Domestic Animal Endocrinology 25 (2003) 389–397 The chicken pituitary expresses an ovoinhibitor-like protein in subpopulations of some, but not all, hormone-producing cell types Cherie M. Oubre a , Els D’Hondt b , Randle W. Moore c , Billy M. Hargis d , Luc R. Berghman e,∗ a Department of Biology, Texas A&M University, 2472 TAMU, College Station, TX 77843-2472, USA b Laboratory of Neuroendocrinology and Immunological Biotechnology, University of Leuven, Naamsestraat 59, B-3000 Leuven, Belgium c USDA ARS SEPRL—Richard B. Russell Research Center, Athens, GA 30605, USA d Poultry Health Research Laboratory, Department of Poultry Science, Fayetteville, AR 72701, USA e Poultry Science and Veterinary Pathobiology, Texas A&M University, 2472 TAMU, College Station, TX 77843-2472, USA Received 17 May 2003; accepted 4 September 2003 Abstract Ovoinhibitor is a serine protease-inhibiting protein that was originally purified from egg whites. It is secreted by the oviduct under the control of estrogen and progesterone and it specifically inhibits serine proteinases such as trypsin and chymotrypsin. During recent attempts to raise monoclonal an- tibodies (Mabs) against chicken bursa of Fabricius proteins, one Mab was produced that specifically recognized chicken ovoinhibitor. This was the first demonstration of ovoinhibitor in an avian immune organ. We presently report on the expression of an ovoinhibitor-like molecule by the pituitary of the chicken as revealed by immunocytochemistry and RT-PCR. Immunofluorescent dual staining ex- periments using the mouse anti-ovoinhibitor Mab in conjunction with polyclonal antibodies against various hypophysial hormones revealed partial co-localization of an ovoinhibitor-like molecule with growth hormone (GH), luteinizing hormone (LH), and pro-opiomelanocortin (POMC), in a subset of the respective hormone producing cells. By contrast, no co-localization with prolactin (PRL) could be reliably demonstrated. RT-PCR of hypophysial mRNA using ovoinhibitor gene-specific primers yielded an amplicon that was 20% shorter than predicted on the basis of the published ovoinhibitor sequence. Sequencing revealed that of the represented exons only the central portion was expressed in the pituitary and that both 5 ′ and 3 ′ ends of each exon had been truncated. While expression of ovalbumin-like serine protease inhibitors (serpins) has been previously reported in ∗ Corresponding author. Tel.: +1-979-845-2994; fax: +1-979-845-1921. E-mail address: berghman@poultry.tamu.edu (L.R. Berghman). 0739-7240/$ – see front matter © 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.domaniend.2003.09.002