Gene expression in sheep skin and wool (hair) D.L. Adelson, * G.R. Cam, U. DeSilva, 1 and I.R. Franklin CSIRO Livestock Industries, 306 Carmody Road, St. Lucia, Queensland 4067, Australia Received 31 December 2002; accepted 25 June 2003 Abstract We sequenced 2939 ESTs from fetal and adult sheep skin. Stages of gestation were picked to coincide with the major events in skin appendage (wool follicle) formation. Clustering analysis generated a nonredundant set of ESTs 2435 strong (83% nonredundant). Approximately 24% of these gave no hit to NCBI build 29 of the human genome, while 35% were tentatively classified by putative function based on BLASTX hits with a p(N) of <10 4 . In addition to bioinformatics analysis of our ESTs and gene mapping, we have generated a large EST spatial expression data set using in situ hybridization. One thousand one hundred forty-two ESTs have been used for in situ localization; about 31% are from adult sheep skin, 39% from late gestation fetal sheep skin, and 30% from midgestation fetal sheep skin. These probes have been used in over 3000 hybridization experiments. In this report, we summarize the results of in situs on adult sheep skin. D 2003 Elsevier Inc. All rights reserved. Keywords: EST; In situ; Sheep; Wool follicle; Hair follicle The use of ESTs was pioneered by Adams et al. [1] as a way of cataloging the genes expressed in various human tissues. Our goal has been to identify genes active in sheep skin during wool follicle initiation and morphogenesis and wool fiber growth, hence our sequencing of ESTs from fetal and adult sheep skin. While a number of fleece characteristics are important in determining how much buyers will pay for wool, wool weight and average fiber diameter are the predominant determinants of price, and hence these two traits are the usual focus of breeding programs. The amount of wool grown is a function of the surface area of the animal, the wool follicle density, and the volume of fiber per follicle produced in a given time. Ideally, the incentive is to breed animals exhibiting high follicle densities, low fiber diame- ter, and a high length growth rate of fiber. Each of these traits are known to be genetically and environmentally correlated. In particular, a high negative genetic correlation between follicle density and fiber diameter is apparent in adult sheep from a variety of breeds and strains [2–4]. This negative correlation is reflected in correlated responses in selection lines for which the selection criteria have been based on one or other of the components of fleece weight. For example, selection for reduced fiber diameter results in an increased follicle density, and vice versa [5]. Also, most selection lines based on fleece weight alone exhibit positive correlated responses in a range of its components, such as fiber diameter, follicle density, and staple length [5]. These (and other) observed genetic relationships indicate that genes affecting one or more of the developmental pathways involved in follicle initiation and fiber growth are likely to exhibit complex and subtle interactions (pleiotropy) be- tween the genes responsible for fleece phenotype. Inasmuch as pleiotropic effects are not predictable without a mecha- nistic understanding of all of the genes involved, pleiotropy constitutes a substantial barrier to the breeding of efficient high-quality wool-producing animals. Hair (fiber) diameter is highly correlated with the size of the hair follicle dermal papilla [6], whose origin can be traced to the dermal condensate, one of the earliest features of the developing hair or wool follicle. The dermal conden- sate is an aggregation of dermal cells at the site of follicle initiation, which is characterized by a thickening of the basal layer of the epidermis. After initiation, the follicle rudiment grows down into the dermis and the dermal condensate remains as a discrete structure, or prepapilla, that maintains its position at the base of the extending follicle plug. 0888-7543/$ - see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0888-7543(03)00210-6 * Corresponding author. Present address: Department of Animal Science, Kleberg Center, Room 432, Texas A&M University, 2471 TAMU, College Station, TX 77843-2471, USA. Fax: +1-979-845-6970. E-mail address: david.adelson@tamu.edu (D.L. Adelson). 1 Present address: Department of Animal Science, Oklahoma State University, Stillwater, OK, USA. www.elsevier.com/locate/ygeno Genomics 83 (2004) 95 – 105