Roles for primary cilia in gonadotrophin-releasing hormone neurones in the mouse

During embryonic development, gonadotrophin-releasing hormone (GnRH) neurones make an extraordinary migration out of the nose and into the brain where, in adulthood, they drive the pituitary regulation of gonadal function and fertility. Primary cilia are antennae-like, immotile organelles that project from the surface of nearly all cells, including GnRH neurones. Links between defects in primary cilia and a variety of human pathologies have been discovered that suggest a role for primary cilia in embryogenesis and reproductive function. The present study aimed to investigate whether GnRH neurone primary cilia are critical for their embryonic migration and the adult control of fertility. To achieve this, we used a Cre-loxP strategy to selectively disrupt primary cilia by deleting Kif3a, an intraflagellar transport protein family member essential for primary cilia assembly and function, specifically in GnRH neurones. Confocal analysis revealed that, in Kif3a(fl/fl) (WT-Kif3a) controls, all GnRH neurones possessed primary cilia, whereas, in GnRH-Cre(+/-) ;Kif3a(fl/fl) (GnRH-Kif3aKO) mice, 60% of GnRH neurones lacked any evidence of primary cilia and the remaining 40% possessed only stunted primary cilia (< 2 μm). Despite abolishing normal primary cilia assembly in GnRH neurones from embryogenesis, adult GnRH neurone distribution and reproductive function was remarkably normal. The total number of GnRH neurones was the same in GnRH-Kif3aKO and WT-Kif3a controls; however, a significant increase (25%) was identified in the number of GnRH neurones sampled through the midpoint of the rostral pre-optic area in GnRH-Kif3aKO mice (P < 0.05). The time to vaginal opening was not different in GnRH-Kif3aKO mice, although they displayed significantly advanced first oestrus (P < 0.05), and oestrous cycle length was increased (P < 0.05). However, females displayed normal basal levels of luteinising hormone, responded normally to oestrogen-induced negative- and positive-feedback, and displayed normal fecundity. Taken together, these data suggest that primary cilia and associated signal transduction pathways play a role in the topographical distribution and specific functions of GnRH neurones; however, they are not essential for fertility.