There are several preadipocyte cell lines reported, but in this chapter, we will describe mainly the 3T3-L1 cells, which are best characterized and widely used for molecular biological studies. The 3T3-L1 cells were clonally isolated by Green and Kehinde from 3T3-Swiss albino. When these cells are growing exponentially, they appear indistinguishable from their parental Swiss/3T3 cells. 3T3-L1 cells, however, undergo a differentiation to adipocytes when they enter a confluent and contact-inhibited resting stage (1 ). Many clones isolated from the original 3T3 stock are able to convert to adipocytes, in most cases, with a much lower frequency than that of L1 cells. Subclones can be generated by serial cloning, which differentiate to adipocytes at a high frequency. 3T3-F422A is such a clone isolated from the same 3T3-Swiss albino stock culture as L1 cells (2 ).
