The aim of the present study was to evaluate the effect of vascular endothelial growth factor (VEGF) on the survival and growth of goat preantral follicles after in vitro culture and to verify the expression of VEGF receptor (VEGFR)-2 in goat ovaries. Ovarian fragments were cultured for 1 or 7 days in minimal essential medium (MEM) with different concentrations of VEGF (1, 10, 50, 100 or 200 ng mL(-1)). Non-cultured (fresh control) and cultured tissues were processed for histological and ultrastructural studies. The results showed that 200 ng mL(-1) VEGF resulted in a similar percentage of normal preantral follicles after 1 and 7 days of culture compared with control. Compared with basic culture medium alone, an increase in follicular and oocyte diameters was observed in the presence of 10 ng mL(-1) VEGF after 7 days culture. Ultrastructural analysis confirmed follicular integrity after 7 days culture in the presence of 200 ng mL(-1) VEGF. Immunohistochemical studies demonstrated the expression of VEGFR-2 in oocytes and granulosa cells of all follicular stages, except in granulosa cells of primordial follicles. In conclusion, the present study has shown that VEGF maintains follicular ultrastructural integrity and promotes follicular growth. In addition, VEGFR-2 is expressed in oocytes of caprine ovarian follicles at all developmental stages and in granulosa cells of developing follicles.
"Other studies have demonstrated weak VEGFA immunostaining of oocytes in primary follicles from adult rat ovaries (Celik-Ozenci et al. 2003). In goat ovaries, KDR expression has been localized to oocytes of primordial and primary follicles and to granulosa cells of primary follicles (Bruno et al. 2009). These data provide further support that VEGFA signaling plays a role in the maintenance and/or activation of primordial follicles. "
[Show abstract][Hide abstract] ABSTRACT: Vascular endothelial growth factor A (VEGFA) has been extensively studied because of its role in follicular development and is a principal angiogenic factor essential for angiogenesis. Since vascularization of the theca layer increases as follicles progress in size through preantral and antral stages, VEGFA might influence follicle growth via the regulation of angiogenesis. However, VEGFA might also influence follicular development through nonangiogenic mechanisms, since its expression has been localized in nonvascular follicles and cells. Alternative mRNA splicing of eight exons from the VEGFA gene results in the formation of various VEGFA isoforms. Each isoform has unique properties and is identified by the number of amino acids within the mature protein. Proangiogenic isoforms (VEGFA_XXX) are encoded by exon 8a, whereas a sister set of isoforms (VEGFA_XXXB) with antiangiogenic properties is encoded by exon 8b. The antiangiogenic VEGFA_XXXB isoforms comprise the majority of VEGFA expressed in most tissues, whereas expression of the proangiogenic VEGFA isoforms is upregulated in tissues undergoing active angiogenesis. Although proangiogenic and antiangiogenic isoforms can now be distinguished from one another, many studies evaluating VEGFA in ovarian and follicular development up to now have not differentiated proangiogenic VEGFA from antiangiogenic VEGFA. Experiments from our laboratory indicate that proangiogenic VEGFA promotes follicle recruitment and early follicular development and antiangiogenic VEGFA inhibits these processes. The balance of proangiogenic versus antiangiogenic VEGFA isoforms is thus of importance during follicle development. Further studies are warranted to elucidate the way that this balance regulates follicular formation and progression.
Cell and Tissue Research 02/2012; 349(3):635-47. DOI:10.1007/s00441-012-1330-y · 3.57 Impact Factor
"Thus, viability assessment appears be a reliable, practical, and fast method to analyze follicular viability. Recently, this method has also been used successfully to evaluate preantral follicle viability in goats  . "
[Show abstract][Hide abstract] ABSTRACT: The aim of the present study was to investigate the effects of fibroblast growth factor-10 (FGF-10) on the survival, activation (transition from primordial to primary follicles), and growth of goat preantral follicles cultured in vitro. Pieces of ovarian cortex were cultured for 1 and 7 d in the absence or presence of FGF-10 (0, 1, 10, 50, 100, and 200 ng/mL). Noncultured and cultured tissues were processed and analyzed by histology, transmission electron microscopy, and viability testing. Results showed that after 7 d, a greater percentage (79.9%) of morphologically normal follicles (containing an oocyte with regular shape and uniform cytoplasm, and organized layers of granulosa cells without a pyknotic nucleus) was observed when cultured with 50 ng/mL of FGF-10 when compared with other concentrations of FGF-10 (0 ng/mL, 67.3%; 1 ng/mL, 68.2%; 10 ng/mL, 63.3%; 100 ng/mL, 64.4%; 200 ng/mL, 52.7%). Ultrastructural analyses and viability testing using fluorescent markers confirmed the follicular integrity of FGF-10 (50 ng/mL)-treated fragments after 7 d of culture. After 7 d, all FGF-10 concentrations reduced the percentage of primordial follicles and increased the percentage of developing follicles. In the presence of 50 ng/mL of FGF-10, follicles increased in diameter after 7 d of culture when compared with other concentrations tested. In conclusion, this study demonstrates that FGF-10 maintains the morphological integrity of goat preantral follicles and stimulates the growth of activated follicles in culture. The culture conditions identified here contribute to the understanding of the factors involved in goat early follicular development.
"Angiogenic factors produced by the follicle, such as vascular endothelial growth factor (VEGF), may promote vascular changes during follicle growth (Hazzard & Stouffer 2000). However, they may also have other roles, as suggested by evidence that VEGF maintains follicular ultrastructural integrity and promotes the growth of caprine preantral follicles during ovarian tissue culture (Bruno et al. 2009). Thus, AMH and VEGF may be valuable markers of follicle maturation and function. "
[Show abstract][Hide abstract] ABSTRACT: A three-dimensional culture system supports the development of primate preantral follicles to the antral stage with appreciable steroid production. This study assessed i) whether in vitro developmental competence of follicles is age dependent, ii) the role of gonadotropins and insulin in supporting folliculogenesis, and iii) anti-Müllerian hormone (AMH) and vascular endothelial growth factor (VEGF) production by growing follicles. Ovaries were obtained from prepubertal, young, and older adult rhesus macaques. Secondary follicles were encapsulated into alginate beads and cultured individually for 40 days in media containing 0.05 or 5 μg/ml insulin, with or without recombinant human (rh) FSH (500 mIU/ml). No follicles survived in the culture without rhFSH. In the presence of rhFSH, survival was lower for follicles from older animals, whereas growth, i.e. follicle diameter, was less by day 40 for follicles from prepubertal animals. The surviving follicles were categorized as no-grow (NG; ≤ 250 μm), slow-grow (SG; 250-500 μm), and fast-grow (FG; ≥ 500 μm) according to their diameters. SG follicles cultured with 5 μg/ml insulin produced more ovarian steroids than those cultured with 0.05 μg/ml insulin by week 5. SG and FG follicles produced more AMH and VEGF than the NG, and levels peaked at weeks 2 and 5 respectively. After 100 ng/ml rh chorionic gonadotropin treatment for 34 h, more healthy oocytes were retrieved from young adults whose follicles were cultured with 5 μg/ml insulin. This culture system offers an opportunity to characterize the endocrine and paracrine function of primate follicles that influence follicle growth and oocyte maturation.
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