Expression of kisspeptins in the hypothalamus of the sea bass (Dicentrarchus labrax L.) is regulated by sex steroids

Abstract

In mammals, Kiss-1 appears to be critical for GnRH secretion and the initiation of puberty. There is evidence that steroid hormones regulate Kiss-1 mRNA expression in rodents, primates, and sheep. This study is conducted in the sea bass, an important farmed fish in which the control of reproduction is essential for the sustainability of its production. Recently, two kisspeptin (kiss1 and kiss2) genes and their expression sites in the brain have been described. The aim of this work is to test whether steroid hormones regulate kisspeptin expression in the brain of sea bass using both in situ hybridization and quantitative real-time PCR techniques. We examined the brains of testis-intact (control) and gonadectomized (GDX) sea bass males, as well as gonadectomized males that received testosterone (GDX+T) replacement. We also analyzed the brains of ovary-intact (control), ovariectomized (OVX) and ovariectomized sea bass females that received estradiol (OVX+E) replacement. In males, kiss1 expression decreased after gonadectomy and increased with T treatment in the rostral mediobasal hypothalamus (MBH) and the nucleus of the posterior recces (NRP). While kiss2 increased in rostral MHB and the dorsal part of the nucleus of the lateral recess (NRLd) after gonadectomy and decreased with T treatment. The relative mRNA expression profiles of kiss1 and kiss2 in the hypothalamus supported these findings. Furthermore, the pituitary expression of fsh¿ was significantly low in GDX+T. In females, kiss1 decreased in NRP while kiss2 incresed in both rostralMBH and NLRd in OVX+E. The expression levels of kiss genes showed no significant differences among groups, although the pituitary expression of fsh¿ showed low levels in OVX+E. These data suggest that although kisspeptins may play a role in the feedback regulation of the reproductive hormone cascade in sea bass, their modes of action remain elusive. Funded by MICINN-AGL2009-11086 and GV-PROMETEO/2010/003. MVA supported by a FPI fellowship-MICINN (Spain).