a serum-free medium after an initial exposure of short duration to (a) serum factors and cholesterol, (b) a relative excess of glutamine, or (c) alkaline pH. Cells stimulated by any of these procedures, and subsequently incubated in serum-free Dulbeccos modified Eagles medium (DMEM) undergo DNA replication and mitosis in the absence of concomitant cellular enlargement (imbalanced growth). However, cellular enlargement is induced after the initial mitogenic stimuli (a, b, and c, as described previously) if the cells are subsequently incubated in DMEM containing greater than or equal to 0.5% serum, supraphysiological concentrations of insulin, or normal concentrations of somatomedin C.

Growth factors and apoptosis

Abstract. Apoptosis is nowadays recognized as an important mechanism by which cells can be eliminated from the organism. In particular its role in tissue modelling during embryogenesis has been highlighted. The human teratoma cell line Tera 2, which in several respects acts as a human embryonic stem cell, can be induced to undergo apoptosis by reducing the serum content of the tissue culture medium. We report here that this process can be reversed by replacing serum with the heparin‐binding growth factors, acidic FGF and basic FGF. In contrast, neither of the mammalian transforming growth factors (TGF‐β‐3) managed to exert any effect on growth or apoptosis in Tera 2 cells.