Pulsatile exocytosis is functionally associated with GnRH gene expression in immortalized GnRH-expressing cells

Area of Science:

• Neuroendocrinology
• Cellular Biology

Background:

• Pulsatile release of Gonadotropin-releasing hormone (GnRH) is vital for reproductive function.
• The molecular mechanisms behind GnRH's intermittent activity remain largely unknown.
• GnRH gene expression (GnRH-GE) and exocytotic pulses have been observed separately in GnRH cells.

Purpose of the Study:

• To investigate the functional link between GnRH gene expression episodes and exocytotic pulses in GnRH-expressing cells.
• To determine if GnRH-GE triggers exocytosis or vice versa.
• To elucidate the molecular basis of pulsatile GnRH release.

Main Methods:

• Monitoring of GnRH-GE using a GnRH promoter-luciferase reporter in GT1-7 cells.
• Measurement of exocytosis via FM1-43 fluorescence in the same living cells.
• Functional assays involving transcriptional inhibition (actinomycin D) and exocytosis blockage (anti-SNAP-25).

Main Results:

• A strong temporal association was observed between exocytotic pulses and GnRH-GE episodes.
• Inhibition of transcription had minimal impact on exocytosis, suggesting exocytosis is not acutely dependent on gene expression.
• Blockage of exocytosis abolished GnRH-GE pulse activity, indicating exocytosis triggers GnRH-GE.

Conclusions:

• Exocytosis plays a crucial role in triggering episodes of GnRH gene expression.
• A balance between GnRH release and biosynthesis is maintained in GnRH neurons.
• This regulatory mechanism may ensure hypothalamic GnRH neurons are poised to respond to reproductive cues.