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Gonadotropin-releasing hormone 3 and gonadotropes relationships in female zebrafish pituitary revealed by single-cell transcriptomics

ABSTRACT: Gonadotropin-releasing hormone (GnRH) governs reproduction in vertebrates by regulating pituitary gonadotropins. Zebrafish, however, is an exception as gnrh3–/– fish, which lack the hypophysiotropic GnRH3, are fertile, suggesting that zebrafish utilizes a Gnrh-independent mechanism to regulate reproduction. To elucidate the role of Gnrh3 and the Gnrh-independent mechanisms that regulate the pituitary gonadotropes, we profiled the gene expression in individual pituitary cells of wild-type and gnrh–/– adult female zebrafish and identified transcriptionally defined cell types. The classical Lh and Fsh gonadotropes expressed both gonadotropin beta subunits with a ratio of 13:1 (lhb:fshb) and 40:1 (fshb:lhb), respectively. We discovered that Lh gonadotropes predominantly express genes encoding receptors for Gnrh (gnrhr2), thyroid hormone, estrogen, dopamine, and steroidogenic factor 1 (SF1). No Gnrh receptor expression was enriched in Fsh gonadotropes, instead, the expression of cholecystokinin receptor (cckrb) and galanin receptor (gal1rb) were enriched in these cells. The hereditary loss of Gnrh3 gene resulted in downregulation of fshb in Lh gonadotropes. Likewise, targeted chemogenetic ablation of Gnrh3 neurons led to a decrease in the number of fshb+/lhb+ cells. Our studies suggest that Gnrh3 directly acts on Lh gonadotropes through Gnrhr2, but the outcome of this interaction is still unknown. Gnrh3 also regulates fshb expression, probably via a non-Gnrh receptor route. Altogether, while Lh secretion and synthesis are likely regulated by multiple factors in a Gnrh-independent manner, Gnrh3 seems to play a role in the cellular organization of the pituitary in zebrafish.

ORGANISM(S): Danio rerio

PROVIDER: GSE272806 | GEO | 2024/11/20

REPOSITORIES: GEO

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			Action	DRS
		Other
	GSE272806_Integrated_filtered_barcodes.tsv.gz	Tabular
	GSE272806_Integrated_filtered_genes.tsv.gz	Tabular
	GSE272806_Integrated_filtered_matrix.mtx.gz	Other
	GSE272806_Integrated_filtered_metadata.csv.gz	Csv

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Project description:Gonadotropin-releasing hormone (GnRH) is secreted in brief pulses from the hypothalamus. GnRH regulates follicle-stimulating hormone b-subunit (FSHb) gene expression in pituitary gonadotropes in a frequency-sensitive manner that is central to reproductive physiology. The mechanisms underlying the preferential and paradoxical induction of FSHb by low frequency GnRH pulses are incompletely understood. Here, we identify growth differentiation factor 9 (GDF9) as a novel autocrine inducer of FSHb gene expression. GDF9 gene expression was preferentially suppressed by high frequency GnRH pulses due to reduced transcription. Exogenous GDF9 induced FSHb mRNA expression and knockdown or immunoneutralization of GDF9 reduced FSHb gene expression. Treatment with GDF9 stimulated Smad2/3 phosphorylation. The activin receptor-like kinase (ALK) receptor inhibitor SB-505124 antagonized GDF9-induced Smad2/3 phosphorylation and FSHb mRNA induction. Smad2 and Smad3 knockdown studies indicated that the induction of FSHb by GDF9 involves both Smad2 and Smad3. GDF9 and GnRH synergistically induced FSHb mRNA expression and high frequency GnRH pulses suppressed GDF9. We hypothesized that GDF9 contributes to a regulatory loop that tunes the GnRH frequency-response characteristics of the FSHb gene. To test this, we determined the effects of GDF9 knockdown on FSHb induction at different GnRH pulse frequencies using a parallel perifusion system. Reduction of GDF9 shifted the characteristic pattern of GnRH pulse frequency sensitivity. These results identify GDF9 as contributing to an incoherent feed-forward loop, comprised of both intracellular and secreted elementscomponents, that regulates FSHb expression in response to activation of the cell surface GnRH receptor. LbT2 microarray datasets as well as RNA-Seq data (GSE42120) were interrogated to determine the levels of expression of ALK4/5/7. LM-NM-2T2 cells were transfected with either scrambled siRNA or Gas siRNA for 48 h. RNA samples were snap-frozen in dry ice prior to whole-genome expression profiling analysis using MouseWG-6 v2.0 Expression BeadChip (Illumina, San Diego, CA). A total of 6 concentrated conditioned media samples were independently prepared: 3 replicates from control siRNA-treated cells, and 3 replicates from Gas siRNA-treated cells. This submission represents the microarray component of study.

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Gonadotropin-releasing hormone 3 and gonadotropes relationships in female zebrafish pituitary revealed by single-cell transcriptomics

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