Changes in activity of chicken medullary bone cell populations in relation to the egg-laying cycle (original) (raw)
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Rapid alterations of avian medullary bone material during the daily egg-laying cycle
Bone, 2014
Bone is a dynamic tissue which is continuously adapting not only to external mechanical stimuli but also to internal metabolic calcium demands. During normal bone remodeling, bone-resorbing osteoclasts release calcium from the bone and digest the collagenous bone matrix, after which bone-depositing osteoblasts form unmineralized collagen matrix, which subsequently mineralizes. The detailed mechanism by which calcium is deposited at the site of mineralization and removed from it during bone resorption is largely unknown. Experimental studies are difficult to conduct because in adult bone only a small fraction of bone tissue is remodeled at any moment in time. Thus, one promising approach is to study mineral deposition and resorption in model systems in which a large fraction of the bone mineral is mobilized in a relatively short period of time. We investigated the microscopic and nanoscopic alterations of avian medullary bone architecture during the egglaying (oviposition) cycle of hens. Medullary bone forms a labile calcium reservoir for eggshell production and is characterized by an extremely rapid and high-flux calcium metabolism. It thus, provides the unique opportunity to study processes of bone remodeling in their most intensive form. We used a combination of synchrotron X-ray tomography together with small angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD) and X-ray fluorescence (XRF) to correlate microscopic medullary bone attributes such as the mineral content, medullary bone volume fraction and medullary bone trabecular thickness with nanoscopic alterations in the mineral particle size (thickness parameter T and length parameter L) during the oviposition cycle. To identify the timing of the different stages of the cycle, ionic calcium, phosphorus and PTH concentrations in the blood of the layers were monitored. We found that the microscopic and nanoscopic architecture of avian medullary bone material changes rapidly during the oviposition cycle. During eggshell calcification, the mineral content and the size of trabeculae of medullary bone decrease markedly. Furthermore, the average mineral particle size increases during resorption, suggesting that the smaller mineral particles are preferrentially removed. Medullary bone thus formes a fastresponding system exhibiting rapid alterations of the material at the micron and nano scale. Those mechanisms are crucial to provide calcium for the high metabolic calcium demand during eggshell mineralization.
Medullary bone and avian calcium regulation
Medullary bone forms in egg-laying birds in response to gonadal steroids and is the most overtly oestrogen-dependent of all bone types. It acts as a labile reservoir for the supply of eggshell calcium. Previous studies indicate that feeding calcium-and vitamin-D-deficient diets to chickens results in resorption of cortical rather than medullary bone. More recent studies in calcium-stressed quail hens question this hypothesis and suggest that during the first 2 weeks of dietary calcium depletion the medullary bone is resorbed while cortical bone volume remains intact. The role of the osteoclast in bone resorption is the focus of much research that has recently included studies of medullary bone osteoclasts. The functional morphology of the avian cells, i.e. changes from quiescent to active osteoclasts with ruffled borders, reflects the rapid changes in medullary bone turnover that occur during the egg-laying cycle. Unlike mammalian osteoclasts, those from avian sources generally appear refractory to inhibitory factors such as calcitonin or raised extracellular calciumconcentration. However, medullary bone osteoclasts cultured in vitro for several days recover their ability to respond to the latter factor by increasing their levels of free cytosolic Ca 2+ , reducing tartrate-resistant acid phosphatase secretion and reducing their cell spread area. It is suggested that factors such as ambient calcium levels and prostaglandins may form part of a system of rapid local control for medullary bone osteoclast activity.
2008
The experiment was carried out on a batch formed by 10 laying hens, ISA Brown hybrid, at the first laying cycles, 50 weeks old, hold single in cages and fed with granulated forage. The hens were watched for 3 weeks in order to establish the moment of the oviposition and depending on that their slaughtering was set out so that the different stages of the egg formation could be observed. The hens were divided into 4 groups – I, II, III, IV- depending on the time elapsed from the last oviposition. Femur fragments have been drawn from the central zone of the diaphises and transformed in hematoxiline-eozine and alcian-blue stained preparations, the trichromic Mallory method and the Dorfmann-Epstein method for the emphasising of the alkaline phosphatasis. At the hens of the first group the presence of the medullary bone is shown and is characterised by an intense ossification process with compact bone structure, with well formed osseus trabeculae that occupy the medullar cavity. There is ...
2009
10 hybrid ISA Brown hens, 50 weeks old, hold single in cages and fed with combined granulated forage, were monitored for a period of 3 weeks. They were divided into 4 groups depending on the stages of the egg formation. When 53 weeks old, the hens were sacrificed and the bones of the inferior members (femur, tibiotarsus) were prevailed and thereafter prepared to determine the content of dry matter, crude ash and minerals (calcium, phosphorous, magnesium) both for samples of the whole bone and for the samples of the cortical and medullary bone. There were no significant differences in the content of dry matter of the cortical and medullary bone samples of the femur, tibia among the individuals (p>0.05). The content in crude ash of the femur falls significantly (p = 0.042) in the hens slaughtered 10 to 12 hours after oviposition. In the cortical bone from the femur the values of calcium, magnesium and phosphorous were not modified irrespective of the egg position in the oviduct. In the medullary bone from the femur the content in calcium and phosphorous was correlated with the egg formation stage; as for magnesium there were no significant differences during the egg formation irrespective of the stage. As for the cortical bone of the tibia of the hens from the 4 groups there are no significant differences (p>0.05) regarding the content in calcium, magnesium and phosphorous. In the medullary bone the content in calcium, magnesium and phosphorous was modified significantly depending on the position of the egg in the oviduct, and on the egg formation stage respectively.
Involvement of osteopontin in egg shell formation in the laying chicken
Matrix Biology, 1995
Expression of the osteopontin (OPN) gene in the oviduct of the laying hen was studied. It was detected only in the egg shell gland (ESG), where massive calcification occurs. No OPN gene expression was detected in any other part of the oviduct, such as the magnum and isthmus. The OPN gene was expressed in a circadian fashion during the daily egg cycle only during the period of egg shell calcification. No OPN gene expression was detected in the ESG of a pre-laying hen before the onset of reproduction, or after forced removal of the egg close to its entrance into the ESG. OPN was found to be synthesized by the epithelial cells of the ESG lining the lumen. Upon synthesis, OPN is immediately secreted out of cells and accumulates in the egg shell. These findings demonstrate for the first time temporal and spatial association of OPN with egg shell calcification. OPN, which was found to be part of the organic matrix of the egg shell, may play an important role in egg shell calcification.
Journal of Structural Biology, 2003
The avian eggshell is an acellular bioceramic containing organic and inorganic phases that are sequentially assembled during the time the egg moves along the oviduct. As it has been demonstrated in other mineralized tissues, mineralization of the eggshell is regulated by extracellular matrix proteins especially the anionic side chains of proteoglycans. Among them, osteopontin has been found in the avian eggshell and oviduct. However, its precise localization in the eggshell or in different oviduct regions during eggshell formation, nor its function have been established. By using anti-osteopontin antibody (OPN 1), we studied its immunolocalization in the isthmus, red isthmus and shell gland of the oviduct, and in the eggshell during formation. In the eggshell, osteopontin was localized in the core of the non-mineralized shell membrane fibers, in the base of the mammillae and in the outermost part of the palisade. In the oviduct, OPN 1 was localized in the ciliated epithelial but not in the tubular gland cells of the isthmus, in the ciliated epithelial cells of the red isthmus, and in the non-ciliated epithelial cells of the shell gland. The occurrence of osteopontin in each of the oviduct regions, coincided with the concomitant presence of the egg in such region. Considering the reported inhibitory function of osteopontin in other mineralized systems, together with its main occurrence in the non-mineralized parts of the eggshell and at the outermost part of the shell, suggests that this molecule could be part of the mechanism regulating the eggshell calcification.
Calcium Isotope and Elemental Differences between Medullary and Cortical Bones in Domestic Chicken
Journal of Hard Tissue Biology, 2023
Female birds have a medullary bone (MB) on the innermost surface of a cortical bone (CB) during the egg-laying cycle. This bone tissue is known to store calcium (Ca) for eggshell formation. As a result of Ca isotopic analyses of MB and CB from the mature female chickens using a multiple collector-ICP-mass spectrometer (ICP-MS), the 43 Ca/ 42 Ca and 44 Ca/ 42 Ca ratios of MB were higher than those of CB in the bones of the same individual. Moreover, elemental mapping of the CB and MB using a laser ablation-ICP-MS revealed that Mn, Zn, and Cu contents in the MB which are used for activating bone morphogenic protein were higher than those in CB. According to the mechanism of Ca isotope fractionation reported in our previous study, the difference in Ca isotope ratio between MB and CB can be explained by the change in bone turnover rate, i.e., the balance between bone formation and resorption. Therefore, the difference in Ca isotope ratio between MB and CB reflects the different Ca balances during the bone tissue formation of each part.
Matrix Biology, 1998
The aim of this study is to evaluate the regulation of the osteopontin (OPN) gene expression by non-hormonal stimuli, such as calcium flux and mechanical strain during the daily egg cycle in the oviduct of the laying hen. After the egg enters the eggshell gland (ESG), the OPN gene is expressed by the epithelium cells in two waves: first by the basal cells and only then by the apical cells of the epithelium. A reduction in OPN gene expression was observed 1 h prior to laying. The calbindin gene, which marks the onset of calcification, was found to be expressed in the glandular epithelium starting 2 h after OPN gene expression. In addition, the formation of soft shells was accompanied by a reduction in calbindin, but not in OPN, gene expression. The application of a mechanical strain comparable to that induced by an egg led to induction of OPN gene expression at a normally quiescent phase in the cyclical expression of this gene. The induction of the gene was time-and strain-dependent and temporally similar to that induced by the entry of the egg into the ESG. In contrast, the calbindin gene was not affected by mechanical strain. The ESG of the laying hen provides a system to study the effect of a mechanical strain on matrix protein production in vivo, in a relevant physiological setting. The finding suggests that, in contrast to calbindin, OPN gene expression is not regulated by calcium flux but rather by the mechanical strain imposed by the resident egg.