SAT-116 - Integrated Multiomic Mapping of Developmentally-Regulated and Hormone-Responsive Distal Elements in Contact with Key Pituitary Factor-Encoding Genes

Although the transcription factors and signaling pathways governing pituitary differentiation have been studied extensively, the contribution of non-coding regulatory elements remains poorly defined. Despite the increasingly abundant data arising from high-throughput genomic studies, linking distal elements to their target genes and understanding their cell-specific and hormone-responsive functions remain challenging. Here we integrated several multiomic approaches to identify and annotate distal regulatory elements controlling key pituitary genes. UMI-4C was performed from the viewpoint of the Cga, Pitx1, Pitx2 and Isl1 promoters in a gonadotrope cell line under basal conditions and following GnRH or activin stimulation. The chromatin contacts were integrated with data that we generated on chromatin accessibility during neonatal pituitary stem-cell differentiation to the gonadotrope lineage, ChIP-seq for lineage-determining transcription factors (TFs), and chromatin-associated RNA profiling. We also built on public datasets including single-nucleus ATAC-seq from adult mouse pituitary, and ChIP-seq for TFs and histone modifications from various sources.
At the Cga locus, the promoter contacted upstream and downstream regions displaying gonadotrope- and thyrotrope-specific accessibility, including a hormonally regulated enhancer ~100 kb upstream and the Platr9 locus downstream, as well as a distal site whose interaction was selectively reduced by activin. The Pitx1 promoter engaged a cluster of upstream enhancers, including the previously reported pituitary enhancer, and additional hormone-responsive regions transcribed to lncRNAs. For Pitx2, we uncovered a previously unreported distal element that opens during neonatal gonadotrope differentiation, binds key pituitary transcription factors, and shows GnRH- and activin-dependent contacts. Long-range interactions of the Isl1 promoter involved multiple upstream and downstream regions with dynamic chromatin accessibility, TF occupancy, lncRNA transcription, and differential sensitivity to GnRH and activin, revealing a more complex, stage- and hormone-dependent regulatory landscape.
This integrated analysis of the characteristics and behaviour of the non-coding genome defines numerous distal regulatory elements that likely establish cell-type-specific and hormone-responsive control of pituitary lineage genes. These findings provide a basis for interpreting non-coding sequence variation in pituitary disorders and for understanding how developmental and endocrine signals converge on three-dimensional genome organization to govern pituitary differentiation and function.

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