Differentiation markers (S-100, GFAP, NSE and D2) in fetal rat brain cells during malignant transformation in cell culture

A time-dependent increase in glial fibrillary acidic protein expression and glutamine synthetase activity in long-term subculture of the GL15 glioma cell line

1. Astrocytes are the most numerous cellular elements in the central nervous tissue, where they play a critical role in physiological and pathological events. The biological signals regulating astrocyte growth and differentiation are relevant for both physiology and pathology, but they are still little understood. 2. Using a poorly differentiated glioma cell line, GL15, we investigated whether, in long-term subculture, this could upregulate the expression of glial fibrillary acidic protein (GFAP), as described in some rodent astrocyte cell lines. Under the same culture conditions, we investigated glutamine synthetase (GS) activity, growth-associated protein (GAP)-43 expression, and expression of several neutrotrophic factors. 3. A dramatic increase in GFAP expression was evidenced by Western blotting during progressive in vitro growth of GL15 cells. GS specific activity was also upregulated in long-term culture. The time spent in vitro by GL15 cells did not affect GAP-43 and neutrophic factor BDNF and NT3 expression as revealed by RT-PCR analysis. 4. Our results suggest that, in GL15, GFAP and GS genes may have common or integrated regulatory mechanisms elicited at the cell confluency which could be relevant for both astrocyte physiology and astrocyte pathology. These mechanisms are not involved in GAP-43 and neutrophic factor BDNF and NT3 expression.

Characterization of rat NCA/CD9 cell surface antigen and its expression by normal and malignant neural cells

As part of investigations on ethylnitrosourea (EtNU)-induced neuro-oncogenesis in the rat, we have produced monoclonal antibodies (Mabs) specific for neural cell surface antigens (NCAs) by immunization with cells of the clonal tumorigenic neural rat cell line BT4Ca. Mabs designated as anti-NCA (alpha NCA1, alpha NCA2, alpha NCA3, alpha NCA4, and alpha NCA5) recognize proteins of 25 kDa and 23 kDa, as shown by immunoprecipitation and Western blot. The predominant 25-kDa protein was purified from BT4Ca cells by immunoaffinity chromatography with immobilized Mab alpha NCA1 and identified by N-terminal sequencing as the rat homologue of the CD9 antigen. Identification of proline as N-terminal amino acid of the purified protein suggests post-translational modification of CD9 in the rat central nervous system. The NCA/CD9 protein was localized in distinct regions of fetal and adult rat brain by immunofluorescence staining of frozen sections. Flow cytometric analyses of isolated fetal rat brain cells (FBC) showed that the proportion and number of NCA/CD9-expressing cells increased during prenatal development. Immunoreactivity of approximately 40% of brain cells isolated 13 days post conception (p.c.) indicated that NCA/CD9 is expressed by neuronal precursors at this stage of development. In primary cultures of rat FBC isolated 18 days p.c., the NCA/CD9 antigen was expressed by all premature and mature astrocytes, oligodendrocytes, ependymal cells, and microglial cells, but not by E-N-CAM-expressing neuronal progenitor cells and neurons. Furthermore, eight out of ten EtNU-induced malignant neural rat cell lines as well as EtNU-induced tumors of the central and peripheral nervous system exhibited intermediate or strong immunoreactivity with Mab alpha NCA1. Expression of the NCA/CD9 protein is, therefore, characteristic of both normal glial precursor cells and their malignant counterparts in the rat.

Surface antigens of cell subpopulations in prenatal rat brain are expressed in a characteristic non-random pattern on their ethylnitrosourea-induced malignant counterparts

Selective induction of neural tumors in the rat by single-dose exposure of the immature nervous system to ethylnitrosourea (EtNU) is a model for the study of cell lineage-, differentiation stage-, and carcinogen-dependent mechanisms in neuro-oncogenesis. Overall yields and relative frequencies of different types of neural tumors vary with the developmental window chosen for the EtNU-pulse. Precursor cells belonging to different neural lineages and targeted by the carcinogen at distinct developmental stages may thus bear a differential risk of malignant conversion. To specify subpopulations of neural precursors in fetal (prenatal day 18) BDIX-rat brain, four monoclonal antibodies (mAbs) recognizing cell surface differentiation antigens were used: mAb RB13-2 directed against O-acetylated gangliosides and binding to approximately 36% of fetal brain cells (FBC); mAb RB13-6 recognizing a 130 kDa glycoprotein (expressed by approximately 8% of FBC); and mAbs RB21-7 and RB21-15 which bind, respectively, to embryonal neural cell adhesion molecules (N-CAM) and a 24 kDa protein (expressed by approximately 55% and 12% of FBC). Antigen expression profiles were compared with those of 14 primary brain tumors and 16 malignant neural cell lines, all of which had been induced by EtNU on prenatal day 18 in vivo. Monoclonal antibodies RB13-2 and RB21-7 did not bind to any of the tumors or cell lines. In contrast, mAbs RB13-6 and RB21-15 both reacted with 14/14 tumors, and with 16/16 and 10/16 cell lines, respectively. Expression of the latter antigens might thus specify lineage-specific stages of FBC development/differentiation particularly susceptible to EtNU-induced malignant transformation. Two-color fluorescence analyses revealed three subsets of FBC binding mAb RB13-6 (RB13-2+/RB13-6+/RB21-15-; RB13-2-/RB13-6+/RB21-15-; and RB13-2-/RB13-6+/RB21-15+), representing successive stages of differentiation.

A cerebral glioma model for experimental therapy and in vivo invasion studies in syngeneic BD IX rats

An in vivo glioma model was developed in syngeneic BD IX rats. The BT4An tumor was derived from serial in vivo passages of the BT4A tumor, originally induced from transformed fetal rat brain cells after transplacental exposure to ethylnitrosourea. The cell line was characterized for the presence of neuroglial differentiation markers, chromosome content and cell cycle distribution as determined by flowcytometry. A standardized method for i.c. tumor induction was developed, and the tumors were investigated by light and electron microscopy and for evidence of blood-brain barrier disruption. Tumor cell ability for phagocytosis was studied, as this property may be important for the invasion pattern of the tumors. We conclude that the model seems suitable for both in vivo therapy and invasion studies. The tumor had 100% tumor take, yielded a predictable symptom-free life span after inoculation, had a characteristic histological picture of an aggressive glioma, and the blood-brain barrier within the tumor was in part disrupted. Compared to the parent cell line, there was loss of neuroglial differentiation markers, the chromosomal distribution was changed, and the ability for phagocytosis was practically lost.

A hypothesis for myeloschisis: overgrowth and reopening. An experimental study

A hypothesis for embryopathogenesis of myeloschisis is described on the basis of experimental studies analyzing the stage specificity and immunohistochemical/histological characteristics of the exposed neural tissue (placode). Myeloschisis developed in six fetuses among 205 chick embryos treated in various stages with teratogens including ethylnitrosourea, and anticonvulsant and antipyretic agents. All but one case (with associated cephalothoracopagus) demonstrated myeloschisis in the thoracic region with a lamina defect of two and three levels. No fetus was exposed to a teratogen prior to or within Hamburger and Hamilton stage 12 (45 to 49 hours postincubation), when the neuropore closes. Immunohistochemical studies of chick myeloschisis clearly indicated that neuron-specific enolase-positive elements were extremely active only in the overgrown placode, corresponding to the histological findings with Kluver-Barrera's special stain. These findings were compared with observations in a case of myeloschisis in a human neonate. The results of this study imply the possibility of another mechanism for the embryopathogenesis of myeloschisis: namely, the overgrowth and reopening hypothesis.

Cell and tissue culture of the central nervous system: recent developments and current applications

A survey of methods for cell and tissue culture of the central nervous system (CNS) is given. This includes a brief historical outline and description of methods in current use. Recent methodological improvements are emphasized, and it is shown how these are applied in modern neurobiological research. Both monolayer cell cultures and three-dimensional organ culture systems are widely used, each having advantages and limitations. In recent years, there has been considerable improvement of culture for prolonged periods in chemically defined media. Brain tissue from a wide spectrum of species have been used, including different types of human brain cells which can be propagated for several months. At present, these culture systems are employed for dynamic studies of the developing, the adult and ageing brain. It is possible to select neurons and the different classes of glial cells for culture purposes. Cell culture of the CNS has given new insights into the biology of brain tumours. Culture systems for experimental tumour therapy in vitro are also available. Recently, it has been shown that organ cultures of brain tissue can be used as targets for invasive glioma cells, enabling a direct study of the interactions between tumour cells and normal tissue to take place.

Invasiveness of primary brain tumors

Primary malignant neoplasms of the nervous system differ from other types of malignancy in several ways. Clinical progression is due to local invasive growth, while metastases outside the skull are rare. The tumors show no sharp delimitation from the surrounding normal tissue. At the edge, an ill-defined area of invasive tumor cells, reacting glial cells and inflammatory cells is present. At the same time the primary brain tumors are biologically heterogeneous. In this review, a short survey of markers for malignancy in primary brain tumors is given, and some properties of importance for invasive behavior, are listed. These include different cellular enzymes, phagocytotic property, locomotive and proliferative characteristics. Studies of primary brain tumors in situ show invasive growth into the surrounding brain tissue, often followed by hemorrhage and necrosis. In addition spread of tumor cells takes place along preexisting intracranial structures. Recently, several systems for the study of brain tumor invasiveness in culture have been elaborated. Both experimental and human gliomas have been tested. The target tissues include organ culture of embryonic chick heart muscle, chorioallantoic membrane, fetal rat brain tissue and reconstructed vessel walls. It has been shown that glioma cells are able to split junctions between normal cells. They destroy and phagocytose the normal cells and penetrate the normal tissue. The use of brain tissue and reaggregated brain cell cultures as target for glioma cells in culture opens the possibility for an elucidation of invasiveness as one of the most important properties of malignancy in the nervous system.