Platelet-derived growth factor promotes division and motility and inhibits premature differentiation of the oligodendrocyte/type-2 astrocyte progenitor cell

The mitogens which modulate cell-cell interactions during development of the central nervous system are unknown. One of the few interactions sufficiently well understood to allow identification of such molecules involves the two glial lineages which make up the rat optic nerve. One population of glial cells in this tissue, the type-1 astrocytes, secrete a soluble factor(s) which promotes division of a second population of bipotential oligodendrocyte/type-2 astrocyte (O-2A) progenitor cells; these progenitors give rise to oligodendrocytes, which myelinate large axons in the CNS, and type-2 astrocytes, which enwrap bare axons at nodes of Ranvier. Type-1 astrocytes also promote progenitor motility, and inhibit the premature differentiation of progenitors into oligodendrocytes which occur when these cells are grown in the absence of type-1 astrocytes. We have now found that platelet-derived growth factor mimics the effects of type-1 astrocytes on O-2A progenitor cells, and antibodies to PDGF block the effects of type-1 astrocytes.

Evidence for migration of oligodendrocyte--type-2 astrocyte progenitor cells into the developing rat optic nerve

Formation of myelinated tracts in central nervous system (CNS) regions such as the optic nerve seems to depend on two glial cell types, both of which derive from a common progenitor cell. This oligodendrocyte--type-2 astrocyte (O-2A) progenitor cell gives rise to oligodendrocytes, which produce internodal myelin sheaths, and to type-2 astrocytes, which extend fine processes in the region of the nodal axolemma. The optic nerve also contains a third glial cell, the type-1 astrocyte, which derives from a separate precursor. These three glial cells develop in a fixed sequence over a two-week period: type-1 astrocytes appear at embryonic day 16 (E16), oligodendrocytes at the day of birth (E21 or postnatal day P0), and type-2 astrocytes between P8 and P10. Type-1 astrocytes secrete a potent mitogen which causes expansion of the O-2A progenitor cell population in vitro. Here, we report that dividing O-2A progenitor cells are highly motile and seem to migrate from the brain into the optic nerve, beginning at its chiasmal end. Our results indicate that long-distance migration along the neural axis is characteristic only of progenitors of the O-2A lineage and may serve to distribute these cells to regions of the CNS that will become myelinated. These results also suggest that the intrinsic neuroepithelial cells of the optic stalk may be even more restricted than previously thought, giving rise only to type-1 astrocytes.

Keratins (K16 and K17) as markers of keratinocyte hyperproliferation in psoriasis in vivo and in vitro

Keratinocyte differentiation in psoriasis was examined using a panel of monospecific monoclonal antibodies to keratins (K), including two recently developed monoclonal antibodies raised to carboxy terminal peptides of K6 (LL020) and K16 (LL025). Keratinocytes from normal skin, untreated psoriatic plaques and non-lesional psoriatic skin, were cultured using multiple in vitro systems. Time-lapse cinephotography was used to measure the intermitotic time of normal and psoriatic keratinocytes in both low calcium-defined and serum-containing media. The intermitotic time did not differ significantly between psoriatic and normal keratinocytes. Keratin expression of psoriatic and normal keratinocytes in vitro was examined by both gel electrophoresis and immunocytochemistry. K6, K16 and K17 were detected suprabasally in all culture systems in vitro, but only in interfollicular psoriatic epidermis in vivo, and not in normal skin. Small subpopulations of keratinocytes expressed simple epithelial keratins K7, K8, K18 and K19 in cultures on plastic substrates, but these keratins were absent in skin equivalents of normal or psoriatic skin. No psoriasis-specific pattern of differentiation was found in vitro. As the K6 peptide antibody reacted with basal cells of normal skin, probably due to K5 cross-reactivity, K16 expression determined by LL025 was found to be the most sensitive indicator of the psoriatic state of differentiation, and this antibody is recommended for future work on psoriasis. K17 had a distinct pattern of tissue distribution in normal skin: K17, but not K16, was present in basal myoepithelial cells in sweat glands, and the deep outer root sheath, but K17 distribution paralleled that of K16 in suprabasal psoriatic epidermis. As keratins K6, K16 and K17 are expressed in keratinocyte hyperproliferation, when high levels of certain cytokines are also expressed, the role of growth factors and regulatory nuclear transcription factors in the control of K6, K16 and K17 expression in psoriasis requires further study, in order to provide insight into the relationship between proliferation and differentiation.

Platelet-derived growth factor is mitogenic for O-2Aadult progenitor cells

We report that platelet-derived growth factor (PDGF) is a potent mitogen for oligodendrocyte type-2 astrocyte (O-2A) progenitor cells derived from the optic nerves of adult rats. Moreover, O-2Aadult progenitors cultured in PDGF express the range of properties we have described previously for O-2Aadult progenitors cultured in the presence of type-1 astrocytes. Similarly, previous studies have demonstrated that PDGF is able to mimic the influence of type-1 astrocytes on O-2Aperinatal progenitors. Specifically, O-2Aadult progenitors and O-2Aperinatal progenitors exposed to PDGF express differences in average cell cycle time (59 +/- 5 h for O-2Aadult progenitors versus 20 +/- 6 h for O-2Aperinatal progenitors), average rate of migration (4.1 +/- 0.6 microns h-1 versus 24.6 +/- 5.4 microns h-1), morphology (unipolar versus bipolar), and antigenic phenotype (04+ vimentin- versus 04- vimentin+). Thus, our present results indicate that a single signalling molecule secreted by type-1 astrocytes produces markedly different cellular behaviours in two related O-2A progenitor populations.

A fine fibrous silica contaminant of flour in the high oesophageal cancer area of north-east Iran

We report here the discovery and characterization of a fibrous mineral contaminant of the diet in that area of north-east Iran where oesophageal cancer has a very high incidence. This contaminant has a smoothly tapering shape and is between 50 and 150 micrometers long. The greatest diameter is between 1 and 10 micrometers and this decreases to a sharply pointed tip with a radius of curvature of between 0.25 and 0.60 micrometers. Electron microscope X-ray analysis shows that this fibre consists almost entirely of silica. It is free from alkali metals, aluminium and iron, and therefore differs from other known natural or manmade mineral fibres. Examination of the seeds of more than sixty different species of weed know to contaminate the wheat in this area of the Middle East shows that the fibre originates from the seeds of the common Mediterranean grass Phalaris minor. This seed bears fibres of the same dimensions, composition and birefringence, borne upon the inflorescence bracts which envelop the pericarp of the seeds of this and other members of the phalaris genus. They are broken off from the seed when the wheat is milled but persist in the flour, where up to 3,000 are found in each gram. Similar fibres can be isolated in quantity from the seeds of related species which are grown commercially, and they have a similar size and composition. When cells of the 3T3 mouse fibroblast line are exposed to these fibres in semi-solid suspension culture, their proliferation is stimulated more than 100-fold. We present an hypothesis for the involvement of these plant mineral fibres in the aetiology of oesophageal cancer in Iran and in other areas of high incidence.

Cerebellar astroglial cells in primary culture: expression of different morphological appearances and different ability to take up [3H]D-aspartate and [3H]GABA

In non-neuronal cultures of cells dissociated from postnatal rat cerebellum astrocytes, identified by the presence of the marker protein glial fibrillary acidic protein (GFAP), displayed two distinct morphological forms. One class was stellate in shape with radially distributed fine processes, while the other class was more varied in shape being polygonal or elongate. [3H]thymidine incorporation experiments revealed that cells of both morphologies were able to incorporate this nucleoside, suggesting the capacity for both cell types to undergo cell division. An autoradiographic study of the uptake of [3H]D-aspartate and [3H]GABA revealed that whilst the two classes of astrocytes took up the aspartate to apparently the same extent, only the stellate cells were found to be heavily labeled following incubation with [3H]GABA. A study of the cultures over a 12-day period showed that there was a disappearance of the stellate astrocytes. The time of disappearance was found to be dependent upon the initial plating density; the stellate morphology was apparent longer in lower density cultures. Time lapse studies suggested that one of the reasons for the disappearance of the stellate cells might be that in fact they underwent a change in shape following certain cell-cell interactions, but cell death also has to be considered as a further possibility. The relationships between the two classes of astroglial cells in these cultures is not yet clear. The possibilities are that they represent two different types of astrocytes, or just one type at different stages of differentiation, or maybe a combination of the two possibilities.

Coexistence of perinatal and adult forms of a glial progenitor cell during development of the rat optic nerve

We have studied the developmental appearance of the O-2A(adult) progenitor cell, a specific type of oligodendrocyte-type-2 astrocyte (O-2A) progenitor cell that we have identified previously in cultures prepared from the optic nerves of adult rats. O-2A(adult) progenitors differ from their counterparts in perinatal animals (O-2A perinatal progenitor cells) in antigenic phenotype, morphology, cell cycle time, rate of migration, time course of differentiation into oligodendrocytes or type-2 astrocytes and sensitivity to the lytic effects of complement in vitro. In the present study, we have found that O-2A(adult) progenitor-like cells first appear in the developing optic nerve approximately 7 days after birth and that by 1 month after birth these cells appear to be the dominant progenitor population in the nerve. However, the perinatal-to-adult transition in progenitor populations is a gradual one and O-2A(adult) and O-2A perinatal progenitors coexist in the optic nerve for 3 weeks or more. In addition, cells derived from optic nerves of P21 rats express characteristic features of O-2adult and O-2A perinatal progenitors for extended periods of growth in the same tissue culture dish. Our results thus indicate that the properties that distinguish these two types of O-2A progenitors from each other are expressed in apparently identical environments. Thus, these cells must either respond to different signals present in the environment, or must respond with markedly different behaviours to the binding of identical signalling molecules.

Narrow linear strips of adhesive substratum are powerful inducers of both growth and total focal contact area

The stimulus to growth that occurs when cells attach to the substratum can be studied with small adhesive islands. Large numbers of these islands can be grouped together into arrays made up of various sizes, and the response of cells to incubation on these arrays allows the anchorage stimulus to be measured. Past work has shown that single isolated cells can be stimulated to proliferate under these circumstances quite as freely as they do in ordinary cultures, and that the maximum response is given by islands whose size is less than 5000 microns 2. This anchorage stimulus might be mediated by the cytoskeleton, which assembles rapidly around the points of attachment to the substratum. One possible approach to testing this hypothesis is to expose cells to islands of different shapes, and to search for common factors among the different arrangements of the cytoskeleton that these different islands cause. Circular islands induced a relatively disordered arrangement of actin fibres. The fibres were attached at one end to foci of vinculin, which sometimes became arranged in a ring around the margin of the island. Triangular islands showed a more orderly arrangement of actin, in three bands parallel to the sides. In this case, the vinculin accumulated at the apices. Long islands only 3 microns wide could also provide effective attachment for the cells. In this shape the actin accumulated in two bands 2 microns or more apart and up to 5 microns high, and the vinculin similarly collected in parallel interrupted bands along the margins of the island. The number of vinculin foci differed on these three different island shapes, and the total area of vinculin was more than three times greater on long islands than on circles or triangles of the same size. Despite these differences, all three different shapes of island were capable of inducing up to 100 microns 2 of vinculin foci in each cell. Round and triangular islands induced this maximum amount of vinculin when their size was 5000 microns 2. Linear islands induced the same amount when they were only 1000 microns 2. The effect of different shapes on total vinculin focal area was paralleled by their effects on growth. All three shapes could support a similar amount of proliferation. Round and triangular islands induced the maximum amount of proliferation when they were 5000 microns 2 in area, and linear islands when they were only 1000 microns 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Intramitotic controls in the fission yeast Schizosaccharomyces pombe: the effect of cell size on spindle length and the timing of mitotic events

We have used a new cinemicroscopy technique in combination with antitubulin immunofluorescence microscopy to investigate the timing of mitotic events in cells of the fission yeast Schizosaccharomyces pombe having lengths at division between 7 and 60 microns. Wild-type fission yeast cells divide at a length of 14 microns. Separation of daughter nuclei (anaphase B) proceeds at a rate of 1.6 +/- 0.2 microns min-1, until the spindle extends the length of the cell. Coincident with spindle depolymerization, the nuclei reverse direction and take up positions that will become the center of the two daughter cells. This post-mitotic nuclear migration occurs at a rate of 1.4 +/- 0.5 microns-1. In cells in which the weel+ gene is overexpressed fivefold and that have an average length at mitosis of 28 microns, the rate of nuclear separation was only slightly reduced but, as spindles in these cells measure 20-22 microns, the duration of anaphase B was extended by approximately 40%. By contrast, in the mutant weel.50, which divides at 7 microns, both the rate and duration of anaphase B were indistinguishable from wild type. Nuclei reach the ends of these cells earlier but remain there until a point corresponding to the time of postmitotic nuclear migration in wild type. Thus, the events of mitosis can be extended but not abbreviated. These results are discussed in terms of a mitotic termination control that monitors many different events, one of which is spindle elongation.

Development and characterization of cisplatin-resistant human testicular and bladder tumour cell lines

Cisplatin-resistant cells were derived in vitro from a human bladder carcinoma cell line (RT112) and a testicular tumour cell line (SuSa) by continuous exposure to increasing concentrations of cisplatin for 14 and 11 months, respectively. Both resistant cell lines had a four-fold level of resistance relative to their parental cell lines, comparing the cisplatin concentration to inhibit colony forming ability by 70%. These levels of resistance were retained in the absence of cisplatin for at least 3 months. In each case, four-fold fewer micronuclei were produced in the resistant lines by the same cisplatin concentrations. Cross-resistance to carboplatin and methotrexate was observed in both resistant cell lines, but neither line was resistant to doxorubicin. Isozyme and DNA analysis with hypervariable probes confirmed the origin of each resistant cell line from its parental line. Population doubling times and intermitotic times were similar in each of the pairs of cell lines. Karyotyping showed that the resistant cell lines had gained and lost marker chromosomes, but there were no changes common to both resistant cell lines.

Postoperative chemotherapy improves survival in patients with resected high-risk Stage II colorectal cancer: results of a systematic review and meta-analysis

AIM

The aim was to assess the benefit of adjuvant chemotherapy in high-risk Stage II colorectal cancer.

METHOD

A systematic literature review and meta-analysis was performed comparing survival in patients with resected Stage II colorectal cancer and high-risk features having postoperative chemotherapy vs no chemotherapy.

RESULTS

Of 1031 articles screened, 29 were included, reporting on 183 749 participants. Adjuvant chemotherapy significantly improved overall survival [hazard ratio (HR) 0.61, P < 0.0001], disease-specific survival (HR = 0.73, P = 0.05) and disease-free survival (HR = 0.59, P < 0.0001) compared to no chemotherapy. Adjuvant chemotherapy significantly increased 5-year overall survival (OR = 0.53, P = 0.0008) and 5-year disease-free survival (OR = 0.50, P = 0.001). Overall survival and disease-free survival remained significantly prolonged during subgroup analysis of studies published from 2015 onwards (HR = 0.60, P < 0.0001; HR = 0.65, P = 0.0001; respectively), in patients with two or more high-risk features (HR = 0.59, P = 0.0001; HR = 0.70, P = 0.03; respectively) and in colon cancer (HR = 0.61, P < 0.0001; HR = 0.51, P = 0.0001; respectively). Overall survival, disease-specific survival and disease-free survival during subgroup analysis of individual high-risk features were T4 tumour (HR = 0.58, P < 0.0001; HR = 0.50, P = 0.003; HR = 0.75, P = 0.05), < 12 lymph nodes harvested (HR = 0.67, P = 0.0002; HR = 0.80, P = 0.17; HR = 0.72, P = 0.02), poor differentiation (HR = 0.84, P = 0.35; HR = 0.85, P = 0.23; HR = 0.61, P = 0.41), lymphovascular or perineural invasion (HR = 0.55, P = 0.05; HR = 0.59, P = 0.11; HR = 0.76, P = 0.05) and emergency surgery (HR = 0.60, P = 0.02; HR = 0.68, P = 0.19).

CONCLUSION

Adjuvant chemotherapy in high-risk Stage II colorectal cancer results in a modest survival improvement and should be considered on an individual patient basis. Due to potential heterogeneity and selection bias of the included studies, and lack of separate rectal cancer data, further large randomized trials with predefined inclusion criteria and standardized chemotherapy regimens are required.

Apparent heterogeneity in the response of quiescent swiss 3T3 cells to serum growth factors: implications for the transition probability model and parallels with "cellular senescence" and "competence"

When subconfluent, Swiss 3T3 cells made quiescent by serum deprivation are stimulated with low concentrations of serum (ca. 1%), only a proportion of them (roughly 50%) enter S phase despite daily replacement with fresh, low-serum medium. The cells that fail to enter S phase are not incapable of doing so, since most of them initiate DNA synthesis after transfer to 10% serum. It would appear that individual cells vary in their growth factor requirements. Using time-lapse cinemicroscopy a few of the cells that respond to low serum were seen to give rise to several generations of progeny, while the majority of cells failed to divide at all, or divided once at most. Despite this, differences between cells in growth factor requirements do not seem to be heritable in the long term, since attempts to enrich for responding cells by prolonged culture in 1% serum have been unsuccessful. Rather, it would appear that the capacity to respond to low serum is an unstable property lost after a few generations in low serum. The loss of responsiveness shows parallels with "cellular senescence" and could conceivably result from decay of the platelet-derived growth factor-induced state of "competence." But regardless of why some cells respond to low serum while others do not, it is clear that the kinetics of entry into S phase after serum stimulation of quiescent 3T3 cells are not strictly first-order, since the labelling index plateaus after roughly 3 days at values substantially below 100%. As such, the kinetics, though not contradicting the transition probability model, cannot be taken to support it as was previously thought.

Lysosomal sorting mutants of coronavirus E1 protein, a Golgi membrane protein

As a model for the intracellular sorting of Golgi membrane proteins, we are studying the E1 protein of the coronavirus Mouse Hepatitis Virus A59. The wild-type protein, when expressed from synthetic RNA, is localised in the Golgi complex. When the second and third of the three predicted membrane-spanning sequences were deleted from the protein, the resulting mutant was retained in the endoplasmic reticulum. In contrast, removal of the first and second membrane-spanning sequences allowed the protein to pass through the Golgi complex and reach the lysosomes. Likewise, when 40 amino acids were deleted from the C-terminal cytoplasmic part of E1, the truncated protein was transported to the lysosomes. We discuss the implications of these results for the structure of the E1 protein and the mechanism by which it is localised in the cell.

An abnormality of cell behaviour in human dystrophic muscle cultures: a time-lapse study

The initiation of monolayer mass cell cultures from adult human biopsies has revealed a striking abnormality in the growth and development pattern of muscle cultures from Duchenne-type dystrophy. This abnormality in cell behaviour was seen as early as 4 days in culture, well before myotube formation or confluence, and consisted of areas where cells clustered together in a multilayered mass rather than showing the typical monolayer distribution normally observed. To gain some insight into the mechanism of cell cluster development, we have examined such a culture by time-lapse cinematography and also the cell behaviour of other control cultures. The results of this study show that the clusters enlarged primarily by cell division and, to a lesser extent, by the acquisition of neighbouring cells. Furthermore, none of the single cells surrounding the clusters exhibited contact inhibition of movement. This behaviour was not observed in the other cultures examined. These findings could be indicative of an abnormality in the cell surface or cell-locomotory machinery of dystrophic cells.

Stimulating the proliferation of quiescent 3T3 fibroblasts by peptide growth factors or by agents which elevate cellular cyclic AMP level has opposite effects on motility

The effects of some chemically defined growth factors on the locomotion of quiescent Swiss 3T3 fibroblasts have been studied. A computer digitiser has been used to facilitate recording the paths followed by cells in time-lapse films; this method allows 500 cell-hours to be recorded in 1 h of real time. Individual cells in the same culture vary widely in speed. This variation is not associated with the positions of the cells in the cell cycle; a small deceleration which seems to occur in G2 cannot account for any significant part of the variation seen. Nor is it related to the time elapsing before the cell divides, although this is equally variable; the speed and age at division of particular cells appear to be entirely independent of one another. Nevertheless, good reproducibility is seen between the mean speeds of large numbers of cells from the same type of culture. The mean speed of quiescent cells is less than 2 microns/h. A mixture of epidermal growth factor (EGF) and vasopressin, in the presence of insulin, is known to be a potent promoter of proliferation in this system. We have found it to increase speed to 30 microns/h. Agents which stimulate the cellular level of cAMP are also known to be potent promoters of proliferation in the presence of insulin. We have found these agents to be inhibitors of locomotion; several cycles of cell division take place while the cells move at a speed no greater than that seen in the presence of cytochalasin B (CB) or colchicine. These findings therefore give further support to the idea that there may be two different classes of growth-promoting factors, with major differences in their mode of action. They show that some members of these two different classes have opposite effects on motility.

The 3T3 cell cycle at low proliferation rates

When the proliferation rate of Swiss 3T3 cells is decreased by limiting the availability of growth factors, cell cycle variability increases, as predicted by the transition probability model. Nevertheless, the transition probabilities would appear to play a relatively minor role in the regulation of proliferation rate. Instead, at least 40% of the increase in the average cycle time is brought about by an elongation of the minimum cycle time (i.e. the ‘deterministic’ part of the cycle). In addition, we have found that a substantial proportion of the cells (roughly 20%, in the present experiments, for doubling times of the order of 35–40 h) drop out of cycle in each generation, leading to a growth fraction of less than 1.0. The non-dividing cells, which we have previously shown to remain capable of division, would seem to support the existence of a Go state outside the normal cell cycle, and distinct from the indeterminate states postulated by the transition probability model. Because of the generation of nondividing cells at low proliferation rates, the log alpha and beta plots (distributions of cycle times, and sibling cycle time differences, respectively) are markedly concave, with a continuously decreasing slope. The transition probabilities cannot therefore be estimated directly and it is impossible to determine the extent to which they contribute to the regulation of proliferation rate. Rather, our data suggest that the transition probabilities are not uniform throughout the population under these conditions, but vary substantially from cell to cell. In addition to the changes in cell cycle kinetics, we also report an increased failure rate of cytokinesis, at low proliferation rates, leading initially to the appearance of binucleate cells. Such failures of cytokinesis may be responsible for the well-known rise in the incidence of binucleate and polyploid cells in the liver, with age.

The G1 distribution of "G1-less" V79 Chinese hamster cells

The V79-8 line of Chinese hamster cells has been reported to lack a measurable G1 phase. However, using a combination of time-lapse cinemicroscopy and [3H]thymidine autoradiography, we have found these cells to have a median G1 duration ranging from 1.4 to 2.6 h in different experiments, accounting for more than 15% of the median cycle time. The youngest cell labelled (in seven experiments) was 0.73 h old at the time of fixation suggesting a minimum G1 of between 0.40 and 0.73 h (the duration of the [3H]thymidine pulse being 0.33 h). In those experiments where steady-state proliferation could be established unequivocally, variability in G1 times accounted for all of the variability in cycle times. In addition, the distribution of G1 times (and cycle times) was well described by the two-transition version of the transition probability model. Nevertheless, changes in the average duration of G1 (and hence changes in the transition probabilities) played a comparatively minor role in determining proliferation rate. Instead, the length of S + G2 was markedly influenced by the composition of the culture medium. For purposes of comparison with the 'G1-less' V79-8 line, we have also examined a revertant derived from it (G1+5c) reported to have regained a substantial G1 phase. We are able to confirm that its G1 is indeed longer, the youngest labelled cell being 2.48 h old at the time of fixation. Unlike the parent line, there appeared to be more variability in G1 times than could be explained by two random transitions alone. The proliferation rate of the G1+5c revertant was unusually sensitive to the composition of the culture medium, suggesting the possibility of a metabolic defect.