HSP70 is involved in the control of chromosomal transcription in the amphibian oocyte

The amphibian oocyte represents an excellent model for the study of transcription regulation. Indeed, any modification of transcriptional activity is directly reflected in lampbrush chromosome structure by concomitant morphological changes. Previous studies have led to the hypothesis of a putative role for heat-shock proteins HSP70 and/or HSC70 in transcriptional processes in the oocyte. In order to dissect out the relative role of HSP70 or HSC70 in these processes, we used an oligo-antisense strategy to specifically inhibit the function of the targeted protein. Effects of hsc70 and hsp70 antisense oligodeoxynucleotides were analyzed in terms of both mRNA quantity and protein synthesis. Their effects on oocyte transcription were analyzed at the level of structural organization of lampbrush chromosomes and nucleolar transcriptional activity. Our results show that specific inactivation of hsc70 mRNA by hsc70 antisense oligos led to a reversible inhibition of lampbrush chromosome transcription. However, such reversible inhibition of transcription is considered non-sequence specific since it is also induced by any oligo. In contrast, specific inactivation of hsp70 mRNA by hsp70 antisense oligos, which is correlated with a drop of HSP70 neosynthesis, results in an irreversible inhibition of lampbrush chromosome transcription. Furthermore, our results show that the inactivation of hsp70 or hsc70 mRNAs does not affect nucleolar transcription. Such data suggest a role for HSP70 in the control of chromatin modifications related to RNA polymerase II transcriptional activity.