Casein gene expression: from transfection to transgenics.

Abstract

Milk-protein gene expression during pregnancy and lactation signals the terminal differentiation of the developing mammary gland. Hence, the synthesis and secretion of milk proteins serve as molecular markers with which to assay the action of both peptide and steroid hormones, as well as the cell-substratum interactions required to achieve lactation. For many years researchers were limited to descriptive analysis of milk-protein gene structure and expression using primary mammary epithelial cell lines and expiant cultures. Now, with the advent of modern gene-transfer technology, the molecular mechanisms regulating milk-protein gene expression can be more thoroughly studied using transgenic mice and transfected mammary epithelial cell lines. However, both these systems have their limitations. Derived from midpregnant mice, the currently available mammary cell lines do not phenotypically represent the mammary epithelial cell during lactation. These cells do not express the complete spectrum of milk proteins, and the level of expression of many of these genes, even under the best culture conditions, is markedly less than that observed during lactation. However, using pooled transfectants does permit the simultaneous analysis of multiple recombinant plasmid constructs. Such studies, certainly less expensive than those in transgenic mice, also circumvent the often deleterious effects associated with random transgene integration. On the other hand, transgenic mice facilitate a comprehensive evaluation of milk-protein gene expression within the context of a developing animal. Expiant cultures can also be derived from individual lines of transgenic mice and can be used to study the response of a transgene to individual hormones. In addition, lines of transgenic mice can be established using transgenes designed to direct oncogene expression to the mammary gland from which immortalized cell lines may be isolated. Such cell lines may represent different stages of mammary gland development and, therefore, can be used to investigate how oncogene expression results in mammary carcinogenesis. From this brief introduction it is evident that both cell culture and transgenic systems should be employed in order to effectively study mammary gene expression at the molecular level.KeywordsTransgenic MouseMammary GlandWhey ProteinMammary Epithelial CellMouse Mammary Tumor VirusThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.