Transcriptional control of macrophage function in the pig and its relationship to infectious disease susceptibility

This project is concerned with detailed studies of the immune system of the pig. The study takes a whole genome approach, and builds upon similar studies of the mouse and human by international consortia in which the Principal Investigator has participated. The focus is on the molecular biology of macrophages, large white blood cells that are the first line of defence against bacterial and some viral diseases. We aim to identify all of the genes that contribute to the host defence function in these cells in the pig, and how their expression is coordinated. Within that set of genes, we aim to identify those that vary in their function between pigs and other species, and between different major breeds of pigs. The outcome of the study will be to provide a rational basis for breeding pigs for improved disease resistance, identification of disease susceptibility genes that could also contribute to human health, and also a basic understanding of the evolution of immunity in mammals.

Macrophages are a major cellular component of the innate immune system. This project is based upon evidence that genes involved in the control of innate immunity diverge rapidly between, and within, species under the intense selection pressure of pathogen challenge. We will extend previous comprehensive studies of the transcriptome of macrophages in mice and humans to the pig. A core technology in the project is CAGE, which is a genome-scale method for identification of transcription start sites and analysis of their relative use with time. CAGE will be combined with cDNA microarrays to identify the full set of transcripts expressed by pig macrophages from different anatomical sites and in various states of activation. We will use this information to construct and test transcriptional network models, and to compare them to similar models we have developed in mouse and human. We will identify genes that are expressed divergently in macrophages between pigs, mice and humans, and between major pig breeds. At least some of this divergence arises from promoter evolution. We will select specific examples of promoter divergence between pigs and other species, and between breeds, and identify the mechanism of promoter divergence via detailed analysis of the promoter activity in transfections. The comparison of transcriptional networks across three species will permit identification of transcriptional regulatory nodes (lineage-specific transcription factors) that are conserved, and by inference are central to the process of macrophage differentiation. The function of these will be confirmed through selective knockdowns.