Gonadal defects and hormonal alterations in transgenic mice expressing a single chain human chorionic gonadotropin–lutropin receptor complex

Abstract

To study the effects of premature and chronic ligand-mediated luteinizing hormone receptor (LHR) activation on reproductive development, we have generated transgenic mice expressing a genetically engineered, constitutively active yoked hormone-receptor complex (YHR), in which a fusion protein of human chorionic gonadotropin (hCG) is covalently linked to the N-terminus of rat LHR. YHR-expressing mice (YHR + ) were analyzed at pre-and post-pubertal ages. Relative to wild type (WT) controls, male mice exhibited prepubertal increases in testosterone levels and seminal vesicle weights, and decreases in serum FSH, serum LH, testes weight, and the size of the seminiferous tubules. In adult male YHR + mice, testosterone and LH levels are not significantly different from WT controls. However, FSH levels and testes weights remain decreased. Female YHR + mice undergo precocious puberty with early vaginal opening, accelerated uterine development, enhanced follicular development, including the presence of corpora lutea, and an increase in serum progesterone. At 12 weeks of age, the ovary exhibits a relative increase in the amount of interstitial tissue, comprised of cells that are hypertrophic and luteinized, as well as follicles that are degenerating. Additionally, hemorrhagic cysts develop in approximately 25% of the transgenic mice. These degenerative changes are consistent with an aging ovary suggesting that CG-induced LHR activation in female mice leads to precocious sexual development and ovarian lesions. Taken together, these data indicate that the single chain YHR is functional in vivo and demonstrate that YHR + mice provide a novel system to further understand the reproductive consequences of aberrant LHR activation.

Constitutively active luteinizing hormone receptors: Consequences of in vivo expression

“…Serum and testicular testosterone levels were significantly elevated (Table 2) and, as expected, accompanied by an increase in seminal vesicle weight. Interestingly, seminal vesicle weights were reduced in adult animals (Meehan et al, 2005). The elevated testosterone suppressed LH and FSH levels, the latter remaining suppressed even in 1 year old YHR + mice when testosterone levels were no longer elevated (unpublished observation).…”

“…RT-PCR analysis of RNA from several tissues showed high levels of expression in the gonads of prepubertal and adult animals (Meehan et al, 2005). Expression was also detected in brain and low levels were detected in the heart (Meehan et al, 2005).…”

“…Transgenes containing the complete coding sequence of D556H LHR with a N-terminal myc tag and YHR were cloned under the control of the inhibin α-subunit promoter and transgenic mice were generated by pronuclear injection (Meehan et al, 2005).…”

“…However, neither of these fertile mice showed gonadal specific expression of D556H. Therefore, gonadal expression of the D556H correlated with infertility (Meehan et al, 2005). A limited analysis of the founder mice was performed at 8 months of age.…”

“…1A) and tested its activity in vitro in cell culture (Wu et al, 1996) and in vivo in transgenic mice (Meehan et al, 2005). We also generated mice expressing rat LHR with a D556H mutation (equivalent to the human D578H mutation) as an example of ligand-independent receptor activation (Meehan et al, 2005).…”