The vascular network formation is fundamental to normal follicle development and function in the ovary. It is established by numerous angiogenic factors, including hypoxia inducible factor 1 alpha (HIF1α), vascular endothelial growth factor (VEGF) system, and angiopoietin (ANGPT) system; however, the importance of angiogenesis in the avian ovary is poorly known. This study was undertaken to examine the expression of essential angiogenic factors, i.e., HIF1α, VEGFA and its receptors VEGFR1 and VEGFR2, ANGPT1 and ANGPT2 and their receptor TIE2, and FGF2 mRNA transcript and protein abundances, as well as protein localization within the chicken ovary in relation to follicle development in laying hens (Experiment 1) and to follicle atresia in hens subjected to fasting-induced pause in laying (Experiment 2). Tissue samples from ovaries were harvested on the sixth day of the experiment from the control hens and hens that had been fasted for five consecutive days. Quantitative RT-PCR and western blot analyses showed changes in the expression of examined molecules throughout follicle development from white, via yellowish and small yellow to the largest preovulatory F3-F1, on mRNA and/or protein levels, as well as differences in the mRNA and/or protein abundance between the layers of the follicle wall. In fasted hens, the occurrence of the yellow follicle atresia was accompanied by: (1) a marked decrease in mRNA transcript abundance of HIF1α in the theca layer of F3 and F2 follicles, and ANGPT1 and ANGPT2 mRNA levels in the wall of F1 follicle; (2) a decrease in transcript abundance of VEGFR1, VEGFR2 , and TIE2 in the yellow atretic follicles; and (3) a decrease in unmodified form of HIFα protein in the wall of F2 and F1, and an increase in modified form of HIFα protein in F3-F1 follicles. In summary, the results suggest that HIF1α and other angiogenesis-related factors play a role in the control of blood vessel formation during follicle development and atresia in the chicken ovary, and consequently may affect overall egg production in hens. Moreover, our observations have yielded novel insights into the molecular regulation of ovarian follicle vascularization during the developmental process and atresia induced by fasting in hens.
Machura et al. (Sun,) studied this question.