Telomere Length Regulation

The number of (TTAGGG)_n repeats at the ends of chromosomes is highly variable between individual chromosomes, between different cells and between species. Progressive loss of telomere repeats limits the proliferation of pre-malignant human cells but also contributes to aging by inducing apoptosis and senescence in normal cells. Despite enormous progress in understanding distinct pathways that result in loss and gain of telomeric DNA in different cell types, many questions remain. Further studies are needed to delineate the role of damage to telomeric DNA, replication errors, chromatin structure, liquid-liquid phase transition, telomeric transcripts (TERRA) and secondary DNA structures such as guanine quadruplex structures, R-loops and T-loops in inducing gains and losses of telomere repeats in different cell types. Limitations of current telomere length measurements techniques and differences in telomere biology between species and different cell types complicate generalizations about the role of telomeres in aging and cancer. Here some of the factors regulating the telomere length in embryonic and adult cells in mammals are discussed from a mechanistic and evolutionary perspective.

Benchmarking challenging small variants with linked and long reads

Genome in a Bottle benchmarks are widely used to help validate clinical sequencing pipelines and develop variant calling and sequencing methods. Here we use accurate linked and long reads to expand benchmarks in 7 samples to include difficult-to-map regions and segmental duplications that are challenging for short reads. These benchmarks add more than 300,000 SNVs and 50,000 insertions or deletions (indels) and include 16% more exonic variants, many in challenging, clinically relevant genes not covered previously, such as PMS2. For HG002, we include 92% of the autosomal GRCh38 assembly while excluding regions problematic for benchmarking small variants, such as copy number variants, that should not have been in the previous version, which included 85% of GRCh38. It identifies eight times more false negatives in a short read variant call set relative to our previous benchmark. We demonstrate that this benchmark reliably identifies false positives and false negatives across technologies, enabling ongoing methods development.

Fat metabolism is associated with telomere length in six population-based studies

Telomeres are repetitive DNA sequences located at the end of chromosomes, which are associated to biological aging, cardiovascular disease, cancer, and mortality. Lipid and fatty acid metabolism have been associated with telomere shortening. We have conducted an in-depth study investigating the association of metabolic biomarkers with telomere length (LTL). We performed an association analysis of 226 metabolic biomarkers with LTL using data from 11 775 individuals from six independent population-based cohorts (BBMRI-NL consortium). Metabolic biomarkers include lipoprotein lipids and subclasses, fatty acids, amino acids, glycolysis measures and ketone bodies. LTL was measured by quantitative polymerase chain reaction or FlowFISH. Linear regression analysis was performed adjusting for age, sex, lipid-lowering medication and cohort-specific covariates (model 1) and additionally for body mass index (BMI) and smoking (model 2), followed by inverse variance-weighted meta-analyses (significance threshold pmeta = 6.5x10-4). We identified four metabolic biomarkers positively associated with LTL, including two cholesterol to lipid ratios in small VLDL (S-VLDL-C % and S-VLDL-ce %) and two omega-6 fatty acid ratios (FAw6/FA and LA/FA). After additionally adjusting for BMI and smoking, these metabolic biomarkers remained associated with LTL with similar effect estimates. In addition, cholesterol esters in very small VLDL (XS-VLDL-ce) became significantly associated with LTL (p = 3.6x10-4). We replicated the association of FAw6/FA with LTL in an independent dataset of 7845 individuals (p = 1.9x10-4). To conclude, we identified multiple metabolic biomarkers involved in lipid and fatty acid metabolism that may be involved in LTL biology. Longitudinal studies are needed to exclude reversed causation.

RECQL5 at the ntersection of eplication and ranscription

Maintenance of genome stability is essential to prevent the accumulation of DNA mutations that can initiate oncogenesis and facilitate tumor progression. Studies of DNA repair genes have revealed a highly dynamic and redundant network of genes and proteins responsible for maintaining genome stability. Cancer cells are often deficient in DNA repair, and the resulting genome instability decreases their fitness but also allows for more rapid evolution under selective pressure. Of particular interest for genome stability are the RecQ class of helicases. Five genes in this class, RECQL1, BLM, WRN, RECQL4, and RECQL5, are unique to mammals, as simpler eukaryotes and bacteria appear to have only one homolog, RecQ. The precise role of each of the five mammalian RecQ helicases remains to be determined. Whereas loss of function mutations of BLM, WRN, and RECQL4 in humans are associated with specific diseases, RECQL1 and RECQL5 have not yet been associated with specific disorders. Mice deficient in Recql5 are more likely to develop cancer, and human cells deficient in RECQL5 display chromosomal instability and elevated sister chromatid exchange events, similar to cells deficient in any of the other RecQ helicases. Recent studies support the hypothesis that RECQL5 can resolve intermediate DNA repair structures resulting from the collision of DNA transcription and replication machinery. In this review, we aim to summarize current knowledge regarding RECQL5 in the context of DNA repair, replication, and transcription to help uncover the role of RECQL5 in the maintenance of genome stability.

Helicases FANCJ, RTEL1 and BLM Act on Guanine Quadruplex DNA in Vivo

Guanine quadruplex (G4) structures are among the most stable secondary DNA structures that can form in vitro, and evidence for their existence in vivo has been steadily accumulating. Originally described mainly for their deleterious effects on genome stability, more recent research has focused on (potential) functions of G4 structures in telomere maintenance, gene expression, and other cellular processes. The combined research on G4 structures has revealed that properly regulating G4 DNA structures in cells is important to prevent genome instability and disruption of normal cell function. In this short review we provide some background and historical context of our work resulting in the identification of FANCJ, RTEL1 and BLM as helicases that act on G4 structures in vivo. Taken together these studies highlight important roles of different G4 DNA structures and specific G4 helicases at selected genomic locations and telomeres in regulating gene expression and maintaining genome stability.

Gender and telomere length: systematic review and meta-analysis

BACKGROUND

It is widely believed that females have longer telomeres than males, although results from studies have been contradictory.

METHODS

We carried out a systematic review and meta-analyses to test the hypothesis that in humans, females have longer telomeres than males and that this association becomes stronger with increasing age. Searches were conducted in EMBASE and MEDLINE (by November 2009) and additional datasets were obtained from study investigators. Eligible observational studies measured telomeres for both females and males of any age, had a minimum sample size of 100 and included participants not part of a diseased group. We calculated summary estimates using random-effects meta-analyses. Heterogeneity between studies was investigated using sub-group analysis and meta-regression.

RESULTS

Meta-analyses from 36 cohorts (36,230 participants) showed that on average females had longer telomeres than males (standardised difference in telomere length between females and males 0.090, 95% CI 0.015, 0.166; age-adjusted). There was little evidence that these associations varied by age group (p=1.00) or cell type (p=0.29). However, the size of this difference did vary by measurement methods, with only Southern blot but neither real-time PCR nor Flow-FISH showing a significant difference. This difference was not associated with random measurement error.

CONCLUSIONS

Telomere length is longer in females than males, although this difference was not universally found in studies that did not use Southern blot methods. Further research on explanations for the methodological differences is required.

The luminal progenitor compartment of the normal human mammary gland constitutes a unique site of telomere dysfunction

Telomeres are essential for genomic integrity, but little is known about their regulation in the normal human mammary gland. We now demonstrate that a phenotypically defined cell population enriched in luminal progenitors (LPs) is characterized by unusually short telomeres independently of donor age. Furthermore, we find that multiple DNA damage response proteins colocalize with telomeres in >95% of LPs but in <5% of basal cells. Paradoxically, 25% of LPs are still capable of exhibiting robust clonogenic activity in vitro. This may be partially explained by the elevated telomerase activity that was also seen only in LPs. Interestingly, this potential telomere salvage mechanism declines with age. Our findings thus reveal marked differences in the telomere biology of different subsets of primitive normal human mammary cells. The chronically dysfunctional telomeres unique to LPs have potentially important implications for normal mammary tissue homeostasis as well as the development of certain breast cancers.

Unusual distribution pattern of telomeric repeats in the shrews Sorex araneus and Sorex granarius

Sorex araneus and Sorex granarius are sibling species within the Sorex araneus group with karyotypes composed of almost identical chromosome arms. S. granarius has a largely acrocentric karyotype, while, in S. araneus, various of these acrocentrics have combined together by Robertsonian (Rb) fusions to form metacentrics, with the numbers and types of metacentrics differing between chromosomal races. Our studies on telomeric sequences in S. araneus and S. granarius revealed differences between chromosomes and between species. In S. araneus (the Novosibirsk race), hybridization signals were present on the telomeres of all the chromosomes after FISH with a PCR-generated telomeric probe. In addition, hybridization signals were observed at high frequencies in the pericentric regions of some but not all metacentrics formed by Rb fusion. There were fewer signals on those metacentrics formed earlier in the evolution of S. araneus. This suggests that S. araneus chromosomes retain at least some telomeric repeats during Rb fusion, but that these repeats are lost or modified over time. These results are critical for the interpretation of the well-studied hybrid zones between chromosomal races of S. araneus, given that Rb fission has been postulated in such hybrid zones and that the likelihood of Rb fission will relate to presence/absence of telomeric sequences at the centromeres of metacentrics. In S. granarius, there were strong signals at the proximal (centromeric) telomeres of the acrocentrics after FISH with a DNA telomeric probe. FISH with a PNA telomeric probe on S. granarius acrocentrics showed that the proximal telomeres were 213 kb on average, while the length of the distal telomeres was 3.8 kb on average. Two-colour FISH, using a telomeric DNA probe and a microdissected probe generated from the pericentric regions of the S. granarius chromosomes a and b, revealed regions on distinct chromatin fibres where telomeric and microdissected probes were colocalized or localized sequentially. The proximal telomeres of S. granarius are highly unusual both in their large size and their heterogeneous structure relative to the telomeres of other mammals.

Modelling perspectives on aging: can mathematics help us stay young?

We survey several types of mathematical models that keep track of age distributions in a population, or follow some aspects of aging, such as loss of replicative potential of stem cells. The properties of a class of linear models of this type are discussed and compared. We illustrate the applicability of such models with a simple example based on hypothetical stem cell dynamics developed to address age-related telomere loss in the human granulocyte pool. We then describe the contrasting behaviour of nonlinear systems. Examples are drawn from the class of "dynamical diseases" to illustrate some of the aspects of nonlinear systems. Applications of these, and other models to the problems of aging and replicative aging are discussed.

Telomere instability in a human cancer cell line

Telomere maintenance is essential in immortal cancer cells to compensate for DNA lost from the ends of chromosomes, to prevent chromosome fusion, and to facilitate chromosome segregation. However, the high rate of fusion of chromosomes near telomeres, termed telomere association, in many cancer cell lines has led to the proposal that some cancer cells may not efficiently perform telomere maintenance. Deficient telomere maintenance could play an important role in cancer because telomere associations and nondisjunction have been demonstrated to be mechanisms for genomic instability. To investigate this possibility, we have analyzed the telomeres of the human squamous cell carcinoma cell line SQ-9G, which has telomere associations in approximately 75% of the cells in the population. The absence of detectable telomeric repeat sequences at the sites of these telomere associations suggests that they result from telomere loss. The analysis of telomere length by quantitative in situ hybridization demonstrated that, compared to the human squamous cell carcinoma cell line SCC-61 which has few telomere associations, SQ-9G has more extensive heterogeneity in telomere length and more telomeres without detectable telomeric repeat sequences. The dynamics of the changes in telomere length also demonstrated a higher rate of fluctuation in telomere length, both on individual telomeres and coordinately on all telomeres. These results demonstrate that telomere maintenance can play a role in the genomic instability seen in cancer cells.

Elongated telomeres in scid mice

Severe combined immunodeficiency (scid) mice are deficient in the enzyme DNA-PK (DNA-dependent protein kinase) as a result of the mutation in the gene encoding the catalytic subunit (DNA-PKcs) of this enzyme. DNA-PKcs is a member of the phosphatidylinositol 3-kinase superfamily, which includes the human protein ATM (ataxia telangiectasia mutated) and the yeast protein Tel1. Using Q-FISH (quantitative fluorescence in situ hybridization), we show here that scid mice from four different genetic backgrounds have, on average, 1.5-2 times longer telomeres than those of corresponding wild-type mice. Our results point to the possibility that DNA-PKcs may, directly or indirectly, be involved in telomere length regulation in mammalian cells.

Telomere length dynamics and chromosomal instability in cells derived from telomerase null mice

To study the effect of continued telomere shortening on chromosome stability, we have analyzed the telomere length of two individual chromosomes (chromosomes 2 and 11) in fibroblasts derived from wild-type mice and from mice lacking the mouse telomerase RNA (mTER) gene using quantitative fluorescence in situ hybridization. Telomere length at both chromosomes decreased with increasing generations of mTER-/- mice. At the 6th mouse generation, this telomere shortening resulted in significantly shorter chromosome 2 telomeres than the average telomere length of all chromosomes. Interestingly, the most frequent fusions found in mTER-/- cells were homologous fusions involving chromosome 2. Immortal cultures derived from the primary mTER-/- cells showed a dramatic accumulation of fusions and translocations, revealing that continued growth in the absence of telomerase is a potent inducer of chromosomal instability. Chromosomes 2 and 11 were frequently involved in these abnormalities suggesting that, in the absence of telomerase, chromosomal instability is determined in part by chromosome-specific telomere length. At various points during the growth of the immortal mTER-/- cells, telomere length was stabilized in a chromosome-specific man-ner. This telomere-maintenance in the absence of telomerase could provide the basis for the ability of mTER-/- cells to grow indefinitely and form tumors.

Telomere length, chromatin structure and chromosome fusigenic potential

Telomeres are specialized structures at chromosome ends that are thought to function as buffers against chromosome fusion. Several studies suggest that telomere shortening may render chromosomes fusigenic. We used a novel quantitative fluorescence in situ hybridization procedure to estimate telomere length in individual mammalian chromosomes, and G-banding and chromosome painting techniques to determine chromosome fusigenic potential. All analysed Chinese hamster and mouse cell lines exhibited shorter telomeres at short chromosome arms than at long chromosome arms. However, no clear link between short telomeres and chromosome fusigenic potential was observed, i.e. frequencies of telomeric associations were higher in cell lines exhibiting longer telomeres. We speculate that chromosome fusigenic potential in mammalian cell lines may be determined not only by telomere length but also by the status of telomere chromatin structure. This is supported by the observed presence of chromatin filaments linking telomeres in Chinese hamster chromosomes and of multibranched chromosomes oriented end-to-end in the murine severe combined immunodeficient (SCID) cell line. Multibranched chromosomes are the hallmark of the human ICF (Immune deficiency, Centromeric instability, Facial abnormalities) syndrome, characterized by alterations in heterochromatin structure.

Kinetic evidence of the regeneration of multilineage hematopoiesis from primitive cells in normal human bone marrow transplanted into immunodeficient mice

Based on initial observations of human CD34+ Thy-1+ cells and long-term culture-initiating cells (LTC-IC) in the bone marrow of some sublethally irradiated severe combined immunodeficient (SCID) mice transplanted intravenously with normal human marrow cells, and the subsequent finding that the NOD/LtSz-scid/scid (NOD/SCID) mouse supports higher levels of human cell engraftment, we undertook a series of time course experiments to examine posttransplant changes in the number, tissue distribution, cycling activity, and in vivo differentiation pattern of various human hematopoietic progenitor cell populations in this latter mouse model. These studies showed typical rapid posttransplant recovery curves for human CD34- CD19+ (B-lineage) cells, CD34+ granulopoietic, erythroid, and multilineage colony-forming cells (CFC), LTC-IC, and CD34+ Thy-1+ cells from a small initial population representing <0.1% of the original transplant. The most primitive human cell populations reached maximum values at 5 weeks posttransplant, after which they declined. More mature cell types peaked after another 5 weeks and then declined. A 2-week course of thrice weekly injections of human Steel factor, interleukin (IL)-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin (administered just before the mice were killed for analysis) did not alter the pace of regeneration of either primitive or mature human hematopoietic cells, or their predominantly granulopoietic and B-lymphoid pattern of differentiation, although a significant enhancing effect on the level of human cell engraftment sustained after 3 months was noted. Cycling studies showed the human CFC present at 4 to 5 weeks posttransplant to be rapidly proliferating even in mice not given human growth factors. However, by 10 weeks and thereafter, only quiescent human CFC were detected; interestingly, even in mice that were given the 2-week course of growth factor injections. These studies indicate the use of this model for future analysis of the properties and in vivo regulation of primitive human hematopoietic cells that possess in vivo repopulating ability.

Quantitation and characterization of human megakaryocyte colony-forming cells using a standardized serum-free agarose assay

Human progenitors of the megakaryocyte (Mk) lineage were detected by their ability to generate colonies-containing from 3 to > 100 Mk, detectable as glycoprotein IIb/IIIa+ cells in APAAP-stained whole mount agarose cultures. Optimal growth conditions were achieved through the use of a defined serum substitute and a suitable cocktail of recombinant cytokines. Under these culture conditions, the smallest Mk-containing colonies (CFC-Mk) were detectable within a week followed by colonies containing larger numbers of Mk over the ensuing 2 weeks. The total number of CFC-Mk at 18-21 d was linearly related to the number of cells plated. Variation in the cytokines added showed that thrombopoietin (TPO) or IL-3 alone would support the formation of large numbers of CFC-Mk. However, optimal yields of colonies containing cells of both Mk and non-Mk lineages required the addition of other growth factors, of which a combination of IL-3, IL-6, GM-CSF and Steel factor (SF) +/- TPO was the best of those tested. The further addition of erythropoietin to this combination reduced the number of large "pure' Mk colonies seen and in their place a corresponding number of mixed erythroid-Mk colonies became detectable. Flt3-ligand alone was unable to support the growth of CFC-Mk nor did it enhance their growth when combined with other factors. Plating of FACS-sorted sub-populations of CD34+ marrow cells in both serum-free agarose and methylcellulose assays demonstrated that most CFC-Mk are generated from CD34+ cells that are CD45RA- and CD71+, approximately half of which are CD41+. Thus, CFC-Mk are more similar to primitive clonogenic erythroid progenitors than to their granulopoietic counterparts in their expression of CD34, CD45RA and CD71. Taken together, these findings support the concept that some erythroid and Mk progenitors may share a common developmental pathway. The availability of sensitive and reproducible procedures for isolating and detecting human Mk progenitors should facilitate future investigations of their biology and role in a variety of haematological conditions.

Selection of retrovirally transduced hematopoietic cells using CD24 as a marker of gene transfer

We have investigated the use of a cell surface antigen as a dominant selectable marker to facilitate the detection and selection of retrovirally infected target cells. The small coding region of the human cell surface antigen CD24 (approximately 240 bp) was introduced into a myeloproliferative sarcoma virus (MPSV)-based retroviral vector, which was then used to infect day 4 5-fluorouracil (5-FU)-treated murine bone marrow cells. Within 48 hours of termination of the infection procedure CD24-expressing cells were selected by fluorescent-activated cell sorting (FACS) with an antibody directed against the CD24 antigen. Functional analysis of these cells showed that they included not only in vitro clonogenic progenitors and day 12 colony-forming unit-spleen but also cells capable of competitive long-term hematopoietic repopulation. Double-antibody labeling studies performed on recipients of retrovirally transduced marrow cells showed that some granulocytes, macrophages, erythrocytes, and, to a lesser extent, B and T lymphocytes still expressed the transduced CD24 gene at high levels 4 months later. No gross abnormalities in hematopoiesis were detected in mice repopulated with CD24-expressing cells. Our results show that the use of the CD24 cell surface antigen as a retrovirally encoded marker enables the rapid, efficient, and nontoxic selection in vitro of infected primary cells, facilitates tracking and phenotyping of their progeny, and should provide a unique tool to identify elements that regulate the expression of transduced genes in the most primitive hematopoietic cells.

Transforming growth factor beta 1 is an inducer of erythroid differentiation

Normal human bone marrow cells, highly enriched for burst-forming units-erythroid (BFU-E), were cultured in serum-free medium, in the presence and absence of various factors, to investigate the mechanisms involved in regulating erythroid differentiation. In cultures containing interleukin 3 (IL-3), Steel factor (SF), and erythropoietin (Ep), benzidine-positive erythroblasts first became detectable on day 6. Their numbers then rapidly increased until, by day 16, > 99% of the cells, which were 20,000-fold amplified over input numbers, were benzidine-positive. It is interesting to note that omission of either SF or Ep from this assay markedly enhanced the rate of differentiation and reduced total cell numbers, whereas omission of IL-3 had no effect on the rate of differentiation and only slightly reduced cell numbers. Of various agents tested, the most potent erythroid differentiation inducer (and inhibitor of cell proliferation) was found to be transforming growth factor beta 1 (TGF-beta 1). This cytokine stimulated both the rapid appearance of hemoglobin-positive cells and an early cessation of cell proliferation. Using fluorescently tagged antibodies to glycophorin A and fluorescence-activated cell sorter (FACS) analysis, this phenomenon was shown to be due to an early induction of erythroid differentiation rather than an aberrant production of hemoglobin. Methylcellulose assays indicated that the well-documented reduction of BFU-E colony numbers observed with TGF-beta 1 may actually be due to a TGF-beta 1-induced "conversion" of BFU-E into colony-forming units-erythroid (CFU-E). Thus, in vivo, TGF-beta 1 might serve, in part, to decrease the number of mature erythrocytes by stimulating BFU-E to skip a number of cell divisions and differentiate early.

Activation of multiple hemopoietic growth factor genes in Abelson virus-transformed myeloid cells

We have recently shown that Abelson murine leukemia (A-MuLV) virus can transform cells in large mixed colonies to give tumorigenic myeloid cell lines capable of autonomous growth in vitro. Initial studies revealed that granulocyte-macrophage colony-stimulating factor (GM-CSF) production was consistently activated in these cells. Using a sensitive S1 RNA mapping technique and additional bioassays, we have now obtained evidence of expression of other hemopoietic growth factor genes. Uniformly 32P-labeled, single-stranded DNA probes (greater than 4 x 10(8) cpm/micrograms) were generated for interleukin 3 (IL-3) and GM-CSF using pTZ based vectors. IL-3 mRNA was detected in four of four cloned transformants (from two different infections) at approximately 1% of the level seen in pokeweed mitogen (PWM)-stimulated spleen cells. GM-CSF mRNA was detected in the two clones that showed the highest IL-3 mRNA levels. Medium conditioned by these cells was able to stimulate IL-3-dependent 32D cells, and IL-3- and GM-CSF-dependent B6SUtA cells, and also supported the growth of a variety of single and multilineage colonies in assays of mouse marrow cells even in the presence of neutralizing antibodies to GM-CSF. Rearrangements of the IL-3 and GM-CSF genes were not apparent by Southern blot analysis. Additional bioassays revealed the presence of two other growth factors: IL-6 (hybridoma growth factor or Ifn-beta 2) assayed on B13.29 cells, a factor-dependent murine B-cell hybridoma; and a new pre-B-cell stimulatory factor different from any of the above. Elucidation of the mechanism underlying this phenomenon may provide important insights into the regulation of hemopoietic growth factor gene expression and the role such genes play in human leukemogenesis.

Improved resolution of flow cytometric measurements of Hoechst- and chromomycin-A3-stained human chromosomes after addition of citrate and sulfite

The resolution of bivariate flow karyotypes of human chromosomes stained with Hoechst 33258 and chromomycin A3 can be increased by adding sodium citrate and sodium sulfite to the chromosomes shortly before measurement. A flow karyotype of a patient with chronic myelocytic leukemia is shown to illustrate that the addition of these compounds allows high-resolution measurements to be made and evaluated reliably from clinical samples.

Interferon beta 2/B-cell stimulatory factor type 2 shares identity with monocyte-derived hepatocyte-stimulating factor and regulates the major acute phase protein response in liver cells

One of the oldest and most preserved of the homeostatic responses of the body to injury is the acute phase protein response associated with inflammation. The liver responds to hormone-like mediators by the increased synthesis of a series of plasma proteins called acute phase reactants. In these studies, we examined the relationship of hepatocyte-stimulating factor derived from peripheral blood monocytes to interferon beta 2 (IFN-beta 2), which has been cloned. Antibodies raised against fibroblast-derived IFN-beta having neutralizing activity against both IFN-beta 1 and -beta 2 inhibited the major hepatocyte-stimulating activity derived from monocytes. Fibroblast-derived mediator elicited the identical stimulated response in human HepG2 cells and primary rat hepatocytes as the monocyte cytokine. Finally, recombinant-derived human B-cell stimulatory factor type 2 (IFN-beta 2) from Escherichia coli induced the synthesis of all major acute phase proteins studied in human hepatoma HepG2 and primary rat hepatocyte cultures. These data demonstrate that monocyte-derived hepatocyte-stimulating factor and IFN-beta 2 share immunological and functional identity and that IFN-beta 2, also known as B-cell stimulatory factor and hybridoma plasmacytoma growth factor, has the hepatocyte as a major physiologic target and thereby is essential in controlling the hepatic acute phase response.

Human endothelial culture supernatant (HECS): a growth factor for hybridomas

Human endothelial culture supernatant (HECS) had strong growth-promotion activity for hybridoma cells: the yield of hybridomas after fusion was increased at least 2-fold over that in the presence of feeder cells, such as mouse macrophages and spleen cells. Moreover, HECS could substitute for feeder cells when hybridomas were cultured at the single-cell level, and strongly enhanced the proliferation of hybrid cells. furthermore, the presence of human endothelial cells prolonged the stability of human-mouse hybridomas, producing human immunoglobulin, hybrids known to survive poorly during culture in vitro.

Human endothelial culture supernatant (HECS): a growth factor for hybridomas

Human endothelial culture supernatant (HECS) had strong growth-promotion activity for hybridoma cells: the yield of hybridomas after fusion was increased at least 2-fold over that in the presence of feeder cells, such as mouse macrophages and spleen cells. Moreover, HECS could substitute for feeder cells when hybridomas were cultured at the single-cell level, and strongly enhanced the proliferation of hybrid cells. furthermore, the presence of human endothelial cells prolonged the stability of human-mouse hybridomas, producing human immunoglobulin, hybrids known to survive poorly during culture in vitro.