Epigenetics and Imprinting in Development and Reproduction
Most organisms inherit DNA from both a mother and a father and the expression of this DNA is equivalent from both male and female genomes. Some genes, however, are only expressed from the maternal or the paternal genome, leaving the non-expressed parent gene completely silenced. This phenomenon is called genomic imprinting and is found in higher organisms ranging from plants to humans. Imprinting, typically takes place in the mammalian placenta and in the plant seed, but recently it was also shown that several genes also are imprinted in the human brain.
Figure 1: Mechanisms involved in imprinting of the MADS-box gene AGL36 in the Arabidopsis seed.
Why are some genes expressed only from one parent? The answer to this is not clear, but a prevailing hypothesis predicts that a parental tug of war on the allocation of available recourses to the developing progeny has led to the evolution of imprinting systems where genes expressed from the mother reduce growth whereas genes expressed from the father are growth enhancers.
What is the mechanistic basis for imprinting? Imprinting is a highly specialized example of epigenetic regulation. Epigenetics involves the modification of DNA and specific amino acid residues in histone tails leading to chromatin rearrangements that allow for or block gene expression.
mammals, and this precludes theelucidation of the epigenetic mechanisms responsible for imprinting. We have therefore used genome-wide transcript profiling of seeds missing paternal contribution to identify seed regulators, and among these imprinted genes. We have identified a cluster of MADS-box transcription factors and could show that some of these were imprinted by an epigenetic mechanism i
nvolving the DNA methylase MET1 and the glycosylase DME. In addition, the expression of the active allele was repressed by the epigenetic regulator Polycomb, identifying a novel mode of regulation of imprinted genes. Read more about our research in the journal PLoS Genetics or forskning.no
Figure 2: Confocal image of the Arabidopsis seed.
Possible Master projects:
1.*The role and epigenetic mechanisms of Type I MADS-box imprinting.
2.*Imprinting and epigenetics in evolution of species barriers 3.*Molecular characterization of novel genes involved in gametophyte development or function
The Objectives: The main focus in these master projects will be to verify imprinted or seed specific genes from microarray profiles and perform a molecular and genetic characterization of one or more genes. A major goal is to analyze the mechanism by which these genes are imprinted! This is done by using mutants in known DNA or histone methyltransferases or by checking methylation status of candidate genes directly. For more details contact Paul Grini.
The Lab: We employ a broad specter of state of the art molecular techniques in combination with genetics, cell biology and bioinformatics. The techniques used include molecular cloning and analysis of reporter and protein fusion constructs, molecular imaging and confocal laser scanning microscopy, parental specific RT PCR using SNP and Lab On a Chip technology and Real-time PCR. Since we use Arabidopsis as a model to study seed development, you will learn how to work with a model organism and see how your experiments effect seed development in planta!
The Team: Paul Grini (Group leader), Katrine Bjerkan (Post doc.), Jonathan Bramsiepe (Post doc.), Karina Hornslien (PhD stud.), Ida Johannessen (PhD stud.), Ellen Andersen (PhD stud.), Ingvild Falkum Ullmann (MSc stud.) Maryam Kalantarian (MSc stud.)