MAPK-regulated Pea3 transcription factors are required for lacrimal gland development.

(A-I) Inactivation of Mek and Erk signaling abolished expression of the Pea3 family of transcription factors, Pea3, Erm and Er81, in the E14.5 lacrimal gland epithelium. (J, M) Lacrimal gland specific ablation of Pea3/Erm/Er81 genes resulted in a smaller lacrimal gland bud as indicated by Pax6 expression. The lacrimal gland buds are marked by dotted lines. (K, N) TUNEL staining indicated an increase in apoptosis in the Pea3 TKO lacrimal gland bud (arrows). (L, O) At the P1 stage, Pea3 TKO mutants displayed a residual lacrimal gland as shown by the GFP reporter. (P) Quantification of the lacrimal gland phenotype in Pea3 TKO mutants at P1. Scale bars, 50μm.