Project Number: 8042-31000-110-005-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jun 1, 2019
End Date: May 31, 2022
Agricultural Research Service is interested in delineating the molecular basis of egg production in turkey hens with an overarching goal of reducing the large variation in egg production that exists within commercial flocks.
Low-egg-producing-hens (LEPH) ovulate less frequently than high-egg-producing-hens (HEPH), as a result of differences in the function of the hen’s HPG axis that ultimately impact reproductive performance. Further understanding of HPG axis regulation of ovulation and how this regulation is distorted in LEPH is necessary to increase the reduced reproductive performance seen in turkey breeding hens. Improvement of the reproductive efficiency of LEPH would greatly decrease the cost of housing and feeding additional breeding hens to meet poult production needs as well as decrease the amount of money lost to reduced poult production. Through deep sequencing of RNA in multiple tissues within the HPG axis of LEPH and HEPH, we identified differences in expression of genes within important gene networks controlling reproduction. Selected results were confirmed by RT-qPCR. These results implicated reduced responsiveness of tissues within the HPG axis of LEPH to trophic stimulation. This reduced responsiveness was confirmed in vitro for pituitary responsiveness to GnRH, F1 granulosa cell responsiveness to LH, and SWF cell responsiveness to FSH. These findings support our overall hypothesis that reduced functionality of the HPG axis in LEPH leads to reduced ovulation and ultimately egg production. Two common themes emerged from our transcriptional profiling of HPG tissues in LEPH and HEPH. Within multiple tissues, differences in activation levels of estrogen and thyroid hormone receptors were implicated. We hypothesize that these differences in estrogenic and/or thyroidal stimulation account for the observed differences in responsiveness of HPG tissues between LEPH and HEPH. Differential expression of genes within the HPG axis could be regulated transcriptionally or post-transcriptionally. To define the mechanisms underlying the differences in egg production among individual turkey hens within a flock, the following Specific Aims will be addressed: 1) Define the influences of estrogen and thyroid hormone on responsiveness of pituitary gonadotrophs to GnRH and GnIH in LEPH and HEPH. 2) Characterize effects of estrogen and thyroid hormone on responsiveness of ovarian granulosa and SWF cells to gonadotropins in LEPH and HEPH. 3) Identify transcription factor proteins and miRNA that regulate important differentially expressed genes within the HPG axis of LEPH and HEPH.