Title

An investigation of the transcriptional regulatory elements of IGF2 in the livebearing fish Poeciliopsis prolifica and the marsupial Monodelphis domestica

Date of Completion

January 2006

Keywords

Biology, Genetics

Degree

Ph.D.

Abstract

The Parent-Offspring Conflict Theory suggests that genomic conflict between maternal and paternal genes is the precipitating factor for imprinting, and implies that organisms possessing a placental structure that allows for the allocation of maternal resources to developing offspring will exhibit imprinting (Haig, 2000). The work conducted in this body of research examined the expression of IGF2 in the matrotrophic livebearing fish Poeciliopsis prolifica, which evolved viviparity independently of mammals, and not only found the gene to be biallelically expressed, but revealed it to be rapidly evolving in some matrotrophic lineages. In addition, the finding that residues near proteolytic sites are undergoing positive selection suggests that these placental fish may be attempting to adapt as a result of genomic conflict. In marsupials, it is already known that imprinting exists, but the mechanism by which it occurs is still unknown. It was demonstrated here that differential methylation between the parental alleles is not a factor in the regulation of expression of IGF2, but elements linked to the function of matrix attachment regions, such as deacetylation, may hold promise as transcriptional regulators. The outcome of this aspect of the study provides support for the premise that marsupials may have retained regulation of imprinting by means of acetylation while eutherians increased control with differential methylation (Wakefield et al., 1997). ^