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Revision with unchanged content. The combinatorial interactions of the homeodomain protein Pit-1 with transcription factors such as C/EBPalpha and with coregulatory proteins control the development of anterior pituitary cells. These cells fail to develop in individuals with mutations affecting the Pit-1 gene, resulting in combined pituitary hormone deficiency. The present work describes biochemical, live-cell imaging and in vivo kinetics studies that provide new insight into the dynamic network interactions inside the pituitary-cell nucleus. The findings reported here support a model where proteins move independently within the nuclear compartment and stochastically associate at specific intranuclear sites as part of metastable complexes. The probability that these proteins assemble in a particular region of the cell nucleus is related to the dominant chromatin-binding activities of the different protein partners, supporting the view that the repositioning of transcription factors and coregulators represents an important mechanism for directing changes in cell-specific gene expression. These studies also suggest an important link between the mislocalization of transcriptional complexes and disease processes.

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was born in Buenos Aires, Argentina. After obtaining his degree in Biology at the University of Buenos Aires in 2000, he joined the Cell Biology Graduate Program at the University of Virginia. In 2007 he joined the Howard Hughes Medical Institute at the University of Chicago where he is now an Irvington Institute postdoctoral fellow

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