Expression And Regulation Of Chicken ANXA2 Gene In Follicular Development

Annexin A2(ANXA2) is a calcium-dependent, phospholipid-binding protein found in various cell types. In vertebrate cells, Annexins was named Annexin A family. ANXA2, one member of Annexin A family, consists of 339 amino acids with the molecular weight of 36 kD, which is mainly expressed on endothelial cells, mononuclear cells and some tumor cells. ANXA2 plays multiple roles in regulating cellular functions and is often up-regulated in various tumor types include ovarian cancer, such as the formation and transport of cell membrane, endocytosis and exocytosis, cell proliferation, signal transduction, cell differentiation and apoptosis, angiogenesis and other important life activities of cells. We and others previously found that ANXA2 was up-regulated in the ovaries of hen with higher laying rate which indicates ANXA2 is involved in avian follicle development.By real-time PCR, we found ANXA2 mRNA was significantly higher in the ovaries of laying hens(23-week-old hens) than pre-pubertal hens(6-week-old hens). Next, we collected SWF, F3, F1 and POF1 from reproductively active hen ovaries and examined ANXA2 expression. ANXA2 mRNA levels progressively increased as the follicle developed from the pre-hierarchical to the pre-ovulatory follicle stage. The highest levels were repeatedly detected in F1 follicles, indicating that ANXA2 is likely involved in ovulation. After ovulation, ANXA2 mRNA expression declined rapidly to notably low levels that were comparable to levels observed in SW follicles. We also collected granulosa and theca cells from the pre-ovulatory follicles(F1~F4) which showed the highest levels of ANXA2 expression and found that ANXA2 expression is significantly higher in theca than granulosa cells in these follicles. In theca cells, ANXA2 mRNA expression could be stimulated by FSH and estrogen but not LH or progesterone. In addition,the core promoter region that controls the basal and FSH-induced ANXA2 gene expression was identified. Forced expression of ANXA2 could induce the transcription of angiogenic factors and receptors in theca cells. Moreover, ANXA2 overexpression results increased vascular endothelial growth factor A(VEGFA) secretion and theca cell proliferation.Our study not only provides the first evidence of expression and regulation of ANXA2 in chicken ovary, but also shows that ANXA2 is involved in the follicular angiogenesis and make for normal follicle development and ovulation.