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R A Roberts

Publications and source records attributed to R A Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1996

Species differences in response to peroxisome proliferators correlate in vitro with induction of DNA synthesis rather than suppression of apoptosis.

Tumorigenesis caused by the peroxisome proliferator (PP) class of non-genotoxic hepatocarcinogens is species restricted; rat and mouse are considered responsive whereas the available evidence suggests that humans, non-human primates, dogs, hamsters and guinea pigs are non-responsive. We have demonstrated previously that the PP, nafenopin can suppress rat hepatocyte apoptosis both in vitro and in vivo. Here we describe the ability of nafenopin to suppress apoptosis in mouse, hamster, guinea pig and rat hepatocytes and induce S-phase in mouse and rat hepatocytes. Hepatocyte monolayers from all species examined degenerated rapidly in culture. However, nafenopin (50 microM) reversibly maintained the viability of both rat and mouse hepatocytes. This maintenance was associated with a decrease (P < or = 0.01) in the number of hepatocytes displaying chromatin condensation patterns characteristic of apoptosis. Treatment of rat and mouse monolayers with 5 ng/ml transforming growth factor-beta 1 (TGF beta 1) induced high levels of apoptosis (P < or = 0.01); co-addition of nafenopin suppressed this induced apoptosis (P < or = 0.01). TGF beta 1 also induced apoptosis in hamster and guinea pig hepatocytes (P < or = 0.01) and unexpectedly nafenopin was able to suppress this induced apoptosis (P < or = 0.01) as well as reversibly maintaining the viability of hamster and guinea pig hepatocyte monolayers. Thus, all the species examined responded to nafenopin by a suppression of both spontaneous and TGF beta 1-induced apoptosis. In contrast, only rat and mouse hepatocytes showed an induction of S-phase in response to nafenopin (P < or = 0.01). Certain key experiments were repeated using the PPs methyl clofenapate (MCP) (100 microM) and Wy-14, 643 (10 microM). Both were able to suppress spontaneous and TGF beta 1-induced apoptosis in rat and guinea pig hepatocytes although the effects of MCP were weak (P < or = 0.05) compared with nafenopin or Wy-14 643 (P < or = 0.01). The rat and mouse liver tumour promoter, phenobarbitone (PB) was assessed also. Rat hepatocytes responded to PB with a suppression of apoptosis and an induction of S-phase (P < or = 0.01). Hamster and guinea pig cells gave no response in the S-phase assay and exhibited no suppression of either spontaneous or TGF beta 1-induced apoptosis. Interestingly, nafenopin suppressed the apoptosis induced by the DNA damaging drugs, etoposide and hydroxyurea (P < or = 0.01) suggesting that PPs can impact on diverse apoptosis signalling pathways. Overall, species differences in response to the non-genotoxic hepatocarcinogens studied, correlate with induction of DNA synthesis rather than with suppression of apoptosis. The data extend our knowledge of the mechanisms of species differences in non-genotoxic hepatocarcinogenesis, posing interesting questions on the relative roles of apoptosis and DNA synthesis in carcinogenesis.

Animals↗
PubMed1996

Perceived environmental stressors for dental hygiene students.

This study identifies stressors for dental hygiene students and examined significant differences in stress levels between first- and last-year dental hygiene students and between dental hygiene and dental students. A modified dental environmental stress (DES) questionnaire was utilized to determine the sources of stress. The questionnaire was completed by 153 (93 percent) first- and last-year dental hygiene students from four programs. Seven stressors were among the top ten stress items cited by both classes of dental hygiene students; seven other stressors exhibited significant differences (p = .01). The authors' hypothesis is that some of these stressors may be remediable. Seven of the top ten stressors for first-year dental hygiene and dental students were shared, while ten exhibited significant differences. Among last-year students, eighteen items were significant, and seven of the top ten stressors were the same.

Age Factors↗
PubMed1996

Types, uses, and evaluation of the plate-form implant.

Plate-form blades have shown a high rate of success over their 25+ years of service. Contributing to their longevity is the design of the implant, which transfers the applied forces over a large area of bone. Three types of implants are being considered: (1) the Ramus Blade, designed for the body and ramus region of the mandible; (2) the Ramus Frame, designed for the totally edentulous mandible with moderate to severe bone atrophy; and (3) the single-tooth replacement, an implant for single or multiple tooth loss. Both 316-L stainless steel and titanium metal types have been used to fabricate each implant type. Blades are, in the author's opinion, the most universal of the implants used today, for they are utilized in so many variable bone widths and heights. Besides being in service for periods of up to 27 years, they are patient-acceptable in terms of comfort, function and minimal maintenance.

Blade Implantation↗
PubMed1995

Enhanced hepatocyte colony growth in soft agar after in vivo treatment with a genotoxic carcinogen: a potential assay for hepatocarcinogens?

We have shown previously that approximately 1 in 10,000 primary hepatocytes isolated from untreated rats undergo clonal growth in soft agar in vitro in response to the synergistic action of nafenopin, a peroxisome proliferator (PP) and epidermal growth factor (EGF), a naturally occurring liver growth regulator. Here, we demonstrate that prior treatment of the animals with the genotoxic hepatocarcinogen diethylnitrosamine (DEN) caused a dose-dependent increase in soft agar colony numbers formed in vitro. These data suggest that the colony assay may offer a method of detecting in vitro hepatocytes transformed in vivo by DEN. It is known that rats treated with DEN develop enzyme altered foci prior to the development of tumours. The majority of these foci express high levels of gamma-glutamyl transpeptidase (GGT). However, foci promoted by PPs do not show this increased enzyme activity. In the present study, the colonies we have generated in vitro mimicked this pattern since the majority (approximately 80%) of the spontaneous colonies expressed GGT whereas colonies promoted by the synergistic action of nafenopin and EGF were mainly (75%) GGT negative. The proportion of colonies positive for GGT were similar using either hepatocytes isolated from control or from DEN-initiated rats. Further studies are required to assess if the hepatocytes selected for clonal expansion by this EGF/nafenopin regime reflect the presumed pre-neoplastic cells induced by genotoxin in vivo and associated with an increased propensity to cancer.

Agar↗
PubMed1995

Species differences in the clonal expansion of hepatocytes in response to the coaction of epidermal growth factor and nafenopin, a rodent hepatocarcinogenic peroxisome proliferator.

Peroxisome proliferators are members of the nongenotoxic family of rodent hepatocarcinogens. There exist substantial species differences in response to peroxisome proliferators among mammalian species. We have reported previously that peroxisome proliferators can synergize with epidermal growth factor (EGF) to promote the clonal expansion of rat hepatocytes associated with the early stages of hepatocarcinogenesis. The aim of the present study was to determine whether responsiveness in this in vitro assay reflected the known species differences in response to peroxisome proliferators. The process of tumorigenicity was modeled in the soft agar cloning assay since growth in soft agar is thought to reflect the early stages of tumorigenesis. This is because clonal expansion under these conditions requires the cells to survive, to undergo mitosis, and to escape from the contact-dependent growth associated with normal cell behavior. The data presented here show that mouse hepatocytes are able to undergo clonal expansion in soft agar in response to nafenopin and EGF giving a three- to fourfold increase in colony numbers over control. This result is comparable to the fivefold increase in rat hepatocyte colony numbers that we have reported previously. In contrast, hamster, guinea pig, and human hepatocytes did not respond to the concerted action of EGF and nafenopin despite their ability to respond to EGF as a mitogen in monolayer culture. These data demonstrate that the clonal expansion of rodent hepatocytes in soft agar in response to peroxisome proliferators and EGF displays the same species differences as other pleiotropic responses to these compounds and is likely therefore to be relevant to the process of hepatocarcinogenesis.

Animals↗
PubMed1995

Dosing-induced stress causes hepatocyte apoptosis in rats primed by the rodent nongenotoxic hepatocarcinogen cyproterone acetate.

It has been proposed that several nongenotoxic compounds act as hepatocarcinogens by suppressing the apoptosis that would normally act to remove damaged or potentially initiated cells from the liver. During our investigations of this hypothesis using a widely applied protocol, we have found that the stress induced by the process of gavage dosing can induce massive apoptosis in livers uniquely primed by withdrawal of the hepatomitogen cyproterone acetate from the hyperplastic rat liver. This effect of gavage dosing was not seen in livers of naive animals. Apoptosis was measured by both in situ end labeling (ISEL) of the DNA damage associated with programmed cell death and conventional hematoxylin and eosin (H&E) staining of apoptotic morphology. Apoptotic rates measured by H&E increased significantly from 0.005 +/- 0.010% on Day 11 to 0.657 +/- 0.315% of hepatocytes on Day 15, 4 days after cessation of 10 days dosing with CPA (120 mg/kg). The readministration of CPA suppressed > 89% of this Day 15 apoptosis. However, the readministration of vehicle alone (corn oil) caused a 390% increase in apoptosis to 2.56 +/- 1.31% of hepatocytes. Similar results were obtained using ISEL. Measurements of liver to body weight ratios and total DNA per liver reflected these changes in cell loss by apoptosis. In a second experiment, CPA was administered for 10 days as before then animals were subjected to readministration of CPA in corn oil, CPA in saline, corn oil, saline, or sham dosed. Again, apoptosis was dramatically suppressed by the readministration of CPA in either vehicle but was dramatically increased to around 2% of hepatocytes in all other groups, including the sham dosed group. Data on food consumption provided no evidence for a reduction in food intake as a causative agent but rather pointed to a less efficient usage of food in the stressed animals. The ability of stress to induce liver apoptosis should be borne in mind in the design and interpretation of future toxicological studies aimed at understanding the putative suppression of apoptosis by liver nongenotoxic carcinogens and other toxicants.

Animals↗
PubMed1995

Non-genotoxic hepatocarcinogens stimulate DNA synthesis and their withdrawal induces apoptosis, but in different hepatocyte populations.

Non-genotoxic hepatocarcinogenesis may involve suppression of the hepatocyte apoptosis that would normally remove damaged or initiated cells. These protected hepatocytes could then remain as preferential targets for promotion by this class of compounds. Here we demonstrate clearly that the non-genotoxic liver carcinogens and hepatomitogens cyproterone acetate (CPA) and nafenopin, a peroxisome proliferator, both suppress the basal level of rat liver apoptosis in vivo. After 10 days of dosing with CPA (120 mg/kg/day) or nafenopin (25 mg/kg/day) there were 0.005 +/- 0.010 and 0.002 +/- 0.021 apoptotic bodies/100 hepatocytes respectively, compared with 0.031 +/- 0.008 per 100 in controls. Concomitant with this suppression of apoptosis, bromodeoxyuridine (BrdU) labelling indices and mitotic figures rose, confirming a perturbation of both sides of the growth equation between cell death and replication. Withdrawal of CPA or nafenopin resulted in a 100- to 200-fold elevation in apoptosis. This was inhibited by the re-administration of either compound. To investigate if cells protected from apoptosis by non-genotoxic carcinogens are targets for replication, we examined the replicative history of the apoptotic bodies generated upon withdrawal of CPA or nafenopin. Rats were administered BrdU during the hyperplastic phase of compound administration (0-10 days). Livers were examined 5 days after compound withdrawal. With both CPA and nafenopin, apoptotic bodies and S phase were predominantly in the periportal region. However, despite this zonal co-localization, very few (< 10%) of the apoptotic bodies were labelled with BrdU. Overall, our data provide in vivo evidence to support the hypothesis that non-genotoxic hepatocarcinogens such as CPA and the peroxisome proliferators suppress apoptosis. Surprisingly, the majority of the hepatocytes generated during compound-induced hyperplasia were protected from apoptosis during liver regression. These data contribute to our understanding of clonal selection and promotion during non-genotoxic hepatocarcinogenesis.

Animals↗
PubMed1995

The rodent non-genotoxic hepatocarcinogen Nafenopin and EGF alter the mitosis/apoptosis balance promoting hepatoma cell clonal growth.

The responses of a series of rat hepatoma cell lines (FaO, HTC, RH1) to the rodent non-genotoxic hepatocarcinogen and per-oxisome proliferator (PP) Nafenopin were studied to determine if this PP acts with EGF, a naturally occurring liver growth regulator, to perturb the balance between mitosis and apoptosis. EGF enhanced the growth of FaO cells (well differentiated) and HTC cells (intermediate differentiation) but not of the poorly differentiated RH1 cell line. Nafenopin also increased FaO cell growth but, surprisingly, retarded the growth of both HTC and RH1 cells. Since population expansion kinetics result from mitosis and death, replicative DNA synthesis (RDS) and apoptotic cell death were measured in HTC cells. As expected, EGF elevated RDS and suppressed cell death. However, Nafenopin depressed HTC net population expansion via a suppression of cell death coupled to a more marked inhibition of RDS. This apparent paradox was investigated using soft agar cloning. This revealed sub-populations with differing growth kinetics suggesting selective clonal expansion via an alteration in the balance between mitosis and apoptotic cell death. At later stages, cells are refractory to EGF and Nafenopin, suggesting that genetic changes may have superseded such factor-dependence.

Journal Article↗
PubMed1994

Suppression of liver cell apoptosis in vitro by the non-genotoxic hepatocarcinogen and peroxisome proliferator nafenopin.

Suppression of apoptosis has been implicated as a mechanism for the hepatocarcinogenicity of the peroxisome proliferator class of non-genotoxic carcinogens. The ability of the peroxisome proliferator nafenopin to suppress or delay the onset of liver apoptosis was investigated using primary cultures of rat hepatocytes and the Reuber hepatoma cell line FaO. 50 microM nafenopin reversibly maintained the viability of primary rat hepatocyte cultures which otherwise degenerated within 8 d of establishment. The maintenance of viability of hepatocyte monolayers was associated with a significant decrease in the number of cells exhibiting chromatin condensation patterns typical of apoptosis. Apoptosis could be induced in hepatocytes by administration of 5 ng/ml TGF beta 1. Co-addition of 50 microM nafenopin significantly reduced TGF beta 1-induced apoptosis by 50-60%. TGF beta 1 (1-5 ng/ml) also induced apoptosis in the FaO rat hepatoma cell line. Cell death was accompanied by detachment of FaO cells from the monolayer and detached cells exhibited chromatin condensation and non-random DNA fragmentation patterns typical of apoptosis. Co-addition of 50 microM nafenopin to TGF beta 1-treated FaO cultures significantly reduced the number of apoptotic cells detaching from the monolayer at 24 h. In contrast, nafenopin had no significant effect on FaO apoptosis induced by the DNA damaging agents etoposide and hydroxyurea. We conclude that suppression of liver cell death by apoptosis may play a role in the hepatocarcinogenicity of the peroxisome proliferators, although the extent of this protection is dependent on the nature of the apoptotic stimulus.

Animals↗
PubMed1994

The peroxisome proliferator class of non-genotoxic hepatocarcinogens synergize with epidermal growth factor to promote clonal expansion of initiated rat hepatocytes.

The mechanisms by which the peroxisome proliferator (PP) class of non-genotoxic carcinogens perturb growth regulation and cause rodent liver cancer are unknown. Using a soft agar cloning assay, we have demonstrated that PPs synergize with the physiological liver mitogen epidermal growth factor (EGF) to cause the clonal expansion of rat hepatocytes associated with the early stages of tumourigenesis. In the presence of EGF (25 ng/ml), the PP nafenopin (100 microM) was able to stimulate a 5-fold increase in the number of colonies (35 colonies/50,000 hepatocytes compared to seven in the control). EGF alone or nafenopin alone gave 11 and 14 colonies respectively. TGF alpha, which acts through the EGF receptor, also synergized with nafenopin, whereas HGF was inactive, despite its potency as an hepatocyte growth factor. The ability to promote colony formation was shared by the potent PP Wyeth-14,643 but not by the less potent compounds methylclofenapate or trichloroacetic acid. TGF beta, a physiological negative regulator of liver growth, was able to inhibit the nafenopin/EGF-stimulated colony formation at 0.25 ng/ml, a concentration below that required for TGF beta-induced hepatocyte apoptosis. The colonies formed are derived from and consist of hepatocytes, since they express the hepatocyte-specific marker albumin, although the majority are negative for the PP-induced cytochrome, P4504A1. Pre-treatment in vivo with the genotoxic carcinogen dimethylhydrazine hydrochloride (150 mg/kg) caused a doubling in the number of colonies from 35 to 75/50,000 hepatocytes. Taken together, these data suggest that some PPs act as hepatocarcinogens by synergizing with EGF and/or TGF alpha to promote the clonal expansion of spontaneously initiated hepatocytes. This clonal expansion may be inhibited by TGF beta. Such a synergy may provide a mechanistic basis for the hepatocarcinogenicity of this class of non-genotoxic carcinogens.

Albumins↗
PubMed1993

Hepatocyte spheroids: prolonged hepatocyte viability for in vitro modeling of nongenotoxic carcinogenesis.

To explore peroxisome proliferator-perturbed hepatocyte growth regulation, robust in vitro models of liver are required. This has always posed a problem since isolated hepatocytes show a rapid loss of viability and differentiation status and cease to be useful after 3-4 days in culture. We now describe a model system in which rat hepatocytes are maintained as three-dimensional spheroids. The maintenance of hepatocyte viability and morphology in these cultures is considerably prolonged over that seen in monolayer culture and is comparable to that obtained by the use of collagen gels or dimethyl sulfoxide. The spheroid system is, however, free of any additives that may lead to artifact and free of excessive exogenous protein that may compromise subsequent analyses. Ultrastructural examination reveals extensive interhepatocyte junctional complexes and interdigitation of adjacent membranes together with the presence of bile cannalicular structures. Furthermore, hepatocytes maintained as spheroids retain expression of liver markers such as albumin and also retain their ability to respond to peroxisome proliferators: even after 12 days in culture, treatment with the peroxisome proliferator nafenopin causes a 4.5-fold increase in cytoplasmic volume fraction of peroxisomes. There is a concomitant induction of peroxisomal bifunctional enzyme and cytochrome P4504A, the enzyme markers associated with peroxisome proliferation. The spheroids also maintain expression of the peroxisome proliferator-activated receptor and preliminary data indicate that they are able to undergo replicative DNA synthesis in response to nafenopin. Hepatocyte spheroids will provide us with a model system for studying the early changes in rodent liver nongenotoxic carcinogenesis.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1993

Non-genotoxic hepatocarcinogenesis in vitro: the FaO hepatoma line responds to peroxisome proliferators and retains the ability to undergo apoptosis.

A range of hepatoma cell lines (RH1, HTC, FaO, 7800C1 and MH1C1), has been studied with the aim of establishing an in vitro model to investigate the molecular mechanisms of hepatocarcinogenicity induced by the peroxisome proliferator class of non-genotoxic carcinogens. In view of speculation that peroxisome proliferators suppress hepatocyte apoptosis in vivo, we have placed particular emphasis on evaluating whether hepatoma cell lines retain the ability to undergo apoptotic cell death. Expression of the liver-specific differentiation marker albumin and the peroxisome proliferator-activated receptor (PPAR) was highest in the Reuber hepatoma cell line, FaO. This cell line also demonstrated the most marked response to the peroxisome proliferator nafenopin with a 2.2-fold induction of the microsomal enzyme cytochrome p450IVA1. This response was found to display intercellular heterogeneity by immunocytochemistry. Thus, the FaO cell line maintained characteristics of hepatocytes, both in vivo and in vitro, in terms of expression of constitutive and inducible markers. However, none of the cell lines tested mirrored the hyperplastic response of hepatocytes to nafenopin, since no increase in cell growth kinetics was observed on addition of nafenopin to the growth medium. The mode of cell death in confluent FaO cultures was characterised as apoptosis, by fluorescence microscopy and agarose gel electrophoresis of extracted DNA. Cells detaching from confluent FaO cultures exhibited chromatin condensation and DNA fragmentation patterns characteristic of cels undergoing apoptotic death.Interestingly, no apoptosis was seen in monolayer cells, suggesting that apoptosis in vitro is associated with cell shrinkage and detachment similar to that documented for the liver in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

An in vitro model of rodent nongenotoxic hepatocarcinogenesis.

An in vitro model of liver in which rat hepatocytes are maintained as cocultures with nonparenchymal epithelial cells (NPC) derived from liver has been developed and characterized with respect to maintenance of hepatocyte viability and differentiated function. The system was then evaluated as a model for studying peroxisome proliferator-induced rodent liver nongenotoxic carcinogenesis. Within the coculture model, hepatocyte viability and morphology were maintained for 1 month or more within a system that is both easily accessible for microscopic examination and is free of any additives that may lead to artifacts. Even after 1 month or more, hepatocyte cocultures retained expression of the constitutive liver marker albumin. In addition, they maintained the ability to show induction of the peroxisome proliferator-inducible enzymes peroxisomal bifunctional enzyme (PBE) and cytochrome P450IVA1 in response to the peroxisome proliferator nafenopin. After 4 weeks, NPC cocultures showed a six- and a fourfold induction of PBE and cytochrome P450IVA1 expression, respectively, which compared well with the three- and fivefold induction seen in freshly isolated cells. This was paralleled by an increase in the cytoplasmic volume fraction of peroxisomes averaging eightfold. Interestingly, great heterogeneity was exhibited between adjacent hepatocytes in terms of the degree of peroxisome proliferation, a finding reflected by immunocytochemical staining which indicated heterogeneity in the level of expression of the peroxisome proliferator-inducible enzymes. Other cell lines representing different tissue types, morphologies, and species were also examined for their ability to support hepatocyte survival but were found to be ineffective, with the exception of a bovine corneal endothelial cell line. This line supported hepatocyte survival and maintenance of differentiated function but to a lesser extent than that observed with NPC. Ultrastructural examination of NPC cocultures revealed extensive interhepatocyte junctional complexes and interdigitation of adjacent membranes together with the presence of bile canalicular structures. There were no junctional complexes between the hepatocytes and the supporting feeder cells with any contact being limited to a close association of the hepatocytes with the extracellular matrix presumably produced by the NPC. The data demonstrate that hepatocytes maintained in vitro within an NPC coculture system retain differentiated function and the ability to respond to the peroxisome proliferator class of nongenotoxic carcinogens. Cocultures will provide us with a model system for the study of changes in hepatocyte growth regulation during rodent liver nongenotoxic carcinogenesis.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1990

Bradykinin receptors undergo ligand-induced desensitization.

Bradykinin binds to specific cell surface receptors on Rat13 fibroblasts with a high affinity (2.1 nM). Prolonged exposure of cells to the ligand causes a concentration-dependent decline in surface levels of the 2.1 nM receptor from 40,000 receptors per cell to undetectable levels with a t1/2 of approximately 2 h. The decline occurs in parallel with the appearance of an equal number of lower affinity binding sites (40 nM), suggesting that ligand exposure causes desensitization by an alteration in receptor affinity. The affinity change is characterized by a faster rate of ligand dissociation while the rate of association remains unaltered. The observed desensitization is dependent on the presence of active cellular metabolism since (i) it does not occur in whole cells maintained at 4 degrees C and (ii) membranes prepared from Rat13 cells retain their high-affinity sites at 37 degrees C despite extensive ligand exposure.

Animals↗
PubMed1989

Persistent intracellular binding of mitoxantrone in a human colon carcinoma cell line.

Incubation of human carcinoma cells with mitoxantrone resulted in an intracellular distribution of the drug into cytoplasmic, nuclear and cytoskeletal compartments occurring within 1 min of drug treatment. Incubation of the cells in drug-free medium resulted in an efflux of the drug such that 80% of the intracellular drug was eliminated from the cells by 72 hr. Approximately 20% of the initial intracellular drug concentration remained in the cells after the drug had been removed from the medium. The majority of the persistent intracellular drug was associated with soluble cytoplasmic proteins and fractions enriched in nucleic acid. Approximately 10% of the persistent drug binding was associated with cellular structures that had been depleted of soluble cytoplasmic protein and nucleic acid. During the persistent drug binding, the cells enlarged at least 2-fold as determined by microscopic examination. An increasing percentage of the cells was also observed to contain a DNA content consistent with a G2 cell cycle arrest. Taken together, these data suggest that the persistent intracellular binding of mitoxantrone results in a G2 cell cycle arrest and cellular damage.

Cell Cycle↗
PubMed1989

Cellular interactions between 3T3 cells and interleukin-3-dependent multipotent haemopoietic cells: a model system for stromal-cell-mediated haemopoiesis.

With the aid of a multipotent stem cell line (FDCP-mix cells) co-cultured with either normal or irradiated Swiss 3T3, cellular interactions between stromal cells and haemopoietic stem cells were studied by electron microscopy and time-lapse video microscopy. When cultured in the presence of interleukin 3 (IL-3) but in the absence of stromal cells, the FDCP-mix cells have a characteristic blast morphology. In the absence of IL-3, the cells die unless they are co-cultured with marrow stromal cells or 3T3 cells. In the latter case, they attach, proliferate, and differentiate on both normal and irradiated Swiss 3T3 cell layers without the addition of extrinsic growth factor (IL-3). At the initial attachment sites of these two cell lines, cellular recognition seemed to be mediated by the formation of microvillus cytoplasmic projections and extracellular matrix. These areas may well be the sites of plasma-membrane-bound signalling/adhesional molecules between the interacting cells.

Animals↗