The anatomy, ultrastructure and fluid dynamics of the developing vasculature of the embryonic chick wing bud

The spatiotemporal sequence of vascular pattern development in the embryonic chick wing bud and surrounding shoulder, flank and belly regions is detailed for Hamburger-Hamilton (1951) stages 20-25. Vasculature was microinjected with an unreactive aqueous tracer (aniline blue), and major traffic patterns were visualized. Formation of extensive avascular regions and the emergence of chondrogenic phenotypes are correlated with the retreat of the vasculature from the wing core. Ultrastructural studies of vascular cells show that vessels remain monolayered and undifferentiated until stage 25, after the adult vascular pattern has been laid down. Vascular cytodifferentiation occurs only in the cells of the brachial artery until stage 35, with the veins and capillaries retaining an 'early' morphology. This vascular pattern may be an important component reflecting or directing limb pattern development.

The effect of isoproterenol on cardiovascular function in the stage 24 chick embryo

The developing cardiovascular system of the chick embryo is susceptible to teratogenic effects of catecholamines. Yet the mechanism for the teratogenetic action is unclear. Since catecholamines affect cardiovascular physiology, we studied the acute effect of the beta-agonist isoproterenol on mean atrial pressure, heart rate, mean dorsal aortic blood flow, mean arterial pressure and vascular resistance in stage 24 chick embryos. Dorsal aortic blood velocity was measured with a 20-MHz pulsed-Doppler velocity meter and intravascular pressure was measured with a servo-null pressure system. Isoproterenol in doses of 2 X 10(-4) micrograms (2.5 micrograms/kg), 8 X 10(-4) micrograms (10 micrograms/kg), and 1.2 X 10(-3) micrograms (15 micrograms/kg) was injected intravenously in 5-microliters aliquots of chick Ringer's solution. Additional groups of embryos were treated with the beta-antagonist propranolol, and isoproterenol plus propranolol. Control embryos received 5 microliters chick Ringer's solution to assess the hemodynamic effects of a volume injection. We found that isoproterenol caused no change in mean atrial pressure, heart rate, or mean arterial pressure. However, isoproterenol caused a dose-related decrease in dorsal aortic blood flow and a 2.5-fold increase in vascular resistance. The effects of isoproterenol were blocked by propranolol, which suggested that the increase in vascular resistance was mediated by beta-receptor stimulation.

Nerve growth factor induces neural differentiation in undifferentiated cell of early chick embryos

Nerve growth factor (NGF) induced differentiation in postnodal pieces (PNPs) of stage 4 chick embryos. This induction was highly selective for neural tissue; no other structures developed in the NGF-treated PNPs. Furthermore, the number of PNPs showing neural differentiation was dependent on the concentration of NGF, but there was no correlation between the concentration of NGF (5-100 ng/ml) and extent of neuralization. The neural inducing capacity of NGF could be abolished by anti-NGF antibody. NGF-induced neural differentiation was accompanied by elevated intracellular levels of cyclic AMP. Exogenous cyclic AMP (175 micrograms/ml) was able to stimulate neural differentiation but, unlike NGF, induced other structures (e.g., notochord and pulsatile tissue). Overall results suggest that cells from chick embryos at developmental stages much earlier than previously thought are responsive to NGF and NGF or a a closely related substance may serve as a neural inducer in the chick embryo.

Alpha actinin distribution and extracellular matrix products during somitogenesis and neurulation in the chick embryo

A discrete stage in two different morphogenetic processes has been examined employing fluorescently labelled alpha-actinin as a probe to localize native alpha-actinin and antibodies to localize fibronectin and collagen type I. The stage of somitogenesis examined is the transition from the compact mesenchymal somitic mass to the epithelial somitic vesicle (ie, epithelialization of the somite). The stage of neurulation examined is the transition from the relatively flat neuroepithelium to the approximation of the neural folds. Before these morphogenetic movements begin, the neuroepithelium is sitting upon a basal lamina and interstitial collagen, and the somite is surrounded by a meshwork of interstitial collagen. During both of these processes, the cells become narrowed at their apices in the region of the tissue that is becoming concave, and alpha-actinin is localized in the apices. The localization of intracellular alpha-actinin and extracellular fibronectin, and the distribution of collagen, suggest that there is a coordinated appearance and distribution of these molecules that is temporally associated with these discrete morphogenetic events.

Thyroidal influence on body growth

This review of thyroid influence on body growth in poultry is organized around the following parameters of growth: increase in body weight and skeletal size, muscle growth, and growth of cartilage and bone. The greatest effect of goitrogens on growth of embryos occurs during late embryogenesis at a time when normal thyroid hormone levels are increasing. Posthatching growth is reduced in severely hypothyroid animals, and body weight gain is affected more than bone growth. Thyroid hormone replacement restores body growth of thyroidectomized chickens, but supplemental hormone in normal animals has no beneficial effect on growth. Excessive T3 (fed at 1 ppm) is detrimental to growth and feed efficiency. No clear correlation between thyroid hormone concentration and growth rate of normal chickens has been identified. Growth depression in sex-linked dwarf birds is at least partially reversed by supplemental T3. Muscle growth is reduced in goitrogen-treated chickens and the growth reduction is reversed by supplemental thyroxine. Total DNA accumulation is reduced in hypothyroid chickens, but muscle mass relative to DNA content is normal following long-term treatment; this suggests some regulation of muscle mass relative to DNA content. T3 increases the number of muscle fiber nuclei in hypothyroid chickens and the uptake of 3H-thymidine into nuclei within the basal lamina. T3 directly stimulates growth and maturation of embryonic chick cartilage and enhances the in vitro action of somatomedins on cartilage growth. There is little information concerning the role of the thyroid in posthatching cartilage and bone growth in poultry.

Lack of effect of weak low frequency electromagnetic fields on chick embryogenesis

Fertilised chicken eggs were incubated for 48 hours while exposed to pulsed trains of square wave magnetic fields having a duration of 0.5 msec and pulse repetition rates of 100 or 1000 Hz at magnetic field flux densities of 1.2 and 12 mu T. After exposure the embryos were scored blind for eight different gross structural features: primary vesicles, anterior neuropore, optic vesicles, auditory pits, truncal nervous system, heart, somites and blood vessels. There were no differences between exposed, sham-exposed and control eggs.

Stimulation of growth of the chick embryo by acute hyperoxia

We have previously demonstrated that continuous incubation in elevated concentrations of ambient oxygen leads to accelerated growth of the chick embryo. We now report that a similar growth response is elicited by acute (72 h) exposure beginning on the 16th day of incubation. White Leghorn eggs were paired by initial weight and incubated in air for 15 days in forced-draft incubators. Embryos were sampled on days 11, 13 and 15 (experiments 1, 2, 3) or 13, 14 and 15 (experiment 4), freed of all extra-embryonic membranes and weighed. On day 16 the experimental group was switched to 60% O2. The control group was maintained in air. A portion of the remaining eggs from each group was opened on days 16, 17 and 18 (experiment 4), or alternatively all the remaining eggs were opened at the end of the 18th day of incubation (experiments 1, 2, 3). Linear regression analysis of growth curves obtained by plotting log wet embryo weight (g) vs log incubation age (d) showed a significantly greater rate of growth (slope) for days 15-18 in embryos exposed to 60% O2. These results support the hypothesis that growth of the chick embryo is normally limited by the availability of oxygen.

Reduction of density and anisotropic distribution of intermediate filaments occur during avian skeletal myogenesis

Chicken skeletal muscle taken from embryos in ovo was examined by thin-section electron microscopy. Measurements of filament diameters reveal three nonoverlapping groups of filaments: thin (actin myofibrillar) filaments with mean diameters of 5.3 +/- 0.6 nm (S.D.), thick (myosin myofibrillar) filaments with mean diameters of 15 +/- 1.4 nm, and intermediate filaments with mean diameters of 9.3 +/- 0.9 nm. During muscle development these diameters do not change. By counting the number of filaments observed in the sarcoplasm at different stages, we find that the spatial density of intermediate filaments decreases during avian myogenesis in ovo, from 91 intermediate filaments/micron 2 at 6 days to 43 intermediate filaments/micron 2 at 17 days in ovo. Initially randomly arranged, some intermediate filaments become associated with Z discs, sarcoplasmic reticulum, nuclear membrane, and the sarcolemma between 6 and 10 days in ovo. These associated intermediate filaments course both parallel and transverse to myofibrils, forming lateral connections between myofibrillar Z discs and longitudinal connections from Z disc to Z disc within myofibrils. Intermediate filaments also appear to connect Z discs with the nuclear membrane. The intermediate filament associations persist through day 17 of development, after which the presence of cytoskeletal filaments is obscured by the densely packed myofibrils and membranes. Intermediate filament distribution becomes anisotropic during development. A greater proportion of intermediate filaments in the immediate perimyofibrillar area are oriented parallel to myofibrils than in other areas, so that the majority of the intermediate filaments nearest the myofibrils course parallel to them. The longitudinal intramyofibrillar intermediate filaments persist throughout development, as shown by their existence in KI-extracted adult myofibrils.

The effects of Janus Green B on the temporal and spatial pattern of feather germ morphogenesis

The normal timing and appearance of feather germs was perturbed by injecting the dye Janus Green B into the amniotic fluid of chick embryos at late stage 28, prior to the first appearance of feather germs. This treatment prevented feather germ morphogenesis in some regions while elsewhere it delayed normal morphological development. The Janus Green B effect lasted for approximately 98 hours. Feather regions, which normally form epidermal placodes during the period of treatment, showed the longest delays in subsequent feather germ formation and were the most likely to remain featherless. These results suggest that the epidermal placode stage is critical for feather germ formation. Janus Green B appears to prevent feather germ morphogenesis by interfering with development prior to this critical stage. Since severely affected regions fail to recover their capacity to form feather germs, even after the period of sensitivity to the dye, a limited period of competence is suggested for feather germ formation.

Hydroxylation of carbon-24 of 25-hydroxycholecalciferol is not necessary for normal embryonic development in chickens

Laying hens fed 25-hydroxycholecalciferol, 24,24-difluoro-25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol or 24,25-dihydroxycholecalciferol were used to investigate whether hydroxylation of C-24 of cholecalciferol is necessary for normal embryonic development in chickens. Laying hens were fed a rachitogenic diet and 25-hydroxycholecalciferol from hatching until normal egg production, fertility and hatchability were achieved. When the hens were 40 weeks old, 25-hydroxycholecalciferol was withdrawn and egg production ceased in 4 weeks. The hens were divided into 6 groups of 5 and dosed daily for 19 weeks with either 2.0 micrograms of 25-hydroxycholecalciferol, 2.0 micrograms of 24,24-difluoro-25-hydroxycholecalciferol, 0.4 microgram of 1,25-dihydroxycholecalciferol, 2.0 micrograms of 24,25-dihydroxycholecalciferol, both 1,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol or vehicle only. Egg production during this period was high for all hens fed the cholecalciferol compounds. Egg production of 3% occurred in hens given vehicle only. Fertility was over 90% for all groups of cholecalciferol compound-fed hens. Hatchability of over 90% was achieved with the eggs from hens given 25-hydroxycholecalciferol or 24,24-difluoro-25-hydroxycholecalciferol and 6% with eggs from hens fed both 1,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol. No eggs from hens fed 1,25-dihydroxycholecalciferol or 24,25-dihydroxycholecalciferol alone hatched (over 140 eggs in each group.

Ultrastructural study of the myocardial wall of the atrio-ventricular canal during the development of the embryonic chick heart

In the early stages of chick embryo development (days 3-5) the myocardium of the atrio-ventricular canal (AV) is continuous with the atrial and ventricular muscles; however, interruption of muscular continuity is observed at later stages (from day 6 to day 8). The most relevant event occurring at the AV canal region is the dissociation of the myocytes due to the loss of their cellular attachments, rather than an invasion of connective tissue cells (endocardial and sub-epicardial) located on both sides of the myocardium. In this study, particular attention was paid to the sequential changes that take place in the myocardium of this region, these being (1) a reduction in the number of desmosomes and intercalated discs with the subsequent appearance of large, inter-cellular spaces between myocytes; (2) migration of these cells through a complex extra-cellular matrix, to which it appears to be closely related, suggesting that the macromolecules of this matrix may be being synthesized by the myocytes, and may take part in the process of cardiac cell separation; (3) incorporation of the myocytes in the developing tricuspid valve, where they co-exist with fibroblasts. The results of the study correspond remarkably well to those previously carried out on the left AV canal myocardium, suggesting that the behaviour of the muscle is the same, at all points around the AV canal.

Effect of semen storage time and number of spermatozoa inseminated on the fertility and hatchability of eggs from dwarf broiler breeder hens

Semen from commercial breeder males was diluted two-fold and stored for 6 and 24 h at 2 to 3 degrees C. For each storage period, groups of caged dwarf broiler breeder hens from the same strain were inseminated with 300, 200 or 100 x 10(6) spermatozoa. Three replicates of 15 birds were inseminated per treatment. Control hens were inseminated with 150 x 10(6) fresh, undiluted spermatozoa. Inseminations were performed for 5 consecutive weeks during a first (32 to 36 weeks of age) and for 6 consecutive weeks during a second experimental period (42 to 47 weeks). During weeks 33 to 36 of the first period, only 24 h storage and 100 x 10(6) spermatozoa produced lower (P less than 0.05) hatchability of all eggs set than the control (84.4 compared to 88.6%). During weeks 43 to 47 of the second period, no significant differences between treatments were observed. Embryonic mortality, measured at different periods during incubation, was not affected by the storage time or the number of spermatozoa inseminated.

The effect of chick embryo hyperflexion on tracheoesophageal development

Chick embryos were hyperflexed by placement of a ligature at two critical stages in the development of the foregut, in order to test the theory that esophageal atresia and tracheoesophageal fistula result from embryonic hyperflexion. Only one "H-type" tracheoesophageal fistula was found. There were no significant disturbances of either tracheal or esophageal growth.

The roles of node regression and elongation of the area pellucida in the formation of somites in avian embryos

Experiments have been carried out on explanted chick embryos to test certain widely accepted concepts about the role of Hensen's node in somite formation. The relationship between elongation of the area pellucida and regression of Hensen's node has also been investigated. We conclude from these experiments that: (a) The timing of somite formation is not controlled by the regression of Hensen's node, nor by the shearing of the mesoderm into right and left halves. (b) Somite size and shape are probably controlled by local conditions in the chick embryo. (c) Elongation and regression are two different events. (d) The position of the probably depends on mechanical tensions in the area pellucida. (e) The notochord is not required for the stability of somites in vivo.

The local expression of adult chicken heart myosins during development. I. The three days embryonic chicken heart

Immunofluorescence studies were performed on serial sections of three days embryonic chicken hearts using antibodies specific for adult atrial and ventricular myosin heavy chains respectively. The anti-ventricular myosin serum reacted with the entire myocardium showing a decreasing intensity going from the truncus arteriosus to the atrial part; however, the antiatrial myosin serum reacted weakly with the myocardium of the atrial part. Two other interesting observations were made, i) the anti-atrial myosin serum reacted with non-myocardial cells in the cardiac jelly, ii) both antisera reacted with a thin myocardial layer, extending from the ventral wall of the atrial part via the medio-dorsal wall of the atrio-ventricular canal to the dorsal wall of the ventricular part.

The ultrastructure of the developing inner and outer segments of the photoreceptors of chick embryo retina as revealed by the rapid-freezing and deep-etching techniques

The ultrastructure of retina cell receptors of chick embryos and of one to three week old chicks was examined paying special attention to the membrane structure of receptor discs, mitochondria, cell membrane and other cell organelles, such as the endoplasmic reticulum and the Golgi apparatus. The retinas were rapid-frozen with a liquid-propane jet, deep-etched, and rotary-shadowed replicas produced. The structure of the photolamellae membranes is asymmetrical. The fracture faces showed a smooth (E-face) and a rough (P-face) surface. Both true surfaces ( interdiscal and intradiscal) were also observable by deep-etching. Transverse fractures of the discs showed the globular structure of their membrane. Spherical or polyhedral particles, probably rhodopsin-associated particles, occupying the width of the membrane are 12 nm in diameter and are constituted by 6 subunits of 1.5-2.0 nm arranged around a channel. These particles seem to extend into the membrane of the photolamellae during the last days of incubation and were also found in variable positions in the width of the disc membrane. When observed in transversal fractures of the photolamellae , they were sometimes seen to protrude into the collapsed intradiscal space and into the cytoplasmic surface. Filament-like or particulate structures connect the discs both to each other and to the cell membrane. During development a relationship between the forming discs and the cell membrane was not observed. The mitochondria aggregated in the ellipsoid are connected by filament-like structures that form during development of the inner segment. The structure of the inner cristae membrane of the mitochondria is characterized by the presence of stalked particles as previously described by Fern andez -Morán (1961) using negative staining. An intracristal space is not present. The fracture of the receptor cell membrane shows a particulate cytoplasmic half with particle-free patches. The glycogen granula situated in the cytoplasm between the smooth ER cisternae show a rosette-like composition.

Distribution of glycogen in the floor plate of the chick spinal cord during development

The present study was undertaken to characterize the structural changes and the glycogen distribution in the floor plate of the developing chick spinal cord. The floor plate consisted of ventricular zone by stage 19 (staged according to Hamburger and Hamilton, 1951). The marginal zone of this plate could be distinguished as a narrow border at stage 21. It increased progressively in thickness and was the same thickness as the ventricular zone at stage 26. It increased again in thickness from stage 38 onward. Glycogen appeared and subsequently disappeared in the floor plate of the chick spinal cord during development. Little, if any, glycogen appeared in the midportion of the floor plate at stage 19. The floor plate was weakly glycogen positive from the cervical through lumbosacral segments at stage 21. In the floor plate of the lumbosacral enlargement the glycogen staining was the highest and was maximal through stages 34-37. The floor plate of the cervical and thoracic segments except for the cervical enlargement continue to have low concentrations of glycogen. The glycogen staining of the floor plate began to decrease from stage 38, and at the same time neuroglial cells began to migrate into the marginal zone of the floor plate, later than in other regions of the cord. The glycogen staining in the floor plate was barely detectable at stage 40. The accumulation of the glycogen granules in the floor plate was found only in the radial glial cells.

Further evidence that formation of the neural tube requires elongation of the nervous system

In previous papers, we have correlated rapid elongation of the midline of the neural plate with the time of closure of the plate into a tube in the newt embryo and at one stage of the chick embryo. We proposed a model in which stretching of the midline of the plate causes the plate to buckle out of the plane and roll into a tube. In this paper, I show for another stage of development in the chick embryo, the period of closure of the brain tube, that rapid elongation of the nervous system accompanies closure of the tube. If elongation of the brain plate causes formation of the tube, then treatments that stop tube formation should also stop brain elongation. I tested this hypothesis by using low fluences of UV irradiation, known to stop tube formation (Davis, '44), and measuring the effects on elongation of the brain plate. The open plates of UV-irradiated embryos failed to elongate normally. Furthermore, photoreactivation with longer wavelengths of light reversed the UV effects and allowed closure of the tube in UV-irradiated embryos. These embryos elongated their brains.

Changes in the activities of NADP+-linked dehydrogenases during ontogenesis in the chicken

Changes in the activities of glucose-6-phosphate dehydrogenase [EC 1.1.1.49], 6-phosphogluconate dehydrogenase [EC 1.1.1.44] and cytoplasmic and mitochondrial "malic" enzyme [EC 1.1.1.40] and NADP+- linked isocitrate dehydrogenase [EC 1.1.1.42] were measured in the liver, heart, lung and brain during ontogenesis in the chicken. In the liver the cytoplasmic malic enzyme was constant during embryonal development, increasing suddenly and markedly thereafter and isocitrate dehydrogenase increased in the embryo and decreased after hatching while their mitochondrial isoenzymes showed parallel but less marked changes. Activities of the other dehydrogenases were essentially unchanged. In the heart only cytoplasmic isocitrate dehydrogenase showed important changes, increasing three-fold during growth after hatching. In the lung, glucose-6-phosphate dehydrogenase and cytoplasmic malic enzyme attained their maximum activities respectively at 16 to 18 d and 14 d of development. Mitochondrial malic enzyme did not change, while isocitrate dehydrogenase reached its maximum between 14 and 18 d. In the brain cytoplasmic malic enzyme was activated only after hatching, while its mitochondrial isoenzyme and isocitrate dehydrogenase showed discontinuous variations of an insignificant magnitude. Other activities were unchanged.

Effect of carbon dioxide on fertility of cock semen incubated in vitro at 41 C

The effect of various atmospheric CO2 concentrations on fertility of cock semen incubated in minimum essential medium (MEM) for 6 hr in vitro at 41 C was evaluated. Fertility following intravaginal insemination was 54, 87, and 78% for semen incubated in .03, 10, and 15% by volume CO2, respectively. No differences in hatchability of fertile eggs were observed between the semen treatments. Oxygen consumption values monitored at the beginning and end of the holding period were similar for semen incubated in 10% atmospheric CO2 but decreased for semen incubated in .03 and 15% CO2.

[Changes in the growth rates, respiration level and mitochondrial mass of the heart during chick embryo development]

The growth of heart during the chick embryo development is accompanied by the increase in total protein content per weight unit of the organ and in the content of the actomyosin complex proteins calculated to the total heart protein. Changes in the rate of heart respiration during development are determined, mainly, by the mass of mitochondria. The growing heart at the early developmental stages is characterized by a very high rate of doubling of the mitochondrial protein mass.

The synthesis and accumulation of cholesteryl esters by the developing embryo of the domestic fowl

A comparative study has been made of the accumulation and synthesis of cholesteryl esters in the liver, yolk sac membrane, and yolk contents of the chick embryo during the last week of development. This involved a comparison of the cholesteryl esters synthesized during incubation in vitro with 14C-cholesterol with those accumulated during incubation in vivo. Results indicated that the considerable accumulation of cholesteryl esters, mainly cholesteryl oleate, that occurred within the liver during embryo development arose from synthesis in the yolk sac membrane. This suggested a specific role in the transport of yolk lipid into the embryo. With the approach of hatching the ability of the liver to synthesize its own cholesteryl esters increased while that of the yolk sac membrane decreased.

Protein composition of cerebrospinal fluid in the developing chick embryo

Proteins from cerebrospinal fluid of chick embryos at 4-19 days of development were qualitative and quantitatively analyzed. The total protein concentration and the relative concentration of each protein fraction were calculated for each day. The main proteins found along development were immunoglobulin G, transferrin, alpha-fetoprotein, serum albumin, ovalbumin, prealbumin, and an unidentified component. alpha-Fetoprotein was found to be the major protein at 4-16 days, and serum albumin at 17-19 days of development. The unidentified fraction was present from 4 to 11 days; at day 5 it represented 28% of the total cerebrospinal fluid protein concentration.