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PubMed2000

Variability of mercury and selenium levels in clutches of Audouin's gulls (Larus audouinii) breeding at the Chafarinas Islands, Southwest Mediterranean.

We determined mercury and selenium in 43 eggs (eggshell, albumen, and yolk) which belong to different clutch sizes of Audouin's gull from the Chafarinas Islands. The results were compared with those obtained previously with the same species at the Ebro Delta. Both, the intra- and the interclutch sources of variability have been examined. There is an effect of the female on mercury and selenium concentrations in a clutch, which supports the use of eggs as monitoring tools. The distribution pattern of mercury among albumen, yolk and eggshell, the dynamics of this element during the laying process, as well as data concerning egg formation strategies suggest that the mercury in the albumen corresponds mainly to the mercury acquired by the female while feeding in the breeding area. The mercury and selenium levels of the eggs from the Chafarinas Islands were lower than those of the Ebro Delta, which can be due to differences in both the marine contamination and the diet in the two colonies.

Animals↗
PubMed2001

Organochlorine contaminants and biomarker response in double-crested cormorants nesting in Green Bay and Lake Michigan, Wisconsin, USA.

Double-crested cormorant (Phalacrocorax auritus) eggs at pipping and sibling 10-day-old chicks were collected from two colonies in Green Bay, WI, one colony in Lake Michigan, WI, and reference colonies in South Dakota and Minnesota. Egg contents and chicks were analyzed for organochlorine contaminants including polychlorinated biphenyl (PCB) congeners. Livers of embryos and chicks were assayed for hepatic microsomal ethoxyresorufin-O-dealkylase (EROD) activity. Eggshell thickness and the physical dimensions of embryo brains were measured. Concentrations of organochlorines, including p,p'-DDE (p,p'-dichlorodiphenyldichloroethylene), PCBs, and PCB congeners were generally an order of magnitude higher in eggs and chicks from Wisconsin than from reference locations. Total PCBs averaged 10-13 microg/g wet weight in eggs from three Wisconsin colonies compared to 0.9 microg/g PCBs from reference locations. Double-crested cormorant chicks accumulated on average 33-66 microg PCBs/day and 7-12 microg p,p'-DDE/day in the Wisconsin colonies compared to 0 microg PCBs/day and 1 microg p,p'-DDE/day in the reference colonies. At pipping, EROD activity in the livers of cormorant embryos was significantly higher in the Wisconsin colonies and significantly correlated with PCBs and the toxic equivalents (TEQs) of aryl hydrocarbon-active PCB congeners relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin. However, in 10-day-old chicks EROD activity was not consistently different among colonies and was not correlated with PCBs or TEQs. A significant negative relationship between embryo brain asymmetry and the size of the egg suggested that physical constraint might be an important factor influencing the response of this bioindicator. Thinner eggshells in two colonies located near Door County, Wisconsin, suggested that historic p,p'-DDE residues associated with orchards are still an important source of p,p'-DDE in the local environment.

Abnormalities, Drug-Induced↗
PubMed1997

Syncytial organization of acanthors of Polymorphus minutus (Palaeacanthocephala), Neoechinorhynchus rutili (Eoacanthocephala), and Moniliformis moniliformis (Archiacanthocephala) (Acanthocephala).

The fine structures of immature and of developed shelled acanthors of three species belonging to the three subgroups of the Acanthocephala were investigated. Acanthors are surrounded by four eggshells (embryonic envelopes) and are composed of three syncytia: a frontal syncytium, a central syncytium, and an epidermal syncytium. Neither a sense organ nor a nervous system has been found. The central syncytium shows a mass of condensed nuclei and 12 decondensed nuclei and gives rise to 10 anterior/posterior subepidermal myofibrillar systems and 2 oblique retractor muscles. Circular muscles are missing. A single decondensed nucleus can be assigned to each of the 12 muscular systems. The epidermal syncytium embeds the other two syncytia and forms the wrinkled epidermis, which shows an extracellular glycocalyx and intrasyncytial condensations. Prominent recurved hooks, which mark the anterior end of each acanthor, and body spines are intraepidermal differentiations. Partly branched tubular infoldings of the epidermal plasma membrane of the acanthor exist and represent precursors of the pore ducts typical of the adult epidermis. Autapomorphies in the ground pattern of the monophylum Acanthocephala are the four eggshells, the early development of three syncytia, the condensed nuclei in the central syncytium, and the differentiation of ten longitudinal muscle bands and two muscle retractors and of intraepidermal hooks and spines. The syncytial organization of the epidermis with intraepidermal skeletal condensations and infoldings of the apical plasma membrane are characteristics inherited from a stem species common to Acanthocephala, Seison, and Rotifera.

Acanthocephala↗
PubMed2000

Comparative ultrastructure of eggs in Echinostoma paraensei, E. caproni, and E. trivolvis (Trematoda: Echinostomatidae).

The 37-collar-spined echinostomes Echinostoma paraensei, E. caproni, and E. trivolvis are digeneans that live in the intestine of small mammals and birds. Comparative studies of the eggs of these species were done using light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The egg of E. caproni was the largest of the three species studied, whereas the egg of E. trivolvis was the smallest in both length and width. The SEM study showed differences in the aboperculum region of the eggs in all three species. The TEM study showed that the eggshell of all three species consisted of three layers, but no difference in eggshell structure was observed in any species.

Animals↗
PubMed2001

Nematode chitin synthases: gene structure, expression and function in Caenorhabditis elegans and the plant parasitic nematode Meloidogyne artiellia.

Although the presence of chitin in nematodes is well documented little is known about its synthesis in this phyletic group. The recently completed genome sequence of Caenorhabditis elegans predicts two sequences with homology to chitin synthases (chitin-UDP acetyl-glucosaminyl transferase; EC 2.4.1.16). We show that these genes are differentially expressed in a pattern that may reflect different functional roles. One gene is expressed predominantly in the adult hermaphrodite (the main egg-producing stage in the nematode) and later larval stages, which is consistent with a role in production of chitin for the eggshell. The other gene, however, is expressed in the cells that form the pharynx, and only in the period directly preceding a moult. These data suggest that the product of this gene is involved in synthesis of the feeding apparatus, which is replaced during each moult. We have also isolated a full-length genomic sequence of a chitin synthase orthologue from the plant parasitic nematode Meloidogyne artiellia. The single gene present in M. artiellia shows an expression pattern that is consistent with a role for the protein in production of the eggshell.

Animals↗
PubMed1994

The role of vitamin D in chorioallantoic membrane calcium transport.

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) is essential for the transport of eggshell calcium to the embryo across the chorioallantoic membrane (CAM). CAM contains the vitamin D receptor that increases following 1,25-(OH)2D3 injection into embryos at day 10 of incubation. Further, a single injection of 100 ng of 1,25-(OH)2D3 into vitamin D-deficient quail eggs at day 10 of incubation resulted in a significant increase in both body and yolk calcium. This is accompanied by an increase in carbonic anhydrase from low levels in deficiency to normal levels. Acetazolamide (AZ), a specific carbonic anhydrase inhibitor injected into the quail embryos, caused hypocalcemia and hyperphosphatemia. This is similar to the hypocalcemia and hyperphosphatemia found in vitamin D-deficient embryos. These results suggest that one mechanism of action of vitamin D in the mobilization of eggshell calcium is the activation of carbonic anhydrase that acidifies the calcium carbonate shell.

Acetazolamide↗
PubMed1983

Isolation of germ line-dependent female-sterile mutation that affects yolk specific sequestration and chorion formation in Drosophila.

Two loci on the X chromosome have been implicated in choriogenesis by in situ hybridization of poly A-containing RNA from choriogenic eggchambers to Drosophila polytene chromosomes (A.C. Spradling and A.P. Mahowald (1979). Cell 16, 589-598): 7E and 12E. At least two genes coding for major eggshell proteins map to region 7E (A.C. Spradling, M.E. Digan, A.P. Mahowald, M. Scott, and E.A. Craig (1980). Cell 19, 905-914). In an effort to elucidate the functional role of the 12E gene product, 3600 EMS-treated X chromosomes were screened for recessive female-sterile mutations that mapped within the region 11F10-12F1. Four independent female-sterile mutations were recovered, three of which fell into one complementation group (fs29, fs117, and fs445). Mapping by analysis of recombinant progeny as well as of trans heterozygotes utilizing other deficiency chromosomes showed that the three noncomplementing mutations all mapped to region 12E1-12F1. Studies comparing chorion morphology and protein synthesis indicate localized perturbations in the extracellular assembly of eggshell components in mutant eggchambers. The germ line dependence of the mutations was established using germ line mosaics constructed by pole cell transplantation. Analysis of eggchamber protein accumulation patterns showed reduced amounts of yolk polypeptides (YPs) in the mutants. The elevated concentrations of YPs found in mutant hemolymph coupled with the normal YP biosynthetic patterns and active uptake of trypan blue by mutant oocytes suggest that 12E sequences play a role in yolk-specific sequestration.

Animals↗
PubMed1984

Localization of a gene for a minor chorion protein in Drosophila melanogaster: a new chorion structural locus.

A minor chorion protein (called s70) with an approximate molecular weight of 70,000 D has been characterized in Drosophila melanogaster. The Staket geographic strain was found to carry an electrophoretic variant of this eggshell component and was used to determine the chromosomal location of the s70 gene. Our results establish a new locus for a chorion gene near yellow on the X chromosome and represent the first mapping of a quantitatively minor eggshell protein.

Animals↗
PubMed1991

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.

Animals↗
PubMed1986

Effects of suppression and resumption of shell formation and parathyroid hormone on uterine calcium-binding protein, carbonic anhydrase activity, and intestinal calcium absorption in hens.

The calcium absorption and duodenal and uterine vitamin D-dependent calcium-binding protein (CaBP-28K) levels were decreased in hens when eggshell calcification was suppressed by premature expulsion of the egg. Nevertheless, these levels remained higher than those of immature pullets or pullets treated with estrogen. The resumption of shell formation by hens which had previously laid soft-shell eggs was associated during calcification of the first egg with increases in intestinal Ca absorption. CaBP concentration, and alkaline phosphatase activity. The increase in uterine CaBP concentration preceded the stage of rapid calcium deposition. Uterine carbonic anhydrase activity was increased by sexual maturity but not consistently by shell formation. Ablation of the parathyroids just before the resumption of shell formation suppressed the increases in duodenal calcium absorption and CaBP concentration elicited by egg calcification. In contrast, the increase in CaBP level was maintained in the uterus of parathyroidectomized hens, in spite of the decreased shell deposition. Previous studies indicated that increased uterine CaBP associated with eggshell calcification is not elicited by vitamin D. The present study confirms this observation and also shows that these changes are not elicited by either PTH or sex steroid hormones.

Animals↗
PubMed1979

Water-vapor conductance of testudinian and crocodilian eggs (class reptilia).

Flexible-shelled eggs of snapping turtles (Chelydra serpentina) have conductances to water vapor that are 55 times higher than predicted for avian eggs of similar size, whereas rigid-shelled eggs of softshell turtles (Trionyx spiniferus) and American alligators (Alligator mississippiensis) have conductances that are only five times higher than expected for comparable eggs of birds. The differences between empirical and predicted values result from the much higher effective pore areas in reptilian eggshells than in those of birds. The relatively high porosities of these reptilian eggs presumably facilitate the transport of oxygen and carbon dioxide eggshells in later stages of incubation when air trapped inside nest chambers may become hypoxic and hypercapnic, yet seem not to lead to excessive transpiration of water vapor owing to the high humidities in nests where incubation occurs.

Alligators and Crocodiles↗
PubMed1982

The initiation of pulmonary respiration in a bird embryo: blood and air cell gas tensions.

The gaseous stimuli for pipping and the initiation of pulmonary respiration were examined in th Wedge-tailed Shearwater (Puffinus pacificus) by measuring blood gas tensions in the chorioallantoic vein and air cell gas tensions (Pao2 and Paco2) prior to and during the pipping process. External pipping (shell fracture) was the first observed pipping event and preceded internal pipping (penetration of air cell and initiation of pulmonary ventilation). This sequence of cracking the eggshell prior to the initiation of pulmonary respiration resulted in higher Pao2 and lower Paco2 values than the pre-pip air cell gas tensions. Pip-cracks in the shell allow greater diffusion than could normally be obtained across the intact eggshell. This also favors the establishment of large partial pressure gradients of O2 and CO2 across the chorioallantois, thereby improving gas exchange across the inner resistance barrier. The gaseous stimuli for pipping may be attenuated and thus favor the 5-6 day pip-to-hatch interval in this species.

Allantois↗
PubMed1988

Development of the chick embryo: effects of egg mass.

We asked to what extent, within a species, differences in egg mass, hence in eggshell surface area and O2 conductance, could affect the development of the avian embryo. Large (L, about 70 g) and small (S, about 55 g) fertile chicken eggs were simultaneously incubated and the embryos studied at day 18, i.e. before the onset of lung ventilation. Embryo mass and O2 consumption (VO2) (measured with a manometric technique) normalized per mass of the freshly laid egg were higher in S than in L, while no differences occurred after normalization by egg surface area (S.A.). Egg water vapour conductance, which is proportional to O2 conductance, was also found to be directly proportional to egg S.A. Hence, the mass and VO2 of the embryo are more closely related to the O2 conductance of the eggshell than to egg mass, giving support to the concept that the avian embryo's VO2 is not an invariable species characteristic, but a variable dependent on O2 availability. Hatching and viability did not differ between L and S, and the specific mass of heart and lung and their cellular (DNA) concentration were also similar between the two groups of embryos. Therefore, differentiation of tissues and organogenesis do not seem to be affected by the differences in total O2 availability determined by the differences in egg mass, while they are probably more important than total tissue mass in setting the time of hatching.

Animals↗
PubMed1994

A new member to the astacin family of metalloendopeptidases: a novel 1,25-dihydroxyvitamin D-3-stimulated mRNA from chorioallantoic membrane of quail.

1,25-Dihydroxyvitamin D-3 is essential for the utilization of eggshell calcium by avian embryo through the chorioallantoic membrane (CAM). A cDNA library was constructed from poly(A)+ RNA extracted from vitamin D-deficient CAMs given 1,25-dihydroxyvitamin D-3. Screening this library by differential hybridization yielded a full-length (approximately 1.8 kb) cDNA, whose corresponding mRNA is increased 3-fold 2.5 h after a single injection of 1,25-(OH)2D3. The complete nucleotide sequence for the full-length cDNA has been determined. An open-reading frame, corresponding to a 310 amino acid, 41 kDa protein was found. Searching protein sequence data bases revealed a strong similarity to the following proteases: astacin, a crayfish digestive protease, Oryzias latipes hatching enzyme constituent protease (Orz), Xenopus laevis developmentally regulated UVS.2 protein secreted by the hatching gland of embryos, the NH2-terminal domain of human bone morphogenetic protein (BMP-1) and Drosophila dorsal-ventral patterning tolloid. The cDNA has approximately 36% overall identity with astacin and BMP-1, and is more than 60% identical to either Orz or UVS.2. Moreover, multiple alignment analysis indicates that 37 residues, including 3 cysteine residues, are strictly conserved in the complete 200-amino acid astacin sequence. All 6 proteins contain a zinc-binding motif (HEXXH), found at the active site of most metalloendopeptidases. This motif is found within an extended sequence of HEXXHXXGFXHE that is unique to this subgroup of metalloendopeptidases. In addition, the 6 proteins have 50% identity (including the present cDNA) and 79% are conserved in 4 of these proteins in a 24-amino acid sequence that includes the putative active site. The level of mRNA for the new protein reaches a maximum at day 12 of embryonic life and declines thereafter. It is suggested that this clone corresponds to an mRNA encoding for a protease that may play a role in the degradation of eggshell matrix.

Allantois↗
PubMed1984

Changes in activity of chicken medullary bone cell populations in relation to the egg-laying cycle.

Osteoblastic and osteoclastic activity was studied in avian medullary bone in vivo. During the active period of eggshell calcification, medullary bone active resorption surface increased ninefold. This correlated with a sevenfold increase in the percentage of active osteoclasts. Osteoblast activity is also increased during the active period, as demonstrated by a twofold increase in the active osteoblastic surface. These findings and our observation that the medullary bone volume remains the same (+/- 13%) whether the eggshell is being formed (active period) or not (inactive period) led to the conclusion that the activities of osteoblasts and osteoclasts rapidly return to balance.

Animals↗
PubMed1993

Accumulation of organochlorine contaminants in double-crested cormorants.

Cormorant eggs and lipid samples from juvenile Cormorants were analyzed for 14 organochlorine contaminants. Low concentrations (geometric mean < 0.05 microg/g) of hexachlorobenzene (HCB), lindane, oxy-chlordane, heptachlor epoxide, dieldrin, endrin, mirex, DDD and DDT in eggs primarily reflected the wintering-ground origin of organochlorine contaminants. Overall geometric mean concentrations of DDE and PCBs in Cormorant eggs were 3.90 and 2.22 microg/g egg respectively, and would not affect reproduction or eggshell thickness. Eggshells averaged 0.44 mm in thickness and no correlation (r2 = 0.17) with log-transformed DDE residues in Cormorant eggs was evident. Only DDE and PCBs were detected in lipid samples from 5- to 8-week-old Cormorants (geometric mean approximately 1.0 microg/g lipid for each compound). The PCB: DDE ratios in Cormorant lipid from some individual colonies were 2-3.5 times greater than the ratio in eggs from the same colony, suggesting an accumulation of PCBs related to local diet. Juvenile Cormorants might serve as regional indicators of chemical residue contamination in Alberta, and provide a temporal perspective on changes in contaminant burdens in aquatic ecosystems.

Journal Article↗
PubMed1995

Reduced breeding success of Cormorants (Phalacrocorax carbo sinensis) in relation to persistent organochlorine pollution of aquatic habitats in The Netherlands.

Cormorants (Phalacrocorax carbo sinensis) breeding in the heavily contaminated sedimentation area of the rivers Rhine and Meuse have a severely reduced breeding success as compared to several other Dutch colonies. A detailed analysis of reproductive performance in combination with chemical analysis of eggs and food from colonies in differently contaminated aquatic habitats is presented. The differences in breeding success between colonies are caused mainly in the egg-stage of breeding. Eggshell thinning and increased embryonic mortality cause the differences in hatching success. The observed effects seem to be related to chlorinated hydrocarbons. Significant correlations are found for concentrations of DDE with eggshell thinning and for concentrations of PCBs with hatching and breeding success. The correlations between concentrations of chlorinated hydrocarbons in eggs and biological effects measured in the field are established both on colony and individual clutch level.

Journal Article↗
PubMed1989

Blood plasma catecholamine concentration of poult embryos during the transition from diffusive to convective respiration.

1. Plasma catecholamines were determined in turkey embryos. 2. Decreased eggshell permeability depressed dopamine and epinephrine, but increased permeability also depressed epinephrine. 3. Norepinephrine (NE) was greatest before transition to convective respiration when hypoxia occurs. 4. NE was associated inversely with eggshell permeability. 5. Catecholamines appear to assist the embryo during hatching hypoxia.

Animals↗