Biological significance of the specific transcription machinery during oocyte growth in the mouse – PICoo

Within a multicellular organism, all cells share the same genetic information but they express it differently depending on their cell types. How regulation of gene expression is mechanistically controlled in different cell types remains a crucial basic question that has important implications in human pathological situations such as cancer, metabolic disease, neural disorders, congenital malformations or infertility.
Formation of the preinitiation complex (PIC) containing RNA polymerase II (Pol II) and 6 general transcription factors (GTFs) is an important regulatory step for gene expression. PIC formation is first regulated by increase DNA template accessibility mediated by co-activator complexes and then, by the stepwise assembly of the GTFs on the core promoters. The evolutionary conserved GTF TFIID complex composed of TBP and 13 TAFs, plays a major role in transcription initiation as it is the first factor to initiate PIC assembly by recognizing the promoter.
The traditional text-book model suggesting that recognition of the core promoter sequences is always mediated by TFIID has been challenged in metazoans. Discovery of specialized TAF paralogs and of three TBP homologs indicated that there is a potential variability in the mechanisms of recognition of the core promoter sequences in vivo that is still poorly understood. This variability also suggests that the transcription initiation context varies between cell types and cell states indicating that the transcription initiation machinery has evolved to adapt to different transcriptional constraints for an efficient spatio-temporal control of gene expression. A major challenge therefore is to understand the nature and the biological function of these alternative TFIID complexes that may be directly involved in the establishment of cell-specific gene expression programs.
We have recently uncovered an oocyte-specific basal transcription machinery as TBP is replaced by its closest paralog TBP-like protein 2 (TBPL2/TRF3) during oocyte growth. Our hypothesis is that TBPL2-driven transcription initiation is playing a major role in the establishment of the future maternal transcriptome and of the oocyte specific characteristics. By combining transdisciplinary approaches and cutting-edge technologies, our collaborative effort aims to gain a more complete understanding of the transcription initiation machinery led by TBPL2 during oocyte growth. Our project will focus on the structural and functional characterization of the alternative TBPL2-containing transcriptional machinery and the understanding of its functional biological significance during oocyte growth in 4 aims: i) characterization of the TBPL2-containing complex composition, ii) analysis of the importance of the transcription initiation machinery transition, iii) characterization of the transcription initiation context during oocyte growth and iv) functional importance of TBPL2-mediated transcription initiation in the reshaping of the maternal transcriptome and in the establishment of the DNA methylome. Our project is crucial because it will explore new regulatory mechanisms of transcription and shed new light on our understanding of gene expression regulation during oogenesis
The main novelty of our multidisciplinary proposal is to address structural, proteomic, transcriptomic and genomic questions in a cell type that is limited in vivo and has no established cell line equivalent. This is also a main challenge as this biological material is scarce but this will be overcome by the expertise of the different partners in their technics and by the use of recently-developed cutting-edge technologies using low number of cells. As a result, our multidisciplinary project will expand our knowledge in the basic mechanisms of transcription initiation but also in the comprehension of new molecular mechanisms linked with female infertility.