Chapter 14 Cell culture

Animal cells in the intact animal are in a complex, dynamic environment. Studies concerning the regulation of the growth and the expression of the differentiated functions of animal cells are best conducted using in vitro primary cell culture systems (initiated directly from the animal), as well as established animal cell lines (which can grow indefinitely). A number of differentiated animal cell lines derived from different tissues are available for study, including neuroblastoma, glioma, adrenocortical, kidney tubule epithelial, and embryonal carcinoma. The development of tissue culture medium has been a limiting factor in the development of new cell culture systems as well as in studies of the control of cell growth and function. Hormonally defined serum-free media have alleviated these limitations considerably. Both normal and malignantly transformed animal cells can be studied in vitro. Transformed cells exhibit such altered in vitro properties as elevated growth rate, increased saturation density, loss of growth factor requirements, and the ability to form colonies in soft agar. The molecular mechanisms responsible for cellular transformation are poorly understood. However, during malignant transformation, alterations very likely occur in signal transduction pathways such as those initiated by EGF. Such alterations may originate from the activation of cellular or viral oncogenes, mutations, or externally applied factors, such as TGF alpha and TGF beta. In vitro cells in culture have been observed to have close similarities to animal cells in vivo. Thus in vitro studies concerning such growth factors may have physiological significance. When using animal cell cultures, it is critical to constantly refer back to the in vivo situation. Similarly, the results of in vivo studies should be further examined in vitro.