Abstract
The chick chorioallantoic membrane (CAM) is a widely used model for the study of angiogenesis, tumour growth, as well as drug efficacy. In spite of this, little is known about the developmental alteration from its appearance to the time of hatching. In the current study the CAM has been studied by classical stereology and allometry. Expression levels of selected angiogenesis-related molecules were estimated by RT-PCR and cell dynamics assessed by proliferation and apoptosis assays. Absolute CAM volume increased from a low of 0.47 ± 0.11 cm3 at embryonic day 8 (E8) to a high of 2.05 ± 0.27 cm3 at E18, and then decreased to 1.6 ± 0.47 cm3 at E20. On allometric analysis, three growth phases were identifiable. Between E8-13 (phase I), the CAM grew fastest; moderately in phase II (E13-18) but was regressing in phase III (E18-20). The chorion, the mesenchyme and the allantoic layers grew fastest in phase I, but moderately in phase II. The mesenchyme grew slowly in phase III while the chorion and allantois were regressing. Chorionic cell volume increased fastest in phase I and was regressing in phase III. Chorionic capillaries grew steadily in phase I and II but regressed in phase III. Both the chorion and the allantois grew by intrinsic cell proliferation as well as recruitment of cells from the mesenchyme. Cell proliferation was prominent in the allantois and chorion early during development, declined after E17 and apoptosis started mainly in the chorion from E14. VEGFR2 expression peaked at E11 and declined steadily towards E20, VEGF peaked at E13 and E20 while HIF 1α had a peak at E11 and E20. Studies targeting CAM growth and angiogenesis need to take these growth phases into consideration
Highlights
The chorioallantoic membrane is a vascular membrane found in embryonated eggs of some amniotes, such as birds and reptiles
Relative expression revels of selected angiogenesis related molecules were accomplished with RT-PCR (Fig 10)
The fusion stage extends from E5 in the chicken embryo when apposition of the chorion and the allantois begins, up to E12 when this process is complete [13] and the chorioallantoic membrane (CAM) covers the entire surface of the egg [15]
Summary
The chorioallantoic membrane (chorioallantois, CAM) is a vascular membrane found in embryonated eggs of some amniotes, such as birds and reptiles. It results from the fusion of the mesodermal layers of two developmental structures: the allantois and the chorion [1]. For much of the incubation, the CAM, the subject of the current study, is the sole source of gaseous exchange. It is formed of three layers, which include the chorionic epithelium, the mesenchyme and the allantoic epithelium. In addition the CAM plays an essential role in osteogenesis by transporting calcium into the embryo from the eggshell [4, 5]
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