Transcription of amphibian lampbrush chromosomes is disturbed by microinjection of HSP70 monoclonal antibodies.

To investigate the possible involvement of HSP70 in nuclear transport of proteins associated with the transcription process in amphibian oocyte lampbrush chromosomes, we examined the effect of anti-HSP70 mouse monoclonal antibodies on the transcriptional activity of lampbrush chromosomes. When injected into the oocyte cytoplasm, anti-HSP70 induced disorganization followed by retraction of chromosomal lateral loops. This retraction reflected inhibition of transcription, which was confirmed by our electron microscopic observations. At the same time, while nucleoli were morphologically disorganized, nucleolar transcription persisted. These modifications were completely reversible. In contrast, no modifications were observed when antibodies were directly microinjected into nuclei. Similar observations were registered at the level of lampbrush chromosomes when wheat germ agglutinin was injected into oocyte cytoplasm. All of these results suggest that HSP70 mediates the nuclear transport of proteins involved in the lampbrush chromosome transcriptional process.