DISRUPTION OF PREMESSENGER RNA SPLICING IN-VIVO RESULTS IN REORGANIZATION OF SPLICING FACTORS

We have examined the functional significance of the organization of pr e-mRNA splicing factors in a speckled distribution in the mammalian ce ll nucleus. Upon microinjection into living cells of oligonucleotides or antibodies that inhibit pre-mRNA splicing in vitro, we observed maj or changes in the organization of splicing factors in vivo. Interchrom atin granule clusters became uniform in shape, decreased in number, an d increased in both size and content of splicing factors, as measured by immunofluorescence. These changes were transient and the organizati on of splicing factors returned to their normal distribution by 24 h f ollowing microinjection. Microinjection of these oligonucleotides or a ntibodies also resulted in a reduction of transcription in vivo, but t he oligonucleotides did not inhibit transcription in vitro. Control ol igonucleotides did not disrupt splicing or transcription in vivo. We p ropose that the reorganization of splicing factors we observed is the result of the inhibition of splicing in vivo.