The role of the IGF-I system for vitellogenesis in maturing female sterlet, Acipenser ruthenus Linnaeus, 1758.
Transition from previtellogeneic to vitellogenic oocyte growth is a critical phase for folliculogenesis in sturgeon and may often be postponed for several years. Recent findings on the involvement of insulin-like growth factor I (IGF-I) in cell differentiation processes of oocyte follicle and ovarian steroidogenesis of teleosts in vitro led to the hypothesis that paracrine IGF-I could function as a potential trigger in vivo. For the first time, IGF-I and its corresponding receptor (IGF-IR) were identified in a non-teleostean fish. Real-time PCR assays for IGF-I and IGF-IR mRNA were established, normalising mRNA expression of the target genes to beta-microglobulin (beta2m). We clearly show that expression of IGF-I in the gonad is a substantial source for IGF-I-mediated effects in follicles compared to liver, brain, muscle and adipose tissue. Among these tissues, IGF-IR mRNA was highest in the gonad. With regard to different cohorts of coexisting follicles, highest expression of IGF-I and IGF-IR were met in developing follicles, indicating that IGF-I functions as an intraovarian modulator of follicle faith. Comparing previtellogenic follicles in females that matured within two years with non-maturing females f the same age, revealed an increases of 2.3-fold for IGF-I and 2.8-fold for IGF-IR mRNA expression in maturing females. These findings implicate an important role of paracrine IGF-I in early vitellogenesis and identify it as candidate vitellogenesis inducing factor (VIF), determining the faith of the follicle.
Wuertz
S
S
Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany. sveno@igb-berlin.de
Nitsche
A
A
Jastroch
M
M
Gessner
J
J
Klingenspor
M
M
Kirschbaum
F
F
Kloas
W
W
D000818:Animals; D001483:Base Sequence; D005260:Female; D005399:Fishes / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010060:Ovulation / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism; D017385:Sequence Homology; D012741:Sexual Maturation / Q000502:physiology*; D013045:Species Specificity; D014818:Vitellogenesis / Q000502:physiology*
D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1