Biosynthesis of calcium-binding protein of chick embryonic chorioallantoic membrane: In vitro organ culture and cell-free translation

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.

Mouse placental 57-kDa calcium-binding protein: I. Cloning of cDNA and characterization of developmental expression

A cDNA clone to the mouse placental 57-kDa calcium-binding protein (MCaBP) [29] was isolated by immunoscreening a mouse placenta cDNA library constructed in the expression phage vector, lambda gt 11. The MCaBP cDNA was 0.7 kb in size, with restriction sites for StuI and Bg/II, and its identity to the MCaBP was confirmed by mRNA hybrid selection. RNA blot hybridization revealed a predominant, 3.9-kb transcript of the MCaBP in day-18 mouse placenta. The expression of the MCaBP during development was analyzed with respect to the levels of protein activity, translatable MCaBP mRNA, and total MCaBP transcript.

Alkaline phosphatase conjugated protein A as a sensitive reagent to immunoscreen an expression cDNA plasmid library: isolation of cDNA to the calcium-binding protein of the chick embryonic chorioallantoic membrane

A highly efficient immunoscreening procedure has been developed to isolate cDNA clones to the calcium-binding protein (CaBP) of the chick embryonic chorioallantoic membrane (CAM). A library of total CAM cDNA was constructed using the expression plasmid vector, pUC 19. Bacterial clones containing plasmids with CaBP cDNA inserts were detected immunohistochemically based on their expression of hybrid CaBP protein sequences. For immunodetection, nitrocellulose bacterial colony replicas were treated with specific antibodies to the CaBP followed by incubation with Staphylococcus aureus Protein A conjugated with alkaline phosphatase (AP) which served as a secondary immunoreagent. Positive clones were then histochemically identified based on AP enzyme activity. The identity of the immunopositive clones was further verified by in vitro translation of mRNA selected by hybridization to the cloned cDNA. The AP-based immunoscreening procedure yields stable reaction products with relatively low background, and should find general application for isolating specific cDNA clones from expression cDNA libraries.

Calcium deficiency induces expression of cartilage-like phenotype in chick embryonic calvaria

A detailed histological study of the chick embryonic calvarium was carried out to characterize the effect of calcium deficiency on cell differentiation during embryonic bone formation. Calcium deficiency on cell differentiation during embryonic bone formation. Calcium deficient chick embryos, produced by means of long-term shell-less (SL) culture, developed skeletal anomalies. In addition to reduced mineralization as detected by alizarin staining, significant changes were also observed in the extracellular matrix of the embryonic bones. First, the undermineralized matrix of the calvaria of SL embryos appeared to be more acidic as shown by more intense hematoxylin staining of the trabecular regions compared to controls. Secondly, the presence of sulfated proteoglycans was suggested by specific Alcian blue staining of the calvaria of Day 14 SL embryos. In addition, indirect fluorescence immunohistochemistry confirmed the developmental appearance of type II collagen in calcium-deficient calvaria, and localized it to undermineralized regions of the bone. These observations demonstrate the emergence of a chondrogenic phenotype in a typically osteogenic tissue during, and perhaps in response to, severe systemic calcium deficiency in the developing chick embryo.