Transcription Control of Liver Development

During liver organogenesis, cellular transcriptional profiles are constantly reshaped by the action of hepatic transcriptional regulators, including FoxA1-3, GATA4/6, HNF1 alpha/beta, HNF4 alpha, HNF6, OC-2, C/EBP alpha/beta, Hex, and Prox1. These factors are crucial for the activation of hepatic genes that, in the context of compact chromatin, cannot access their targets. The initial opening of highly condensed chromatin is executed by a special class of transcription factors known as pioneer factors. They bind and destabilize highly condensed chromatin and facilitate access to other non-pioneer factors. The association of target genes with pioneer and non-pioneer transcription factors takes place long before gene activation. In this way, the underlying gene regulatory regions are marked for future activation. The process is called bookmarking, which confers transcriptional competence on target genes. Developmental bookmarking is accompanied by a dynamic maturation process, which prepares the genomic loci for stable and efficient transcription. Stable hepatic expression profiles are maintained during development and adulthood by the constant availability of the main regulators. This is achieved by a self-sustaining regulatory network that is established by complex cross-regulatory interactions between the major regulators. This network gradually grows during liver development and provides an epigenetic memory mechanism for safeguarding the optimal expression of the regulators.

Automated summary

During liver organogenesis, a series of hepatic transcriptional regulators reshape cellular transcription profiles to activate hepatic genes. Pioneer factors open highly condensed chromatin to facilitate the action of other transcription factors. The bookmarking mechanism provides transcriptional competence for future activation of target genes, accompanied by a dynamic maturation process preparing for stable and efficient transcription.