Sheep - Wool I WEIGHTED CO-EXPRESSION NETWORKS SHED LIGHT ON THE MOLECULAR MECHANISM OF ACTION OF METYRAPONE ON WOOL FOLLICLE DEVELOPMENT N.S. Watson-Haigh 1 , H.N. Kadarmideen 2 , M. McDowall 3 , G.S. Nattrass 4 , H.A. McGrice 3 and P.I. Hynd 3 1 CSIRO Livestock Industries, St Lucia 2 CSIRO Livestock Industries, Rockhampton; 3 The University of Adelaide and 4 South Australian Research & Development Institute (SARDI) SUMMARY The density of Merino wool follicles is established early in fetal development. This commercially important trait dictates wool fibre diameter which is the key driver of the price paid for wool. Merino lambs exposed to metyrapone (an inhibitor of cortisol synthesis) in utero show a lifetime alteration in wool growth parameters. Microarray data from a metyrapone treatment experiment were analysed within a systems biology framework using Weighted Gene Co-expression Network Analysis (WGCNA). Four networks were created to determine those genes involved in metyrapone mediated improvement of wool growth parameters. Using the WGCNA approach, we were able to detect co-expressed gene modules associated with metyrapone treatment. Gene ontology enrichment analysis of the genes comprising these modules identified a Bone Morphogenetic Protein (BMP4), a ligand known to be involved in hair/wool follicle development and expressed at the time of branching of secondary-derived follicles in Merino sheep. INTRODUCTION Merino sheep have a characteristically high follicle density of up to 60/mm 2 and a total of 10-100 million follicles compared to the estimated 5 million follicles in human skin. Primary follicles are the first to form, followed by secondary follicles and then secondary-derived follicles that branch from the secondary follicles. It is this high concentration of secondary-derived follicles which is a distinctive feature of Merino sheep. Branching of the secondary original follicles is essential in the Merino fleece as it is the major source of fine fibres (Hardy and Lyne 1956; Adelson et al. 2004). More detail is provided in a recent review (Rogers 2006). Fleece density, quality and length are important commercial traits, so improvements in these are beneficial. A previous study showed that lambs exposed to metryrapone, an inhibitor of cortisol synthesis, in utero between day 55 and 65 of gestation have been shown to possess lifetime improvements in their fleeces (in prep.). The identification of genes responsible for this fleece improvement would facilitate the development of other pharmaceutical intervention strategies to improve wool growth. A microarray experiment was performed on foetal skin samples in an attempt to determine those genes involved in metyrapone mediated improvement of wool parameters. We follow a general framework for constructing gene co-expression networks (Zhang and Horvath 2005) and used the WGCNA R package (Langfelder and Horvath 2008). For details of network concepts and terminology used see (Langfelder and Horvath 2008; Dong and Horvath 2007). MATERIALS AND METHODS Experimental Design. Twenty time-mated (synchronised with progesterone sponges and then artificially inseminated) pregnant Merino ewes were allocated to 4 equally sized treatment groups receiving daily intramuscular injections of a control (5ml of 0.6 M tartaric acid in 5% Tween 20) or metyrapone (5 ml of 1.76g metyrapone in 0.6 M tartaric acid in 5% Tween 20) between day 55 322