Intracellular trafficking of the nuclear receptor COUP-TF in live sea urchin embryos

COUP-TFs comprise a family of highly conserved transcription factors within the steroid-thyroid-retinoic acid super-family of nuclear receptors, The h igh degree of conservation among the COUP-TFs suggests that their function among distantly related species might also be conserved. In order to give s ome insight into this question, we have tested the ability of human COUP-TF to mimic a specific sub-cellular localization pattern characteristic of en dogenous SpCOUP-TF in early sea urchin embryos. Similarly, experiments were undertaken to determine if five conserved domains within COUP-TF could act as distinct entities, independent of the complete COUP-TF protein. Fusion constructs were created between the Green Fluorescent Protein (GFP) and the entire human COUP-TF as well as various sub-domains of the sea urchin SpCO UP-TF. Intracellular trafficking of the fusion proteins in live embryos was monitored by confocal fluorescent microscopy. The results of this study su ggest that, independent of intact COUP-TFs, the various domains tested are not by themselves sufficient for maintaining the correct subcellular locali zation pattern. The two intact transcription factors, although they belong to such evolutionarily distant animals, do demonstrate similar intracellula r localization in the developing sea urchin embryos, indicating functional conservation between the COUP-TFs.