MOLECULAR MECHANISMS INVOLVED IN LPXRFA AND GNRH3 REGULATION OF THE BRAIN-PITUITARY-GONAD AXIS OF THE ZEBRAFISH (Danio rerio)

Thumbnail Image

Files

Spicer_umbc_0434D_11553.pdf (7.16 MB)

Links to Files

Permanent Link

http://hdl.handle.net/11603/15661

Collections

UMBC Theses and Dissertations

Author/Creator

Author/Creator ORCID

Date

2016-01-01

Type of Work

dissertations
Text

Department

Marine-Estuarine Environmental Sciences

Program

Marine-Estuarine-Environmental Sciences

Citation of Original Publication

Rights

This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
Distribution Rights granted to UMBC by the author.

Subjects

Gnrh3
Lpxrfa
reproduction
zebrafish

Abstract

Vertebrate reproduction is regulated by the brain-pituitary-gonad axis, which translates internal/external cues into reproductive output. Gonadotropin-releasing hormone (GNRH) stimulates the production of gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), from the pituitary that induce gonadal development. Recently, gonadotropin-inhibitory hormone (GNIH) was implicated in the inhibition of gonadotropin release via direct pituitary contact or GNRH neurons in birds and mammals. While teleost GNIH (Lpxrfa) exhibits stimulatory and/or inhibitory effects on gonadotropins, there is little information on the modes of action by which Lpxrfa exerts its functions. The goal of this study was to elucidate the mechanisms by which Lpxrfa and hypophysiotropic Gnrh3 coordinately regulate reproduction in the zebrafish, by neuroanatomical distribution, functional effects, and ligand-receptor relationships. In adults, Lpxrfa soma are localized to the ventral zone of the periventricular hypothalamus and project throughout the brain/pituitary. Pituitary explants incubated with zebrafish Lpxrfa-3 demonstrate that Lpxrfa acts directly on gonadotropes to downregulate lh? and cg?. Receptor activation studies in vitro demonstrated that Lpxrfa peptides activate only Lpxrf-R2 and -R3 via the PKA/cAMP pathway. Concurrently, zebrafish Lpxrfa-2 and -3 are capable of antagonizing Kiss2'sactivation of Kiss1ra at lower concentrations than those needed to activate Lpxrf-Rs, offering another, more sensitive pathway for Lpxrfa to elicit its functions. This study demonstrated that Lpxrfa also acts on Gnrh3 to exert its negative effect on reproduction. Lpxrfa-3 downregulates gnrh3 expression in the brain in vitro, and Lpxrfa fibers interact with forebrain Gnrh3 soma. Although we could not establish an lpxrfa-/- line, we generated a gnrh3-/- line and determined how lpxrfa is affected by the loss of Gnrh3. While developmental expression profiles of lpxrfa indicate that Gnrh3 may upregulate lpxrfa, lpxrfa expression in gnrh3-/- adult female brains differs from that in wild-type only in the evening, suggesting that Lpxrfa and Gnrh3 participate in the female'sreproductive cyclicity. The gnrh3-/- fish also exhibited no major reproductive phenotypes, having normal gametogenesis and reproduction, suggesting that a compensatory mechanism is being activated. In conclusion, Lpxrfa and Gnrh3 are central neuropeptides in the zebrafish that interact to coordinate and exert functions upon the gonadotropins to regulate the neuroendocrine control of reproduction.