PARENT SESSION
Follicular Development

MOLECULAR CLONING AND EXPRESSION OF THE INHIBIN RECEPTOR IN THE CHICKEN.

Sweeney, Sheila¹, Yoo, Seung-Jun¹, Johnson, Patricia¹, ¹

ABSTRACT- Inhibin is a gonadal protein hormone composed of an alpha- and beta-subunit. The alpha-subunit is unique to inhibin while the beta-subunit also contributes to the molecule activin. We have previously cloned the chicken inhibin subunits and studied their expression relative to follicle development in the hen. Although it is believed that inhibin plays a role in regulating the reproductive system at both an endocrine and paracrine level, there has been relatively little insight into the mechanism of inhibin action due to the difficulty in isolating the inhibin receptor. Recently, a membrane associated protein was isolated from bovine pituitary based upon its affinity for inhibin and expression in inhibin target cells (Endo. 141:2600, 2000). The cDNA sequence of this protein was found to match a previously reported human cDNA (GenBank Y10523) and the rat cDNA equivalent was subsequently cloned. It is believed that this protein (p120) may be a membrane component of the inhibin signaling pathway. To better understand the role of inhibin in avian follicular development, we have cloned a chicken cDNA homolog of rat p120 by reverse transcription-polymerase chain reaction (RT-PCR). We designed primers based on the rat sequence and cloned a 360 bp fragment from chicken pituitary RNA. Sequence analysis indicated approximately 90% identity within this fragment of the chicken sequence to rat p120. Northern blot analysis was performed using the cloned 32P-labeled chicken inhibin receptor fragment. One main band of expression was detected at approximately 4.0 kb in chicken pituitary and the granulosa cell layer RNA. No expression was observed in the chicken whole ovary or testis, although these tissues are not pure cell types. In addition, no expression was found in the liver which was used as a negative control. In conclusion, we have characterized a chicken homolog to the reported bovine inhibin receptor component as well as identified expression in the primary target organ for inhibin (pituitary) and in the granulosa cell layer (a pure cell layer), another likely target for the hormone. Supported by USDA #00-35203-9116

KEY WORDS: inhibin receptor, chicken, inhibin