Has anyone used Crispr/Cas to induce a knock-in in MEF cells?
From this paper:


  We chose to test for Cas9-driven targeted mutagenesis on the
  endogenous Trp53 gene in mouse embryonic fibroblasts (MEFs), a cell
  line in which the biology of p53 has been thoroughly characterized and
  where the gene is structurally intact.


Furthermore:


  Seventy-two hours post-transduction, cells were cultured in the
  presence or absence of Nutlin-3a, a specific inhibitor of the MDM2–p53
  interaction (Tovar et al. 2006). Cells were scored for the fraction of
  GFP+ cells after 4 d of Nutlin-3a exposure using flow cytometry (Fig.
  2B). Nutlin-3a potently activates a p53-dependent anti-proliferative
  cellular response, which strongly and specifically selects for any
  cells with disrupted Trp53 function (Efeyan et al. 2007). Much like
  MLP-p53.1224 infected cells, the pQCiG-p53 GFP+ cells were rapidly
  enriched for in the presence of Nutlin-3a, suggesting that
  CRISPR-mediated gene disruption had initially occurred in at least a
  proportion of the initial Cas9-expressing cells.