Molecular Cloning of the GTH II-β Subunit cDNA and Profiles
of GTH mRNA Transcript Levels at Different Stages in the Wild
Female Japanese Eel
Y. S. Han 1, I C. Liao2, W. N. Tzeng 1, Y. S. Huang3 and J. Y. L. Yu4*
1
Institute of Zoology, College of Science, National Taiwan University.
2
Taiwan Fisheries Research Institute, 199 Hou-Ih Road, Keelung, Taiwan, ROC.
3
National Museum of Marine Biology & Aquarium, 2 Houwan Road, Checheng, Pingtung, Taiwan
994, ROC.
4
Endocrinology Laboratory, Institute of Zoology, Academia Sinica, Taipei, Taiwan, ROC.
The complete complementary DNA (cDNA) encoding pituitary gonadotropin
II-β subunit (GTH II-β) of Japanese eel Anguilla japonica was sequenced and the
profiles of pituitary glycoprotein hormone α subunit (PGH-α), GTH I-β, and GTH
II-β mRNA transcript levels at different stages of ovarian development in the wild
females were investigated. The maturity of female eels were divided into four stages
namely, juvenile, yellow adult, pre-silver, and silver stages based on ovarian
developments and skin color. The GTH II-β cDNA was obtained by reverse
transcription and polymerase chain reaction (RT-PCR) amplification from total
pituitary RNA. The full length GTH II-β cDNA was obtained using 5’- and 3’- rapid
amplification of cDNA ends (RACE). The GTH II-β subunit possessed a putative
signal peptide of 24 amino acids and a mature peptide of 116 amino acids. The
sequences of matured GTH II-β subunit were identical among 8 available species of
Anguillid eels. Quantitative RT-PCR analysis showed that the transcript levels of α
subunit steadily increased during eel silvering. The expression of GTH I-β and II-β
mRNA levels, however, varied in different ovarian developmental stages. In juveniles,
the expression of GTH I-β mRNA level was higher than that of GTH II-β. However,
in yellow adults, the transcript levels of GTH II-β was higher than that of GTH I-β.
The transcript level of GTH I-β in pre-silver and silver stages increased nearly 3 folds
from the juvenile stage, while the transcript level of GTH II-β in pre-silver and silver
stages increased nearly 5 and 7 folds, respectively, from the juvenile stage. These
results indicated differentiated transcription patterns of GTH I and GTH II before and
during eel silvering.