Insulin-like growth factor-3 (IGF-3) in male and female gonads of the tilapia: development and regulation of gene expression by growth hormone (GH) and 17alpha-ethinylestradiol (EE2).
Recently, in addition to IGF-1 and IGF-2 the existence of a third form of IGF, termed IGF-3, limited to fishes, to be present only in the gonads and encoded by a separate gene has been reported. However, no further data have been presented on IGF-3. The present study on tilapia (Oreochromis niloticus) uses quantitative real-time PCR specific for tilapia IGF-1 and IGF-3. The organ distribution of IGF-3 mRNA in adult fish and the early ontogeny of IGF-3 in male and female gonads were studied. The potential sensitivity of IGF-3 to GH was revealed by intraperitoneal injections of bream GH using IGF-1 as control gene. The effects of 17alpha-ethinylestradiol (EE2) exerted after feeding of high EE2 doses and exposure to low environmentally relevant EE2 doses on IGF-3 expression in testis and ovary during early development were determined. Low IGF-3 mRNA expression levels were detected in most organs studied, with the highest extra-gonadal amount in the pituitary. During development, the IGF-3 gene was significantly upregulated in male but downregulated in female gonad. Injections of GH elevated IGF-1 mRNA in male and female liver and ovary. IGF-3 did not respond to GH treatment neither in ovary nor in testis. Both EE2 treatments resulted in significant downregulations of IGF-3 mRNA in testis while ovarian IGF-3 mRNA did not respond. Thus, IGF-3 may be involved in reproduction of fishes most likely in the male gonad only. Whether IGF-3 also has some physiological significance in ovary or other organs should be the topic of further studies.
Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, 8057 Zürich, Switzerland.
Giorgi
G
Berishvili
Jean-François
JF
Baroiller
Elisabeth
E
Eppler
Manfred
M
Reinecke
D000818:Animals; D004997:Ethinyl Estradiol / Q000494:pharmacology*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects* / Q000235:genetics; D013006:Growth Hormone / Q000494:pharmacology*; D008297:Male; D010053:Ovary / Q000187:drug effects / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013737:Testis / Q000187:drug effects / Q000378:metabolism; D017210:Tilapia / Q000254:growth & development / Q000378:metabolism*
D004997:Ethinyl Estradiol; D013006:Growth Hormone