Single-cell c-myc gene expression in relationship to nuclear domains
Nuclear locations of the c-myc gene and its transcripts (c-myc(T)) have been investigated in relation to nuclear domains involved in RNA synthesis and processing. Transcription of the c-myc gene appears to be linked to the late G(1)- and preferentially to S-phases of the cell cycle. The c-myc gene and its transcripts were positioned non-randomly within the interphase nucleus; additionally, c-myc RNA signals accumulated at nucleoli. Using oligoprobes, designed to exon II and exon III of the c-myc gene, single c-myc(T) was preferentially observed in human carcinoma HT29 and A549 cells. Conversely, human embryonal teratocarcinoma NTERA cells were characterized by the presence of multiple c-myc RNA signals located in both the nucleoli and nucleoplasm. When accumulated at nucleoli, c-myc(T) occupied the periphery of this organelle, though not those associated with the cultivation surface. In HT29 cells, approximately 80% of c-myc T co-localized with the RNAP II positive regions, so-called transcription factories. However, in similar to 20% of the cells with c-myc transcripts, the c-myc(T) was released from the site of synthesis, and was not associated with either transcription factories or SC35 domains. In similar to 60% of nuclei with c-myc(T), these signals were located in close proximity to the SC35 regions, but promyelocytic leukaemia bodies were associated with c-myc(T) only in similar to 20% of the nuclei. Taken together, c-myc RNA signals were positioned in the most internal parts of the cell nuclei preferentially associated with the nucleoli. Specific nuclear and nucleolar positioning probably reflects the kinetics of c-myc RNA metabolism.