GnRH signaling pathways regulate differentially the tilapia gonadotropin subunit genes

Area of Science:

• Endocrinology
• Molecular Biology
• Fish Reproduction

Background:

• Gonadotropin-releasing hormone (GnRH) is a key regulator of reproduction in vertebrates.
• Understanding GnRH signaling pathways is crucial for fish aquaculture and reproductive biology.

Purpose of the Study:

• To investigate the specific intracellular signaling pathways involved in salmon gonadotropin-releasing hormone (sGnRH)-induced gonadotropin subunit gene expression in tilapia pituitary cells.
• To elucidate the roles of protein kinase C (PKC), extracellular signal-regulated kinase (ERK), and protein kinase A (PKA) in mediating these responses.

Main Methods:

• Primary tilapia pituitary cells were cultured and exposed to sGnRH, phorbol ester (TPA), forskolin, and specific inhibitors (GF109203X, H89, PD98059).
• Levels of phosphorylated ERK (pERK) and mRNA for alpha, FSHbeta, and LHbeta subunits were quantified using Western blot and RT-PCR, respectively.

Main Results:

• sGnRH increased pERK levels and mRNA expression of alpha, FSHbeta, and LHbeta subunits.
• PKC activation was required for sGnRH-induced pERK and alpha/LHbeta mRNA levels, but not FSHbeta.
• ERK activation, modulated by PKC, was essential for alpha and LHbeta mRNA induction.
• PKA activation by forskolin also influenced pERK and gonadotropin subunit mRNA levels, suggesting a role in FSHbeta regulation.

Conclusions:

• sGnRH employs distinct signaling pathways to regulate tilapia gonadotropin subunit gene expression.
• The PKC-ERK cascade mediates the induction of alpha and LHbeta subunit mRNAs.
• FSHbeta subunit mRNA induction is independent of the ERK pathway and likely involves cAMP-PKA signaling or other mitogen-activated protein kinase cascades.