Follicle-stimulating hormone beta, luteinizing hormone beta and glycoprotein hormone alpha subunit mRNA levels in artificially maturing Japanese eel Anguilla japonica and naturally maturing New Zealand longfinned eel Anguilla dieffenbachii

Abstract

cDNAs for three subunits of gonadotropin, namely follicle‐stimulating hormone (FSH) β, luteinizing hormone (LH) β and glycoprotein hormone (GP) α, of the New Zealand longfinned eel Anguilla dieffenbachii were cloned. Based on their nucleotide sequences, which were more than 98% identical to those of the Japanese eel Anguilla japonica, a real‐time reverse transcription–polymerase chain reaction method for the quantitative assay of gonadotropin subunit mRNAs of the two eel species was developed using the same primer sets. Accordingly, changes in pituitary gonadotropin mRNA levels were analyzed in female Japanese eels induced to develop artificially by salmon pituitary homogenate (SPH) treatment and in naturally maturing female New Zealand longfinned eels collected from the wild. In Japanese eels, the FSH β mRNA level was very high at the previtellogenic stage (PV) and decreased remarkably after SPH injection, whereas the reverse was seen in New Zealand longfinned eels. The mRNA levels of LH β and GP α increased during gonadal development in both species, albeit to a much greater extent in Japanese eels. As the Japanese and New Zealand longfinned eels are closely related species of the same genus, the different gonadotropin expression patterns are likely to reflect differences in maturational conditions rather than species. Our findings are indicative of aberrant gonadal development and may explain the poor quality eggs obtained from artificially matured Japanese eels.

Differential Regulation of Luteinizing Hormone and Follicle-Stimulating Hormone Expression during Ovarian Development and under Sexual Steroid Feedback in the European Eel

“…These results are in agreement with our previous studies, where an increase in pituitary content of LH hormone, as measured by RIA, was observed in experimentally matured eels [43]. In addition, our results are in agreement with those obtained in the Japanese eel, showing an increase in LHβ and GPα mRNA levels during the induction of ovarian development [44, 45]. These data indicate that the increase in pituitary LH synthesis during induced ovarian development in the eel is mediated by increases in LHβ and GPα mRNA levels.…”

“…In contrast, our results from in situ hybridization as well from dot-blot analysis indicate that, in untreated female silver eels, both FSHβ and LHβ were detectable and expressed at a low level, suggesting potential roles of the two gonadotropins during the early stages of vitellogenesis. Similarly, a low expression of FSHβ at the early vitellogenic stage was also observed in the New Zealand long-finned eel [45] contrasting a high expression of FSHβ found in the Japanese eel [45]. These studies suggest some common and some different features in the expression and potential roles of LH and FSH during gonadal development among different eel species.…”

“…Supposing that FSH hormone synthesis and release follow the same profile as its mRNA expression, it is likely that FSH does not play a crucial role at the final stages of eel gonadal development, in contrast with LH. However, we must be aware that these results were obtained under experimentally induced maturation and hormonal patterns might be different under natural conditions, as suggested by recent results obtained in New Zealand long finned eels, Anguilla dieffenbachii [45]. …”

Study of male reproductive physiology and sperm conservation in the european EEL ( Anguilla anguilla, L.)

“…Probably the reduction in FSHβ in the present study has been caused by an increase in testosterone induced by hCG injection. This decrease in the FSHβ expression has been also observed in European eel female after salmon pituitary extracts treatment [58], likewise in Japanese eel female [61][62][63] injected with salmon pituitary extracts or salmon gonadotropin fraction. In order to know if the gonadotropin profiles observed in artificially matured eels are similar to the natural pattern, Saito et al [63] compared the gonadotropin expression in naturally maturing New Zealand longfinned eel with artificially maturing Japanese eel.…”

“…This decrease in the FSHβ expression has been also observed in European eel female after salmon pituitary extracts treatment [58], likewise in Japanese eel female [61][62][63] injected with salmon pituitary extracts or salmon gonadotropin fraction. In order to know if the gonadotropin profiles observed in artificially matured eels are similar to the natural pattern, Saito et al [63] compared the gonadotropin expression in naturally maturing New Zealand longfinned eel with artificially maturing Japanese eel. With the first injections a quickly decrease in the FSHβ expression was observed in artificially maturing female eels, whereas in New Zealand longfinned eels in mid-vitellogenic stage a FSHβ increase was observed.…”