A new experimental approach was designed to test different predictions of 
current models of the nuclear architecture with respect to the topography of 
transcription. We constructed a plasmid, termed pIndi, which carries a reporter 
gene coding for a red cytoplasmic fluorescent reporter protein. Transcription of 
the reporter gene is regulated by the inducible promoter of the human 
immunodeficiency virus (HIV) and is strongly dependent on the HIV-1 Tat protein. 
Expressing the red fluorescent reporter protein allowed us to distinguish 
between cells with active and silent reporter genes. Importantly, transient 
transfection resulted in the clustering of plasmids, forming one or several 
extra-chromosomal pIndi bodies. Repetitive lac operator sequences in pIndi 
allowed us to visualize these bodies in living cells by the binding of LacI 
proteins tagged with a fluorescent protein. Using this model, we analyzed the 
three-dimensional nuclear topography of pIndi bodies with active or silent 
reporter genes. Our results are compatible with predictions of the chromosome 
territory-interchromatin compartment (CT-IC) model. We demonstrate that pIndi 
bodies localize in the IC, both in the silent and active state. Activation of 
transgene transcription resulted in the recruitment of RNA polymerase II and 
NFkappaB and a closer positioning to splicing speckles.