Establishment of spontaneously immortalized keratinocyte lines from wild-type and mutant mice

A considerable number of transgenic or knockout mice in which epidermal keratinocytes have been targeted die shortly after birth due to barrier defects. In this case, recovery and cultivation of keratinocytes from these animals provide an opportunity for in vitro studies. Working with isolated keratinocytes is also interesting for certain experiments which cannot be performed in live animals. Primary human keratinocytes can be kept in culture for a variable number of passages and then senescence. Immortalization can be achieved by transduction with constructs encoding viral genes. Murine keratinocytes can be kept in culture as primary cells. Naturally the numbers of cells obtained by direct isolation from mouse epidermis is restricted and sometimes not sufficient for certain biochemical analyses. To overcome this restriction some permanent murine keratinocyte lines have been generated by transfection with SV40T or HPV E6E7 genes. This is, however, not suitable if established or hypothetical biochemical links exist between these genes and the pathways or processes to be analysed in the respective experiment. We describe an easy and reproducible method of establishing permanent keratinocyte lines from spontaneously immortalized primary murine keratinocytes. This method employs co-cultivation of keratinocytes with 3T3-J2 fibroblast feeder cells for several passages during which immortalization occurs. The resulting keratinocyte lines do not only grow infinitely but, in many cases, individual lines from the same genetic background also exhibit similar growth characteristics, hence they are especially valuable for comparative studies.