Dissecting an epigenetic process that extrinsically govern fetal size

In mammals, embryonic growth is finely tuned and the placenta provides sufficient support for optimal embryonic growth. Too little support will have an adverse effect as embryonic growth is restrained which can result in intrauterine growth restriction. Too much support is wasteful and uses up maternal resources needlessly. It is therefore critical that the fetus and the supporting structures are working in harmony. Imprinted genes, which are expressed in mammals from only one parental allele, play a key role in this process. We are investigating a group of imprinted genes that are located within a discrete chromosomal region that is regulated by a single imprinting centre. Any global change in the expression of these genes has catastrophic consequences on both embryonic development and placental growth. We have already identified one of these genes, Cdkn1c, as the major regulator of embryonic growth within this domain. Several other genes are expressed in the placenta and some have been shown to play a critical role in placental development. In this proposal, we will determine whether two of these genes, known as Phlda2 and Slc22a18, act synergistically with Cdkn1c to balance embryonic growth and placental function. This work is important in our understanding how the placenta functions for optimal health. Intriguingly, the genes we are working on are adjacent in the genome and by studying them we may learn more about the functional consequences of imprinting these genes and how this may have influenced the evolution of the mammalian placenta. Critically, we will also learn more about the consequences of deregulated expression of these genes on development and disease.

We have previously shown that genetic loss of expression of one imprinted gene, Cdkn1c, initially provides a significant growth advantage to the embryo. However, this advantage is not maintained later in embryogenesis. In this proposal, we will test the hypothesis that at least one other imprinted gene sharing the same imprint control region as Cdkn1c is required to compliment the intrinsic growth advantage provided by imprinting Cdkn1c. We have identified two candidate genes that may perform this function: Phlda2, which encodes a rheostat for placental growth, and the adjacent gene Slc22a18, which encodes an organic cation transporter. In this proposal we aim to test our hypothesis by Characterising the developmental consequences of the combined alteration in Phlda2 and Slc22a18 in our existing transgenic model Genetically rescuing excess expression of Phlda2 to isolate the individual contribution of Slc22a18 and, by inference, also Phlda2 Performing a series of experiments to test the functional capacity of the Phlda2-deficient placenta This last objective will be achieved by providing a tetraploid Phlda2-deficient placenta to an embryo with an intrinsic growth advantage and characterising fetal growth. By using a Cdkn1c-deficient embryo, in addition to testing our hypothesis, we will also distinguish the phenotypic consequences of loss of Cdkn1c expression in the embryo from loss of expression in the placenta. This work will further establish the role of imprinting in the subtle interplay between the intrinsic potential of the embryo and functional capacity of the placenta required for optimal growth.