Fig. 7. Lhx4 and Prop1 function together in promoting anterior pituitary formation. Analysis of Lhx4 mutants revealed that this gene is necessary for initial activation of LHX3 expression at the appropriate time and for cell survival. Ames dwarf mutant analysis showed that Prop1 is essential for repressing dorsal expansion of the primordium and SF1 expression, as well as for the expansion of the anterior lobe. In the absence of both of these genes, no specification of corticotropes, gonadotropes or thyrotropes occurs in the anterior lobe. The schematic of the defects in the Lhx4 mutant pituitary is depicted at E12.5 and the Prop1 mutant pituitary at P0.