DNA strand specificity for UV-induced mutations in mammalian cells.

The influence of DNA repair on the molecular nature of mutations induced by UV light (254 nm) was investigated in UV-induced hprt mutants from UV-sensitive Chinese hamster cells (V-H1) and the parental line (V79). The nature of point mutations in hprt exon sequences was determined for 19 hprt mutants of V79 and for 17 hprt mutants of V-H1 cells by sequence analysis of in vitro-amplified hprt cDNA. The mutation spectrum in V79 cells consisted of single- and tandem double-base pair changes, while in V-H1 cells three frameshift mutations were also detected. All base pair changes in V-H1 mutants were due to GC----AT transitions. In contrast, in V79 all possible classes of base pair changes except the GC----CG transversion were present. In this group, 70% of the mutations were transversions. Since all mutations except one did occur at dipyrimidine sites, the assumption was made that they were caused by UV-induced photoproducts at these sites. In V79 cells, 11 out of 17 base pair changes were caused by photoproducts in the nontranscribed strand of the hprt gene. However, in V-H1 cells, which are completely deficient in the removal of pyrimidine dimers from the hprt gene and which show a UV-induced mutation frequency enhanced seven times, 10 out of 11 base pair changes were caused by photoproducts in the transcribed strand of the hprt gene. We hypothesize that this extreme strand specificity in V-H1 cells is due to differences in fidelity of DNA replication of the leading and the lagging strand. Furthermore, we propose that in normal V79 cells two processes determine the strand specificity of UV-induced mutations in the hprt gene, namely preferential repair of the transcribed strand of the hprt gene and a higher fidelity of DNA replication of the nontranscribed strand compared with the transcribed strand.

Cloning and characterization of MN1, a gene from chromosome 22q11, which is disrupted by a balanced translocation in a meningioma.

We have isolated a gene, called MN1, which resides on chromosome 22 and which was found to be disrupted by a balanced translocation (4;22) in meningioma 32. The MN1 gene spans about 70 kb and consists of at least two large exons of approximately 4.7 kb and 2.8 kb. The MN1 cDNA codes for a protein of 1319 amino acids when the first methionine in the open reading frame is used. The MN1 cDNA contains two CAG repeats, one of which codes for a string of 28 glutamines. The t(4;22) disrupts the 5'-exon within the open reading frame. In meningioma 32 no expression of the MN1 mRNA is observed. These results suggest that inactivation of the MN1 gene in this tumour may contribute to its pathogenesis.

Cytogenetic, molecular genetic and pathological analyses in 126 meningiomas.

In a series of 126 meningiomas, tumor and patient characteristics were investigated and statistically analyzed. A combined cytogenetic and molecular genetic approach was used to study chromosomal abnormalities and loss of markers on chromosome 22q. This approach was successfully applied to 93 meningiomas. In 66 cases, complete or partial loss of chromosome 22 was observed and in at least 12 of them this chromosome was involved in structural aberrations. In addition to chromosome 22 changes, chromosomes 1, 6, 11, 13, 14, 18, 19, X, and Y were also frequently involved in structural and numerical aberrations. Statistical analysis revealed a significant association between the number of chromosomal abnormalities and tumor grade. Complex karyotypes predominated in the group of grade II/III meningiomas. Furthermore, other variables showed statistically (or marginally statistically) significant differences. Meningiomas from the convexity were more often grade II/III, displayed predominantly (partial) loss of chromosome 22 and had complex karyotypes more often. These features were frequently found in meningiomas from males. Base meningiomas, on the other hand, occurred more often in females; they were usually grade I, showed loss of (parts of) chromosome 22 less often and displayed fewer additional chromosomal abnormalities.

Ecotoxicological suitability of floodplain habitats in The Netherlands for the little owl (Athene noctua vidalli).

This study describes the actual risks of exposure to contaminants, which little owls (Athene noctua vidalli) face in Dutch river floodplains. The results indicate that PCBs pose a risk: not only are levels in little owls from floodplains higher than levels found in little owls from a reference site but the PCB patterns in owls from the floodplains also indicate induction of hepatic cytochrome P450 enzymes by dioxin like compounds, possibly PCBs. Of the heavy metals, only cadmium is thought to pose a risk in certain conditions, for example, when little owls are feeding only on earthworms over a prolonged period of time. The results do not indicate any effects on the occurrence of prey items of the little owl like for instance earthworm, beetles and shrews. Hence, it is not expected that little owls will be affected by diminishing prey availability due to contamination.

Development of multilayer constructs for tissue engineering.

The rapidly developing field of tissue engineering produces living substitutes that restore, maintain or improve the function of tissues or organs. In contrast to standard therapies, the engineered products become integrated within the patient, affording a potentially permanent and specific cure of the disease, injury or impairment. Despite the great progress in the field, development of clinically relevantly sized tissues with complex architecture remains a great challenge. This is mostly due to limitations of nutrient and oxygen delivery to the cells and limited availability of scaffolds that can mimic the complex tissue architecture. This study presents the development of a multilayer tissue construct by rolling pre-seeded electrospun sheets [(prepared from poly (l-lactic acid) (PLLA) seeded with C2C12 pre-myoblast cells)] around a porous multibore hollow fibre (HF) membrane and its testing using a bioreactor. Important elements of this study are: 1) the medium permeating through the porous walls of multibore HF acts as an additional source of nutrients and oxygen to the cells, which exerts low shear stress (controllable by trans membrane pressure); 2) application of dynamic perfusion through the HF lumen and around the 3D construct to achieve high cell proliferation and homogenous cell distribution across the layers, and 3) cell migration occurs within the multilayer construct (shown using pre-labeled C2C12 cells), illustrating the potential of using this concept for developing thick and more complex tissues.

High content imaging in the screening of biomaterial-induced MSC behavior.

Upon contact with a biomaterial, cells and surrounding tissues respond in a manner dictated by the physicochemical and mechanical properties of the material. Traditionally, cellular responses are monitored using invasive analytical methods that report the expression of genes or proteins. These analytical methods involve assessing commonly used markers for a predefined readout, masking the actual situation induced in the cells. Hence, a broader expression profile of the cellular response should be envisioned, which technically limits up scaling to higher throughput systems. However, it is increasingly recognized that morphometric readouts, obtained non-invasively, are related to gene expression patterns. Here, we introduced distinct surface roughness to three PLA surfaces, by exposure to oxygen plasma of different duration times. The response of mesenchymal stromal cells was compared to smooth untreated PLA surfaces without the addition of differentiation agents. Morphological and genome wide expression profiles revealed underlying cellular changes which was hidden for the commonly used gene markers for osteo-, chondro- and adipogenesis. Using 3 morphometric parameters, obtained by high content imaging, we were able to build a classifier and discriminate between oxygen plasma-induced modified sheets and non-modified PLA sheets where evaluating classical candidates missed this effect. This approach shows the feasibility to use noninvasive morphometric data in high-throughput systems to screen biomaterial surfaces indicating the underlying genetic biomaterial-induced changes.

Clonal growth of colorectal-carcinoma cell lines transplanted to nude mice.

It is generally assumed that tumor progression is a microevolutionary process in which increasingly aggressive clones, generated through genetic instability, emerge in an initially monoclonal lesion. The present study was undertaken to determine how rapidly a dominant clone will emerge from an initial polyclonal situation, and whether dominance of these clones is a prerequisite for the onset of metastasis. To this end, colon-carcinoma cells were infected in culture with an amphotropic retroviral vector containing the neomycin-phosphotransferase gene, which makes cells resistant to neomycin. A heterogeneous population of neomycin-resistant cells carrying random retroviral integrations was xenografted to the subcutis and to the cecum of nude mice. The xenografts obtained, as well as the available metastases, were analyzed as to viral integrations by Southern blotting. The results show that, (i) clonal selection already takes place during growth of the primary tumor; (ii) dominant clones also generate metastases. The retroviral integration pattern of metastases turned out to be identical to that found in the primary xenografts. This pattern remained unchanged in tumors obtained after serial transplantations of cells cultured from metastases.

A leucine-to-proline mutation in the insulin receptor in a family with insulin resistance.

We have determined the primary structure of a mutant insulin receptor of a leprechaun patient born from a consanguineous marriage. A characteristic feature of leprechaunism is an extreme resistance to insulin. In this patient the insulin resistance seems to result from an observed lack of insulin binding to intact cells. Solubilization of cells in non-ionic detergents leads to the appearance of insulin receptors which can bind insulin. However, the insulin-stimulated autophosphorylation of the receptor's beta subunit is markedly reduced. Cloning and sequencing of cDNA derived from insulin receptor mRNA of this patient revealed a leucine-to-proline mutation at position 233 in the alpha subunit. By means of DNA amplification we found that the patient is homozygous for this mutation and that the parents and two grandparents from the consanguineous line are heterozygous. The heterozygous individuals all show decreased insulin binding to cultured fibroblasts. In addition, they are mildly insulin resistant in vivo. These observations show a linkage between the leucine-to-proline mutation and the observed insulin resistance in this family. We therefore conclude that the mutation in the homozygous form is responsible for the extreme insulin resistance in the leprechaun patient. The mutation for the first time characterizes a region in the insulin receptor which seems to be involved in transmitting the insulin binding signal to the tyrosine kinase domain.

A t(4;22) in a meningioma points to the localization of a putative tumor-suppressor gene.

Cytogenetic analysis of meningioma cells from one particular patient (MN32) displayed the stem-line karyo-type 45, XY, -1, 4p+, 22q-, 22q+, which thus had rearrangements of both chromosomes 22. The 22q+ marker appeared as a dicentric: 22 pter----q11::1p11----qter. The reciprocal product of this translocation has presumably been lost because it lacked a centromere. The 22q- chromosome also appeared to have lost sequences distal to band q11. We assumed that this marker could have been the result of a reciprocal translocation between chromosomes 4 and 22. To investigate the 4p+ and 22q- chromosomes in more detail, human-hamster somatic cell hybrids were constructed that segregated the 22q- and 4p+ chromosomes. Southern blot analysis with DNA from these hybrids showed that sequences from 22q were indeed translocated to 4p+ and that reciprocally sequences from 4p were translocated to 22q-, demonstrating a balanced t(4;22)(p16;q11). On the basis of these results we presume that in this tumor a tumor-suppressor gene is deleted in the case of the 22q+ marker and that the t(4;22) disrupts the second allele of this gene. The latter translocation was mapped between D22S1 and D22S15, a distance of 1 cM on the linkage map of this chromosome. The area in which we have located the translocation is within the region where the gene predisposing to neurofibromatosis 2 has been mapped.

A novel gene which is up-regulated during colon epithelial cell differentiation and down-regulated in colorectal neoplasms.

To identify new molecular markers for differentiation of normal and neoplastic colon epithelium, we have studied changes in gene expression during the in vitro differentiation of the HT29-D4 colon carcinoma cell line. Using a modified differential display procedure, we cloned a novel cDNA, designated differentiation-related gene 1 (Drg1). Drg1 mRNA has a length of approximately 3 kb and is induced approximately 20-fold during in vitro differentiation of the colon carcinoma cell lines HT29-D4 and Caco-2. The absence of Drg1 induction in growth-inhibited A431 epidermoid carcinoma cells indicates that Drg1 up-regulation in colon carcinoma cells is not a result of decreased proliferation. The Drg1 cDNA contains an open-reading frame of 1182 bp that encodes a protein with a predicted molecular weight of 43 kd. Drg1 mRNA is expressed most prominently in placental membranes and prostate, kidney, small intestine, and ovary tissues. Compared to normal colon mucosa, Drg1 mRNA expression is decreased in colon adenomas and adenocarcinomas. An antiserum raised against recombinant Drg1 protein detected a band of the expected size in Western blots. Immunohistochemistry showed that in normal colon Drg1 protein is expressed in the cytoplasm and basolateral membranes of surface epithelial cells that border the gut lumen, indicating that Drg1 protein is expressed late during differentiation, just before apoptosis and shedding of cells into the colon lumen.

Frequent NF2 gene transcript mutations in sporadic meningiomas and vestibular schwannomas.

The gene for the hereditary disorder neurofibromatosis type 2 (NF2), which predisposes for benign CNS tumors such as vestibular schwannomas and meningiomas, has been assigned to chromosome 22 and recently has been isolated. Mutations in the NF2 gene were found in both sporadic meningiomas and vestibular schwannomas. However, so far only 6 of the 16 exons of the gene have been analyzed. In order to extend the analysis of an involvement of the NF2 gene in the sporadic counterparts of these NF2-related tumors, we have used reverse transcriptase-PCR amplification followed by SSCP and DNA sequence analysis to screen for mutations in the coding region of the NF2 gene. Analysis of the NF2 gene transcript in 53 unrelated patients with meningiomas and vestibular schwannomas revealed mutations in 32% of the sporadic meningiomas (n = 44), in 50% of the sporadic vestibular schwannomas (n = 4), in 100% of the tumors found in NF2 patients (n = 2), and in one of three tumors from multiple-meningioma patients. Of the 18 tumors in which a mutation in the NF2 gene transcript was observed and the copy number of chromosome 22 could be established, 14 also showed loss of (parts of) chromosome 22. This suggests that in sporadic meningiomas and NF2-associated tumors the NF2 gene functions as a recessive tumor-suppressor gene. The mutations detected resulted mostly in frameshifts, predicting truncations starting within the N-terminal half of the putative protein.

Constitutional DNA-level aberrations in chromosome 22 in a patient with multiple meningiomas.

We describe a patient who developed multiple meningiomas but had no clear evidence of neurofibromatosis type 2. Four of the tumors, derived from three different sites, were analyzed cytogenetically and/or at the DNA level using chromosome 22 specific probes. All four tumors showed loss of the same copy of chromosome 22. On the chromosome that was retained in the tumors, we found two constitutional aberrations, a 1.5 kb deletion and a point mutation. The patient had inherited both alterations from her father. The father has not developed any meningiomas so far but he has been treated for a well-differentiated adenocarcinoma of the lung and a brain metastasis from this tumor. The mother and 75 unrelated individuals did not show any of the chromosome 22 alterations. The multiple tumors found in the patient suggest that she has a predisposing gene for the development of meningiomas. The finding that all investigated tumors lost the same, constitutionally normal copy of chromosome 22 could indicate that the predisposing gene resides on chromosome 22 and was affected by the constitutional mutations.