Serum protein synthesis in the early chick embryo

Cdx regulates gene expression through PRC2-mediated epigenetic mechanisms

The extra-embryonic yolk sac contains adjacent layers of mesoderm and visceral endoderm. The mesodermal layer serves as the first site of embryonic hematopoiesis, while the visceral endoderm provides a means of exchanging nutrients and waste until the development of the chorioallantoic placenta. While defects in chorioallantoic fusion and yolk sac hematopoiesis have been described in Cdx mutant mouse models, little is known about the gene targets and molecular mechanisms through which Cdx members regulate these processes. To this end, we used RNA-seq to examine Cdx-dependent gene expression changes in the yolk sac. We find that loss of Cdx function impacts the expression of genes involved in yolk sac hematopoiesis, as previously described, as well as novel Cdx2 target genes. In addition, we observed Cdx-dependent changes in PRC2 subunit expression accompanied by altered H3K27me3 deposition at a subset of Cdx target genes as early as E7.5 in the embryo proper. This study identifies additional Cdx target genes and provides further evidence for Cdx-dependent epigenetic regulation of gene expression in the early embryo, and that this regulation is required to maintain gene expression programs in the extra-embryonic yolk sac at later developmental stages.

Yolk sac endoderm is the major source of serum proteins and lipids and is involved in the regulation of vascular integrity in early chick development

An important function of the vascular system is nutrient delivery. In adult animals, this is mediated through a close contact of the mesoderm-derived vasculature with the endoderm-derived enterocytes and hepatocytes. During embryonic development, the yolk sac (YS) endoderm has been suggested to play a similar role. Physiological and molecular nature of the contact between the YS endoderm and the vasculature is not well-understood. To understand roles of the YS endoderm in early development, we used the avian model and carried out a gene expression profiling analysis of isolated area vasculosa YS endoderm tissues from embryonic day 2-4 chick embryos, covering the first 48 hr of postcirculation development. Genes involved in lipid metabolism are highly enriched, indicating an active modification of lipid components during their transfer from the yolk to the circulatory system. We also uncovered genes encoding major serum proteins and key regulators of vascular integrity. In particular, PTGDS, an enzyme controlling the last step of prostaglandin D2 production, shows high expression in the YS endoderm. Experimental introduction of prostaglandin D2 into embryonic circulation led to intraembryonic vessel rupture. These data suggest that the YS endoderm is the major, if not exclusive, source of lipid and protein constituents of the early embryonic serum and plays an important role in the regulation of vascular integrity in developing embryo.

Clinicochemical follow-up of broiler rearing--a five-week study

Commercial broilers were raised in a 5-week period and a detailed clinicochemical follow-up was carried out, to characterise a flock selected for one-sided muscle mass production. Blood samples were drawn at the ages of 1 day, 1, 2, 3, 4 and 5 weeks, and plasma enzyme activities, metabolite and ion concentrations were determined. Early increases were found for all plasma nitrogenous compounds (total protein, albumin, creatinine and urate). Triglyceride showed a posthatch peak with a significant effect of age. Plasma total cholesterol was characterised by a marked post-hatch concentration peak, while during the first week its concentration decreased markedly. Plasma AST showed an increase during the rearing, while a one-magnitude increment was found for creatine kinase activity during the study. The main results of the study outlined a typical precocial bird (post-hatch triglyceride peak; decreasing cholesterol and early peaking plasma protein and urate concentrations) with very quick skeletal muscle mass growth (increasing creatine kinase and AST activities, slight hyperkalaemia).

Trace mineral metabolism in the avian embryo

Trace mineral metabolism in the developing avian embryo begins with the formation of the egg and the trace mineral stores contained within it. Vitellogenin, the yolk precursor protein, serves as a trace mineral transporting protein that mediates the transfer of these essential nutrients from stores within the liver of the hen to the ovary and developing oocyte, and hence, to the yolk of the egg. Lipovitellin and phosvitin, derived from intraoocytic proteolytic processing of vitellogenin, are also trace mineral binding proteins that form important storage sites within the granule subfraction of yolk. The mobilization and uptake of egg trace mineral stores is mediated by the extra-embryonic membranes, principally the yolk sac membrane. The yolk sac also serves as a short-term storage site for trace minerals. Because it is an important site of plasma protein synthesis, the yolk sac has the ability to regulate the export of trace minerals to the embryo during development. Within the embryo, specific metaloproteins function in the interorgan transport cellular uptake, and intracellular storage of trace minerals. Thus, embryonic trace mineral homeostasis is established through the coordinated actions of the yolk sac, which mobilizes and exports trace minerals derived from egg stores; the vitelline circulation, which transports them to the embryo; and the liver, which accumulates trace minerals and distributes them to the rest of the tissues of the embryo via the embryonic circulation.

Expression of the albumin gene in the yolk sac and liver during chick embryogenesis

1. Albumin mRNA is first detectable in vascular yolk sac on the third day of egg incubation, increases to peak level on day 14 and declines to zero by day 19. 2. Vascular yolk sac RNA contains a 6-10-fold higher level of albumin transcripts compared to non-vascularized yolk sac, suggesting a role for vascularization in promoting albumin gene expression. 3. Embryonic liver albumin transcripts are first detectable at day 6.5, increase 6-fold by day 8, continue to rise at a lower rate until day 14 and remain constant thereafter. 4. Albumin protein synthesis in liver cubes also exhibits a large increase over days 7-10. In contrast, another liver-specific constitutive protein, apolipoprotein B, shows a different biosynthetic pattern. 5. The data suggest development of hepatic albumin gene-specific regulatory factors over days 7-10.

Mineral metabolism in the developing turkey embryo--I. The effects of developmental age and shell-less culture on trace element contents of selected tissues

1. Turkey embryos were incubated in ovo or in long-term shell-less culture (ex ovo) for 14, 18, 22 or 26 days. The embryos incubated ex ovo exhibited a progressive decline in the rate of growth and were hypocalcemic and hypoproteinemic compared to their in ovo counterparts from day 18 to day 26 of incubation. 2. The ratio of the concentrations of alpha-fetoprotein and albumin (AFP/A) in serum was determined for both groups of embryos. The AFP/A ratio may be useful as a biochemical index to stage avian embryonic development. Using this index it was concluded that ex ovo embryos exhibited a progressive developmental retardation compared to in ovo embryos. 3. Significant differences were observed in serum trace element concentrations for embryos incubated in ovo vs ex ovo. Most notably, serum copper concentration was significantly lower in ex ovo embryos on days 18 and 22 of incubation and significantly higher on day 26 of incubation compared to serum from embryos incubated in ovo. 4. Livers from embryos incubated ex ovo exhibited significant differences trace element levels compared to those incubated in ovo. By day 26 of incubation the concentration and total amount of zinc and iron were markedly elevated, whereas copper was greatly reduced in the livers of embryos incubated ex ovo compared to the corresponding in ovo levels. 5. Hearts from embryos incubated ex ovo contained less zinc and copper and more iron by day 26 of incubation than those from embryos incubated in ovo.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogenesis of transthyretin gene expression in chicken choroid plexus and liver

1. Chicken liver transthyretin cDNA hybridizes strongly with choroid plexus transthyretin mRNA from chickens, pigeons, quails and ducks. 2. In the chicken at hatching the choroid plexus has reached 70%, total brain 30%, and liver 5.8% of their organ masses in adults. 3. The proportion of transthyretin mRNA in total RNA is 0.45-times the adult value in the choroid plexus of the chicken at hatching. 4. In the liver at hatching, the proportion of transthyretin mRNA in total RNA is 1.1-times the value in adult chickens. 5. The pattern of maturation of transthyretin gene expression in chicken liver is comparable to that in precocial, but differs from that in altricial mammals.

Duck hepatitis B virus replicates in the yolk sac of developing embryos

Duck hepatitis B virus (DHBV) is the only member of the hepadnavirus family in which nearly 100% vertical transmission from carrier mother to embryo has been reported. Large quantities of maternally transmitted virus particles are present in the yolk prior to incubation of the eggs, and replicative forms of DHBV DNA are detectable in the liver at 6 days of incubation. Since the yolk sac is similar to the liver in its production of serum proteins, we examined the yolk sacs of developing embryos for signs of viral replication. We detected the supercoiled form of DHBV DNA, DHBV RNA transcripts similar to those in the virus-replicating liver, and DNA polymerase activity and viral DNA in corelike particles in extracts of yolk sac tissue of naturally infected eggs. DHBV core antigen was strongly stained in only the endodermal layer of the yolk sac by immunofluorescence. DHBV RNA was detectable in the yolk sac from 4 days of incubation until hatching, and a larger quantity of DHBV RNA was present in the yolk sac than in the liver during all the stages of embryogenesis. Our data indicate that DHBV replicates actively in the yolk sac from an earlier stage than that previously reported in studies of embryonic liver and that replication is limited to the endodermal cell layer, which is ontogenetically and functionally related to the liver. The yolk sac may support the vertical transmission of DHBV.

Alpha-fetoprotein expression in intra- and extraembryonic fluids of developing chick embryo

The ontogeny of alpha-fetoprotein (AFP) has been studied in the chicken (from 7 days of incubation until 2 days after hatching) using (1) the two-dimensional immunoelectrophoresis technique, (2) the polyacrylamide gel electrophoresis, and (3) the high resolution two-dimensional polyacrylamide gel electrophoresis. The molecular weight of AFP was estimated at 71,000. AFP was seen as a heterogeneous population composed of four isoforms which slightly differ by their isoelectric points. Up to the 18th day of development, qualitative changes in AFP heterogeneity do not occur. Only traces of the two alkaline isoforms were observed in plasma of 2 days post-hatching chickens. AFP has been identified in allantoic and cerebrospinal fluids but is not present in amniotic fluid. At 7 days of embryonic age, all the plasma AFP species are present in cerebrospinal fluid.

Synthesis of serum proteins by cultures of chick embryo yolk sac endodermal cells

Endodermal cells were isolated from yolk sacs of 3-day chick embryos and cultured for 6 days in Eagle's minimal essential media plus 10% fetal calf serum. During this period cells rapidly lost their ability to synthesize DNA as judged by [3H]thymidine incorporation into DNA. In spite of this loss of DNA synthesis serum protein synthesis and secretion remained at a constant 45% of total protein synthesis and secretion. This was determined by immunoprecipitation of culture media using antibodies directed against embryonic chick serum proteins. Media were also analyzed for the synthesis and secretion of specific serum proteins using polyacrylamide gel electrophoresis. The relative synthesis and secretion of the individual serum proteins followed that previously observed in ovo with the exception of alpha-globulin-a which became undetectable. When culture media were supplemented with ovalbumin or insulin the relative synthesis and secretion of certin specific serum proteins were altered. However, analysis of these same media samples showed that the total amounts of serum protein synthesis and secretion were unaffected.