Molecular cloning and localization of the luteinizing hormone beta subunit and glycoprotein hormone alpha subunit from Japanese anchovy Engraulis japonicus

Effects of Luteinizing Hormone Releasing Hormone A2 on Gonad Development in Juvenile Amur Sturgeon, Acipenser schrenckii, Revealed by Transcriptome Profiling Analysis

Acipenser schrenckii is an economically important aquatic species whose gonads require particularly long times to reach sexual maturity. Luteinizing hormone plays important roles in gonad development, and luteinizing hormone releasing hormone A2 (LH-A2) is used as an oxytocin to promote ovulation in aquaculture of A. schrenckii. In this study, we aimed to determine the effects of LH-A2 on gonad development in juvenile A. schrenckii through transcriptome profiling analysis of the pituitary and gonads after LH-A2 treatment at a dose of 3 μg/kg. The 17β-estradiol (E2) levels gradually increased with LH-A2 treatment time, and significantly differed from those of the control group on days 5 and 7 (p < 0.01). However, the content of testosterone (Testo) gradually decreased with LH-A2 treatment time and showed significant differences on day 3 (p < 0.05), and on days 5 and 7 (p < 0.01), compared to those in the control group. Thus, LH-A2 promotes the secretion of E2 and inhibits the secretion of Testo. Transcriptome profiling analysis revealed a total of 2,883 and 8,476 differentially expressed genes (DEGs) in the pituitary and gonads, respectively, thus indicating that LH-A2 has more regulatory effects on the gonads than the pituitary in A. schrenckii. Signal transduction, global and overview maps, immune system, endocrine system and lipid metabolism were the main enriched metabolic pathways in both the pituitary and gonads. Sixteen important genes were selected from these metabolic pathways. Seven genes were co-DEGs enriched in both signal transduction and endocrine system metabolic pathways. The other co-DEGs were selected from the immune system and lipid metabolism metabolic pathways, and showed mRNA expression changes of >7.0. The expression of five DEGs throughout LH-A2 treatment was verified to show the same patterns of change as those observed with RNA-seq, indicating the accuracy of the RNA-seq in this study. Our findings provide valuable evidence of the regulation of gonad development of juvenile A. schrenckii by LH-A2 and may enable the establishment of artificial techniques to regulate gonad development in this species.

Development of a flatfish-specific enzyme-linked immunosorbent assay for Fsh using a recombinant chimeric gonadotropin

In flatfishes with asynchronous and semicystic spermatogenesis, such as the Senegalese sole (Solea senegalensis), the specific roles of the pituitary gonadotropins during germ cell development, particularly of the follicle-stimulating hormone (Fsh), are still largely unknown in part due to the lack of homologous immunoassays for this hormone. In this study, an enzyme-linked immunosorbent assay (ELISA) for Senegalese sole Fsh was developed by generating a rabbit antiserum against a recombinant chimeric single-chain Fsh molecule (rFsh-C) produced by the yeast Pichia pastoris. The rFsh-C N- and C-termini were formed by the mature sole Fsh β subunit (Fshβ) and the chicken glycoprotein hormone common α subunit (CGA), respectively. Depletion of the antiserum to remove anti-CGA antibodies further enriched the sole Fshβ-specific antibodies, which were used to develop the ELISA using the rFsh-C for the standard curve. The sensitivity of the assay was 10 and 50 pg/ml for Fsh measurement in plasma and pituitary, respectively, and the cross-reactivity with a homologous recombinant single-chain luteinizing hormone was 1%. The standard curve for rFsh-C paralleled those of serially diluted plasma and pituitary extracts of other flatfishes, such as the Atlantic halibut, common sole and turbot. In Senegalese sole males, the highest plasma Fsh levels were found during early spermatogenesis but declined during enhanced spermiation, as found in teleosts with cystic spermatogenesis. In pubertal males, however, the circulating Fsh levels were as high as in adult spermiating fish, but interestingly the Fsh receptor in the developing testis containing only spermatogonia was expressed in Leydig cells but not in the primordial Sertoli cells. These results indicate that a recombinant chimeric Fsh can be used to generate specific antibodies against the Fshβ subunit and to develop a highly sensitive ELISA for Fsh measurements in diverse flatfishes.

Identification and distribution of three gonadotropin-releasing hormone (GnRH) isoforms in the brain of a clupeiform fish, Engraulis japonicus

To gain a better understanding of the reproductive endocrinology of a primitive order clupeiform fish (Japanese anchovy, Engraulis japonicus), cDNAs encoding three gonadotropin-releasing hormone (GnRH) isoforms were isolated from the brain, and their distribution was analyzed using insitu hybridization (ISH). The three GnRH isoforms include GnRH1 (herring GnRH), GnRH2 (chicken GnRH-ll) and GnRH3 (salmon GnRH), and their full-length cDNAs encode 88, 86, and 89 deduced amino acids (aa), respectively. Alignment analysis of Japanese anchovy GnRH isoforms showed lower identities with other teleost fish. The major population of GnRH1 neurons was localized in the ventral telencephalon (VT) and nucleus preopticus (NPO) of the preoptic area (POA) with minor population in the anterior olfactory bulb (OB). GnRH2 neurons were restricted to the midbrain tegmentum (MT), specific to the nucleus of the medial longitudinal fasciculus (nMLF). GnRH3 neurons were localized in the olfactory nerve (ON), ventral OB, and transitional area between OB and ON. Interestingly, GnRH1 neurons were also localized in the olfactory bulb, in addition to its major population in the preoptic area. These results indicate the differential distribution of three GnRH isoforms expressed in the brain of the Japanese anchovy.