(-)-Hydroxycitric Acid Influenced Fat Metabolism via Modulating of Glucose-6-phosphate Isomerase Expression in Chicken Embryos

The current research aimed to explore the impact of (-)-hydroxycitric acid (HCA) on fat metabolism and investigate whether this action of (-)-HCA was associated with modulation of glucose-6-phosphote isomerase (GPI) expression in chicken embryos. We constructed a recombinant plasmid (sh2-GPI) to inhibit GPI expression, and then embryos were treated with (-)-HCA. Results showed that (-)-HCA reduced lipid droplet accumulation, triglyceride content, and lipogenesis factors mRNA level and increased lipolysis factors mRNA expression, while this effect caused by (-)-HCA was markedly reversed when the chicken embryos were pretreated with sh2-GPI. (-)-HCA increased phospho (p)-acetyl-CoA carboxylase, enoyl-CoA hydratase short chain-1, carnitine palmitoyl transferase 1A, p-AMP-activated protein kinase, and peroxisome proliferators-activated receptor α protein expression, and this action of (-)-HCA also dispelled when the chicken embryos were pretreated with sh2-GPI. These data demonstrated that (-)-HCA decreased fat deposition via activation of the AMPK pathway, and the fat-reduction action of (-)-HCA was due to the increasing of GPI expression in chicken embryos.

Cadmium effects on early development of chick embryos

The toxic potential of cadmium (Cd) is well-documented for young and adult vertebrates, but it is still poorly understood in the early stages of development. In this study, cadmium effects were investigated on Gallus gallus embryos after injection of CdCl(2) (5μM and 50μM) within the egg air chamber, and incubation for 48 and 72h. After exposure, morphological and enzymatic analyses for glucose-6-phosphate dehydrogenase (G6PDH) and glutathione S-transferase (GST) were performed. Critical morphological abnormalities occurred after exposure to the highest concentration of cadmium, mainly in the cephalic region, indicating the powerful teratogenic effect of Cd to chick embryos. Cd exposure did not alter enzymatic activities when compared to the control group, but the levels of G6PDH activity were highest in older embryos at stage 19, indicating that antioxidant defenses are not so robust in the earliest embryo stages.

Spots and stripes: pleomorphic patterning of stem cells via p-ERK-dependent cell chemotaxis shown by feather morphogenesis and mathematical simulation

A key issue in stem cell biology is the differentiation of homogeneous stem cells towards different fates which are also organized into desired configurations. Little is known about the mechanisms underlying the process of periodic patterning. Feather explants offer a fundamental and testable model in which multi-potential cells are organized into hexagonally arranged primordia and the spacing between primordia. Previous work explored roles of a Turing reaction-diffusion mechanism in establishing chemical patterns. Here we show that a continuum of feather patterns, ranging from stripes to spots, can be obtained when the level of p-ERK activity is adjusted with chemical inhibitors. The patterns are dose-dependent, tissue stage-dependent, and irreversible. Analyses show that ERK activity-dependent mesenchymal cell chemotaxis is essential for converting micro-signaling centers into stable feather primordia. A mathematical model based on short-range activation, long-range inhibition, and cell chemotaxis is developed and shown to simulate observed experimental results. This generic cell behavior model can be applied to model stem cell patterning behavior at large.

Identification and characterization of the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) in hen egg

Using zymography and mass spectrometry, we identified for the first time the precursor of chicken matrix metalloprotease 2 (pro-MMP-2) as a complex with TIMP-2 (tissue inhibitor of metalloproteinases) in egg white and yolk. Real-time polymerase chain reaction confirmed that MMP-2 and its inhibitors TIMP-2 and TIMP-3 were expressed all along the oviduct and in the liver of laying hens. We also demonstrated that the processing of pro-MMP-2 into mature MMP-2 by serine proteases does not occur in vivo, although purified pro-MMP-2 undergoes proteolytic maturation by these proteases in vitro. Moreover, the relative pro-MMP-2 activity assessed by gelatin zymography was shown to decrease in egg white during the storage of unfertilized or fertilized eggs. However, the mature form of 62 kDa MMP-2 could not be detected. The fact that MMP-2 is found as a proform in fresh eggs suggests that the activity of this metalloprotease is regulated under specific conditions during embryonic development.

[Efficacy of various methods of a reporter gene transfer to chicken embryonic cells]

The methods of transfection ofa plasmid with a reporter gene involving DNA injection into chicken embryonic cells were studied. The parameters of the efficient transfection of chicken blastodermal cells with a foreign gene have been determined (20-24 and up to 40% in culture and embryos, respectively). A high efficiency of transfection of primordial germ cells isolated from the gonads has been obtained after DNA injection into the dorsal aorta of 2.5-day-old chicken embryos.

Hepatic lipogenesis in broiler chickens with different fat deposition during embryonic development

In order to identify the genes involved in the fatness variability, we studied the expression of several genes implicated in the hepatic lipid metabolism of broiler chickens with different fat deposition patterns during embryonic development. The mRNA expression of acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), malic enzyme (ME) and apolipoprotein B100 (apoB100) genes were determined using reverse transcriptase-polymerase chain reaction (RT-PCR). Samples of livers were collected from Arbor Acres (AA) and Sanhuang (SH) chickens on day 9, 14 and 19 of embryonic development as well as at hatching. This study showed that hepatic triglyceride (TG) level was found to increase suddenly during day 14 of embryonic development, to gradually increase thereafter, and to remain relatively constant at hatching. FAS gene expression in AA and SH broilers occurred prior to hatching and at hatching. The gene was expressed more in the former breed. ACC gene expression was observed beginning at the earlier development stage of days 9. No breed difference was observed in ME and apoB gene expression. This study indicated that the expression of lipogenic enzyme genes of the liver in broiler chickens exhibited scheduling during embryogenesis. The ACC gene started to express earlier than the FAS gene during embryonic development. This suggested that embryonic liver synthesized fatty acid, and breed difference was noticed prior to hatching.

Cyp26 genes a1, b1 and c1 are down-regulated in Tbx1 null mice and inhibition of Cyp26 enzyme function produces a phenocopy of DiGeorge Syndrome in the chick

Cyp26a1, a gene required for retinoic acid (RA) inactivation during embryogenesis, was previously identified as a potential Tbx1 target from a microarray screen comparing wild-type and null Tbx1 mouse embryo pharyngeal arches (pa) at E9.5. Using real-time PCR and in situ hybridization analysis of Cyp26a1 and its two functionally related family members Cyp26b1 and c1, we demonstrate reduced and/or altered expression for all three genes in pharyngeal tissues of Tbx1 null embryos. Blockade of Cyp26 function in the chick embryo using R115866, a specific inhibitor of Cyp26 enzyme function, resulted in a dose-dependent phenocopy of the Tbx1 null mouse including loss of caudal pa and pharyngeal arch arteries (paa), small otic vesicles, loss of head mesenchyme and, at later stages, DiGeorge Syndrome-like heart defects, including common arterial trunk and perimembranous ventricular septal defects. Molecular markers revealed a serious disruption of pharyngeal pouch endoderm (ppe) morphogenesis and reduced staining for smooth muscle cells in paa. Expression of the RA synthesizing enzyme Raldh2 was also up-regulated and altered Hoxb1 expression indicated that RA levels are raised in R115866-treated embryos as reported for Tbx1 null mice. Down-regulation of Tbx1 itself was observed, in accordance with previous observations that RA represses Tbx1 expression. Thus, by specifically blocking the action of the Cyp26 enzymes we can recapitulate many elements of the Tbx1 mutant mouse, supporting the hypothesis that the dysregulation of RA-controlled morphogenesis contributes to the Tbx1 loss of function phenotype.

Transition from ectothermy to endothermy: the development of metabolic capacity in a bird (Gallus gallus)

The evolution of endothermy is one of the most significant events in vertebrate evolution. Adult mammals and birds are delineated from their early ontogenetic stages, as well as from other vertebrates, by high resting metabolic rates and consequent internal heat production. We used the embryonic development of a bird (Gallus gallus) as a model to investigate the metabolic transition between ectothermy and endothermy. Increases in aerobic capacity occur at two functional levels that are regulated independently from each other: (i) upregulation of gene expression; and (ii) significant increases in the catalytic activity of the main oxidative control enzymes. Anaerobic capacity, measured as lactate dehydrogenase activity, is extremely high during early development, but diminishes at the same time as aerobic capacity increases. Changes in lactate dehydrogenase activity are independent from its gene expression. The regulatory mechanisms that lead to endothermic metabolic capacity are similar to those of ectotherms in their response to environmental change. We suggest that the phylogenetic occurrence of endothermy is restricted by its limited selective advantages rather than by evolutionary innovation.

Prokaryotic and eukaryotic monothiol glutaredoxins are able to perform the functions of Grx5 in the biogenesis of Fe/S clusters in yeast mitochondria

The Saccharomyces cerevisiae monothiol glutaredoxin Grx5 participates in the mitochondrial biogenesis of iron-sulfur clusters. Grx5 homologues exist in organisms from bacteria to humans. Chicken (cGRX5) and human (hGRX5) homologues contain a mitochondrial targeting sequence, suggesting a mitochondrial localization for these two proteins. We have compartmentalized the Escherichia coli and Synechocystis sp. homologues, and also cGRX5 and hGRX5, in the mitochondrial matrix of a yeast grx5 mutant. All four heterologous proteins rescue the defects of the mutant. The chicken cGRX5 gene was significantly expressed throughout the embryo stages in different tissues. These results underline the functional conservation of Grx5 homologues throughout evolution.

Regulation of Thyroid Hormone Availability by Iodothyronine Deiodinases at the Blood-Brain Barrier in Birds

It is accepted that type II iodothyronine deiodinase (D2) is predominantly found in brain, where it maintains homeostasis of thyroid hormone (TH) levels. The current study describes the production of a polyclonal D2 antiserum and its use in the comparison of D2 protein distribution with that of type I (D1) and type III (D3) deiodinase protein in the chicken choroid plexus (CP). Immunocytochemistry showed high D2 protein expression in the epithelial cells of the CP, whereas the D1 and D3 proteins were absent. Furthermore, dexamethasone treatment led to an upregulation of the D2 protein in these cells.

Cloning of chicken choline acetyltransferase and its expression in early embryonic retina

The enzyme choline acetyltransferase [EC 2.3.1.6] (ChAT) synthesizes the neurotransmitter acetylcholine that plays a key morphogenic role in vertebrate retina development. As the embryonic avian retina is particularly useful for morphogenetic studies, we cloned the complete coding region of chicken ChAT cDNA. At the deduced amino acid level, chicken ChAT is approximately 76% identical to mammalian ChAT proteins. We also report here the cloning of the complete 5' end of the complex cholinergic locus. This locus contains both the ChAT gene and the nested intronless gene for the vesicular acetylcholine transporter (VAChT). The genomic organization of the 5' end of the chicken cholinergic locus is similar to that reported in other vertebrate species. A 5.7 kb mRNA corresponding to the ChAT message was detected in both embryonic retina and post-hatch brain. An analysis of the ChAT mRNA in embryonic chick retina shows that the message can be detected by E6 and its level increased during early retinal development. Vertebrate ChAT mRNAs can contain one or more of three non-coding exons, M, N or R and by RT-PCR we demonstrate, at least, a chicken ChAT mRNA containing exon M.

MMP-2 plays an essential role in producing epithelial-mesenchymal transformations in the avian embryo

To investigate the roles that matrix-degrading proteases may have in development of the chicken embryo, we documented the expression pattern of matrix metalloprotease-2 (MMP-2, 72-kDa type IV collagenase or gelatinase A) and perturbed its function in vitro and in vivo. MMP-2 is expressed as neural crest cells detach from the neural epithelium during an epithelial-mesenchymal transformation (EMT) but is rapidly extinguished as they disperse. It is also expressed in the sclerotome and in the dermis at the time that the EMT is initiated, and also as these cells migrate, and is down-regulated once motility has ceased. These patterns suggest that MMP-2 plays a role in cell motility during the EMT and during later morphogenesis. Inhibitors of MMPs, including BB-94 and TIMP-2 (tissue inhibitor of metalloprotease-2), prevent the EMT that generates neural crest cells, both in tissue culture and in vivo, but do not affect migration of the cells that have already detached from the neural tube. Similarly, knockdown of MMP-2 expression in the dorsal neural tube using antisense morpholino oligos perturbs the EMT, but also does not affect migration of neural crest cells after they have detached from the neural tube. On the other hand, when somites in culture are treated with TIMP-2, some mesenchymal cells are produced, suggesting that they undergo the EMT, but show greatly reduced migration through the collagen gel. MMP-2 is also expressed in mesenchyme where tissue remodeling is in progress, such as in the developing feather germs, in the head mesenchyme, in the lateral plate mesoderm, and in the limb dermis, especially in the regions where tendons are developing. Comparisons of these expression patterns in multiple embryonic tissues suggest a probable role for MMP-2 in the migration phase of the EMT, in addition to mesenchyme dispersion and tissue remodeling. Developmental Dynamics 229:42-53, 2004.

A Potential Role for beta-Carotene in Avian Embryonic Development

Vitamin A is essential for vertebrate embryonic development; dietary carotenoids are the primary source of vitamin A since animals cannot synthesize it de novo. To study the role of beta-carotene during embryonic development, we analyzed in chick embryos the expression of beta,beta-carotene 15,15'-oxygenase (beta-oxy) which cleaves beta-carotene to produce two molecules of retinal. beta-oxy transcripts were detected in one-and-a-half- to five-day-old embryo homogenates and in situ hybridization in five-day-old embryos, revealing their presence in tissues including the central nervous system, lungs, limbs, and cardiovascular system. Moreover, we detected beta-oxy enzymatic activity in extracts from five-day-old embryos as well as small amounts of beta-carotene in the egg yolk. These results indicate that beta-oxy is present during early developmental stages, raising the possibility that yolk-stored beta-carotene is utilized as a source of vitamin A. Thus, our results suggest that beta-carotene could play an important role in early avian embryonic development as a local source of vitamin A in specific tissues.

A non-mitochondrial carboxylase, related to glutamate action is synthesized in the retina of the chick embryo

SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot of chick retinal proteins at 21 days after intravitreal injection with 5 or 10 microM/eye Glu showed decreases in 37, 42, 53 and 57 kDa proteins and increases in 35, 72 and >94 kDa proteins. These proteins were carboxylases except for the 35 and 37 kDa proteins. With > or =15 microM/eye Glu, non-specific loss of retinal proteins was observed. In embryonic retinas, the 42 kDa protein was seen a few days before hatching, with biotin incorporation on days 3-6 after hatching. Immunohistochemistry indicated that this protein was a component of both the inner nuclear layer and the photoreceptor. Immunocytochemistry located it to the cell surface.

Differential expression of iodothyronine deiodinases in chicken tissues during the last week of embryonic development

In the current study, the authors examined the type 1 (D1), type 2 (D2), and type 3 deiodinase (D3) activity and mRNA expression patterns in thyroid, lung, brain, pituitary, heart, liver, spleen, gonads, skin, muscle, intestine, Fabricius' bursa, and kidney during the last week of chicken embryonic development and the first 2 days posthatch. The D3 was the most widely expressed, occurring in all examined tissues. Also, the D1 knows a widespread distribution, although no D1 activity or mRNA expression could be detected in the brain, the thyroid, the muscle, and the skin. In contrast, the D2 has a much more restricted expression pattern, since the brain is the only organ where, prior to hatching, both in vitro D2 activity and D2 mRNA expression can be detected. Taken together, these results demonstrate that during the last week of chicken embryonic development, the majority of tissues express D3, together with either D1 or D2, indicating that each tissue possesses the necessary tools to regulate local thyroid hormone levels at least partly independent from T(3) and T(4) levels in plasma. In addition, the deiodinase expression data could be correlated to certain thyroid hormone dependent tissue-specific developmental events. This strongly suggests that in birds, as in mammals and amphibians, the correct spatial and temporal expression of iodothyronine deiodinases are essential for normal embryonic development.

Ontogeny of 5-aminolevulinic dehydratase and porphobilinogen deaminase activities in the yolk sac membrane and liver of chick embryos

1. Chick embryos of 7, 9, 11, 12, 13, 14, 15, 17 and 19 d of embryonic development were examined to determine the activities of 5-aminolevulinic dehydratase (ALA-D, EC 4.2.1.24) and porphobilinogen deaminase (PBG-D, EC 4.3.1.8). 2. Liver and yolk sac membrane ALA-D specific activities showed a maximum between 12 and 13 d of embryonic development, yolk sac membrane PBG-ase activity a maximum at 9 d and at 7 d in liver. Total activities of ALA-D and PBG-D were not constant during the course of embryonic development but probably related to the changes of intensity of haem synthesis. 3. ALA-D and PBG-ase activities were higher in yolk sac membrane than in liver, showing the importance of the yolk sac membrane as erythropoietic tissue. PBG-D catalysed the rate-limiting reaction of the cytosolic steps in the biosynthetic pathway in both tissues.

Caspase activity is involved in, but is dispensable for, early motoneuron death in the chick embryo cervical spinal cord

We examined the role of caspases in the early programmed cell death (PCD) of motoneurons (MNs) in the chick embryo cervical cord between embryonic day (E) 4 and E5. An increase in caspase-3-like activity in MNs was observed at E4.5. Treatment with an inhibitor of caspase-3-like activity, Ac-DEVD-CHO, for 12 h blocked this increase and revealed that caspase-3-like activity is mainly responsible for DNA fragmentation and the nuclear changes during PCD but not for degenerative changes in the cytoplasm. When a more broad-spectrum caspase inhibitor was used (bocaspartyl (OMe)-fluoromethyl ketone, BAF), the appearance of degenerative changes in the cytoplasm was delayed by at least 12 h. However, following treatment with either Ac-DEVD-CHO or BAF for 24 h, the number of surviving healthy MNs did not differ from controls, indicating a normal occurrence of PCD despite the inhibition of caspases. These results suggest that caspase cascades that occur upstream of and are independent of the activation of caspase-3-like activity are responsible for the degenerative changes in the cytoplasm of dying cervical MNs. These data also suggest that, although one function of caspases may be to facilitate the kinetics of PCD, caspases are nonetheless dispensable for at least some forms of normal neuronal PCD in vivo.

Introduction of DT40 cells into chick embryos

AIM

To examine the transfection of exogenous genes into chick embryos, applying the characteristics of avian leukosis virus (ALV)-induced chicken B cell line DT40 to the production of chimeric birds.

METHODS

The DT40 cells incorporated with exogenous gene ( lacZ constructs encoding Escherichia coli beta-galactosidase: beta-gal) were introduced into chick embryos by the injection of cells into stage X blastoderm. Manipulated eggs were incubated for 3 (trial 1) or 6 (trial 2) days, and the expression of lacZ DNA was detected by a histochemical staining method of beta-galactosidase and polymerase chain reaction (PCR) analysis.

RESULTS

The survival rates of the manipulated embryos incubated for 3 days (stage 18-20: trial 1) and 6 days (stage 28, 30: trial 2) were about 42% and 38%, respectively. The expression rates of the lacZ gene in the embryos in the trials 1 and 2 were about 60% and 23%, respectively, for the survived embryos.

CONCLUSION

The rate of embryonic viability and expression rate of introduced genes were not so high, but it suggested the possibility of utilizing the DT40 cells as a vector for carrying exogenous genes into chick embryos.

Co-ordinated induction of beta-carotene cleavage enzyme and retinal reductase in the duodenum of the developing chicks

The developmental patterns of expression of beta-carotene cleavage enzyme activity were compared with those of retinal reductase and NAD-dependent retinol dehydrogenase activities in chick duodenum during the perinatal period. The beta-carotene cleavage enzyme activity was not detected in the duodenum before hatching, but it increased rapidly during 24 h after hatching. On the other hand, a considerable level of beta-carotene cleavage enzyme activity was observed in the liver of embryonic stages and its activity gradually rose during the perinatal period. Comparison of kinetic constants for the beta-carotene cleavage enzyme activities in the duodenum and the liver indicated that the enzyme in the duodenum possessed a lower affinity for beta-carotene than that in the liver. The retinal reductase activity was detected in the microsomes of the duodenum at the earliest time examined, i.e. day 16 of embryogenesis and its activity began to rise on the last day of embryogenesis, which was followed by a gradual increase until 1 day of age. The NAD-dependent retinol dehydrogenase activity was also seen in the microsomes of the duodenum in embryonic stages and its activity increased in parallel with the retinal reductase activity around the hatching period. These developmental inductions of beta-carotene cleavage enzyme and retinal reductase activities in the duodenum coincided with those of cellular retinol-binding protein, type II (CRBPII) and lecithin: retinol acyltransferase (LRAT). These results suggest that a co-ordinated induction mechanism should be operative for beta-carotene cleavage enzyme and retinal reductase, both of which are inevitable in the process of beta-carotene absorption and metabolism.

Expression of protein tyrosine kinases and stem cell factor in chicken blastodermal cells

Chicken blastodermal cells (CBC) from Stage X embryos, which were isolated from newly laid, fertile, unincubated eggs, are pluripotent cells and can produce somatic and germline chimeras when injected into recipient stage X embryos. The CBC retain their pluripotential ability for up to 7 d in vitro. The molecular mechanisms that control proliferation and differentiation of CBC are largely unknown, although protein tyrosine kinases (PTK) are known to play important roles in these processes in similar cells. To understand better the molecular mechanisms of proliferation and differentiation in CBC, expression profiles of PTK and stem cell factor (SCF) were analyzed by reverse transcription polymerase chain reaction (RT-PCR) using gene-specific and degenerate oligonucleotide primers. Seventeen distinct PTK, including 14 receptor-type and 3 nonreceptor-type PTK and SCF were identified by RT-PCR. Expression of all of the genes was confirmed by northern blot analysis. The northern blot analysis showed that all probes hybridized with one or more transcripts at various expression levels. The expression of the 17 PTK and SCF genes in CBC suggests that they might play a role in signal transduction pathways that control the proliferation or differentiation in CBC.

Specialised cell types in the chorioallantoic membrane express carbonic anhydrase during chick embryogenesis

The expression of carbonic anhydrase in the chorioallantoic membrane (CAM) of the chick embryo was investigated by means of the histochemical localisation of the enzyme catalytic sites and the immunohistochemical identification of its isoenzymatic forms. The results show that carbonic anhydrase is developmentally expressed in a subset of cells both in the ectodermal and the endodermal epithelium. The distribution patterns from both methodological approaches indicated that carbonic anhydrase is a marker of the villus cavity cells and the mitochondria-rich cells in the ectodermal and the endodermal epithelium, respectively. Such a cell-specific pattern of the enzyme expression provides a further contribution to characterising the heterogeneous cell population of the chick CAM and supports specific functional involvement for the distinct cell types in CAM-mediated processes, such as calcium transport, maintenance of acid-base balance and water and electrolyte reabsorption, during chick embryogenesis.

Protein kinase C-like immunoreactive cells in embryo and adult chicken retinas

Morphological evidence of a temporal parallelism between the appearance of the alpha isoform of protein kinase C (PKC) and some processes such as synaptogenesis in the plexiform layers of the chicken retina is offered. Immunostaining experiments were performed throughout embryonic, young and adult chicken life. The results help to understand the development of rod bipolar cells.

Proteins in vacuo: a molecular dynamics study of the unfolding behavior of highly charged disulfide-bond-intact lysozyme subjected to a temperature pulse

Molecular dynamics simulations were used to interpret a variety of experimental data on highly charged disulfide-bond-intact lysozyme in vacuo. The simulation approach involved submitting a model of the protein [Reimann, Velázquez, and Tapia, J. Phys. Chem. B 102, 9344 (1998)] in a given charge state to a 3-ns-long heat pulse (usually at 500 K) followed by cooling or relaxation for 1 ns back to room temperature (293 K). This treatment yielded a charge threshold around Q(0)=8+ for obtaining significant unfolding, as indicated by an enhancement in collision cross section and conformer length. The collision cross sections and lengths theoretically obtained, along with the threshold charge state for initiating unfolding, were compatible with experimental results on lysozyme in vacuo. The unfolded, highly elongated conformations obtained for Q> or = 9+ displayed a significant level of non-native beta-sheet content which appeared to be additionally stabilized by charge self-solvation.

Ornithine decarboxylase activity in developing chick embryos after exposure to 60-hertz magnetic fields

Fertilized white leghorn eggs were exposed to a 4 micro-Tesla (microT) 60 Hz horizontal magnetic field for 15, 18, 23 and 28 h. After exposure to the magnetic field, the embryos were isolated and assayed for ornithine decarboxylase (ODC) activity. ODC activity in magnetic field-exposed embryos was compared to ODC activity in sham-exposed embryos. ODC activity in magnetic field-exposed embryos was not statistically elevated above sham-exposed embryos.

Differential distribution of retinoic acid synthesis in the chicken embryo as determined by immunolocalization of the retinoic acid synthetic enzyme, RALDH-2

Retinaldehyde dehydrogenase type 2 (RALDH-2) is a major retinoic acid generating enzyme in the early embryo. Here we report the immunolocalization of this enzyme (RALDH-2-IR) in stage 6-29 chicken embryos; we also show that tissues that exhibit strong RALDH-2-IR in the embryo contain RALDH-2 and synthesize retinoic acid. RALDH-2-IR indicates dynamic and discrete patterns of retinoic acid synthesis in the embryo, particularly within the somitic mesoderm, lateral mesoderm, kidney, heart, and spinal motor neurons. Prior to somitogenesis, RALDH-2-IR is present in the paraxial mesoderm with a rostral boundary at the level of the presumptive first somite; as the somites form, they exhibit strong RALDH-2-IR. Cervical presomitic mesoderm exhibits RALDH-2-IR but thoracic presomitic mesoderm does not. Neural crest cells do not express detectable levels of RALDH-2, but migrating crest cells are associated with RALDH-2 expressing mesoderm. The developing limb mesoderm expresses little RALDH-2-IR; however, RALDH-2-IR is strongly expressed in tissues adjacent to the limb. The most lateral, earliest-projecting motor neurons at all levels of the spinal cord exhibit RALDH-2-IR. Subsequently, many additional motor neurons in the brachial and lumbar cord regions express RALDH-2-IR. Motor neuronal expression of RALDH-2-IR is present in the growing axons as they extend to the periphery, indicating a potential role of retinoic acid in nerve influences on peripheral differentiation. With the exception of a transient expression in the facial/vestibulocochlear nucleus, cranial motor neurons do not express detectable levels of RALDH-2-IR.

Effects of polychlorinated biphenyls on thyroid hormones and liver type I monodeiodinase in the chick embryo

Polychlorinated biphenyls (PCBs) are widespread environmental contaminants which can biomagnify to higher tropic level organisms including birds. Circulating thyroid hormones (TH) and growth are decreased by PCB exposure. The first set of studies investigated the effects of PCBs on an enzyme responsible for TH homeostasis, hepatic type I monodeiodinase (MDI) in chicken embryos. Fertile chicken eggs were injected with Aroclor 1242, Aroclor 1254, 2,2',6, 6'-tetrachlorobiphenyl (TCB), 3,3',4,4'-TCB, or 3,3',5,5'-TCB on Day 0 and studies were terminated on Incubation Day 21. Hepatic MDI activity was reduced in embryos treated with the Aroclor mixtures. No effects on MDI activities were observed after PCB isomer treatment. Liver weights from embryos treated with Aroclor 1242 were decreased. In the second study, chick embryos were exposed to these same PCBs in order to evaluate their effect on circulating THs and growth. Treatment with PCBs had no effect on body weight. Femur length were decreased with Arcolor 1242 treatment. A decrease in plasma concentration of thyroxine was observed after treatment with Aroclor 1242 and Aroclor 1254. Based on these findings, it is evident that PCBs alter the thyroid axis. Bird circulating TH levels, which are generally reported, may not be a good biomarker for low-dose exposure to PCBs. However, the reduction in MDI activity was more sensitive to PCB mixture exposure and may be a useful biomarker.

Enhancement in the lysozyme activity of the hen egg white foam matrix by cross-linking in the presence of N-acetyl glucosamine

Lysozyme naturally present in raw hen egg white was immobilized by cross-linking the egg white foam with glutaraldehyde. Inclusion of N-acetyl glucosamine, a competitive inhibitor of lysozyme, was found to enhance the yield of lysozyme activity by fivefold.

Sites of aspecific ATP-phosphohydrolase activity in the branchial region of chick embryos, with particular emphasis on the myogenic cell population

The distribution pattern of unspecific ATP-phosphohydrolase (ATP-PH) activity was studied in serial sections through the branchial region of chick embryos from HH stage 14 to 27. A selective reaction was found in the prospective myogenic mesoderm of voluntary muscles of the first three branchial arches. This property initially characterized uncondensed myogenic cell populations in the mandibular and hyoid arches and appeared later on in the third arch. In each case, the positive premuscular mesoderm was closely apposed to the lateral wall of the corresponding aortic arch. Myogenic primordia retained a strong ATP-PH activity up to stage 27 when they began to segregate into smaller premuscular units. Discrete changes observed in the mandibular and hyoid blastemas suggested that non reacting cells probably of neural crest origin invade their proximal core and contribute to the subsequent pathfinding of muscular nerves. Other selective sites of ATP-PH reactivity were detected in the odd-numbered rhombomeres, rhombencephalic floorplate, notochord, arterial endothelial cells, prospective dermis and perichondrium.

Protective role of thyroxine in methylparathion intoxicated chick embryos

The efficacy of thyroxine against methylparathion poisoning in chick embryos was studied. The mortality rate and survival rate, frequency of abnormalities, growth rate and size of embryos, and also the change in cholinesterase activity were determined to evaluate the protective effect of thyroxine and atropine. It was observed that the survival rate, growth rate and size, and the cholinesterase activity significantly declined in the methylparathion treated group while the mortality rate and the frequency of abnormalities increased. When thyroxine was given, a significant reversal in these parameters was seen, indicating an effective protective action of thyroxine against methylparathion intoxication in chick embryos. The results also showed that the therapeutic treatment of the combination of thyroxine and atropine did not further improve the effects. Since in many respects, chick embryo development parallels that of mammalian embryos, a short term use of thyroxine as an effective protective agent against organophosphate methylparathion (perhaps other compounds) poisoning may have important implications.

A novel role for vitamin K1 in a tyrosine phosphorylation cascade during chick embryogenesis

The development of the embryo is dependent upon a highly coordinated repertoire of cell division, differentiation, and migration. Protein-tyrosine phosphorylation plays a pivotal role in the regulation of these processes. Vitamin K-dependent gamma-carboxylated proteins have been identified as ligands for a unique family (Tyro 3 and 7) of receptor tyrosine kinases (RTKs) with transforming ability. The involvement of vitamin K metabolism and function in two well characterized birth defects, warfarin embryopathy and vitamin K epoxide reductase deficiency, suggests that developmental signals from K-dependent pathways may be required for normal embryogenesis. Using a chick embryogenesis model, we now demonstrate the existence of a vitamin K1-dependent protein-tyrosine phosphorylation cascade involving c-Eyk, a member of the Tyro 12 family, and key intracellular proteins, including focal adhesion kinase (pp125FAK), paxillin, and pp60src. This cascade is sensitive to alteration in levels or metabolism of vitamin K1. These findings provide a major clue as to why, in the mammalian (and human) fetus, the K-dependent proteins are maintained in an undercarboxylated state, even to the point of placing the newborn at hemorrhagic risk. The precise regulation of vitamin K1-dependent regulatory pathways would appear to be critical for orderly embryogenesis.

In vivo gene transfer into the blastoderm of early developmental stage of chicken

An attempt was made to improve gene transfer into chick embryos in order to produce transgenic chickens. The beta-actin-lacZ/MiwZ, a marker gene in transfection reagent, was injected into the blastodisc of either unincubated fertilized eggs (stage X) or eggs induced from the shell gland by treating the hens intravenously with oxytocin or arginine vasotocin (stages IV-VI). All the manipulated embryos were incubated to reach stage XIV, the period at which primordial germ cells (PGCs) migrate from the germinal crescent to the gonadal anlage via the blood stream. MiwZ was detected in the embryos, extraembryonic tissues and blood by the histochemical staining method of beta-galactosidase. The MiwZ DNA was detected in 57% (127/221) of the survival embryos and in 9% (12/127) of the embryonic tissues. The expression was observed mosaically in the epidermis, heart and neural tube. The PGCs in the blood collected from the vitelline artery or dorsal aorta also showed a positive histochemical staining. However, the expression of MiwZ using the soft shelled eggs was more intense in the extraembryonic tissues, although it did not emerge in the embryos. Thus, it is possible to introduce an exogenous gene into the embryonic tissues using incubated fertilized eggs without sacrificing the hens. This technique for successive genetic operations should facilitate the production of transgenic chickens.

Involvement of transglutaminase in myofibril assembly of chick embryonic myoblasts in culture

Involvement of transglutaminase in myofibrillogenesis of chick embryonic myoblasts has been investigated in vitro. Both the activity and protein level of transglutaminase initially decreased to a minimal level at the time of burst of myoblast fusion but gradually increased thereafter. The localization of transglutaminase underwent a dramatic change from the whole cytoplasm in a diffuse pattern to the cross-striated sarcomeric A band, being strictly colocalized with the myosin thick filaments. For a brief period prior to the appearance of cross-striation, transglutaminase was localized in nonstriated filamental structures that coincided with the stress fiber-like structures. When 12-o-tetradecanoyl phorbol acetate was added to muscle cell cultures to induce the sequential disassembly of thin and thick filaments, transglutaminase was strictly colocalized with the myosin thick filaments even in the myosacs, of which most of the thin filaments were disrupted. Moreover, monodansylcadaverine, a competitive inhibitor of transglutaminase, reversibly inhibited the myofibril maturation. In addition, myosin heavy chain behaved as one of the potential intracellular substrates for transglutaminase. The cross-linked myosin complex constituted approximately 5% of the total Triton X-100-insoluble pool of myosin molecules in developing muscle cells, and its level was reduced to below 1% upon treatment with monodansylcadaverine. These results suggest that transglutaminase plays a crucial role in myofibrillogenesis of developing chick skeletal muscle.

Alteration in liver plasma membrane phospholipids and protein kinase activities during the development of chick embryo

The changes in phospholipid compositions, membrane fluidity and protein kinase A, protein kinase C, tyrosine and casein kinase activities in chick embryo liver plasma membranes during development have been investigated. The percentage participation of sphingomyelin increased while that of phosphatidylserine decreased during chick embryo development. The alterations in membrane sphingomyelin accompanied an increase of steady-state fluorescence anisotropy (rs) of membrane bilayer. Regression analysis indicated positive linear correlations between the percentage participation of sphingomyelin in total membrane phospholipids and (i) protein kinase C (r = 0.903); (ii) casein kinase (r = 0.936); (iii) protein kinase A (r = 0.850); (iv) tyrosine kinase (r = 0.960) activities. We suggest that sphingomyelin might be an specific activator for all types of protein kinase activities investigation.

A radiometric microassay for choline acetyltransferase. Some observations on the spinal cord of the chicken embryo

This paper describes cation-exchange methods for separating acetyl[3H] coenzyme A from [acetyl-3H]choline. Blanks for the routine method were approximately 0.05% of the substrate radioactivity; product recoveries were approximately 97%. The cation-exchange method was more efficient than the standard methods using either anion-exchange chromatography or periodide precipitation. The cation-exchange method was also more specific than either of the other two standard methods for estimating choline acetyltransferase (ChAT) activity. ChAT activity was detected in the chicken lumbar spinal cord on embryonic day (E) 2 1/4 with the cation-exchange method. This developmental stage is about 6 hours before the final mitosis of any neuroblast in the ventral horn. Total ChAT activity per lumbar spinal cord increased more than 10,000-fold between E 3 and E 18. Changes in ChAT activity in the lumbar spinal cord following limb-bud extirpation appeared to mirror (with a phase lag) the changes in the number of motoneurons in the lateral motor column.

Embryonic adenosine triphosphate:phosphodiesters ratios obtained with in vivo nuclear magnetic resonance spectroscopy (phosphorus-31): a new technique for selecting leaner broiler chickens

Phosphorus-containing compounds of 18-d-old embryos from two broiler chicken lines, differing in body fat content, were measured using in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. Subsequently, the same birds were slaughtered at 8 wk of age and the whole body was analyzed for body fat content. The birds of the fat line had lower (P = .002) embryonic adenosine triphosphate (ATP):phosphodiester (PDE) ratios, higher (P = .002) body fat content when adjusted to common BW, and higher (P = .047) dry matter content than the lean line. No differences (P > .05) were detected for BW between the two lines. Females of the two lines had lower (P = .002) ATP:PDE ratios, lower (P = .001) BW, higher (P = .003) adjusted fat contents, and higher (P = .003) dry matter content than the males. No interaction (P > .05) between sexes and lines was detected for any variables. Regression equations indicating a linear negative relationship (Ybody fat content = 369.05 - 407.27 XATP:PDE + .1295 XBW, R2 = .62 to .78; or Ybody fat % = 30.57 - 19.4 XATP:PDE, R2 = .49 to .71) between embryonic ATP:PDE ratios and body fat content were developed.

Regulation of tyrosine aminotransferase activity by glucagon and cAMP analogues in chick embryos in ovo

Glucagon, dibutyryl cAMP (Bt2cAMP) and 8-(4-chlorophenylthio) cAMP (CptcAMP), singly or when combined, stimulated tyrosine aminotransferase (TAT) activity in 17-day-old chick embryos in ovo. Maximal induction was produced within 4 hr of injection of the inducers. The effects of glucagon and the cAMP analogues were not additive. Glucagon administration was accompanied by a rapid increase in hepatic cAMP concentration which remained elevated for at least 4 hr. The stimulated increase in TAT activity elicited by the hormone or cyclic nucleotide was prevented by injection of cycloheximide or cordycepin. These results are discussed vis-à-vis the possible regulation of TAT in ovo by physiological concentrations of glucagon and the likely role of cAMP as a second messenger in this process during chick embryogenesis.

The esterification of cholesterol in the liver of the chick embryo

The development of the chick embryo was characterised by the accumulation of large droplets of lipid in the cytoplasm of the embryonic liver, as revealed by electron microscopy. Analysis of the lipid composition of the livers indicated that this accumulation resulted from a dramatic increase in the cholesteryl ester content of the tissue during the the latter part of the embryonic period. This lipid is apparently derived from yolk cholesterol and may be taken up by the liver in the form of lipoprotein remnants. Significant levels of acyl-CoA: cholesterol acyltransferase (ACAT) activity were expressed in the liver throughout the second half of the developmental period, and this activity was maximal at the time when lipid transfer from the yolk was most intensive. The activity of microsomal cholesterol ester hydrolase (CEH) was very low throughout development, and no CEH activity was detected in the cytosolic fraction. In addition, substantial amounts of a cytosolic protein which inhibits CEH activity were present. Thus the relative activities of these enzymic systems are consistent with the net accumulation of cholesteryl ester which occurs in the liver during development.

Quantification of chicken alpha-fetoprotein: a useful tool in studies of embryo development and pathology

Chicken alpha-fetoprotein (AFP) from the plasma of 12-day-old chick embryos was purified by electroelution from SDS/PAGE gels, and used to produce polyclonal and monoclonal antibodies. Both reagents were then used to design a sandwich-type enzyme-immunoassay for the quantification of AFP in biological fluids. The assay was used to quantify AFP in the serum and amniotic fluid of chick embryos with abnormalities of the neural tube. Serum AFP was significantly greater in these embryos than in normal ones of similar age. Moreover, substantial amounts of AFP were demonstrated in the amniotic fluid, whereas this protein was undetectable in the amniotic fluid of normal embryos. This method of assay may provide a reliable tool for studies of chick embryogenesis and abnormalities of embryonal differentiation.

Cholinesterases regulate neurite growth of chick nerve cells in vitro by means of a non-enzymatic mechanism

Cholinesterases present homologies with some cell adhesion molecules; however, it is unclear whether and how they perform adhesive functions. Here, we provide the first direct evidence showing that neurite growth in vitro from various neuronal tissues of the chick embryo can be modified by some, but not all, anticholinesterase agents. By quantifying the neuritic G4 antigen in tectal cell cultures, the effect of anticholinesterases on neurite growth is directly compared with their cholinesterase inhibitory action. BW 284C51 and ethopropazine, inhibiting acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively, strongly decrease neurite growth in a dose-dependent manner. However, echothiophate which inhibits both cholinesterases, does not change neuritic growth. These quantitative data are supplemented by morphological observations in retinal explant cultures grown on striped laminin carpets, viz., defasciculation of neurite bundles by BW 284C51 and Bambuterol occurs, indicating that these drugs disturb adhesive mechanisms. These data strongly suggest that a) cholinesterases can participate in regulating axonal growth, b) both AChE and BChE can perform such a nonsynaptic function, and c) this function is not the result of the enzyme activity per se, since at least one drug was found that inhibits all cholinesterase activities but not neurite growth. Thus, a secondary site on cholinesterase molecules must be responsible for adhesive functions.

Butyrylcholinesterase from intestinal epithelial cells of quail, chick and duck: a comparative study during development

1. Epithelial cells of avian intestine express non-specific cholinesterase (butyrylcholinesterase, BuChE) activity both in the embryo and adult animal. 2. Quail, duck and chick exhibit increased BuChE activity during the late embryonic period followed by decreased activity. The minimum value is reached after hatching at day 1 in quail, day 4 in chick and day 6 in duck. 3. The three species display marked sex-related differences mainly during the peri-hatching period. BuChE activity is higher in females than in males. 4. The three globular forms, G1, G2 and G4, are detected during the last days of embryonic development. After hatching, changes in the relative amounts of these forms are related to the disappearance of G2 and the gradual decrease of G4. In adult quail and duck, G4 is not detected and BuChE activity corresponds only to the G1 form. 5. The changes in BuChE activity and distribution of the molecular forms occur in a similar manner in all three species although the embryonic periods differ notably, suggesting that hormonal factors secreted during this period and involved in the preparation of hatching may regulate BuChE activity.

Erythroid carbonic anhydrases of developing chick embryos. Coordinate expression with primitive and definitive embryonic haemoglobins

Erythroid carbonic anhydrase activity of chick embryos from the 3rd day of incubation to the egg hatching has been determined. Three minor activity peaks at 3, 9 and 15 days of development and a major one at 19 days were found. The enzyme molecular forms were purified by affinity chromatography from haemolysates of embryos at several stages of development. As has been found for the adult erythrocytes, only type II isozyme was detected in the embryo red cells. Isoelectrofocusing analysis demonstrated that two different molecular forms of this isozyme are synthesized by the red cells of developing embryos. Only the early form is present up to 5 days of development; the late form, which is indistinguishable from the adult isozyme, appears in the haemolysate at 6-7 days and quickly replaces the early form. Analysis of purified primitive and definitive erythroid lines from 7-days-old embryos showed a compartmentalization of the early and late forms into the primitive and definitive erythroid cells, respectively.

Effect of magnetic fields on membrane associated enzymes in chicken embryos, permanent or transient?

Exposure to a 60Hz, 4 microT electromagnetic field resulted in a significant reduction in the activity level of 5' nucleotidase in normal live embryos. Levels of acetylcholinesterase and alkaline phosphatase were not affected. The effect of the field on 5'NT levels appears to be permanent, as incubation in a field free environment for a further 15 days did not result in enzyme levels returning to control values.

Tissue-specific changes in lipid composition and lipoprotein lipase activity during the development of the chick embryo

Lipoprotein lipase was present at a high specific activity in adipose tissue and heart of the chick embryo at the 14th day of development. The enzyme was also present in skeletal muscle but was absent from brain and liver. Major increases in the activity of lipoprotein lipase in adipose tissue and heart occurred from day 12 of development, concomitant with the beginning of the period of lipid uptake from the yolk. These results suggest that lipoprotein lipase may be involved in the utilisation of yolk-derived lipid by the tissues of the embryo. Relatively high levels of docosahexaenoic acid (22:6(n--3)) were present in the triacylglycerol isolated from plasma, adipose tissue, heart and liver. The relative proportions of this fatty acid in the triacylglycerol of the different tissues may be explicable in terms of the substrate specificity of lipoprotein lipase.

Isolation and characterization of a chicken tyrosinase cDNA

Complementary DNA clones coding for chicken tyrosinase were isolated from retinal pigmented epithelium of chicken embryo. Sequence analysis shows that one of the cDNA clones consisting of 1,997 nucleotides has an open reading frame coding for 529 amino acids. The deduced protein has nine N-glycosylation sites and a transmembrane region. A sequence comparison of the deduced chicken tyrosinase with the mouse and human homologues revealed that amino acid sequences are conserved for the entire polypeptides. Seventy-two percent and 73% of amino acids in the chicken sequence are identical to that of the mouse and human tyrosinases, respectively. Histidines neighboring the postulated copper-binding sites and the cysteines are well conserved. RNA blotting analysis showed that a major transcript of 2.5 kb is detected in retinal pigmented epithelium of a 9-day-old chicken embryo.

Ontogeny of type I and type III deiodinase activities in embryonic and posthatch chicks: Relationship with changes in plasma triiodothyronine and growth hormone levels

1. The ontogeny of type I and type III deiodinase activities was studied in embryonic and posthatch chicks. 2. Hepatic type I activity showed a 3-fold increase up to the period of pipping and hatching and decreased slowly thereafter. 3. Hepatic type III activity increased by 3-fold from E14 to E17 and decreased more than 10-fold from E17 to C0. Posthatch levels were very low. 4. Type I activity in the kidney decreased slowly after hatching while type III activity was very low over the whole period studied. 5. Developmental changes during the late embryonic period suggest a causal relationship between the increase in plasma GH and T3 levels and the decrease in hepatic type III activity.

O6-alkylguanine-DNA alkyltransferase in the chick embryo during development

In the whole embryo, O6-alkylguanine-DNA alkyltransferase (AT) activity increased until day 9 of development and declined sharply after day 13. AT activity of the liver was greatest between day 12 and day 20 and decreased fast after hatching. In the brain, AT activities reached a maximum at day 17 and 18 and declined sharply after hatching. At two developmental stages with different AT activities (day 10 and day 17) DNA alkylation in the brains was estimated 6, 12, 24 and 48 h after administration of N-methyl-N-nitrosourea in ovo by viscometric measurement of DNA fragmentation. The high AT activities of the chicken embryo brain at the 17th day of development correlated with minor DNA fragmentation following a repair period of 12-24 h. It is suggested that the high basal level of AT in the chick embryo might have a protective function against the persistence of the genotoxic lesion O6-methylguanine during development.

Comparison between avian and human prolyl 4-hydroxylases: studies on the holomeric enzymes and their constituent subunits

Prolyl 4-hydroxylase, a key enzyme in collagen biosynthesis, catalyzes the conversion of selected prolyl residues to trans-hydroxyproline in nascent or completed pro-alpha chains of procollagen. The enzyme is a tetramer composed of two nonidentical subunits, designated alpha and beta. To compare the enzyme and its subunits from different sources, the chick embryo and human placental prolyl 4-hydroxylases were purified to homogeneity and their physicochemical and immunological properties were determined. Both enzymes were glycoproteins with estimated apparent molecular weights ranging between 400 and 600 kDa. Amino acid and carbohydrate analyses showed slight differences between the two holomeric enzymes, consistent with their deduced amino acid sequences from their respective cDNAs. Human placental prolyl 4-hydroxylase contained more tightly bound iron than the chick embryo enzyme. Immunodiffusion of the human placental enzyme with antibodies raised against the purified chick embryo prolyl 4-hydroxylase demonstrated partial identity, indicating different antigenic determinants in their tertiary structures. The enzymes could be separated by high-resolution capillary electrophoresis, indicating differential charge densities for the native chick embryo and human placental proteins. Electrophoretic studies revealed that the human prolyl 4-hydroxylase is a tetrameric enzyme containing two nonidentical subunits of about 64 and 62 kDa, in a ratio of approximately 1 to 2, designated alpha and beta, respectively. In contrast, the chick embryo alpha and beta subunit ratio was 1 to 1. Notably, the human alpha subunit was partially degraded when subjected to electrophoresis under denaturing conditions. Analogously, when the chick embryo enzyme was subjected to limited proteolysis, selective degradation of the alpha subunit was observed. Finally, only the alpha subunit was bound to Concanavalin A demonstrating that the alpha subunits of prolyl 4-hydroxylase in both species were glycosylated. Using biochemical techniques, these results demonstrated that the 4-trans-hydroxy-L-proline residues in human placental collagens are synthesized by an enzyme whose primary structure and immunological properties differ from those of the previously well-characterized chick embryo enzyme, consistent with their recently deduced primary structures from cDNA sequences.

Cytochemical localization of sorbitol dehydrogenase in kidney and liver from Myiopsitta m. monachus (Boddaert, 1783), during embryonic development

A histochemical study to determine the localization of sorbitol dehydrogenase (SDH) in kidney and liver from embryionic, young and adult Myiopsitta m. monachus was performed. The enzyme activity increased with age in both organs. In the kidney, the enzyme appeared at the proximal convoluted tubules, and increased in the basal cytoplasm of the tubular cells. In the liver the localization was diffuse in the lobule but more intense in the cytoplasm of hepatocytes, especially in the perinuclear areas. These studies indicate that the cytochemical enzyme localization differs in this species, which is more evolutioned than Gallus gallus, and would be related to ontogenetic and phylogenetic differentiation.

Embryolethality and induction of 7-ethoxyresorufin O-deethylase in chick embryos by polychlorinated biphenyls and polycyclic aromatic hydrocarbons having Ah receptor affinity

The lethality and 7-ethoxyresorufin O-deethylase (EROD)-inducing potency of some individual polycyclic aromatic hydrocarbons (PAHs) and coplanar polychlorinated biphenyls (PCBs) in chick embryos were measured in order to compare the mechanisms of action of these compounds. In previous studies it was found that coplanar PCBs and certain PAHs have a high embryolethality in the chicken and that they induce embryonic EROD activity. Although the most potent PAHs were almost as embryolethal as the PCBs when injected into hens' eggs 72 h prior to measurement, they were considerably less potent EROD inducers. In the present study, three coplanar PCBs (3,3',4,4'-tetrachlorobiphenyl (TCB), 3,3',4,4',5-pentachlorobiphenyl (PeCB) and 3,3',4,4',5,5'-hexachlorobiphenyl (HCB)) and four of the most toxic PAHs (benzo[a]anthracene (BaA), benzo[k]fluoranthene (BkF), indeno[1,2,3-cd]pyrene (IP) and dibenzo[a, h]-anthracene (DBahA] were administered to chick embryos in different ways, including co-administration. Additive embryolethality was found when BkF and PeCB were co-administered as well as when BaA and DBahA were given simultaneously. The PAHs were more effective as EROD inducers when injected on day 9 (24 h prior to measurement) than when injected on day 7 (72 h prior to measurement). The opposite was found for PeCB and HCB, whereas no difference in potency was noted when comparing TCB injected 24 and 72 h before EROD determination. These substance-related differences were probably due, at least partly, to differences in biotransformation rates. EROD activities found after treatment with high doses of BkF, IP, or DBahA on day 9 were similar to those measured after treatment with PeCB in doses high enough to give maximal induction. Co-administration of high doses of BkF and PeCB did not further increase the activity, indicating that the PAHs and coplanar PCBs induce EROD to a common maximal value. To decrease the influence of metabolization of the PAHs on their EROD-inducing potency, EROD was determined early in development (day 8) and soon after treatment (24 h) in one experiment. In that experiment, the PAHs proved to be only a few times less potent EROD inducers in relation to their embryolethalities compared with the PCBs. The results of the present study, a previously observed similarity in pathology between chick embryos treated with PAHs and embryos treated with coplanar PCBs, and the fact that the most toxic PAHs also are the most avid Ah receptor binders suggest that the coplanar PCBs and the PAHs largely exert their toxicity in chick embryos via an Ah receptor-mediated mechanism. The differences between the compounds in their EROD-inducing potency/embryolethality ratios could probably be explained by their different rates of biotransformation.

Amylase activity increases in the yolk of fertilized eggs during incubation in chickens

Amylase activity was detected in the egg of chickens. In unfertilized eggs, no change of amylase activity was observed during 22 days incubation, however, in fertilized eggs, amylase activity increased markedly during embryonic development. The increase depended upon an increase of amylase in the yolk, not in the albumen. Isoamylases in the yolk were electrophoretically identical to those in the pancreas of the embryo or the hen.