(A and B) Loss of OTX2 in the ventral diencephalon results in a smaller, dysmorphic pituitary gland. (A) e10.5, e12.5, e14.5 and e16.5 sagittal pituitary sections were stained using hematoxylin and eosin. At e10.5, there is no difference between Otx2FX/+wild-type (top panel) and Otx2FX;Nkx2.1-cre mutants (bottom panel). At e12.5 through e16.5, there is a lack of invagination of the infundibulum and a smaller anterior lobe in the mutants compared with the wild types. The e10.5 and e14.5 photos were taken at ×200. Scale bar: 50 μm. The e12.5 and e16.5 photos were taken at ×100. Scale bar: 100 μm. (B) e14.5 coronal pituitary sections were stained using hematoxylin and eosin, revealing a slight invagination of ventral diencephalon in the mutants (black arrow). TLE4 immunostaining at e14.5 identifies the reduced evagination of the posterior lobe in the Otx2FX;Nkx2.1-cre mutants (white arrow). OTX2 immunostaining in control and Otx2FX;Nkx2.1-cre-mutant animals at e14.5 reveals some OTX2 protein in the small mutant posterior lobe (white arrowhead.) In situ hybridization for Otx2 in the control and Otx2FX;Nkx2.1-cre mutants reveals some transcripts in the small, mutant posterior lobe (black arrow head). III—third ventricle, A—anterior lobe, P—posterior lobe. Photos were taken at. Scale bar: 50 μm.