Study on intracellular trafficking pathway of Orthodenticle Homeobox 2 transcription factor

Abstract

Transcription factors (TFs) move between the cytoplasm and the nucleus within a cell and regulate gene expression inside the nucleus. Homeoproteins (HPs), TFs containing the homeodomain (HD), bind to target deoxyribonucleic acid (DNA) sequences using the HD and regulate gene expression temporal-spatially to determine the cell fate during embryonic development. This inherent role as a transcriptional regulator led us to believe that HPs function in the nucleus of the cells expressing them. However, unlike general TFs, HPs have the property of migrating to adjacent cells, allowing cells to perform appropriate functions during postnatal development. In this dissertation, I give a methodology for the intracellular trafficking pathway of orthodenticle homeobox 2 (OTX2) involved in postnatal visual system maturation. First, I tracked the cytoplasmic vesicles observed near the nucleus during the nuclear egress of OTX2 and found that the lysosomes are related to the intracellular transport of OTX2. Next, based on ultrastructural analysis, I revealed that the factors involved in the vesicle formation during the nuclear egress of OTX2 are the torsin family 1 member A (TOR1A) adenosine triphosphatase associated with diverse cellular activities (AAA+ ATPase) and the linker of nucleoskeleton and cytoskeleton (LINC) complex. Finally, using mutations in these factors, I blocked the nuclear egress process of OTX2 by inhibiting the formation of perinuclear vesicles. Consequently, I found the immaturity of the visual system and the formation of OTX2 aggregates in the nucleus. Taken together, I suggest that the nuclear egress of OTX2 not only enables the proper functioning of recipient cells but also prevents aggregates-induced cell death following OTX2 accumulation within the nucleus of donor cells.