Reciprocal Interactions of Pit1 and GATA2 Mediate Signaling Gradient–Induced Determination of Pituitary Cell Types

AbstractThe mechanisms by which transient gradients of signaling molecules lead to emergence of specific cell types remain a central question in mammalian organogenesis. Here, we demonstrate that the appearance of four ventral pituitary cell types is mediated via the reciprocal interactions of two transcription factors, Pit1 and GATA2, which are epistatic to the remainder of the cell type–specific transcription programs and serve as the molecular memory of the transient signaling events. Unexpectedly, this program includes a DNA binding–independent function of Pit1, suppressing the ventral GATA2-dependent gonadotrope program by inhibiting GATA2 binding to gonadotrope- but not thyrotrope-specific genes, indicating that both DNA binding–dependent and –independent actions of abundant determining factors contribute to generate distinct cell phenotypes

Cooperative regulation in development by SMRT and FOXP1

A critical aspect of mammalian development involves the actions of dedicated repressors/corepressors to prevent unregulated gene activation programs that would initiate specific cell determination events. While the role of NCoR/SMRT corepressors in nuclear receptor actions is well documented, we here report that a previously unrecognized functional interaction between SMRT and a forkhead protein, FOXP1, is required for cardiac growth and regulation of macrophage differentiation. Our studies demonstrate that SMRT and FOXP1 define a functional biological unit required to orchestrate specific programs critical for mammalian organogenesis, linking developmental roles of FOX to a specific corepressor

Pax6 is essential for establishing ventral-dorsal cell boundaries in pituitary gland development

Pax6, a highly conserved member of the paired homeodomain transcription factor family that plays essential roles in ocular, neural, and pancreatic development and effects asymmetric transient dorsal expression during pituitary development, with its expression extinguished before the ventral → dorsal appearance of specific cell types. Analysis of pituitary development in the Small eye and Pax6 −/− mouse mutants reveals that the dorsoventral axis of the pituitary gland becomes ventralized, with dorsal extension of the transcriptional determinants of ventral cell types, particularly PFrk. This ventralization is followed by a marked decrease in terminally differentiated dorsal somatotrope and lactotrope cell types and a marked increase in the expression of markers of the ventral thyrotrope cells and SF-1-expressing cells of gonadotrope lineage. We suggest that the transient dorsal expression of Pax6 is essential for establishing a sharp boundary between dorsal and ventral cell types, based on the inhibition of Shh ventral signals