Ovarian development and changes in the expression of pituitary gonadotropin subunits during the reproductive cycle of female Malaysian river catfish, Hemibagrus nemurus (Valenciennes, 1840), in captivity

Abstract

Determining the expression level of genes encoding the subunit gonadotropic hormones is critical in understanding the reproductive cycle and gonadal development in fish species. The objectives of this study were to monitor changes in the mRNA expression of three gonadotropin (GtH) subunits (α, FSHβ, and LHβ) during gonadal development of the female Malaysian river catfish, Hemibagrus nemurus, in captivity. In the study a quantitative real-time PCR approach was developed to assess these three mRNA transcript GtH subunit profiles and compare them with ovarian development. The number of transcript encoding GtH hormone, α, FSHβ, and LHβ subunits in pituitary glands of female H. nemurus was measured throughout the reproductive cycle from August 2013 to October 2015, with fish aged 1–27 months. The mRNA expression of GtH subunits increased with ovarian development throughout the reproductive cycle. The FSHβ mRNA level increased during ovarian development, reached its peak in mid-vitellogenesis, and was reduced during ovulation and spawning, whereas the LHβ mRNA level significantly increased in late vitellogenesis and reached its peak during the ovulation and spawning season (April–May). In α subunit, the mRNA level corresponded to FSHβ and LHβ, with a peak expression during ovulation. The findings suggest that FSH was strongly activated during vitellogenesis, whereas LH was involved at the end of gonadal development process, during ovulation, and in the final oocyte maturation.