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At least 487 records · Page 27Linked to original sources
PubMed2004

Interaction of FIE, a polycomb protein, with pRb: a possible mechanism regulating endosperm development.

Inactivation of the Arabidopsis protein FERTILIZATION INDEPENDENT ENDOSPERM (FIE) induces division of the central cell of the embryo sac, leading to endosperm development in the absence of fertilization. The mechanism whereby FIE regulates this process is unknown. We postulated that activation of central cell division in fie mutant plants might involve the retinoblastoma protein (pRb), a cell cycle regulatory element. Pull-down and surface plasmon resonance assays demonstrated that FIE interacts in-vitro with the pRb homologues from Arabidopsis (AtRb), maize (ZmRb) and human (HuRb). The interaction of FIE with ZmRB and HuRb in the yeast two-hybrid system supports the possibility that a FIE-pRb interaction may occur also in planta. Mutational analysis showed that this interaction does not occur via the LxCxE motif of the FIE protein nor via the pocket B domain of pRb. These results suggest that FIE may inhibit premature division of the central cell of the embryo sac, at least partly, through interaction with pRb, and suppression of pRb-regulated genes.

Arabidopsis↗
PubMed2007

Polycomb-like genes are necessary for specification of dopaminergic and serotonergic neurons in Caenorhabditis elegans.

The molecular mechanisms underlying the formation of neurons with defined neurotransmitters are not well understood. In this study, we demonstrate that the PcG-like genes in Caenorhabditis elegans, sop-2 and sor-3, regulate the formation of dopaminergic and serotonergic neurons and several other neuronal properties. sor-3 encodes a novel protein containing an MBT repeat, a domain that contains histone-binding activity and is present in PcG proteins SCM and Sfmbt in other organisms. We further show that mutations in sor-3 lead to ectopic expression of Hox genes and cause homeotic transformations. Specification of certain neuronal identities by these PcG-like genes appears to involve regulation of non-Hox gene targets. Our studies revealed that the PcG-like genes are crucial for coordinately regulating the expression of discrete aspects of neuronal identities in C. elegans.

Amino Acid Motifs↗
PubMed2004

Identification of new members of Fertilisation Independent Seed Polycomb Group pathway involved in the control of seed development in Arabidopsis thaliana.

In higher plants, double fertilisation initiates seed development. One sperm cell fuses with the egg cell and gives rise to the embryo, the second sperm cell fuses with the central cell and gives rise to the endosperm. The endosperm develops as a syncytium with the gradual organisation of domains along an anteroposterior axis defined by the position of the embryo at the anterior pole and by the attachment to the placenta at the posterior pole. We report that ontogenesis of the posterior pole in Arabidopsis thaliana involves oriented migration of nuclei in the syncytium. We show that this migration is impaired in mutants of the three founding members of the FERTILIZATION INDEPENDENT SEED (FIS) class, MEDEA (MEA), FIS2 and FERTILIZATION INDEPENDENT ENDOSPERM (FIE). A screen based on a green fluorescent protein (GFP) reporter line allowed us to identify two new loci in the FIS pathway, medicis and borgia. We have cloned the MEDICIS gene and show that it encodes the Arabidopsis homologue of the yeast WD40 domain protein MULTICOPY SUPRESSOR OF IRA (MSI1). The mutations at the new fis loci cause the same cellular defects in endosperm development as other fis mutations, including parthenogenetic development, absence of cellularisation, ectopic development of posterior structures and overexpression of the GFP marker.

Arabidopsis↗
PubMed1988

Ectopic expression of homeotic genes caused by the elimination of the Polycomb gene in Drosophila imaginal epidermis.

The morphological patterns in the adult cuticle of Drosophila are determined principally by the homeotic genes of the bithorax and Antennapedia complexes. We find that many of these genes become indiscriminately active in the adult epidermis when the Pc gene is eliminated. By using the Pc3 mutation and various BX-C mutant combinations, we have generated clones of imaginal cells possessing different combinations of active homeotic genes. We find that, in the absence of BX-C genes, Pc- clones develop prothoracic patterns; this is probably due to the activity of Sex combs reduced which overrules Antennapedia. Adding contributions of Ultrabithorax, abdominal-A and Abdominal-B results in thoracic or abdominal patterns. We have established a hierarchical order among these genes: Antp less than Scr less than Ubx less than abd-A less than Abd-B. In addition, we show that the engrailed gene is ectopically active in Pc- imaginal cells.

Animals↗
PubMed1995

Functional analysis of the chromo domain of HP1.

Heterochromatin protein 1 (HP1) is a non-histone chromosomal protein in Drosophila with dosage-dependent effects on heterochromatin-mediated gene silencing. An evolutionarily conserved amino acid sequence in the N-terminal half of HP1 (the 'chromo domain') shares > 60% sequence identity with a motif found in the Polycomb protein, a silencer of homeotic genes. We report here that point mutations in the HP1 chromo domain abolish the ability of HP1 to promote gene silencing. We show that the HP1 chromo domain, like the Polycomb chromo domain, has chromosome binding activity, but to distinct chromosomal sites. We constructed a chimeric HP1-Polycomb protein, consisting of the chromo domain of Polycomb in the context of HP1, and show that it binds to both heterochromatin and Polycomb binding sites in polytene chromosomes. In flies expressing chimeric HP1-Polycomb protein, endogenous HP1 is mislocalized to Polycomb binding sites, and endogenous polycomb is misdirected to the heterochromatic chromocenter, suggesting that both proteins are recruited to their distinct chromosomal binding sites through protein-protein contacts. Chimeric HP1-Polycomb protein expression in transgenic flies promotes heterochromatin-mediated gene silencing, supporting the view that the chromo domain homology reflects a common mechanistic basis for homeotic and heterochromatic silencing.

Amino Acid Sequence↗
PubMed1994

Molecular characterisation of the Polycomblike gene of Drosophila melanogaster, a trans-acting negative regulator of homeotic gene expression.

The Polycomblike gene of Drosophila melanogaster, a member of the Polycomb Group of genes, is required for the correct spatial expression of the homeotic genes of the Antennapaedia and Bithorax Complexes. Mutations in Polycomb Group genes result in ectopic homeotic gene expression, indicating that Polycomb Group proteins maintain the transcriptional repression of specific homeotic genes in specific tissues during development. We report here the isolation and molecular characterisation of the Polycomblike gene. The Polycomblike transcript encodes an 857 amino acid protein with no significant homology to other proteins. Antibodies raised against the product of this open reading frame were used to show that the Polycomblike protein is found in all nuclei during embryonic development. Antibody staining also revealed that the Polycomblike protein is found on larval salivary gland polytene chromosomes at about 100 specific loci, the same loci to which the Polycomb and polyhomeotic proteins, two other Polycomb Group proteins, are found. These data add further support for a model in which Polycomb Group proteins form multimeric protein complexes at specific chromosomal loci to repress transcription at those loci.

Amino Acid Sequence↗
PubMed1989

In vivo binding pattern of a trans-regulator of homoeotic genes in Drosophila melanogaster.

The specification and maintenance of the metameric pattern in Drosophila melanogaster is regulated by complicated gene interactions. The differential expression of the homoeotic genes of the Antennapedia complex (ANT-C) and bithorax complex (BX-C), which determine segmental identities, is partly controlled by cross-regulatory interactions of loci within the two clusters and partly by trans-acting factors located outside the two complexes. One of the trans-regulatory genes, Polycomb (Pc), acts as a repressor of the ANT-C and BX-C. Mutations of Polycomb result in a complete depression of the homoeotic genes, leading to abdominal transformations of all body segments. Polycomb is part of a large class of trans-regulatory genes (Pc-group), estimated to comprise up to 40 loci. We have raised antibodies against the Polycomb protein, and, using an improved immunostaining technique, showed that the Polycomb protein binds to 60 discrete sites along the polytene chromosomes of salivary glands. These sites comprise the ANT-C and the BX-C as well as several locations of Pc-group genes. This is the first clear evidence for a direct interaction of Polycomb with homoeotic loci and other Pc-group genes.

Animals↗
PubMed1996

The Drosophila Enhancer of zeste gene encodes a chromosomal protein: examination of wild-type and mutant protein distribution.

The Drosophila Enhancer of zeste [E(z)] gene is a member of the Polycomb-group and, as such, is involved in maintaining the transcriptional repression of the homeotic genes of the Antennapedia (ANT-C) and bithorax (BX-C) complexes. It has been proposed that Polycomb-group (Pc-G)-mediated silencing requires the formation of heteromeric protein complexes which modify the chromatin structure of target genes. We describe the in vivo distribution of the E(Z) protein and show it to be ubiquitously present in embryonic and larval nuclei. In salivary gland polytenized nuclei, the identifiable E(Z) chromosome binding sites are a subset of those described for other Polycomb-group proteins, suggesting that E(Z) may also participate in Polycomb-group complexes. E(Z) binds to chromosomes in a DNA sequence-dependent manner, as illustrated by the creation of a new E(Z)-binding site at the location of a P element reporter construct that previously has been shown to contain a Polycomb response element (PRE). We also present the sequences of one null and three temperature-sensitive E(z) alleles, describe the effects these mutations have on the in vivo distribution of E(Z) protein and discuss their implications concerning putative functional domains. Finally, we describe the effect a trithorax mutation has on E(Z) chromosome binding.

Animals↗
PubMed2002

Transcription through intergenic chromosomal memory elements of the Drosophila bithorax complex correlates with an epigenetic switch.

The proteins of the trithorax and Polycomb groups maintain the differential expression pattern of homeotic genes established by the early embryonic patterning system during development. These proteins generate stable and heritable chromatin structures by acting via particular chromosomal memory elements. We established a transgenic assay system showing that the Polycomb group response elements bxd and Mcp confer epigenetic inheritance throughout development. With previously published data for the Fab7 cellular memory module, we confirmed the cellular memory function of Polycomb group response elements. In Drosophila melanogaster, several of these memory elements are located in the large intergenic regulatory regions of the homeotic bithorax complex. Using a transgene assay, we showed that transcription through a memory element correlated with the relief of silencing imposed by the Polycomb group proteins and established an epigenetically heritable active chromatin mode. A memory element remodeled by the process of transcription was able to maintain active expression of a reporter gene throughout development. Thus, transcription appears to reset and change epigenetic marks at chromosomal memory elements regulated by the Polycomb and trithorax proteins. Interestingly, in the bithorax complex of D. melanogaster, the segment-specific expression of noncoding intergenic transcripts during embryogenesis seems to fulfill this switching role for memory elements regulating the homeotic genes.

Animals↗