We have examined the expression of the ovine clusterin gene in the sheep pituitary gland, with the aim of determining its site of synthesis in this tissue. Northern blotting analysis of extracted polyadenylated RNA, using a 32 P-labelled rat clusterin cDNA probe, detected the greatest amounts of clusterin mRNA in the anterior part of dissected pituitary glands. In situ hybridisation studies showed clusterin mRNA in anterior and intermediate Journal of Molecular Endocrinology (1999) 23, 199-208 INTRODUCTIONClusterin is a highly sulphated glycoprotein that is expressed in a wide range of tissues, often in association with tissue remodelling or apoptosis, in response to injury or pathology, or connected with lipid transport or atherosclerotic vascular disease (Fritz & Murphy 1993). It is expressed in many endocrine tissues, including ovary, testis, prostate and uterus (Sylvester & Griswold 1995), pancreas (Scaglia et al. 1995) and breast tissue (Tenniswood et al. 1992, Welsh 1994. Clusterin is known to be an adrenal chromaffin granule constituent and its expression increases in the adrenal in response to histamine or forskolin treatment (Palmer & Christie 1990, Laslop et al. 1993. In gonadal tissue, large amounts of clusterin mRNA have been measured in extracts of ovine corpora lutea (Fleming et al. 1992) and high concentrations of clusterin protein are synthesised in the ram rete testis (Tung & Fritz 1985).There is further evidence for a role for this protein in search of a function (Fritz 1995) in neural tissue, where its expression is upregulated in pathologies such as Alzheimer's disease (Finch & May 1995). Clusterin is induced in reactive astrocytes in response to neurotoxic injury (Zwain et al. 1994, Walton et al. 1996, Tornquist et al. 1997 and appears to have a protective role in the brain, possibly acting as a local inhibitor of the complement cascade (Tornquist et al. 1996).Clusterin expression is known to be suppressed by gonadal steroids in prostate, mammary gland and uterus (Bettuzzi et al. 1992, Wunsche et al. 1998 and by glucocorticoids in brain and kidney cells (Finch & May 1995, Gutacker et al. 1996. These observations led us to investigate clusterin expression in the ovine pituitary gland, with the aim of determining the distribution of clusterin mRNA and protein in the different parts of this tissue. In previous studies of bovine pituitary, the protein was detected in both the anterior and posterior lobes (Laslop et al. 1993). However, the site of clusterin mRNA transcription remains unclear. Aronow et al. (1993) did not detect clusterin mRNA in mouse anterior pituitary, whereas Laslop et al. (1993) (Fleming et al. 1997) was used as a positive control on Northern blots probed with the growth hormone gene probe.Pituitary glands for immunohistochemistry and in situ hybridisation were obtained from five 4-to 6-year-old Romney ewes killed with Euthatal (Southern Veterinary Supplies, Christchurch, New Zealand; 100 mg/kg, i.v.), at the mid-luteal phase of the oestrous cycle. Whole glands were ...