A human lamin A cDNA was subcloned into the pTracer-CMV vector (Invitrogen Corp.). The linearized vector was transfected into lamin A/C −/− mouse embryonic fibroblasts (MEFs). Stable clones were selected using Zeocin, according to the manufacturer's instructions and the clones pooled. Subsequent analysis showed that the cells in the pool were heterogeneous with regard to lamin A expression.