Lung Kruppel-like factor (LKLF) is a member of the Kruppel-like family of zinc finger transcription factors and is closely related to erythroid kruppel-like factor (EKLF), which is necessary for β-globin gene expression. While EKLF is expressed exclusively in erythroid cells, LKLF is expressed temporally during early embryonic development and predominantly in the adult mouse lung. To understand the role this novel transcription factor plays in development as well as tissue differentiation and function, animals lacking LKLF were produced using gene targeting technology. Mice lacking LKLF die in utero between day 11.5 and 13.5 of embryonic life and exhibit retarded growth, craniofacial abnormalities, abdominal bleeding and signs of anaemia. Although the yolk sac erythropoiesis is normal in mutant embryos, in vitro fetal liver cultures of these embryos fail to give rise to erythroid cells. Expression of other erythroid specific genes such as EKLF, GATA1 and ...