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During early development, pre-implantation mammalian embryos dynamically reprogram gene transcription and nuclear organisation. However, the causal relation between these two processes are the object of intense debates. To answer this question, we studied the spatial position and the transcription of ribosomal DNA sequences (rDNA) and repeated neighboring sequences. Initially these two types of sequences are positionned around the nucleolus precursor (NPB), superposed structures that play a role in the remodeling of chromatin during early development in mice. By combining DNA-3D-FISH and RNA-FISH, we found a unique organization for the rDNA inside the NPB, which is associated with the rDNA transcription state; the inhibition of this transcription leads to drastic changes in their organization. Finally, we showed that the disturbance of this 3D organization leads to a reduced thranscription of neighbor satellite repeats, suggesting that the reorganization of the chromatin during rRNA transcription provides an environment that facilitates expression of major repeat satellites. In conclusion, thiq study provides new important information on the interaction between the 3D nuclear structure and transcription.

Contact :

• Amelie Bonnet-Garnier, UMR BREED, Centre Jouy-en-Josas Antony.