Single-Cell Gene Profiling Reveals Social Status-Dependent Modulation of Nuclear Hormone Receptors in GnRH Neurons in a Male Cichlid Fish.

Satoshi Ogawa,Ishwar S Parhar

doi:10.3390/ijms21082724

Satoshi Ogawa, Ishwar S Parhar

Open Access

https://doi.org/10.3390/ijms21082724

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Abstract

Gonadotropin-releasing hormone (GnRH) is essential for the initiation and maintenance of reproductive functions in vertebrates. To date, three distinct paralogue lineages, GnRH1, GnRH2, and GnRH3, have been identified with different functions and regulatory mechanisms. Among them, hypothalamic GnRH1 neurons are classically known as the hypophysiotropic form that is regulated by estrogen feedback. However, the mechanism of action underlying the estrogen-dependent regulation of GnRH1 has been debated, mainly due to the coexpression of low levels of estrogen receptor (ER) genes. In addition, the role of sex steroids in the modulation of GnRH2 and GnRH3 neurons has not been fully elucidated. Using single-cell real-time PCR, we revealed the expression of genes for estrogen, androgen, glucocorticoid, thyroid, and xenobiotic receptors in GnRH1, GnRH2, and GnRH3 neurons in the male Nile tilapia Oreochromis niloticus. We further quantified expression levels of estrogen receptor genes (ERα, ERβ, and ERγ) in three GnRH neuron types in male tilapia of two different social statuses (dominant and subordinate) at the single cell level. In dominant males, GnRH1 mRNA levels were positively proportional to ERγ mRNA levels, while in subordinate males, GnRH2 mRNA levels were positively proportional to ERβ mRNA levels. These results indicate that variations in the expression of nuclear receptors (and possibly steroid sensitivities) among individual GnRH cells may facilitate different physiological processes, such as the promotion of reproductive activities through GnRH1 neurons, and the inhibition of feeding and sexual behaviors through GnRH2 neurons.

Highlights

Gonadotropin-releasing hormone (GnRH, known as luteinizing hormone-releasing hormone, LHRH) is essential for the initiation and maintenance of reproductive functions
Plasma estrogen levels were significantly (p < 0.05) high in subordinate (211.9 ± 24.7 pg/mL) as compared with control males (72.4 ± 20.2 pg/mL), but there was no difference between dominant (146.8 ± 47.8 pg/mL) and subordinate or control males (Figure 1)
We found that GnRH2 and ERβ mRNA levels were positively correlated in GnRH2 neurons of subordinate males, while at the single cell level, ERα mRNA levels were higher in subordinate males compared to dominant males

Summary

Introduction

Gonadotropin-releasing hormone (GnRH, known as luteinizing hormone-releasing hormone, LHRH) is essential for the initiation and maintenance of reproductive functions. Prenatal and adult GnRH1 neurons in rodents and GT1-7 GnRH-secreting neurons possess the ER subtypes (ERα and ERβ) mRNA and protein [7]. These results strengthen the assumption that estrogen may directly regulate gene expression in GnRH1 neurons. Divergent results (see reviews [8,9,10]) and the failure to observe classical ERα protein and mRNA in GnRH1 neurons led to the general hypothesis that estrogen regulates GnRH1 neurons via nongenomic mechanisms such as transsynaptic [11], glial interactions [12], methylation [13], interaction with signaling kinases [14], or through membrane estrogen receptors [15]

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