GnRH-Gonadotropes Interactions Revealed by Pituitary Single-cell Transcriptomics in Zebrafish

Area of Science:

• Endocrinology
• Neuroscience
• Genetics

Background:

• Gonadotropin-releasing hormone (GnRH) regulates reproduction by controlling pituitary gonadotropins.
• Zebrafish lacking GnRH (gnrh-/-) are fertile, unlike most vertebrates, indicating alternative regulatory mechanisms.

Purpose of the Study:

• To investigate the role of hypophysiotropic-Gnrh3 and other factors in regulating pituitary gonadotropes in zebrafish.
• To profile gene expression in individual pituitary cells of wild-type and gnrh3-/- zebrafish using single-cell RNA sequencing.

Main Methods:

• Single-cell RNA sequencing of pituitary cells from wild-type and gnrh3-/- adult female zebrafish.
• Analysis of gonadotropin beta subunit (lhb and fshb) expression ratios.
• Identification of enriched receptor transcripts in LH and FSH gonadotropes.
• Chemogenetic ablation of Gnrh3 neurons.

Main Results:

• LH and FSH gonadotropes showed distinct expression patterns of lhb and fshb.
• Gnrh3 deficiency led to fshb downregulation in LH gonadotropes and altered expression of other pituitary hormones.
• Gnrh3 neurons were ablated, decreasing fshb+, lhb+, and double-positive cells.
• Gnrh3 appears to act on LH gonadotropes via Gnrhr2 and influences fshb expression through a non-receptor pathway.

Conclusions:

• Gnrh3 directly influences LH gonadotropes via Gnrhr2, though the functional outcome is unclear.
• Gnrh3 regulates fshb expression in both gonadotrope types, potentially through non-GnRH receptor mechanisms.
• LH secretion and synthesis may be GnRH-independent, but Gnrh3 impacts pituitary cellular organization.
• Coexpression of lhb and fshb in gonadotropes may explain the fertility of gnrh3-/- zebrafish.