Mouse embryo cells cultured in vitro in serum-supplemented media undergo growth crisis, resulting in the loss of genomically normal cells prior to the appearance of established, aneuploid cell lines. Mouse embryo cells established and maintained for multiple passages in the absence of serum did not exhibit growth crisis or gross chromosomal aberration. Cells cultured under these conditions were dependent on epidermal growth factor for survival. Proliferation was reversibly inhibited by serum or platelet-free plasma, suggesting that mouse embryo cultures maintained by conventional procedures are under the influence of inhibitory factors.

We have derived serum-free mouse embryo (SFME) cultures in a basal nutrient medium supplemented with insulin, transferrin, epidermal growth factor (EGF), high-density lipoprotein (HDL), and fibronectin. These cells are nontumorigenic, lack gross chromosomal aberrations, and exhibit several other unique properties, including dependence on EGF for survival and growth inhibition by serum. We have examined the concentration dependence of the growth stimulatory effects of protein supplements used in the SFME medium formulation and surveyed other supplements that might act as alternative or complementary additions to the culture medium. Insulin could be replaced by insulin-like growth factor I and EGF could be replaced by transforming growth factor alpha in the same concentration range. Transferrin could be replaced by higher concentrations of lactoferrin. Deterioration of cultures in the absence of EGF began within 8 hours of the removal of the growth factor, and could be prevented by the addition of fibroblast growth factor/heparin-binding growth factor. Attachment proteins other than fibronectin were effective on SFME cells, but limited success was obtained when substituting other lipid preparations for HDL. These data introduce a precise system for exploring the unusual characteristics of SFME cells and contribute additional information that may be useful in the extension of these approaches to other cell types and species.

Serum-free mouse embryo (SFME) cells, derived in medium in which serum is replaced with growth factors and other supplements, display distinctive properties: (i) SFME cells do not lose proliferative potential or show gross chromosomal aberration upon extended culture, (ii) these cells depend on epidermal growth factor for survival; and (ii) SFME cell proliferation is reversibly inhibited by serum. Treatment of SFME cells with serum or transforming growth factor j3 led to the appearance of glial fibrillary acidic protein, a specific marker for astrocytes. The appearance of glial fibrillary acidic protein in cultures was reversed upon removal of transforming growth factor (3 or serum. Cells with properties similar to SFME cells were also isolated from adult mouse brain. These results suggest a role for transforming growth factor (3 in astrocyte differentiation in developing organisms and in response to injury and identify the cell type that has the unusual properties of SFME cells.Serum-free mouse embryo (SFME) cells initiated and maintained multipassage in a rich basal nutrient medium supplemented with insulin, transferrin, epidermal growth factor (EGF), high-density lipoprotein, and fibronectin display several distinctive properties (1)(2)(3)(4)(5)(6). Mouse embryo cells derived in conventional serum-supplemented medium undergo a period in which proliferative potential is lost or reduced, and then genetically altered cells with indefinite proliferative potential emerge (2,7,8). SFME cells do not exhibit any loss of proliferative potential or gross chromosomal aberration and maintain a relatively stable karyotype when cultured for >10 times the population doublings achieved with karyotypically normal mouse embryo cells in serum-containing medium. Although the period in which reduced growth rate can be detected may be minimal or absent in cultures in serumcontaining medium maintained in a passaging protocol involving high plating densities, the protocols used to derive SFME cells lead to a well-defined period of limited proliferative potential in cultures maintained in serum-containing medium (2, 7) that is not seen when the cells are cultured in serum-free medium. SFME cells also depend on EGF for survival, and cycloheximide or actinomycin D prevents death from EGF deprivation (5), suggesting that cell death requires the synthesis of RNA and protein, a phenomenon of programmed cell death similar to that reported for neuronal cell death in the absence of nerve growth factor (NGF) (9). In addition, proliferation of SFME cells is reversibly inhibited by serum or platelet-free plasma (1, 4, 6), and thus these cells would not be propagated under conventional culture conditions using serum-supplemented medium. As for most mouse embryo cell lines, the precise nature of the cells giving rise to the continuously growing SFME cultures was unknown. The unusual characteristics of SFME cells led us to attempt to determine the cell type represented by these cells.We found that treatment of SFME cells with serum or We a...

No abstract

No abstract

Abstract. Serum-free mouse embryo (SFME) cells, derived in medium in which serum is replaced with growth factors and other supplements, are proastroblasts that are acutely dependent on epidermal growth factor (EGF) for survival. Ultrastructurally, an early change found in SFME cells deprived of EGF was a loss of polysomes which sedimentation analysis confirmed to be a shift from polysomes to monosomes. The ribosomal shift was not accompanied by decreased steady-state level of cytoplasmic actin mRNA examined as an indicator of cellular mRNA level. With time the cells became small and severely degenerate and exhibited nuclear morphology characteristic of apoptosis. Genomic DNA isolated from cultures undergoing EGF deprivation-dependent cell death exhibited a pattern of fragmentation resulting from endonuclease activation characteristic of cells undergoing apoptosis or programmed cell death. Flow cytometric analysis indicated that cultures in the absence of EGF contained almost exclusively Gl-phase cells. Some of the phenomena associated with EGF deprivation of SFME cells are similar to those observed upon NGF deprivation of nerve cells in culture, suggesting that these neuroectodermal-derived cell types share common mechanisms of proliferative control involving peptide growth factor-dependent survival.

Serum-free mouse embryo cells, cultured in basal nutrient medium supplemented with insulin, transferrin, epidermal growth factor, fibronectin, and high-density lipoprotein, do not exhibit growth crisis, lack detectable chromosomal aberrations, are nontumorigenic in vivo, are dependent on epidermal growth factor for survival, and are growth inhibited by serum or platelet-free plasma. These cells after transfection with the human Ha-ras or rat neu oncogenes no longer required epidermal growth factor for survival, were tumorigenic in vivo, and also proliferated in serum-containing medium. Autocrine activity capable of replacing epidermal growth factor was detected in conditioned medium from ras-transformed cultures, but little such activity was detected in medium from neu-transformed cultures. In addition, the capability of ras or neu-transformed cells to grow in serum-containing medium could not be mimicked in untransformed cells by the addition of growth factors or conditioned medium from transformed cells. These results suggest that the known structural similarity of the neu gene product to the EGF receptor is also reflected in a functional similarity by which the mutationally activated neu protein can replace the ligand-activated EGF receptor. These results also suggest that the ability of ras- and neu-transformed cells to escape the effect of the inhibitory serum activity is a nonautocrine property distinct from the acquisition of EGF autonomy.

Mouse embryo cells derived in a serum-free medium formulation (SFME cells) do not exhibit growth crisis or chromosomal abnormalities and are nontumorigenic in vivo; these cells are also reversibly growth inhibited by serum or platelet-free plasma (Loo et al.; Science, 236:200-202, 1987). A portion of the inhibitory activity of serum could be extracted by charcoal, a procedure that removes steroid and thyroid hormones. Both L-3,5,3'-triiodothyronine (T3) and hydrocortisone inhibited growth of SFME cells in a reversible manner. The inhibitory activity of serum also was partially removed by treatment with anion exchange resin in a procedure designed to deplete serum of thyroid hormone. However, the effect of serum on untransformed SFME cells could not be prevented by addition of the antiglucocorticoid RU38486, and ras-transformed clones of SFME cells, which are capable of growing in serum-containing medium, retained inhibitory responses to glucocorticoid and, with some clonal variability, to T3. These results suggest that glucocorticoid or thyroid hormones may contribute to the inhibitory activity of serum on SFME cells, but additional factors are also involved.