Graduate Studies

 

First Advisor

Brett R. White

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Amy Desaulniers, Benny Mote, Clay Lents

Department

Animal Science

Date of this Version

5-2025

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Animal Science (Physiology)

Under the supervision of Professor Brett R. White

Lincoln, Nebraska, May 2025

Comments

Copyright 2025, Caitlin Elizabeth Ross. Used by permission

Abstract

Pigs are the only mammalian livestock species encoding functional proteins for the second form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II). In the first study, GnRHR-II localized to developing germ cells and the connecting piece of ejaculated spermatozoa. Concurrently, GnRH-II was most abundantly produced in the testis compared with other reproductive tract organs and was present within seminal plasma. Moreover, treatment of extended semen with GnRHR-II analogues altered sperm motility, morphology, and kinematics. For remaining studies, we utilized a swine line with ubiquitous knockdown of GnRHR-II (GnRHR-II KD) developed in our laboratory. The second study demonstrated that circulating GnRH-II concentrations were reduced (75%) in GnRHR-II KD boars and GnRHR-II protein levels in transgenic spermatozoa were diminished (60%), but seminal plasma GnRH-II concentrations were similar between GnRHR-II KD and littermate control boars. Functional analyses revealed that GnRHR-II KD boars produced more voluminous semen ejaculates, whereas transgenic sperm exhibited reduced motility, more bent tails, fewer proximal droplets, and decreased membrane integrity. Further, differential proteins detected in seminal plasma-derived extracellular vesicles from GnRHR-II KD versus control ejaculates have been implicated in sperm quality and fertilization. In females, the third study discovered that compared with littermate controls, GnRHR-II KD gilts: 1) secreted 20% less serum 17β-estradiol throughout the follicular phase of the estrous cycle, independently of gonadotropin secretion; 2) exhibited reduced serum concentrations of progesterone upon luteolysis; and 3) possessed similar numbers of preovulatory follicles that were 10% larger. After discovering GnRH-II and GnRHR-II in granulosa cells (GC) and theca cells (TC) of porcine preovulatory follicles, the fourth study determined that GnRHR-II KD females produce 40% less GnRHR-II protein in TC compared with control TC or transgenic GC; however, no protein difference was observed between genotypes for GC. Further, concentrations of GnRH-II in follicular fluid were not different between genotypes. Transgenic preovulatory follicles also displayed fewer hypertrophic TC than control follicles, but similar numbers of hypotrophic GC. Differentially expressed proteins in TC and GC from GnRHR-II KD preovulatory follicles suggest impairments in steroidogenesis and cellular homeostasis. This research demonstrates that GnRH-II and GnRHR-II are novel regulators of porcine semen quality and follicular function.

Advisor: Brett R. White

Download

Share

COinS