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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #343751

Title: Utilization of GnRH-II receptor knockdown pigs to explore steroidogenesis in the testis

item DESAULNIERS, A - University Of Nebraska
item CEDERBERG, R - University Of Nebraska
item MILLS, G - University Of Nebraska
item Lents, Clay
item WHITE, B - University Of Nebraska

Submitted to: Transgenic Animal Research Conference
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2017
Publication Date: 10/1/2018
Citation: Desaulniers, A.T., Cederberg, R.A., Mills, G.A., Lents, C.A., White, B.R. 2018. Utilization of GnRH-II receptor knockdown pigs to explore steroidogenesis in the testis [abstract]. Transgenic Animal Research Conference. 27(5):471-472.

Interpretive Summary:

Technical Abstract: The historical form of gonadotropin-releasing hormone (GnRH-I) is well established as an important regulator of mammalian reproduction. More recently, a second form of GnRH (GnRH-II) was identified in mammals. GnRH-II is also a decapeptide, differing from GnRH-I by only 3 amino acids (His5, Trp7, Tyr8). Unlike GnRH-I, the gene for GnRH-II is ubiquitously expressed, opening the possibility of its function in other reproductive tissues. Additionally, a 7-transmembrane, G protein-coupled receptor specific for GnRH-II (GnRHR-II) was discovered. The GnRHR-II is produced by a different gene, has only 40% homology to GnRHR-I and contains an intracytoplasmic tail that is absent in GnRHR-I. The GnRHR-II gene is widely expressed throughout the body with transcript levels most abundant in peripheral tissues rather than brain regions associated with gonadotropin secretion. Many species (e.g., cow, sheep and human) retain the GnRHR-II gene but lack the appropriate coding sequence to produce a full-length protein due to gene coding errors, whereas other animals lack the gene (e.g., mouse) or most exons (e.g., rat) entirely. In contrast, old world monkeys, musk shrews and pigs encode a functional GnRHR-II. A biological role for GnRHR-II in mammals has been elusive, largely due to the lack of animal models to examine functional receptors. Binding of GnRH-II to its receptor has been linked to the interaction between nutritional status and sexual behavior in females and both the GnRH-II and GnRHR-II genes are overexpressed in human reproductive tumors, representing potential targets for cancer treatments. Furthermore, research from our laboratory indicates that the GnRH-II/GnRHR-II system regulates LH-independent testosterone production within the porcine testis. To further explore the role of GnRH-II and its receptor in line testis biology, we produced a line of GnRHR-II knockdown (KD) swine that has 70% lower testicular GnRHR-II mRNA levels compared to littermate controls. Founder animals were produced via sub-zonal microinjection of zygotes with lentiviral particles produced from a construct overexpressing both shRNA specific to the porcine GnRHR-II and ZsGreen1. During pubertal development, testosterone concentrations tended to be reduced in transgenic boars (P < 0.06) whereas LH release was unaffected. Also, predicted testis volumes of GnRHRII KD males were smaller than controls (P < 0.05), despite similar body weights (P > 0.05). In mature boars, diurnal testosterone secretion was reduced by 82% in GnRHR-II KD compared to control animals (0.8 vs. 4.1 ng/mL; P < 0.05). Moreover, mass spectrometry results revealed that 10 different steroid hormones were significantly reduced in serum of GnRHR-II KD boars. Sections of the testicular parenchyma from GnRHR-II males contained fewer Leydig cells and seminiferous tubules compared to controls that surprisingly, had undergone significant hypertrophy. Consistent with this, protein levels of some steroidogenic enzymes were elevated in transgenic boars. Thus, the testes of GnRHR-II KD males are trying to produce testosterone in a futile attempt to offset dramatically reduced circulating levels of testosterone. Understanding how GnRH-II and its receptor regulate testicular function will lead to new technologies to improve fertility in boars, enhancing the sustainability/profitability of pork producers. Supported by Agriculture and Food Research Initiative (AFRI) Competitive Grants no. 2017-67015-26508 to BRW and no. 2011-67015-30059 to CAL from the USDA National Institute of Food and Agriculture (NIFA) as well as a USDA-NIFA AFRI ELI predoctoral fellowship (2017-67011-26036) to ATD.