GENERAL AND COMPARATIVE ENDOCRINOLOGY 83, W-26 fl%l) Cloning of a Turkey Prolactin cDNA: Expression of Prolactin mRNA throughout the Reproductive Cycle of the Domestic Turkey (Meleagris gallopavo) ERIC A. WONG,* NEAL H. FERRIN, JANET L. SILSBY, AND MOHAMED E. EL HALAWANI *Department of Animal Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0306; and Department of Animal Science, University of Minnesota, St. Paul, Minnesota 55108 Accepted July 26, 1990 A cDNA-encoding turkey prolactin (PRL) has been isolated from a turkey pituitary li- brary. The 953-base pair cDNA clone contains a 229-amino acid open reading frame which consists of a 30-amino acid signal peptide followed by a 199~amino acid mature PRL. The deduced amino acid sequence of turkey PRL shows greater than 90% homology to chicken PRL and X-78% homology to other mammalian prolactins. A mRNA of 1100 nucleotides was detected in total RNA extracted from turkey pituitaries. Levels of PRL mRNA in- creased approximately lo-, 20-, and lOO-fold in photostimulated, laying, and incubating hens, respectively, relative to that found in nonphotostimulated hens. The corresponding increases in plasma PRL levels were 2-, 5.5, and 50-fold and in pituitary PRL content were 2-. 4-, and 13.4-fold, respectively. The transition from incubation to the photorefractory phase resulted in a IO-fold reduction in PRL mRNA. a 3.7-fold decrease in pituitary PRL, and a dramatic 50-fold decrease in plasma PRL. The changes in the abundance of pituitary PRL mRNA appear to be related to the changes in PRL-releasing activity observed at each of the reproductive stages. This study provides the first characterization of pituitary PRL mRNA and its comparison with plasma and pituitary PRL levels during the avian reproductive CyCk. 0 1991 Academic Press. Inc Prolactin (PRL) is a member of a family of related hormones which includes growth hormone, placental lactogen, and prolif- erin. These hormones share structural and biological properties and are thought to have evolved from a common ancestral gene via a gene duplication (Niall et al., 1971; Miller and Eberhardt, 1983; Nicoll et al., 1986). In vertebrates, PRL appears to be involved in regulating a variety of phys- iological functions such as lactogenesis in mammals (Shiu and Friesen, 1980) or osmo- regulation in fish (Ensor, 1978; Clarke and Bern, 1980). In birds the role of PRL is not well understood, but it appears to be in- volved in stimulating crop “milk” produc- tion in Columbiformes as well as growth and osmoregulation (Ensor, 1978; deVlam- ing, 1979; Clarke and Bern, 1980). Onset of incubation activity in turkey hens is corre- lated with declining levels of gonadotropins and a dramatic rise in circulating PRL lev- els. It is this rise in PRL which has been implicated as the cause for cessation of ovulation, ovarian regression, and induc- tion of incubation (Sharp et al., 1984; Buntin, 1986; Hall et al., 1986; El Halawani et al., 1988). To study the expression of PRL at the mRNA level in birds, an avian PRL cDNA is necessary. cDNAs encoding chicken PRL have recently been cloned (Hanks et al., 1989; Kumar et al., 1989; Watahiki et al., 1989). We report here the isolation of a cDNA-encoding turkey PRL (tPRL) and its use in determining the steady-state levels of tPRL mRNA from pi- tuitaries of hens at different stages of the reproductive cycle. 18 0016~6480/91 $1.50 Copyright 0 1991 by Academic Press. Inc. All rights of reproduction in any form reserved.