US-AUSTRALIAN ACADEMIES JOINT WORKSHOP

US-AUSTRALIAN ACADEMIES JOINT WORKSHOP ON VERTEBRATE COMPARATIVE GENOMICS
Beckman Conference Centre, Irvine, California, 23-25 May 2007

Rapid evolution of genomic imprinting
by Ross Tellam

Dr Ross Tellam is a Senior Principal Research Scientist with CSIRO Livestock Industries at the Queensland Bioscience Precinct, St Lucia, Brisbane, Queensland, Australia. He also has an adjunct academic appointment at Griffith University, Brisbane. Before joining CSIRO Dr Tellam held positions as a Research Fellow at the Australian National University in Canberra and the Washington University School of Medicine in St Louis. His research interests include skeletal muscle development, microRNA function in myogenesis, genomic imprinting, innate immune responses in mammary tissue, and milk bioactive proteins. Dr Tellam is the CSIRO representative on the Bovine Genome Sequencing Project.

Genomic imprinting gives rise to different phenotypes in offspring in a parent of origin dependent manner. The imprint is an epigenetic mark arising during gametogenesis that results in expression of only one of the two parental alleles of a gene. Imprinting is largely restricted to eutherian mammals and marsupials although it is also present in some angiosperms. About 1% of genes in mammals are thought to be imprinted. In general, paternally expressed genes promote foetal growth while maternally expressed genes suppress foetal growth. This characteristic has led to the conceptual framework of the parental conflict hypothesis¹, which posits that imprinting reflects the conflict of interest between paternal and maternal genomes in regulating foetal growth. Analysis of imprinting in the two most intensively investigated species, mouse and man, as well as limited studies in other species, indicates that imprinting is poorly conserved and in several instances associated with species-specific genes, particularly genes encoding noncoding RNA. Using the Dlk1 locus as a model, we and others² suggest that the imprinting associated with this locus may be controlled by a very long noncoding RNA (>0.5 Mb) - a characteristic feature of several imprinted loci. The functional interdependencies of this long RNA, histone modifications and site specific DNA methylation probably orchestrate the silencing of one of the alleles in this region. How imprinting first arose is not clear. One hypothesis is that there was an ancestral partially silenced chromosome and during gene duplication events imprinting control elements were copied and then propagated onto newly formed chromosomes in descendent species³.  

1. Haig, D. (1992) Semin. Devel. Biol. 3, 153-160.
2. Seitz et al., (2004) Genome Research 14, 1741-1748.
3. Walter, J. and Paulsen, M. (2003) Human Molecular Genetics 12, R215-R220.

Contact details:
CSIRO Livestock Industries
Queensland Bioscience Precinct, St Lucia, Brisbane, Queensland, Australia

Tel: +61 7 3214 2476
Fax: +61 7 3214 2900
Email: Ross.Tellam@csiro.au