Up-regulation of p21 in SMN-deficient ES cells and spinal cord tissues derived from SMA mice. Control (C) and SMA (S) ES cells as described in 3A were processed for western blotting using antibodies against p21 and p27. The same membrane was stripped and re-probed with anti-ERK antibody for protein loading control (A). Spinal cord tissues from three control (C) and three SMA (S) mice were collected and lysates were prepared. Equal amount of protein lysates were separated on a SDS-PAGE and transferred to a membrane. The blot was probed with antibodies against p21 or SMN. The same blot was stripped and re-probed with anti-ERK antibody for protein loading control (B). Undiff. = undifferentiated cells and Diff. = differentiated cells.