In both mammals and teleosts, spermiogenesis, i.e. the differentiation of postmeiotic spermatids to spermatozoa, is thought to be controlled by androgens produced in response to the activation of the LH/choriogonadotropin receptor (LHCGR) by the luteinizing hormone (LH) in the interstitial Leydig cells. Accordingly, LH controls the expression of genes involved in the steroidogenic cascade in Leydig cells. Interestingly, in some teleosts, such as the flatfish Senegalese sole (Solea senegalensis) LH can also regulate different genes implied in spermiogenesis and sperm maturation. However, a non-steroidal role of LH mediating the spermiogenic pathway in vertebrates remains unclear. In Senegalese sole, spermatogenesis occurs in spermatocysts which develop within semi-cystic seminiferous lobules (SLs), where round spermatids are released from the supporting Sertoli cells into the SL lumen (SLL) where they elongate and transform into spermatozoa. Using this model, here we show that sole spermatids released into the SLL express the homolog of the tetrapod LHCGR (Lhcgrba) in the plasma membrane. Immunodetection of both native Lh and intramuscularly injected recombinant Lh (rLh) bound to free spermatids in the SLL indicated that circulating gonadotropin can reach the intratubular compartment. In vitro incubation of isolated spermatids with rLh specifically promoted their differentiation into spermatozoa in a dose-dependent manner, while homologous recombinant follicle-stimulating hormone or steroid hormones had no effect. Using a repertoire of molecular markers and inhibitors, we find that the Lh-Lhcgrba induction of spermiogenesis is mediated through a cAMP/PKA signaling pathway that initiates the transcription of genes potentially involved in the function of spermatozoa. The Lhcgrba expression in late spermatocytes and/or spermatids was also found in distantly related fishes with cystic spermatogenesis, such as zebrafish (Danio rerio) and gilthead seabream (Sparus aurata), suggesting that this feature is likely conserved in teleosts regardless of the type of germ cell development . These data reveal a novel role of Lh in vertebrate germ cells, whereby a Lhcgrbaactivated signaling cascade in haploid spermatids directs gene expression and the progression of spermiogenesis

27th Conference of European Comparative Endocrinologists (CECE 2014), 25-29 August 2014, Rennes, France.-- 1 page

Funded by the Spanish Fundación Ramón Areces

Peer Reviewed