Biomedical subjects

Charles Spillane

Publications and source records attributed to Charles Spillane.

6 recordsLinked to original sources

PubMed2006

Genomic imprinting, methylation and molecular evolution of maize Enhancer of zeste (Mez) homologs.

Imprinted gene expression refers to differential transcription of alleles depending on their parental origin. To date, most examples of imprinted gene expression in plants occur in the triploid endosperm tissue. The Arabidopsis gene MEDEA displays an imprinted pattern of gene expression and has homology to the Drosophila Polycomb group (PcG) protein Enhancer-of-zeste (E(z)). We have tested the allele-specific expression patterns of the three maize E(z)-like genes Mez1, Mez2 and Mez3. The expression of Mez2 and Mez3 is not imprinted, with a bi-allelic pattern of transcription for both genes in both the endosperm and embryonic tissue. In contrast, Mez1 displays a bi-allelic expression pattern in the embryonic tissue, and a mono-allelic expression pattern in the developing endosperm tissue. We demonstrate that mono-allelic expression of the maternal Mez1 allele occurs throughout endosperm development. We have identified a 556 bp differentially methylated region (DMR) located approximately 700 bp 5' of the Mez1 transcription start site. This region is heavily methylated at CpG and CpNpG nucleotides on the non-expressed paternal allele but has low levels of methylation on the expressed maternal allele. Molecular evolutionary analysis indicates that conserved domains of all three Mez genes are under purifying selection. The common imprinted expression of Mez1 and MEDEA, in concert with their likely evolutionary origins, suggests that there may be a requirement for imprinting of at least one E(z)-like gene in angiosperms.

Alleles↗

PubMed2004

Genetic interaction of an origin recognition complex subunit and the Polycomb group gene MEDEA during seed development.

The eukaryotic origin recognition complex (ORC) is made up of six subunits and functions in nuclear DNA replication, chromatin structure, and gene silencing in both fungi and metazoans. We demonstrate that disruption of a plant ORC subunit homolog, AtORC2 of Arabidopsis (Arabidopsis thaliana), causes a zygotic lethal mutant phenotype (orc2). Seeds of orc2 abort early, typically producing embryos with up to eight cells. Nuclear division in the endosperm is arrested at an earlier developmental stage: only approximately four nuclei are detected in orc2 endosperm. The endosperm nuclei in orc2 are dramatically enlarged, a phenotype that is most similar to class B titan mutants, which include mutants in structural maintenance of chromosomes (SMC) cohesins. The highest levels of ORC2 gene expression were found in preglobular embryos, coinciding with the stage at which homozygous orc2 mutant seeds arrest. The homologs of the other five Arabidopsis ORC subunits are also expressed at this developmental stage. The orc2 mutant phenotype is partly suppressed by a mutation in the Polycomb group gene MEDEA. In double mutants between orc2 and medea (mea), orc2 homozygotes arrest later with a phenotype intermediate between those of mea and orc2 single mutants. Either alterations in chromatin structure or the release of cell cycle checkpoints by the mea mutation may allow more cell and nuclear divisions to occur in orc2 homozygous seeds.

Arabidopsis↗

PubMed2004

Apomixis technology development-virgin births in farmers' fields?

Apomixis is the process of asexual reproduction through seed, in the absence of meiosis and fertilization, generating clonal progeny of maternal origin. Major benefits to agriculture could result from harnessing apomixis in crop plants. Although >400 apomictic plant species are known, apomixis is rare among crop plants, and the transfer of apomixis to crop varieties by conventional breeding has been largely unsuccessful. Because apomictic and sexual pathways are closely related, de novo engineering of apomixis might be achieved in sexually reproducing crops. Early consideration of issues relating to biosafety and intellectual property (IP) management can facilitate the acceptance and deployment of apomixis technology in agriculture.

Agriculture↗

PubMed2003

The Polycomb-group protein MEDEA regulates seed development by controlling expression of the MADS-box gene PHERES1.

The Polycomb-group (PcG) proteins MEDEA, FERTILIZATION INDEPENDENT ENDOSPERM, and FERTILIZATION INDEPENDENT SEED2 regulate seed development in Arabidopsis by controlling embryo and endosperm proliferation. All three of these FIS-class proteins are likely subunits of a multiprotein PcG complex, which epigenetically regulates downstream target genes that were previously unknown. Here we show that the MADS-box gene PHERES1 (PHE1) is commonly deregulated in the fis-class mutants. PHE1 belongs to the evolutionarily ancient type I class of MADS-box proteins that have not yet been assigned any function in plants. Both MEDEA and FIE directly associate with the promoter region of PHE1, suggesting that PHE1 expression is epigenetically regulated by PcG proteins. PHE1 is expressed transiently after fertilization in both the embryo and the endosperm; however, it remains up-regulated in the fis mutants, consistent with the proposed function of the FIS genes as transcriptional repressors. Reduced expression levels of PHE1 in medea mutant seeds can suppress medea seed abortion, indicating a key role of PHE1 repression in seed development. PHE1 expression in a hypomethylated medea mutant background resembles the wild-type expression pattern and is associated with rescue of the medea seed-abortion phenotype. In summary, our results demonstrate that seed abortion in the medea mutant is largely mediated by deregulated expression of the type I MADS-box gene PHE1.

Arabidopsis↗

PubMed2002

Evolutionary origins of the endosperm in flowering plants.

The evolutionary origin of double fertilization and the resultant endosperm tissue in flowering plants remains a puzzle, despite over a century of research. The recent resurgence of approaches to evolutionary developmental biology combining comparative biology with phylogenetics provides new understanding of endosperm origins.

Evolution, Molecular↗

PubMed2002

Genomic imprinting during seed development.

Genomic imprinting allows parent-of-origin specific control over gene expression. Although imprinted genes (or entire chromosomes) are homologous sequences that can be inherited from either parent, they are differentially marked by a heritable epigenetic modification (imprint), which can condition their behavior in term of gene expression. Imprinting-based regulation of entire chromosomes is observed in both insects (paternal genome elimination) and mammals (nonrandom X inactivation). Until recently, it was unknown whether plants possessed a similar epigenetic system discriminating between homologous chromosomes from either paternal or maternal origin. There is now experimental evidence for a genome-wide imprinting phenomenon during seed development in Arabidopsis. Genomic imprinting at the gene (or locus) level is observed in both mammals and flowering plants. In maize, only a few allelic variants of several nonessential genes expressed in the endosperm are imprinted. In Arabidopsis, gene-specific imprinting has recently been demonstrated for the MEDEA (and FIS2) gene, which is essential for normal seed development. Unlike the imprinted maize genes, so far all tested MEA alleles are subjected to regulation by imprinting. MEDEA and FIS 2 are members of the FIS class of genes (FERTILIZATION INDEPENDENT SEED) involved in regulation of growth and cell proliferation during seed development. MEDEA shares several paradigmatic features with imprinted mammalian genes. The MEDEA phenotypes provide empirical support for theories of an intragenomic parental conflict during seed development, whereby imprinting is proposed as a means to differentially balance the selfish interests of each sex's genome during the development of the progeny.

Alleles↗