To generate this line, TRE-ErbB2V664E mice were mated with Mlc1-tTA mice. Pregnant mice and their offspring were fed with Dox until weaning occurred at P21, whereas bi-transgenic Mlc1-tTA;TRE-ErbB2V664E (Mlc1-ErbB2V664E) mice and littermate controls were allowed to grow to adulthood. Feeding the bi-transgenic Mlc1-ErbB2V664E mice with Dox blocked ErbB2V664E expression, while withdrawal of Dox initiated it (Figure 4a). It is notable that ErbB2V664E expression induced by Dox withdrawal was accompanied by an increase in GFAP in a time-dependent manner (Figure 4a). Immunostaining showed that GFAP+ cells increased dramatically throughout the brain 20 days after Dox withdrawal (Figure 4b).