Loss of ATF4 activity affects primary MEF proliferation, postnatal growth, and embryonic lens formation.

(A) In vitro proliferation defect in primary MEFs from ATF4^−/− embryos. Passage-2 MEFs derived from 15.5-dpc embryos were plated at a density of 2 × 10⁴ cells/60-mm plate. Representative regions at 5 days of culture of cells from wild-type (left) and ATF4^−/− (right) embryos are shown. Magnification 40 ×. (B) Quantitation of the MEF growth rate from 15.5-dpc embryos. Fibroblasts were derived from ATF4^+/+(n = 3), ATF4^+/− (n = 7), and ATF4^−/−(n = 5) 15.5-dpc embryos. Error bars represent SEM. (C) Seven-day-old ATF4^+/+ and ATF4^−/− mice. The ATF4^−/− mouse (bottom) is smaller and shows a delay in hair growth compared with its wild-type littermate (top). (D) ATF4^+/− and ATF4^−/− littermates 4 weeks after birth. The ATF4^−/− mouse (bottom) is runted and has severe microphthalmia. The heterozygote (top) is normal in appearance. (E) Histologic study of lens from 16-dpc embryos. The lens from the ATF4^−/− embryo is considerably smaller and consists of primary lens fiber cells with no apparent formation of secondary lens fiber cells. Magnification 100 ×.