Six structurally distinct insulin-like growth factor binding proteins have been isolated and their cDNAs cloned: IGFBP1
(146730), IGFBP2 (146731), IGFBP3 (146732), IGFBP4, IGFBP5 (146734), and IGFBP6 (146735). The proteins display
strong sequence homologies, suggesting that they are encoded by a closely related family of genes.
General function
Extracellular binding protein
Comment
Cellular localization
Secreted
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Ovarian function
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Expression regulated by
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Ovarian localization
Theca, Stromal cells
Comment
Arraztoa JA, et al 2002
analyzed IGFBP mRNA expression patterns in ovaries from mid-cycle rhesus monkeys using in situ hybridization. IGFBP-1 mRNA was concentrated in theca-interstitial cells and was present at low levels in granulosa cells of atretic follicles. IGFBP-2 mRNA was expressed in the ovarian surface epithelium and granulosa cells of all antral follicles, including obviously atretic as well as dominant follicles. IGFBP-3 mRNA was localized in oocytes and in the ovarian vascular endothelium; this mRNA was also concentrated in the superficial cortical stroma in which it was distinctly more abundant in the nondominant ovary. Granulosa cells of mature dominant and ovulatory follicles selectively expressed IGFBP-5 mRNA. IGFBP-5 mRNA was also widely expressed in the ovarian stroma, in which, in contrast to IGFBP-3, it was distinctly more abundant in dominant, compared with nondominant, ovary. IGFBP-6 mRNA was present at low levels in the ovary interstitium and theca externa and was more abundant in the ovary surface epithelium. These novel data reveal distinctive cellular expression patterns for IGFBPs 1, 2, 3, 5, and 6 in the nonhuman primate ovary, suggesting distinct roles for each binding protein in ovarian function.