Transepithelial calcium transport in the chick chorioallantoic membrane. I. Isolation and characterization of chorionic ectoderm cells

Functional complexity in the chorioallantoic membrane of an oviparous snake: Specializations for calcium uptake from the eggshell

The chorioallantoic membrane of oviparous reptiles forms a vascular interface with the eggshell. The eggshell contains calcium, primarily as calcium carbonate. Extraction and mobilization of this calcium by the chorioallantoic membrane contributes importantly to embryonic nutrition. Development of the chorioallantoic membrane is primarily known from studies of squamates and birds. Although there are pronounced differences in eggshell structure, squamate and bird embryos each mobilize calcium from eggshells. Specialized cells in the chicken chorionic epithelium transport calcium from the eggshell aided by a second population of cells that secrete protons generated by the enzyme carbonic anhydrase. Calcium transporting cells also are present in the chorioallantoic membrane of corn snakes, although these cells function differently than those of chickens. We used histology and immunohistology to characterize the morphology and functional attributes of the chorioallantoic membrane of corn snakes. We identified two populations of cells in the outer layer of the chorionic epithelium. Calbindin-D_28K , a cellular marker for calcium transport expressed in squamate chorioallantoic membranes, is localized in large, flattened cells that predominate in the chorionic epithelium. Smaller cells, interspersed among the large cells, express carbonic anhydrase 2, an enzyme not previously localized in the chorionic epithelium of an oviparous squamate. These findings indicate that differentiation of chorionic epithelial cells contributes to extraction and transport of calcium from the eggshell. The presence of specializations of chorioallantoic membranes for calcium uptake from eggshells in chickens and corn snakes suggests that eggshell calcium was a source of embryonic nutrition early in the evolution of Sauropsida.

The Chicken Embryo Chorioallantoic Membrane as an In Vivo Model for Photodynamic Therapy

For many decades the chicken embryo chorioallantoic membrane (CAM) has been used for research as an in vivo model in a large number of different fields, including toxicology, bioengineering, and cancer research. More specifically, the CAM is also a suitable and convenient model system in the field of photodynamic therapy (PDT), mainly due to the easy access of its membrane and the possibility of grafting or growing tumors on the membrane and, interestingly, to study the PDT effects on its dense vascular network. In addition, the CAM is simple to handle and cheap. Since the CAM is not innervated until later stages of the embryo development, its use in research is simplified compared to other in vivo models as far as ethical and regulatory issues are concerned. In this review different incubation and drug administration protocols of relevance for PDT are presented. Moreover, data regarding the propagation of light at different wavelengths and CAM development stages are provided. Finally, the effects induced by photobiomodulation on the CAM angiogenesis and its impact on PDT treatment outcome are discussed.

Solubilization and identification of hen eggshell membrane proteins during different times of chicken embryo development using the proteomic approach

A fertilized chicken egg is a unit of life. During hatching, transport of nutrients, including calcium, have been reported from the egg components to the developing embryo. Calcium is mobilized from the eggshell with the involvement of Ca(2+)-binding proteins. In addition, other unknown proteins may also play some important roles during embryo developing process. Therefore identification and prediction of biological functions of eggshell membrane (ESM) proteins during chick embryo development was conducted by proteome analysis. Comparison of different lysis solutions indicated that the highest ability to extract ESM proteins could be obtained with 1 % sodium dodecyl sulfate in 5 mM Tris-HCl buffer pH 8.8 containing 0.1 % 2-mercaptoethanol. In this study fertilized Cornish chicken eggs were incubated at 37 °C in humidified incubators for up to 21 days. At selected times (days 1, 9, 15 and 21), samples were taken and the ESMs were carefully separated by hand, washed with distilled water, and air-dried at room temperature. The ESM proteins were then solubilized and analyzed by proteome analysis. Sodium dodecyl sulfate polyacrylamide gel electrophoresis combined with high performance liquid chromatography and mass spectrometry revealed 62 proteins in the ESM; only keratin is known ESM protein, 8 of which are egg white proteins and related while 53 others have not previously been reported. Some differences in the types of proteins and their molecular functions were noted in ESM at different incubation times. One protein which was present only at days 15 and 21 of egg incubation was identified as a calcium binding protein i.e. EGF like repeats and discoidin I like domain 3 (EDIL3 homologous protein).

The chick chorioallantoic membrane: a model of molecular, structural, and functional adaptation to transepithelial ion transport and barrier function during embryonic development

The chick chorioallantoic membrane is a very simple extraembryonic membrane which serves multiple functions during embryo development; it is the site of exchange of respiratory gases, calcium transport from the eggshell, acid-base homeostasis in the embryo, and ion and H(2)O reabsorption from the allantoic fluid. All these functions are accomplished by its epithelia, the chorionic and the allantoic epithelium, by differentiation of a wide range of structural and molecular peculiarities which make them highly specialized, ion transporting epithelia. Studying the different aspects of such a developmental strategy emphasizes the functional potential of the epithelium and offers an excellent model system to gain insights into questions partly still unresolved.

The influence of non-toxic concentrations of DDT and DDE on the old world vulture estrogen receptor alpha

Seven of the nine vulture species in South Africa are listed as endangered on the International Union for the Conservation of Nature (IUCN) red list. From these, the Cape Griffon vulture (Gyps corprotheres) is the most endangered species in the region. Although inadequate nutritional support has been blamed on the constant decline in populations, the process of vulture restaurants has failed to improve the population status over the last twenty years. One possible reason for the decline may be an underlying reproductive disorder as described in endocrine disruptive syndromes. Both DDT and p,p'-DDE have been detected previously at very high concentrations in the mid 1980s, with lower concentrations still being detectable as late as 2001. To establish the effect of DDT and DDE, the vulture estrogen receptor alpha (ERalpha) was sequenced from two species using 5' and 3' rapid amplification cDNA ends (RACE). Using transient transfected mammalian cell assays, vulture ERalpha estrogen-dependent transcription activity was validated using various estrogens and DDT derivatives. The receptor assay was sensitive to p,p'-DDT, o,p'-DDT and p,p'-DDE with EC(50) of 2.41x10(-6), 3.47x10(-7) and 3.81x10(-5)M. When compared to results obtained from human, zebrafish, chicken, salamander and turtle, the vulture ERalpha showed high sensitivity to o,p'-DDT and intermediately responsive to p,p'-DDE. Vulture ERalpha is, however, not responsive to the DDT and DDE levels reported in the plasma of vultures from the last population survey, indicating that the Southern African vulture are not currently exposed to disruptive levels of these contaminants.

Carbonic Anhydrases in Chick Extra-embryonic Structures: A Role for CA in Bicarbonate Reabsorption Through the Chorioallantoic Membrane

The villus cavity cells, a specific cell type of the chick chorioallantoic membrane, express both cytosolic carbonic anhydrase in their cytoplasm and HCO3(-)/Cl(-) anion exchangers at their basolateral membranes. By immunohistochemical analysis, we show here that villus cavity cells specifically react with antibodies directed against the membrane-associated form of carbonic anhydrase, CAIV. Staining is restricted to the apical cell membranes, characteristically invaginated toward the shell membrane, as well as to endothelia of blood vessels present in the mesodermal layer. The occurrence of a membrane-associated CA form at the apical pole of villus cavity cells, when definitively confirmed, would be fairly consistent with the role proposed for these cells in bicarbonate reabsorption from the eggshell so to prevent metabolic acidosis in the embryo during development.

Annexins as cell-type-specific markers in the developing chicken chorionallantoic membrane

Between day E8 and E12 of embryonic development, the chicken chorioallantoic membrane (CAM) undergoes massive structural rearrangement enabling calcium-uptake from the eggshell to supply the growing embryo. However, the contribution of the various cell types of the chorionic epithelium including the capillary covering (CC) cells, villus cavity (VC) cells, endothelial-like cells, and basal cells to this developmental program is largely unknown. In order to obtain markers for the different cell types in the chorionic epithelium, we determined the expression patterns of various calcium-binding annexins in the developing chicken CAM. By reverse transcription/polymerase chain reaction with primers deduced from nucleotide sequences available in various databases, the presence of annexin (anx)-1, anx-2, anx-5, and anx-6 was demonstrated at days E8 and E12. Quantitative immunoblotting with novel antibodies raised against the recombinant proteins revealed that anx-1 and anx-5 were significantly up-regulated at day E12, whereas anx-2 and anx-6 expression remained almost unchanged in comparison to levels at day E8. Immunohistochemistry of paraffin-embedded sections of E12 CAM revealed anx-1 in CC cells and VC cells. Anx-2 was localized in capillaries in the chorionic epithelium and in basal cells of the allantoic epithelium, whereas anx-6 was detected in basal cells or endothelial-like cells of the chorionic epithelium and in the media of larger vessels in the mesenchyme. A 2-day exposure of the CAM to a tumor cell spheroid resulted in strong proliferation of anx-1-expressing CC cells suggesting that these cells participate in the embryonic response to experimental intervention. Thus, annexins exhibit complementary expression patterns and represent appropriate cell markers for the further characterization of CAM development and the interpretation of results obtained when using CAM as an experimental model.

Expression of calbindin-D28K by yolk sac and chorioallantoic membranes of the corn snake,Elaphe guttata

The yolk splanchnopleure and chorioallantoic membrane of oviparous reptiles transport calcium from the yolk and eggshell to the developing embryo. Among oviparous amniotes, the mechanism of calcium mobilization to embryos has been studied only in domestic fowl, in which the mechanism of calcium transport of the yolk splanchnopleure differs from the chorioallantoic membrane. Transport of calcium is facilitated by calbindin-D(28K) in endodermal cells of the yolk splanchnopleure of chickens but the chorioallantoic membrane does not express calbindin-D(28K). We used immunoblotting to assay for calbindin-D(28K) expression in yolk splanchnopleure and chorioallantoic membrane of the corn snake, Elaphe guttata, to test the hypothesis that the mechanism of calcium transport by extraembryonic membranes of snakes is similar to birds. High calbindin-D(28K) expression was detected in samples of yolk splanchnopleure and chorioallantoic membrane during late embryonic stages. We conclude that calbindin-D(28K) is expressed in these extraembryonic membranes to facilitate transport of calcium and that the mechanism of calcium transport of the chorioallantoic membrane of the corn snake differs from that of the chicken. Further, we conclude that calbindin-D(28K) expression is developmentally regulated and increases during later embryonic stages in the corn snake.

The chick chorioallantoic membrane as a model tissue for surgical retinal research and simulation

PURPOSE

We describe the use of chick chorioallantoic membrane (CAM) as a model system for the study of the precision and safety of vitreoretinal microsurgical instruments and techniques.

METHODS

The CAM was prepared for experimentation with and without its inner shell membrane (ISM) attached for in vivo and in vitro experiments that simulated medical and surgical interventions on the retina.

RESULTS

The CAM's ease of use, low cost, and anatomic structure make it a convenient model for surgical retinal and retinal vascular modeling.

CONCLUSION

While CAM has been used extensively in the past for ocular angiogenesis studies, we describe the tissue as a useful tool for a variety of other applications, including (1) testing of novel surgical tools and techniques for cutting and coagulating retina and its vasculature, (2) testing vessel cannulation and injection techniques, (3) angiographic studies, and (4) endoscopic surgery.

Mineral status of embryos of domestic fowl following exposure in vivo to the carbonic anhydrase inhibitor acetazolamide

Eggs of domestic fowl were given daily injections of vehicle (DMSO) or vehicle plus acetazolamide, a potent inhibitor of the enzyme carbonic anhydrase, beginning on day 12 of incubation. Embryos were removed from eggs on days 16 and 18, and carcasses and yolks were analyzed for calcium, magnesium, and phosphorus. Treatment with acetazolamide did not affect the quantity of calcium or phosphorus in carcasses and the effect, if any, on magnesium in carcasses was small. However, calcium content of yolk was reduced substantially by acetazolamide both on day 16 and day 18. The reduction in calcium content of yolk led, in turn, to a reduction in the total quantity of calcium in eggs on days 16 and 18. Embryos exposed to acetazolamide seemingly mobilized less calcium from the eggshell than did control embryos. When faced with a shortfall in the availability of calcium from the eggshell, embryos defended carcass calcium, and the shortfall was reflected in a reduction in the quantity of calcium deposited in yolk. The results of this study support the concept that the enzyme carbonic anhydrase plays a role in solubilization of the eggshell and provision of calcium to embryos.

The effects of nest environment on calcium mobilization by leatherback turtle embryos (Dermochelys coriacea) during development

We investigated the effect of sand moisture content and sand temperature on developmental success and the mobilization of calcium during development using laboratory incubated eggs (n=251) collected from leatherbacks nesting at Parque Nacional Marino Las Baulas, Costa Rica. Calcium concentrations of egg components [eggshell, yolk plus albumen (Y+A) and embryo] changed significantly through incubation for both viable and undeveloped eggs. In developed eggs, eggshell calcium content decreased 42.9% by day 60 of incubation. The Y+A calcium decreased by 20.8% until the last quarter of incubation, and then increased to 0.99% above initial Y+A calcium concentrations just prior to hatching. In undeveloped eggs, eggshell calcium content decreased by 25.7%, with the rate of decrease slowing significantly beyond day 30 of incubation. In contrast, Y+A calcium increased steadily through the 60-day incubation period. Embryos incorporated a higher proportion of calcium when incubated at a lower sand moisture content (5% H(2)O>12% H(2)O) and at lower sand temperatures (28.5 degrees C, 29.5 degrees C>31.0 degrees C). The total wet mass of freshly oviposited eggs was negatively correlated with calcium concentration per gram of eggshell (r=-0.569; P<0.001). Thus, each yolked egg, regardless of initial wet mass, had an average of 1.23 g (+/-0.43 g) of calcium per egg (Mean egg mass: 76.24+/-1.21 g). Both developmental success (24.1%) and hatching success (7.4%) of laboratory-incubated eggs were dependent to a greater extent on temperature than on moisture, with an increase in mortality as sand temperature increased. For natural nests on Playa Grande, developmental success (37.4%) and hatching success (19.8%) were similar in magnitude to the results obtained from the laboratory. The recent ENSO (El Niño Southern Oscillation) event and increased tidal activity may be responsible for the high embryonic mortality measured during the 1997-1998 nesting season.

Functional analysis of placental 57-kDa Ca(2+)-binding protein: overexpression and downregulation in a trophoblastic cell line

The placental trophoblastic epithelium functions to transport nutrients needed by the fetus, including calcium, which is required in the greatest amounts during the last third of pregnancy when the majority of fetal skeletal mineralization occurs. The mechanism of placental calcium transport and the developmental changes in the trophoblast that facilitate this process are currently incompletely understood. We have previously identified a 57-kDa, Ca(2+)-binding protein (CaBP) functionally implicated in placental calcium transport and trophoblast differentiation. In this study we have directly examined the role of CaBP in these processes by (1) recombinantly overexpressing CaBP in an inducible manner and (2) downregulating CaBP expression using antisense technology, using the rat choriocarcinoma cell line Rcho-1 as a trophoblastic cell model system. Our results show that overexpression of CaBP stimulates both cellular calcium uptake and vectorial calcium transport activities in Rcho-1 cells. Those cells stably expressing CaBP also exhibit higher levels of steady-state intracellular calcium and enhanced calcium-buffering ability. In addition, prolonged overexpression of CaBP in Rcho-1 cultures promotes trophoblast differentiation. Conversely, downregulation of CaBP expression had a negative effect on calcium uptake, calcium transport, and trophoblast differentiation in Rcho-1 cells. These data indicate that CaBP plays a direct role in placental calcium transport, functioning both as an intracellular calcium buffer and as a shuttle. These results also support a more direct role for CaBP in the trophoblast differentiation pathway.

Evaluation of a protocol for studying the chick chorioallantoic membrane in vitro

Explants of eggshell with and without the chorioallantoic membrane were taken from fertile chicken eggs on day 16 of incubation and exposed in vitro to inhibitors (acetazolamide and benzolamide) of carbonic anhydrase to determine if enzyme inhibition affected release of calcium from the shell. A separate experiment examined the effect of the metabolic poison dinitrophenol (DNP) on release of calcium from explants. Explants with the chorioallantois in situ released more calcium than those lacking the epithelium, but neither the enzyme inhibitors nor DNP affected release of calcium. The lack of effect of the enzyme inhibitors could indicate that activity of carbonic anhydrase is not as important to the release of calcium from the eggshell as has been assumed. However, the absence of an effect of DNP instead indicates that release of calcium mediated by the chorioallantois in vitro simply lacks physiological relevance. Thus, results of this investigation raise doubts that the mechanism underlying release of calcium from the eggshell can be assessed in vitro.

Placental 57-kDa Ca(2+)-binding protein: regulation of expression and function in trophoblast calcium transport

During gestation, transport by placental trophoblasts is solely responsible for nutrient supply to the developing fetus. The calcium (Ca) transport machinery of the placenta thus represents the primary tissue site for regulating fetal Ca homeostasis. The exact mechanism of trophoblast Ca transport is not known. However, there is evidence suggesting that a developmentally expressed cytosolic, trophoblast-specific, high M(r) 57-kDa Ca-binding protein (CaBP) plays an important role in regulating and/or shuttling cytosolic Ca. We report here the cloning of a full-length cDNA of the mouse CaBP which shows significant homology with calreticulin, an endoplasmic reticulum-associated Ca binding protein. The functional role of CaBP in cellular Ca handling was investigated using a trophoblastic cell line, Rcho-1, derived from a rat choriocarcinoma. Upon differentiation, Rcho-1 cells exhibit enhanced Ca uptake compared to undifferentiated Rcho-1 stem cells, and CaBP expression is upregulated. To analyze the regulation of CaBP expression, placenta organ cultures and Rcho-1 cells were treated for 48 h in vitro with a series of agents implicated in Ca homeostasis. In both placenta organ cultures and undifferentiated as well as differentiated Rcho-1 cells, treatment with 1,25-dihydroxy vitamin D3, estrogen, parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrP 1-34), and Ca had no effect on CaBP mRNA and protein levels, which were significantly stimulated by PTHrP 67-84. PTHrP 67-84-treated Rcho-1 cells also exhibited higher Ca uptake activity than untreated control cells. The upregulation of CaBP expression during and/or following the differentiation of Rcho-1 cells into trophoblastic giant cells supports the importance of CaBP in trophoblast maturation and the validity of the Rcho-1 rat model cell system. In addition, the action of PTHrP on placental trophoblast Ca transport is likely to involve the regulation of CaBP expression to handle the increasing Ca requirements of the developing fetus.

The effect of calcium-regulating hormones on transport of calcium across the chorioallantoic membrane of the chicken embryo

The hormonal form of vitamin D3 (1,25(OH)2D3), parathyroid hormone (PTH), or appropriate vehicle were injected into the yolk sac of eggs of domestic fowl on days 16 and 17 of incubation. The chorioallantoic membrane (CAM) and overlying inner shell membrane were removed from eggs on day 18 and mounted in a Ussing-type apparatus. Transport of calcium was assessed by monitoring movements of radiolabeled calcium. Transport of calcium from the chorionic aspect of the CAM to the allantoic aspect increased considerably with time for all treatment groups except the one receiving PTH. "Back-flux" of calcium (movement of calcium from the allantoic aspect to the chorionic) was negligible for all treatment groups at all sampling periods. PTH treatment did not affect flux of calcium from allantois to chorion but reduced flux from chorion to allantois considerably. The underlying cause of this effect has not been identified. The hormonal form of vitamin D3 did not affect flux of calcium in either direction. These data raise the possibility that control of calcium transport by the CAM may not be the primary function of the vitamin D hormone.