Histochemical studies of Ca-ATPase, succinate and NAD+-dependent isocitrate dehydrogenases in the shell gland of laying Japanese quails: with special reference to calcium-transporting cells

The Effect of Different Levels of Dietary Magnesium on Eggshell Quality and Laying Hen's Performance

This study aimed to investigate the effects of different levels of dietary magnesium (Mg) on eggshell quality and laying hen's performance. Four dietary treatments including a commercial-type basal diet containing 3.19 g/kg Mg and three additional diets supplemented with 2, 4, or 6 g/kg magnesium oxide (MgO) to provide 4.03, 4.87, or 5.71 g/kg Mg were used in a completely randomized design. A total of 120 Bovans White layers at the age of 35 weeks were fed with dietary treatments for 8 weeks. Results indicated that increasing concentrations of Mg in the diets significantly increased hen-day egg production and feed intake (P < 0.05). Dietary Mg supplementation had no effect on egg weight, feed conversion ratio, and average daily weight gain. Eggshell weight, thickness, and strength were significantly increased by adding Mg to the diets (P < 0.05). Dietary treatments significantly increased yolk weight (P < 0.05) but decreased yolk color (P < 0.05). Albumen weight, Haugh unit, yolk shape, and egg shape index were similar among the dietary treatments. Eggshell Mg content (g/kg of dry matter) was significantly increased by the inclusion of Mg in the diets. In conclusion, the results of this study indicated that supplementation of Mg up to 5.71 g/kg diet improved eggshell quality and laying hen's performance.

Combining Random Forests and a Signal Detection Method Leads to the Robust Detection of Genotype-Phenotype Associations

Genome wide association studies (GWAS) are a well established methodology to identify genomic variants and genes that are responsible for traits of interest in all branches of the life sciences. Despite the long time this methodology has had to mature the reliable detection of genotype-phenotype associations is still a challenge for many quantitative traits mainly because of the large number of genomic loci with weak individual effects on the trait under investigation. Thus, it can be hypothesized that many genomic variants that have a small, however real, effect remain unnoticed in many GWAS approaches. Here, we propose a two-step procedure to address this problem. In a first step, cubic splines are fitted to the test statistic values and genomic regions with spline-peaks that are higher than expected by chance are considered as quantitative trait loci (QTL). Then the SNPs in these QTLs are prioritized with respect to the strength of their association with the phenotype using a Random Forests approach. As a case study, we apply our procedure to real data sets and find trustworthy numbers of, partially novel, genomic variants and genes involved in various egg quality traits.

The shell gland in laying and natural moulting commercial egg-type chickens: A histomorphological and ultrastructural study

The purpose of the present study was to determine the histological and ultrastructural changes in the luminal epithelium of the shell gland associated with natural moulting. Samples of the shell gland from laying (32 weeks old) and moulting (75 weeks old) hens were studied using histological, histochemical and electron microscopic techniques. In addition, TUNEL was used to demonstrate the distribution of apoptotic cells in the luminal epithelium of the shell gland. Autophagy, characterized by the presence of autophagosomes and autolysosomes, was evident in the early stages of degeneration in non-ciliated, ciliated and mitochondrial cells. The intermediate and advanced stages of regression in non-ciliated as well as mitochondrial cells occurred via apoptosis, while both apoptotic and necrotic ciliated cells were observed during the later stages of degeneration. The results of the present study suggest that a synergy of autophagy, apoptosis and necrosis is involved in the involution of the shell gland during natural moulting.

Calcium transport in strongly calcifying laying birds: mechanisms and regulation

Birds that lay long clutches (series of eggs laid sequentially before a "pause day"), among them the high-producing, strongly-calcifying Gallus gallus domesticus (domestic hen) and Coturnix coturnix japonica (Japanese quail), transfer about 10% of their total body calcium daily. They appear, therefore, to be the most efficient calcium-transporters among vertebrates. Such intensive transport imposes severe demands on ionic calcium (Ca2+) homeostasis, and activates at least two extremely effective mechanisms for Ca2+ transfer from food and bone to the eggshell. This review focuses on the development, action and regulation of the mechanisms associated with paracellular and transcellular Ca2+ transport in the intestine and the eggshell gland (ESG); it also considers some of the proteins (calbindin, Ca2+ATPase, Na+/Ca2+ exchange, epithelial calcium channels (TRPVs), osteopontin and carbonic anhydrase (CA) associated with this phenomenon. Calbindins are discussed in some detail, as they appear to be a major component of the transcellular transport system, and as only they have been studied extensively in birds. The review aims to gather old and new knowledge, which could form a conceptual basis, albeit not a completely accepted one, for our understanding of the mechanisms associated with this phenomenon. In the intestine, the transcellular pathway appears to compensate for low Ca2+ intake, but in birds fed adequate calcium the major drive for calcium absorption remains the electrochemical potential difference (ECPD) that facilitates paracellular transport. However, the mechanisms involved in Ca2+ transport into the ESG lumen are not yet established. In the ESG, the presence of Ca2+-ATPase and calbindin--two components of the transcellular transport pathway--and the apparently uphill transport of Ca2+ support the idea that Ca2+ is transported via the transcellular pathway. However, the positive (plasma with respect to mucosa) electrical potential difference (EPD) in the ESG, among other findings, indicates that there may be major alternative or complementary paracellular passive transport pathways. The available evidence hints that the flow from the gut to the ESG, which occurs during a relatively short period (11 to 14 h out the 24- to 25.5-h egg cycle), is primarily driven by carbonic anhydrase (CA) activity in the ESG, which results in high HCO3(-) content that, in turn, "sucks out" Ca2+ from the intestinal lumen via the blood and ESG cells, and deposits it in the shell crystals. The increased CA activity appears to be dependent on energy input, whereas it seems most likely that the Ca2+ movement is secondary, that it utilizes passive paracellular routes that fluctuate in accordance with the appearance of the energy-dependent CA activity, and that the level of Ca2+ movement mimics that of the CA activity. The on-off signals for the overall phenomenon have not yet been identified. They appear to be associated with the circadian cycle of gonadal hormones, coupled with the egg cycle: it is most likely that progesterone acts as the "off" signal, and that the "on" signal is provided by the combined effect of an as-yet undefined endocrine factor associated with ovulation and with the mechanical strain that results from "egg white" formation and "plumping". This strain may initially trigger the formation of the mammillae and the seeding of shell calcium crystals in the isthmus, and thereafter initiate the formation of the shell in the ESG.

Calcium ATPase expression in the oviducts of the skink, Lampropholis guichenoti

Lampropholis guichenoti is an oviparous lizard that lays eggs with a calcareous outer shell. We used immunofluorescence microscopy to describe the occurrence and distribution of Ca2+ ATPase pumps in the uterus of L. guichenoti at different stages of the reproductive and egg-shelling cycles. Ca2+ ATPase pumps were not demonstrated by immunofluorescent techniques in any uterine tissue until egg-shelling had commenced and at least partly calcified eggs were in the uterus. During egg-shelling, Ca2+ ATPase pumps occur on the apical and baso-lateral surfaces of uterine epithelial cells, and those of associated shell glands in the stroma of the uterus. We conclude that Ca2+ ATPase pumps provide a major mechanism for deposition of the calcareous eggshell of L. guichenoti and that the pumps are up-regulated when required in the reproductive cycle. Furthermore, it is likely that specific calcium glands in the stroma of the uterus are involved in the rapid transport required for egg-shelling, but the differential contribution of luminal and glandular epithelial cells is not known.

The tight junctional protein occludin is found in the uterine epithelium of squamate reptiles

Occludin, an integral protein associated with the mammalian tight junction, has for the first time been identified in the uterus of squamate reptiles. The tight junction is made up of anastamosing strands and forms a selective barrier that regulates paracellular diffusion of solutes across uterine epithelium. Occludin exclusively labels tight junctional strands and is an excellent marker for tight junction permeability. Using western blotting and immunohistochemistry, occludin expression was examined in the uterine epithelium of five species of Australian skinks at different stages of gestation. More occludin was detected during late stage pregnancy/gravidity compared to the lower levels of occludin detected in vitellogenic and post-parturient females in three of the five species. We conclude that the paracellular permeability of the squamate uterine epithelium decreases as gestation progresses. As placental transport of ions and solutes to the embryo is highest during the last third of pregnancy in viviparous squamates, it is likely that a decrease in paracellular permeability is compensated by an upregulation of other transporting mechanisms such as histotrophy.

Sodium and anion transport across the avian uterine (shell gland) epithelium

The uterine (shell gland) epithelium from the domestic chicken was mounted in Ussing chambers, bathed in symmetric avian saline solution on both apical and basolateral aspects and voltage clamped at 0 mV. The epithelium exhibited a basal short circuit current (I(sc)) that was partially inhibited by the epithelial Na(+) channel (ENaC) blockers, amiloride and benzamil (IC(50) values of 0.8 and 0.12 micromol l(-1), respectively). Inhibition of basal Na(+) absorption by 10 micromol l(-1) amiloride was confirmed by measurements of transepithelial Na(+) and Cl(-) fluxes, where inhibition of the apical-to-basolateral and net Na(+) flux occurred, but no significant effects on Cl(-) fluxes were detected. The amiloride-insensitive portion of the basal I(sc) was both Cl(-) and HCO(3)(-) dependent and was inhibited by the Cl(-) channel blocker, diphenyl-2-carboxylate (DPC; 100 micromol l(-1)). Stimulation with 8-(4-chlorophenylthio)-cyclic 3'-5', adenosine monophosphate (8-cpt cAMP) produced a sustained increase in I(sc) that was dependent on both Cl(-) and HCO(3)(-). The magnitude of the amiloride-sensitive I(sc) was approximately twofold greater in birds where shell formation was complete, but oviposition had not yet occurred. In addition, the amiloride-sensitive I(sc) was greater in hens over the age of 55 weeks and in molting birds. The anion-dependent component of the basal I(sc) was reduced in older birds, and electrogenic HCO(3)(-) transport was nearly absent in molting birds. These results demonstrated that electrogenic Na(+) transport in avian shell gland was similar to the mammalian uterine epithelium and increased with age and during molting. Electrogenic Cl(-) and HCO(3)(-) transport were coupled under basal and cAMP stimulated conditions and basal anion transport decreased with age and during molting.

Na(+)-K(+)-ATPase gene expression in the avian eggshell gland: distinct regulation in different cell types

The avian eggshell gland (ESG) is a tissue specialized in transporting the Ca(2+) required for eggshell formation and represents a unique biological system in which the calcification process takes place in a circadian fashion. With the use of RNA fingerprinting, a set of genes differentially induced at the time of calcification was detected, one of which was identified as the alpha(1)-subunit of Na(+)-K(+)-ATPase. The gene was expressed in a circadian manner in both cell types populating the ESG, but in different temporal patterns, suggesting distinct mechanisms of regulation. Ca(2+) flux and mechanical strain were found to regulate gene expression in the inner glandular epithelium and the pseudostratified epithelium facing the lumen, respectively. Mechanical strain also affected gene expression in cell layers facing the lumen in other parts of the oviduct. Only the alpha(1)-isoform, not the alpha(2)- or alpha(3)-isoform, of Na(+)-K(+)-ATPase was expressed in the ESG. In summary, we demonstrate that the alpha(1)-subunit Na(+)-K(+)-ATPase gene is expressed in different epithelial cell types in the ESG and is regulated by various mechanisms, which may reflect the disparity in the physiological roles of the cells in the process of eggshell formation.

DDE-induced eggshell thinning in birds: effects of p,p'-DDE on the calcium and prostaglandin metabolism of the eggshell gland

1. The focus of this review is the effects and mechanism of action of p,p'-DDE on eggshell formation in birds. Inhibition of prostaglandin synthesis in the eggshell gland mucosa is a probable mechanism for p,p'-DDE-induced eggshell thinning. 2. The duck is sensitive to p,p'-DDE-induced eggshell thinning but the domestic fowl is not, and studies comparing the two species in regard to the calcium and prostaglandin metabolism of the eggshell gland have shown that eggshell thinning induced by p,p'-DDE in ducks is accompanied by reduced activity of prostaglandin synthetase, reduced levels of prostaglandin E2, and reduced uptake of 45Ca by the eggshell gland mucosa. The content of calcium, bicarbonate, chloride, sodium, and potassium are also reduced in the eggshell gland lumen in ducks exhibiting eggshell thinning. None of these effects are seen in the domestic fowl. 3. Inhibition of prostaglandin synthesis is a specific effect of p,p'-DDE. The detrimental effects of p,p'-DDE on the eggshell gland seem to be unique when comparing the compound with structurally related substances, i.e., similar treatment regimens with o,p'-DDE, p,p'-DDT, o,p'-DDT, and p,p'-DDD do not cause eggshell thinning in ducks. Neither do they inhibit prostaglandin synthesis in the eggshell gland mucosa. 4. Administration of other compounds that do inhibit prostaglandin synthesis, e.g., indomethacin, does cause the same effects as those seen with p,p'-DDE, i.e., eggshell thinning and the described effects on the calcium and prostaglandin metabolism of the eggshell gland.

Immunohistochemical localization of a calcium pump and calbindin-D28k in the oviduct of the laying hen

The localization of a plasma membrane calcium pump in the oviduct of the laying hen was investigated by immunohistochemical techniques, utilizing a monoclonal antibody (5F10) produced against the human erythrocyte calcium pump. This antibody was shown to react with an epitope of the pump in oviductal tissue, and prominent staining was observed on the microvilli of the tubular gland cells of the hen shell gland (uterus) and the isthmus. The Ca2+ pump was not detectable in the infundibulum or the magnum. Calbindin-D28k, also localized by immunohistochemical means, was observed to be present in the tubular gland cells of the shell gland and the distal isthmus (adjacent to shell gland) but not in either the proximal isthmus (adjacent to the magnum), the magnum or the infundibulum. The localization of the Ca2+ pump in the oviduct corresponds to known sites of mineral deposition during egg shell formation. The distribution of calbindin-D28k differed, co-localizing with the Ca2+ pump in the shell gland and distal isthmus but not in the proximal isthmus. This might reflect a greater rate of active Ca2+ secretion in the distal isthmus and shell gland as compared to the proximal isthmus.

Determination of fiber types of chicken skeletal muscles based on reaction for actomyosin, calcium+2, magnesium+2-dependent adenosine triphosphatase

Muscle fiber subtypes, determined with the actomyosin Ca+2,Mg+2-adenosine triphosphatase (ATPase) reaction in chicken anterior latissimus dorsi and posterior latissimus dorsi muscles, were demonstrated only after acid or alkaline preincubation followed by a 60-min enzyme incubation. In contrast, subtypes were demonstrated in the sartorius muscle either with or without preincubation. A single-step procedure was therefore possible with this muscle. The results were generally similar to those obtained previously with the mycosin Ca+2-ATPase procedure. Both methods revealed corresponding muscle fiber subtypes, with the exceptions noted below. The actomyosin Ca+2,Mg+2-ATPase procedure, following preincubation at pH 9.4 and 10.3, resulted in a similar reaction intensity in all fiber types. With the myosin Ca+2-ATPase procedure, the IRA (slow) type in anterior latissimus dorsi and sartorius muscles and the I (slow), IIR (fast oxidative-glycolytic), and IIW (fast glycolytic) types in posterior latissimus dorsi muscle had a higher reaction intensity following preincubation at pH 9.4 than at pH 10.3. Fiber Types IIR and IIW in sartorius muscle were easily distinguished with the actomyosin Ca+2,Mg+2-ATPase procedure.

Ultracytochemical investigation of calcium-activated adenosine triphosphatase (Ca++-ATPase) in chick tibia

The ultrastructural distribution of Ca++-ATPase in bone cells of growing chick tibia was investigated by a cytochemical method in order to gain insight into possible sites of calcium ion translocation. Both osteoclasts and osteoblasts showed a polar distribution of reaction product along the plasma membrane. In osteoclasts, enzymatic activity occurred along the portion of the plasma membrane facing the marrow but not along the ruffled border or clear zone. The reaction product in these cells was due solely to Ca++-ATPase action. In osteoblasts, the plasma membrane facing away from bone (apical and lateral membrane) was very intensely stained, whereas the basal membrane was unstained. The reaction product in these cells appeared to be the result of both Ca++-ATPase and Ca++,Mg++-ATPase. In osteocytes, no plasma membrane staining was detectable. Mitochondrial staining in all three types of cells was more sensitive to fixation than was the plasma membrane enzyme, suggesting that mitochondrial and plasma membrane Ca++-ATPases are chemically distinct, as biochemical studies have shown. In general, mitochondria in osteoclasts stained more intensely than those in osteoblasts or osteocytes. Mitochondrial and vesicular sites of activity may be related to intracellular calcium storage, whereas calcium ATPases of the plasma membrane are presumed to be involved in calcium efflux from the cells. Calcitonin treatment did not alter the enzymatic distribution or intensity in osteoclasts. The striking polar distribution of both osteoclast and osteoblast plasma-membrane activity suggests that directional calcium pumping by these cells may be of importance in bone-forming and bone-resorbing mechanisms.

Calcium transport by a calmodulin-regulated Ca-ATPase in the enamel organ

Using aldehyde-fixed rat incisor enamel organ, we localized Ca-ATPase activity ultracytochemically in the plasma membranes, the mitochondrial inner membranes, and the Golgi membranes of secretory ameloblasts and the cells of stratum intermedium at the secretory stage and papillary layer cells at the maturation stage, but not in maturation ameloblasts. This Ca-ATPase activity was totally dependent on substrate ATP, the enzyme activator CaCl2, and also sensitive to the specific calmodulin blocker trifluoperazine (TFP) in the incubation media. Specific antigenic sites of endogenous calmodulin were demonstrated in polyribosomes, the nucleus, mitochondria, and the cytoplasmic matrix along the plasma membranes of secretory ameloblasts, by the protein A-immunogold technique using sheep antiserum against bovine testis calmodulin. All other enamel organ cells-such as stratum intermedium, papillary layer cells, and maturation ameloblasts-were also weakly immunoreactive. In control sections incubated with antiserum pre-absorbed with an excess of calmodulin and protein A-gold complex, only a few gold particles were observed to be randomly associated with the tissues. Daily intraperitoneal injection of TFP (1 and 5 mg per 100 g body weight) for one week resulted in prominent migration of mitochondria from the infranuclear to supranuclear regions of secretory ameloblasts but caused no other morphological alterations in the enamel organ cells. EDX analysis of ultrathin sections revealed significantly lower peaks of Ca and P in the forming enamel of TFP-injected rats than those in controls. However, little reduction in the Ca and P levels in the maturing enamel was observed in TFP-injected rats. When growing enamel surfaces were exposed with NaOCl and examined with SEM, a remarkable defect in the enamel matrix was observed in the forming enamel but not in the maturing enamel. These results suggest that early enamel mineralization is dependent upon an intact calmodulin-regulated Ca-transporting ATPase in secretory ameloblasts and that enamel maturation is controlled by different mechanism(s).

Mitochondrial migration and Ca-ATPase modulation in secretory ameloblasts of fasted and calcium-loaded rats

Migration of mitochondria and modulation of Ca-ATPase activity in secretory ameloblasts were investigated ultrastructurally and ultracytochemically by using lower incisors taken from normally fed, 30-hr-fasted, and calcium (Ca)-loaded rats. In normally fed rats, almost all mitochondria were localized in a narrow infranuclear compartment between the nucleus and proximal cell webs of secretory ameloblasts. In 30-hr-fasted rats, a prominent migration of many mitochondria into the supranuclear region of the cells was noted. Mitochondria returned to the infranuclear compartment and seldom appeared in the supranuclear region when fasted rats were Ca-loaded by transcardiac perfusion with physiological Ca solution. Normally, the mitochondria of secretory ameloblast exhibited moderate Ca-ATPase activity along their inner membranes. This mitochondrial Ca-ATPase was decreased by a 30-hr fast and became prominent again after Ca loading. Plasma-membrane Ca-ATPase was demonstrated in the entire cell surface of secretory ameloblasts. An especially abundant reaction was found along the invaginated cell surface of the Tomes process. This Ca-ATPase also became very weak and was almost abolished from the Tomes process after fasting, but Ca loading caused reappearance of an intense Ca-ATPase activity on the entire cell surface, including along Tomes's processes. These results suggest that 1) mitochondrial localization in secretory ameloblasts is influenced by the Ca concentration of the extracellular milieu, and 2) the level of mitochondrial and cell-membrane ATPase activity is responsive to the concentration of extracellular calcium.

Cytochemical studies of Ca++-ATPase activity in the vestibular epithelia of the guinea pig

We used ultracytochemistry to examine Ca++-ATPase activity in the vestibular epithelia of the guinea pig. Many reaction products were found along the basolateral plasma membrane of the vestibular dark cell. There were also marked reaction deposits on the apical and lateral cell membranes of the transitional cells, and the utricular and saccular wall cells. Both sensory and supporting cells showed Ca++-ATPase activity along their ciliary membrane and apical-lateral cell surfaces. Our findings indicate that the Ca++-ATPase activity found on the plasma membrane is closely related to Ca++-transport across the plasma membrane. When either Ca++ or ATP was omitted from the incubation medium, enzyme activity (as seen by the staining reaction present) was completely abolished. Our present results suggest that Ca++-ATPase located in the vestibular epithelia plays a significant role in the regulation of the Ca++-concentration in the vestibular endolymph.