Alternative splicing is a major source of diversity for the proteome. A few years ago, our laboratory provided pioneering data showing that chromatin and chromatin factors play a role the regulation of this alternative splicing.
Along this track, we have now shown in collaboration with the laboratory of A. Harel-Bellan (CEA, Saclay) that alternative splicing is affected by a novel machinery combining nuclear proteins involved in RNAi and splicing factor.
Within this machinery, Argonaute 1 and 2 (AGO1 and AGO2) participate in the recruitment to intragenic chromatin of both chromatin-structuring factors (HP1 and histone methylases) and components of the spliceosome in response to activation of the MAP kinase pathway (Figure 1).
Altogether, our data suggests that this machinery facilitates inclusion of alternative exons by locally assisting the rapid assembly of a functional spliceosome and by generating chromatin structures interfering with the elongation rate of the RNA polymerase II.
Currently, we are exploring the mechanism allowing for the targeted recruitment of the machinery inside the coding region of actively transcribed genes with a special interest for the nature and the origin of the small RNAs associated with AGO1 and AGO2 in the nucleus.
In parallel, we have elaborated an in vitro transcription-splicing system on chromatinized templates that allows us to biochemically explore the connections between chromatin and splicing. This system has now provided the first in vitro evidence for an impact of chromatin on the efficiency of splicing.
Finally, with a reversed approach, we have shown that the activity of several enzymes catalysing histone modifications is affected by alternative splicing events. This represents an additional layer of complexity in the crosstalk between chromatin and splicing.
Figure 1: AGO proteins participate in the inducible and targeted recruitment of the spliceosome while also affecting the elongation rate of the RNA polymerase II by favouring the writing of repressive histone modifications. Together, these effects facilitate inclusion of alternative exons.