Response of shell-less cultured chick embryos to exogenous parathyroid hormone and 1,25-dihydroxycholecalciferol

A non-invasive photographic modification for recording early vascular development in the chick

The chick embryo shell-less culture technique allows continuous observation and access to the developing vessels of the area vasculosa (AV); hence, its value as an angiogenesis assay system. The main drawback of the method is that adequately contrasted photographs cannot be achieved without injection of a contrast medium which kills the embryo making further observation of the same specimen impossible. Furthermore, injection prior to 72 h incubation has a high failure rate. In an attempt to overcome these problems, we explored the possibility of using a high-contrast photographic process. Embryos were explanted into shell-less culture after 48 h incubation and photographed through a stereo microscope. After trials with different films we found that Kodalith ortho Type 3 (Kodak) and Technical Pan film (Kodak) produced images of the vasculature which were identical in contrast and detail to India-ink-injected specimens photographed with conventional film. In addition, excellent images could be recorded as early as 48 h of incubation.

Effects of calcium deficiency on chondrocyte hypertrophy and type X collagen expression in chick embryonic sternum

Maintenance of chick embryos in long-term culture without their calcareous egg-shell is a useful method for studying the relationship between calcium homeostasis and cell differentiation during skeletogenesis. Previously, we have shown that in shell-less (SL) embryos, calcium deficiency induces a cartilage-like phenotype in osteogenic tissues, such as calvaria (Jacenko and Tuan [1986] Dev. Biol. 115:215). In this investigation, we have studied the relationship between cartilage calcification and hypertrophy, and the expression of type X collagen, a specific product of hypertrophic chondrocytes. For this study, the cephalic (calcifying) and caudal (permanently cartilaginous) regions of sterna from day 18 and day 20 normal (NL) and SL embryos were metabolically labeled with [14C]-proline. Analysis of the biosynthetic products revealed significant differences in type X collagen expression in the cephalic region of sternal cartilage. In NL tissues, type X collagen production increased from 13.1% of total collagen at day 18 to 43.7% at day 20. In contrast, in SL embryos, type X collagen was not detectable until day 20, when it represented only 1% of total collagen. Comparison of the NL and SL embryos with respect to their serum calcium level and sternal calcium content and histology revealed a direct relationship between low systemic calcium and limited cartilage hypertrophy, undermineralization, and decreased type X collagen production in the sternal cephalic cartilage. Supplementation of CaCO3 to SL embryos increased their serum and sternal calcium, and restored cartilage hypertrophy, mineralization, and type X collagen synthesis in the cephalic portion of the sterna. These findings confirm that a critical relationship exists between calcium homeostasis, chondrocyte hypertrophy, mineralization, and type X collagen synthesis in the cephalic region of sternal cartilage. These results further demonstrate the importance of calcium in the morphogenetic events of endochondral ossification, in particular the transition from hyaline cartilage to hypertrophic cartilage, and eventually to bone.

Use of slow-release pellets to administer calcitriol to avian embryos: effects on plasma calcium, magnesium, and phosphorus

Calcitriol (1,25-dihydroxycholecalciferol) was administered to embryos of domestic fowl by slow-release pellets inserted into eggs on Day 10 of incubation. Mortality among embryos receiving 10 pg/day was no different from that of controls, but mortality among embryos receiving 100-1000 pg/day was elevated in later stages of incubation. Concentrations of calcium in plasma did not vary over the course of incubation among surviving embryos receiving carrier, but concentrations of magnesium and inorganic phosphorus declined with time. All doses of calcitriol elicited increases in plasma Ca and Mg on Day 12, and embryos may have responded also with a dose-dependent hypophosphatemia. The increases in plasma Ca and Mg were not sustained for the remainder of incubation, but the hypophosphatemia seemingly was of longer duration. This study demonstrates a new procedure for administering hormones to avian embryos and reveals that embryonic chickens respond in the expected manner to very small quantities of calcitriol.

Variation during development in the response of chicken embryos to calcitriol administered via slow-release pellets

Embryonic chickens were exposed to 0, 30, or 300 pg of calcitriol per day via slow-release pellets implanted adjacent to the chorioallantoic membrane. Pellets were placed in eggs on Days 10 and 15, and eggs were sampled on Days 12 and 17, respectively. The hormone induced high mortality among embryos receiving pellets on Day 10, but not among those whose treatment was begun on Day 15. Embryos receiving hormone were hypercalcemic and hypophosphatemic on both Day 12 and Day 17, but the concentration of magnesium in plasma was not affected. Size of embryos sampled on Day 12 was not affected by hormone treatment, but embryos sampled on Day 17 showed a dose-related reduction in size. Yolk-free carcasses of the embryos sampled on Day 17 also showed dose-dependent reductions in phosphorus and magnesium, but calcium content of carcasses on Day 17 was unaffected by treatment. These results indicate that both younger and older embryos respond to very small quantities of calcitriol administered via slow-release pellets. The absence of sustained hypercalcemia in earlier studies that used this protocol to dispense hormone was not caused by exposing older embryos to subthreshold quantities of calcitriol. The fact that reduced body size in late embryos receiving calcitriol was not accompanied by a reduction also in calcium content may mean that embryos deposit calcium in the carcass in an effort to deal with the extreme hypercalcemia induced by calcitriol.

Vitamin D and chick embryonic yolk calcium mobilization: identification and regulation of expression of vitamin D-dependent Ca2(+)-binding protein, calbindin-D28K, in the yolk sac

The developing chick embryo acquires calcium from two sources. Until about Day 10 of incubation, the yolk is the only source; thereafter, calcium is also mobilized from the eggshell. We have previously shown that during normal chick embryonic development, vitamin D is involved in regulating yolk calcium mobilization, whereas vitamin K is required for eggshell calcium translocation by the chorioallantoic membrane. We have studied here the biochemical action of 1,25-dihydroxy vitamin D3 in the yolk sac by examining the expression and regulation of the cytosolic vitamin D-dependent calcium-binding protein, calbindin-D28K. Two types of embryos are used for this study, normal embryos developing in ovo and embryos maintained in long-term shell-less culture ex ovo, the latter being dependent solely on the yolk as their calcium source. Our findings are (1) calbindin-D28K is expressed in the embryonic yolk sac, detectable at incubation Days 9 and 14; (2) the embryonic yolk sac calbindin-D28K resembles that of the adult duodenum in both molecular weight (Mr 28,000) and isoelectric point, as well as the presence of E-F hand Ca2(+)-binding structural domains; (3) systemic calcium deficiency caused by shell-less culture of chick embryos results in enhanced expression of calbindin-D28K in the yolk sac during late development; (4) yolk sac calbindin-D28K expression is inducible by 1,25-dihydroxy vitamin D3 treatment in vivo and in vitro; and (5) immunohistochemistry revealed that yolk sac calbindin-D28K is localized exclusively to the cytoplasm of the yolk sac endoderm. These findings indicate that the chick embryonic yolk sac is a genuine target tissue of 1,25-dihydroxy vitamin D3.

Action of 1,25-dihydroxyvitamin D3 and parathyroid hormone on 45calcium uptake by the yolk sac membrane of chick embryos

During development, the chick embryo mobilizes the calcium it needs from two extraembryonic sources, initially from the yolk and later from the eggshell. Calcium may be hormonally regulated during avian embryogenesis, but details of this regulation are lacking. We investigated the effects of 1,25-dihydroxycholecalciferol [1,25(OH)2D3], bovine parathyroid hormone [bPTH], and vehicle [ethanol or saline] on blood calcium values and incorporation of 45Ca into the yolk sac membrane of 9, 12, and 15 day chick embryos. Control data were also collected from uninjected 6 day embryos. Solutions were injected directly into the yolk sac compartment 48 and 24 hours prior to the experiment. Exogenous 1,25(OH)2D3 induced hypercalcemia in all age groups examined, while exogenous PTH induced hypercalcemia in day 12 and 15 embryos. Small disks of yolk sac membrane were incubated in medium to which 45Ca was added and assayed for 45Ca content at various intervals after start of incubation. In control yolk sac tissue, the uptake of 45Ca was greatest in younger embryos with decreasing uptake at developmentally more advanced ages; 1,25(OH)2D3 treatment significantly enhanced the uptake of 45Ca into yolk sac tissue in all groups (9, 12, and 15 day embryos). PTH treatment caused a significant elevation in 45Ca uptake in the day 12 and 15 embryos.

Calcium and calmodulin levels in late embryonic and early hatched Japanese quail brain

Characterizing the last phases of embryonic avian brain development are increased brain activity and increased absorption of shell calcium. The calcium-binding protein, calmodulin, regulates many activities of calcium. In neural tissue, calmodulin modulates neural transmission, and is required for the phosphorylation of synaptosomal proteins. Therefore, the objective was to compare levels of brain calcium and calmodulin in the Japanese quail. Brain extracts from embryonic days 11, 15, hatch, and 5 days post-hatch (n = 7/group) were analysed for calcium, protein and calmodulin. Despite increases in protein between embryonic (X = 0.126 and 0.145 mg/mg wet wt) and hatched groups (X = 0.183 and 0.221 mg), no significant increases in calmodulin were observed (237-279 ng/mg protein). Calcium levels in the brain were U-shaped with low levels at embryonic day 1 (341 micrograms/mg wet wt) and post-hatch day 5 (315 micrograms/mg wet wt) with higher levels on embryonic day 15 (425 micrograms/mg wet wt) and at hatch (433 micrograms/mg wet wt). Calmodulin levels do not show a developmental pattern similar to calcium and protein levels or with reports of brain activity.

The avian embryo as a model for early developmental endocrinology

Studies utilizing the developing chicken embryo have significantly augmented our understanding of the ontogeny of endocrine regulation during major critical periods of embryonic development. These embryos currently provide the only available models for elucidating the onset of endocrine function during all stages of in situ amniote development, for examining chronic calcium deficiency during embryogenesis, and for experiments in basic renal function during periods when only the mesonephros is normally functioning, as well as mixed meso/metanephric function and solely metanephric kidney function.

The action of various vitamin D3 metabolites on calcium and phosphorus metabolism in chick embryo calvariae

Chick embryos from vitamin D-deficient hens given physiological doses of 1,25-dihydroxyvitamin D3 or 24,25-dihydroxyvitamin D3 or both become severely hypocalcemic, hyperphosphatemic and fail to hatch as compared to those derived from hens given 25-hydroxyvitamin D3 or 24,25-difluoro-25-hydroxyvitamin D3. Calvariae from the former contain less mineral and on incubation in vitro produce significantly lower calcium and higher phosphate concentration in the medium than do the calvariae derived from the embryos of hens supported on 25-hydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3.

Effects of varying chamber construction and embryo pre-incubation age on survival and growth of chick embryos in shell-less culture

Shell-less culture involves culturing chick embryos with associated yolk and albumen outside of the eggshell and shell membranes. The technique allows direct access to and continuous observation of cultured embryos almost to the time of hatching. The plastic wrap/culture tripod technique described in this paper allows normal embryonic growth and differentiation from 48 hours (in ovo pre-incubation age) through at least 10 days of total incubation. As the duration of in ovo pre-incubation is decreased below 36 hours, there is a concomitant increase in the percentage of grossly abnormal embryos associated with decreased survival and retarded growth and differentiation. Survival of embryos pre-incubated for 72 hours through 13 and 18 days of total incubation is greater than 80% and 40%, respectively. The wrap/tripod technique allows substantially better survival and more normal development of cultured embryos than does the petri dish technique of Auerbach et al. (1974). Embryonic growth in 7.8-cm-diameter chambers is significantly greater than in either larger (10.6 cm) or smaller (5.2 cm) diameter chambers. Some gas exchange through the culture chamber walls appears necessary for optimal embryonic survival and growth. Suspending egg contents in either Safeway or Handi-Wrap plastic wrap (both of intermediate permeability) in 7.8-cm tripods resulted in superior growth and/or survival compared to suspension in Silastic sheeting (high permeability), Saran Wrap (low permeability), glass dishes (nonpermeable), or glass dishes lined with an inner layer of Safeway wrap(nonpermeable).