Follicle stimulating hormone (FSH) and luteinizing hormone (LH) gene expression during larval development in Senegalese sole ( Solea senegalensis)

The gonadotropins (GTHs), follicle stimulating hormone (FSH) and luteinizing hormone (LH), determine the reproductive competence of adult breeders, but also participate in the establishment of the reproductive axis at early stages of life. The present study aimed at studying, by real-time qPCR, the gene expression levels of GTH subunits (FSHβ, LHβ and the common glycoprotein α -GPα- subunit) during early development in Senegalese sole, from 1 to 100 days post hatching (dph). The FSHβ, LHβ and GPα transcripts were first detected at 1, 5 and 3 dph, respectively. Transcript levels of FSHβ, and GPα, increased continuously to peak levels at mid metamorphosis (15 dph), decreasing thereafter; levels were maintained low until a second increment detected at 90 and 100 dph. Contrarily, transcript levels of LHβ were very low and only detectable around metamorphosis. All three subunits were highly expressed in 1-year old soles, with FSHβ and GPα transcript levels 10-fold higher than those of LHβ. These results suggest, i) activity of the reproductive axis early after hatching (1 dph), which was highest during the metamorphic climax and, ii) a predominant role of FSH, rather than LH, in the early development of the reproductive axis in Senegalese sole.