The Role of Nuclear Pore Proteins in Developmental Gene Regulation. Martin W. Hetzer. Salk Inst for Biological Studies, La Jolla, CA.

   Faithful execution of developmental gene expression programs occurs at multiple levels and involve many different components such as transcription factors, histone-modification enzymes and mRNA processing proteins. Recent findings from our laboratory suggest that nucleoporins, well known components that control nucleo-cytoplasmic trafficking, have wide-ranging functions in developmental gene regulation that potentially extend beyond their role in nuclear transport. Analysis of chromatin-binding behavior of Drosophila Nups, achieved by different methods such as immunostaining of polytene chromosomes and ChIP, revealed the presence of several NPC components at active genes and a functional requirement for their presence in transcription of their binding targets. Reducing levels of Nup98 or and a member of the Nup107/160 complex by RNA interference (RNAi) resulted in decreased levels of transcriptional activity and mRNA levels of its target genes, which included the developmentally induced ecdysone-responsive genes. Surprisingly, the NUP-chromatin contacts were commonly found to occur in the nucleoplasm, away from the NE-embedded NPCs. Whether the unexpected role of nuclear pore proteins in transcription regulation, which initially has been described in yeast, also applies to human cells remained unknown. Recent data from our group suggest that at a genome-wide level Nup98 associates with developmentally regulated genes active during human embryonic stem cell differentiation. Overexpression of a dominant negative fragment of Nup98 levels decreases expression levels of Nup98-bound genes. In addition, we identify two modes of developmental gene regulation by Nup98 that are differentiated by the spatial localization of Nup98 target genes. Genes in the initial stage of developmental induction can associate with Nup98 that is embedded in the nuclear pores at the nuclear periphery. Alternatively, genes that are highly induced can interact with Nup98 in the nuclear interior, away from the nuclear pores. This work demonstrates that Nup98 dynamically associates with the human genome during differentiation, revealing a role of a nuclear pore protein in regulating developmental gene expression programs.