Gfi1-mediated stabilization of GATA3 protein is required for Th2 cell differentiation

The differentiation of naive CD4 T cells into Th2 cells requires the T cell receptor-mediated activation of the ERK MAPK cascade. Little is known, however, in regard to how the ERK MAPK cascade regulates Th2 cell differentiation. We herein identified Gfi1 (growth factor independent-1) as a downstream target of the ERK MAPK cascade for Th2 cell differentiation. In the absence of Gfi1, interleukin-5 production and the change of histone modification at the interleukin-5 gene locus were severely impaired. Furthermore, the interferon gamma gene showed a striking activation in the Gfi1(-/-) Th2 cells. An enhanced ubiquitin/proteasome-dependent degradation of GATA3 protein was observed in Gfi1(-/-) Th2 cells, and the overexpression of GATA3 eliminated the defect of Th2 cell function in Gfi1-deficient Th2 cells. These data suggest that the T cell receptor-mediated induction of Gfi1 controls Th2 cell differentiation through the regulation of GATA3 protein stability.     

Regulation of the Drosophila engrailed gene by Polycomb repressor complex 2

Suppressor-of-zeste-12 (Su(z)12) is a core component of the Polycomb repressive complex 2 (PRC2), which has a methyltransferase activity directed towards lysine residues of histone 3. Mutations in Polycomb group (PcG) genes cause de-repression of homeotic genes and subsequent homeotic transformations. Another target for Polycomb silencing is the engrailed gene, which encodes a key regulator of segmentation in the early Drosophila embryo. In close proximity to the en gene is a Polycomb Response Element, but whether en is regulated by Su(z)12 is not known. In this report, we show that en is not de-repressed in Su(z)12 or Enhancer-of-zeste mutant clones in the anterior compartment of wing discs. Instead, we find that en expression is down-regulated in the posterior portion of wing discs, indicating that the PRC2 complex acts as an activator of en. Our results indicate that this is due to secondary effects, probably caused by ectopic expression of Ubx and Abd-B.     

Regulation of GATA gene expression during vertebrate development

GATA factors regulate critical events in hematopoietic lineages (GATA-1/2/3), the heart and gut (GATA-4/5/6) and various other tissues. Transgenic approaches have revealed that GATA genes are regulated in a modular fashion by sets of enhancers that govern distinct temporal and/or spatial facets of the overall expression patterns. Efforts are underway to resolve how these GATA gene enhancers are themselves regulated in order to elucidate the genetic and molecular hierarchies that govern GATA expression in particular developmental contexts. These enhancers also afford a raft of tools that can be used to selectively perturb and probe various developmental events in transgenic animals.     

Loss of the Polycomb group gene polyhomeotic induces non-autonomous cell overproliferation

Polycomb group (PcG) proteins are conserved epigenetic regulators that are linked to cancer in humans. However, little is known about how they control cell proliferation. Here, we report that mutant clones of the PcG gene polyhomeotic (ph) form unique single-cell-layer cavities that secrete three JAK/STAT pathway ligands, which in turn act redundantly to stimulate overproliferation of surrounding wild-type cells. Notably, different ph alleles cause different phenotypes at the cellular level. Although the ph-null allele induces non-autonomous overgrowth, an allele encoding truncated Ph induces both autonomous and non-autonomous overgrowth. We propose that PcG misregulation promotes tumorigenesis through several cellular mechanisms.     

Programming of gene expression by Polycomb group proteins

Polycomb group (PcG) complexes maintain epigenetically repressed states that need to be reprogrammed when cells become committed to differentiation. In contrast to the previously held belief that PcG complexes regulate only a few selected genes, recent efforts have revealed hundreds of potential PcG targets in mammals, insects and plants. These results have changed our perception about PcG recruitment and function on chromatin. Both in animals and plants, evolutionarily conserved PcG complexes mark the chromatin of their target genes by methylation at histone H3 lysine 27. Surprisingly, however, both the proteins recognizing this mark and the mechanisms causing gene repression differ between both kingdoms. This suggests that different developmental strategies used in plant and animal development entailed the evolution of different repressive maintenance mechanisms.     

Regulation of the cell expansion gene RHD3 during Arabidopsis development

The RHD3 (ROOT HAIR DEFECTIVE3) gene encodes a putative GTP-binding protein required for appropriate cell enlargement in Arabidopsis. To obtain insight into the mechanisms of RHD3 regulation, we conducted a molecular genetic dissection of RHD3 gene expression and function. Gene fusion and complementation studies show that the RHD3 gene is highly expressed throughout Arabidopsis development and is controlled by two major regulatory regions. One regulatory region is located between -1,500 and -600 bp upstream of the RHD3 gene and is required for vascular tissue expression. The other region is intragenically located and includes the 558-bp first intron, which is responsible for high-level expression of RHD3 throughout the plant. The presence and location of this intron is essential for gene function because constructs lacking this intron or constructs with the intron in an abnormal position are unable to functionally complement the rhd3 mutations. We also analyzed the role of other RHD genes and the plant hormones auxin and ethylene in RHD3 regulation, and we determined that these act downstream or independently from the RHD3 pathway. This study shows that multiple levels of regulation are employed to ensure the appropriate expression of RHD3 throughout Arabidopsis development.