Bruce H. Howard, MD, Chief
The Laboratory of Molecular Growth Regulation (LMGR) conducts research on the control of cell proliferation, DNA replication, and gene regulation. With respect to the last, independent groups work in complementary areas, including regulation of the developing immune system, gene expression during early embryogenesis, chromatin-mediated gene silencing, and transcription of small RNA-encoding genes.
Keiko Ozato's group, the Section on Molecular Genetics of Immunity, studies transcription factors that control cell proliferation and differentiation in the immune system. Studies on ICSBP/IRF-8 have revealed its importance for IL-12p40–dependent development of macrophages, granulocytes, and dendritic cells (DCs). Among some 50 genes identified as IRF-8 targets, several are crucial for macrophage/DC function. The Section showed that Brd4, another transcription factor under investigation, and IRF-8 both function by regulating the activity of chromatin. As shown by FRET and FLIP, Brd4 recognizes acetylated histones in live cells and remains bound to chromosomes during mitosis, implying a role in epigenetic memory. Brd4 associates with the key regulatory factor P-TEFb and is required by P-TEFb for transcriptional activation.
The investigations carried out by the Section on Eukaryotic Gene Regulation, led by Mel DePamphilis, concern control of gene expression during early mouse embryogenesis, which has been linked to the transcription factor mTEAD-2. Experiments have identified YAP65 as a crucial co-activator of the TEAD family of transcription factors. An independent project concerns cell cycle control and the role of the ORC complex in DNA replication. ORC1 is ubiquitinated and released from chromatin during S phase; further, it is excluded from chromatin during mitosis through an association with Cdk1(Cdc2)/cyclin A. Both modes of ORC1 regulation reflect its key role as a link between DNA replication and cell metabolism.
Another area of study relates to the multifunctional factor known as human La antigen. Work in the Section on Molecular and Cell Biology, under the direction of Richard Maraia, has indicated that La antigen is essential for development beyond the blastocyst stage of growth. The protein is a regulatory chaperone for nascent RNAs and is required for proper nuclear trafficking and the successful processing of tRNAs. Phosphorylation of La modulates its interaction with nascent transcripts as well as its localization to the nucleolus.
A research group led by David Clark, the Section on Chromatin and Gene Expression, brings to the LMGR expertise in both yeast genetics and the characterization of purified chromatin structures. Studies with the latter have revealed that gene activation can be accompanied by SWI/SNF- and Isw1-dependent chromatin remodeling over entire target gene domains. An unexpected and intriguing finding is that Spt10 binding at core histone promoters can explain the putative role of that factor in global control of gene expression.
A major effort of the Human Genetics Section, led by Bruce Howard, focuses on higher-order chromatin structures, in particular how defects in the maintenance of such structures may underlie developmental disorders and age-related diseases. Random genome sampling, customized search algorithms for comparisons of multiply annotated genomes, and genomics-style high-throughput approaches facilitate the detection and mapping of age-related areas of chromatin remodeling.