Generation and Validation of a GnRH-iCreERT2-tdTomato Mouse Line for Genetic Manipulation in GnRH Neurons

Gonadotropin-releasing hormone (GnRH) neurons play a key role in the hypothalamic-pituitary-gonadal axis. We generated a new GnRH-P2A-iCreERT2-P2A-tdTomato (hereafter referred to as the GnRH-CT-tdT line) knock-in mouse line utilizing CRISPR/Cas9 technology. Characterization analysis of this line revealed that tdTomato expression precisely recapitulates endogenous GnRH expression and iCreERT2 recombines in GnRH neurons with excellent specificity and sensitivity. Therefore, this newly constructed GnRH-CT-tdT mouse line provides a useful tool to perform genetic manipulation in GnRH neurons. As a proof-of-principle, we used this line to investigate the role of Chd7 (Chromodomain helicase DNA-binding protein 7), a gene with its loss-of-function associated with isolated gonadotropin-releasing hormone deficiency (IGD). Surprisingly, ablation of Chd7 in GnRH neurons does not affect the number of GnRH neurons, pubertal onset, and reproductive organ morphology. Therefore, Chd7 is dispensable in GnRH neurons after they have initiated GnRH expression. In summary, the GnRH-CT-tdT mouse line is a valuable tool to study gene function in GnRH neurons and to dissect the pathogenesis of IGD.