Complete nucleotide sequence of the messenger RNA coding for chicken muscle glyceraldehyde-3-phosphate dehydrogenase

Characterization of interleukin-1beta mRNA expression in chicken macrophages in response to avian reovirus

Inhibitors of viral disassembly or RNA and protein synthesis, viral disassembly intermediates (infectious subviral particles, ISVP), binary ethylenimine-inactivated virions, and viral particles lacking genomic double-stranded (ds) RNA (empty particles) were used to assess the expression of interleukin-1beta (IL-1beta) mRNA in chicken (chIL-1beta) macrophages in response to avian reovirus. The results demonstrate that two distinct expression patterns of chIL-1beta mRNA mediated by different steps in viral replication were found. Viral disassembly was required for the induction of a rapid, transient expression pattern of chIL-1beta mRNA that was rapidly induced at 30 min, with maximal levels reached by 2 h, and fell to a low level within 6 h post-inoculation, while viral RNA synthesis rather than protein translation, which was subsequent to membrane penetration, was required to induce a stable, sustained expression pattern of chIL-1beta mRNA that occurred at and after 6 h post-inoculation. In addition, the induction of chIL-1beta mRNA expression by the empty particles and ISVP was extremely weak, compared with the active dsRNA(+) virions or binary ethylenimine-inactivated virions, suggesting that the presence of dsRNA, even if transcriptionally inactive, may be an important factor in this response.

Sequence and phylogenetic analysis of interleukin (IL)-1beta-encoding genes of five avian species and structural and functional homology among these IL-1beta proteins

Interleukin (IL)-1beta-encoding regions of chicken, duck, goose, turkey and pigeon were cloned and sequenced. Each IL-1beta-encoding region of chicken, duck, goose and turkey is 804 nucleotides long and encodes IL-1beta protein that is 268 amino acids. Pigeon IL-1beta-encoding region is 810 nucleotides long and encodes IL-1beta protein that is 270 amino acids. Two one-nucleotide and one four-nucleotide insertions of pigeon IL-1beta-encoding region sequence were found, resulting in two amino acid insertions in pigeon IL-1beta. Pairwise sequence analysis showed that the sequence identities of IL-1beta-encoding genes ranged from 77% to 99%, which were also found for IL-1beta protein sequence identities, with an average level of both sequence identities of 89%. Phylogenetic analysis indicated that IL-1beta-encoding regions and the encoded proteins of chicken, duck, goose and turkey clustered together and evolved into a distinct phylogenetic lineage from that of pigeon which evolved into a second lineage. The results from the binding reaction of antiserum against each recombinant IL-1beta (r IL-1beta) protein to homologous or heterologous rIL-1beta, the enhancement levels of K60 mRNA expression in rIL-1beta-treated DF-1 cells or the reduction levels of K60 mRNA expression in DF-1 cells treated with rIL-1beta that was preincubated with homologous or heterologous antiserum showed that all five rIL-1beta were functional active and shared significantly structural and functional homology.

Highly pathogenic H5N1 influenza virus causes coagulopathy in chickens

Severe hemorrhage at multiple organs is frequently observed in chickens infected with highly pathogenic avian influenza (HPAI) A viruses. In this study we examined whether HPAI virus infection leads to coagulation disorder in chickens. Pathological examinations showed that the fibrin thrombi were formed in arterioles at the lung, associated with the viral antigens in endothelial cells of chickens infected intravenously with HPAI virus. Hematological analyses of peripheral blood collected from the chickens revealed that coagulopathy was initiated at early stage of infection when viral antigens were detected only in the endothelial cells and monocytes/macrophages. Furthermore, gene expression of the tissue factor, the main initiator of blood coagulation, was upregulated in the spleen, lung, and brain of HPAI virus-infected chickens. These results suggest that dysfunction of endothelial cells and monocytes/macrophages upon HPAI virus infection may induce hemostasis abnormalities represented by the excessive blood coagulation and consumptive coagulopathy in chickens.

Zebrafish and chicken lipocalin-type prostaglandin D synthase homologues: Conservation of mammalian gene structure and binding ability for lipophilic molecules, and difference in expression profile and enzyme activity

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is a bifunctional protein possessing both the ability to synthesize PGD(2) and to serve as a carrier protein for lipophilic molecules. L-PGDS has been extensively studied in mammalian species, whereas little is known about non-mammalian forms. Here, we identified and characterized the L-PGDS homologues from non-mammals such as zebrafish and chicken. Phylogenetic analysis revealed that L-PGDSs of mammalian and non-mammalian organisms form a "L-PGDS sub-family" that has been evolutionally separated from other lipocalin gene family proteins. The genes for zebrafish and chicken L-PGDS homologues consisted of 6 exons, and all of the exon/intron boundaries were completely identical to those of mammalian L-PGDS genes. Zebrafish and chicken L-PGDS genes were clustered with several lipocalin genes in the chromosome, as in the case of mouse and human genes. Gene expression profiles were different among chicken, mouse, human, except for conservation of abundant expression in the brain and heart. The chicken L-PGDS homologue carried weak PGDS activity, whereas the zebrafish protein did not show any of the activity. However, when the amino-terminal region of the zebrafish L-PGDS homologue was exchanged for that of mouse L-PGDS carrying the Cys residue essential for PGDS activity, this chimeric protein showed weak PGDS activity. Both zebrafish and chicken L-PGDS homologues bound thyroxine and all-trans retinoic acid, like mammalian L-PGDSs and other lipocalin gene family proteins. These results indicate that non-mammalian and mammalian L-PGDS genes evolved from the same ancestral gene and that the non-mammalian L-PGDS homologue was the primordial form of L-PGDS but whose major function was and is to serve as a carrier protein for lipophilic molecules. During molecular evolution, the mammalian L-PGDS protein might have acquired effective PGDS activity through substitution of several amino acid residues, especially in the amino-terminal region including the Cys residue, which is essential for PGDS activity.

Regulation of growth hormone expression by thyrotropin-releasing hormone through the pituitary-specific transcription factor Pit-1 in chicken pituitary

Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone- (GH), prolactin- (PRL) and thyroid stimulating hormone beta- (TSHbeta) encoding genes. Pit-1 has been identified in several mammalian and avian species. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and it stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully developed a competitive RT-PCR for the detection of Pit-1 expression in the chicken pituitary, that was sensitive enough to detect picogram levels of Pit-1 mRNA. Applying this method, the effect of TRH injections on Pit-1 mRNA expression was determined in the pituitary of chick embryos and growing chicks. In both 18-day-old embryos and 10-day-old male chicks the Pit-1 mRNA expression was significantly increased following TRH injection, thereby indicating that the stimulatory effects of TRH on several pituitary hormones is mediated via its effect on Pit-1 expression. Therefore, a semi-quantitative RT-PCR method was used to detect possible changes in GH levels. TRH affected the GH mRNA levels at both developmental stages. These results, combined with the data on Pit-1 mRNA expression, indicate that Pit-1 has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH.

Inhibition of the cardiac alpha-actin gene in embryonic cardiac myocytes by dominant-negative serum response factor

Serum response factor (SRF), a transcription factor ubiquitously involved in the processes of cellular proliferation and differentiation, has been implicated in cardiac and skeletal muscle development because of its strong expression in embryonic muscle lineages, and its necessity for the transcription of transiently transfected muscle genes that contain SRF binding sites. This study was designed to ascertain whether SRF is required for the expression of an endogenous SRF-dependent gene during differentiation of early embryonic cardiac myocytes by introducing a dominant-negative SRF construct via retroviral delivery. Although no effect on overt cellular differentiation was detected, semi-quantitative RT-PCR revealed that expression of the SRF-dependent gene cardiac alpha-actin was inhibited, whereas expression of the non-SRF-dependent genes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and cardiac troponin-C was unaffected. No effect on myocyte proliferation was detected. Curiously, immunohistochemical localization of SRF protein suggested that whereas endogenous SRF was homogeneously dispersed throughout the cytoplasm and nucleus, the dominant-negative SRF protein was concentrated in the nucleus. These results extend previous findings using transiently transfected genes to the endogenous level, indicating that SRF is required for the full expression of muscle genes that contain SRF binding sites during cardiac myocyte differentiation.

An interferon-gamma-binding protein of novel structure encoded by the fowlpox virus

Poxviruses have evolved various strategies to counteract the host immune response, one of which is based on the expression of soluble cytokine receptors. Using various biological assays, we detected a chicken interferon-gamma (chIFN-gamma)-neutralizing activity in supernatants of fowlpox virus (FPV)-infected cells that could be destroyed by trypsin treatment. Secreted viral proteins were purified by affinity chromatography using matrix-immobilized chIFN-gamma, followed by two-dimensional gel electrophoresis. Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis indicated that the viral IFN-gamma-binding protein in question was encoded by the FPV gene 016. The chicken IFN-gamma binding and neutralizing activity of the recombinant FPV016 protein was confirmed using supernatants of cells infected with a recombinant vaccinia virus that lacked its own IFN-gamma-binding protein but instead expressed the FPV016 gene. The FPV016 gene product also neutralized the activity of duck and human IFN-gamma but failed to neutralize the activity of mouse and rat IFN-gamma. Unlike previously known cellular and poxviral IFN-gamma receptors, which all contain fibronectin type III domains, the IFN-gamma-binding protein of FPV contains an immunoglobulin domain. Remarkably, it exhibits no significant homology to any known viral or cellular protein. Because IFN-gamma receptors of birds have not yet been characterized at the molecular level, the possibility remains that FPV016 represents a hijacked chicken gene and that avian and mammalian IFN-gamma receptors have fundamentally different primary structures.

Heart-selective expression of the chicken FK506-binding protein (FKBP) 12.6 gene during embryonic development

FKBP12.6, a member of the family of FK506-binding proteins, selectively associates with the cardiac isoform of the ryanodine receptor and thereby stabilizes this Ca(2+) release channel. A chicken FKBP12.6 (chFKBP12.6) cDNA was cloned and shown to encode a protein of 108 amino acids. The deduced amino acid sequence of chFKBP12.6 is 91-92% identical to those of mammalian FKBP12.6 proteins. Northern blot analysis revealed that chFKBP12.6 mRNA is largely restricted to the heart during embryonic development and that the abundance of this mRNA in the heart decreases, and it becomes restricted to the atrium during cardiogenesis. In situ hybridization revealed that chFKBP12.6 mRNA is localized to the precardiac mesoderm before formation of the primitive heart tube. Expression of the chFKBP12.6 gene was initially apparent throughout the developing multichambered heart but became restricted to the atria before hatching. Reverse transcription and polymerase chain reaction analysis demonstrated that chFKBP12.6 mRNA is present in the embryo from early gastrulation and is most abundant immediately after the onset of the heartbeat. These observations suggest that the chFKBP12.6 gene is expressed before heart morphogenesis to play a role in excitation-contraction coupling in cardiomyocytes and that the function of the encoded protein becomes increasingly restricted to the atrium during embryonic development.

Competency of embryonic cardiomyocytes to undergo Purkinje fiber differentiation is regulated by endothelin receptor expression

Purkinje fibers of the cardiac conduction system differentiate from heart muscle cells during embryogenesis. In the avian heart, Purkinje fiber differentiation takes place along the endocardium and coronary arteries. To date, only the vascular cytokine endothelin (ET) has been demonstrated to induce embryonic cardiomyocytes to differentiate into Purkinje fibers. This ET-induced Purkinje fiber differentiation is mediated by binding of ET to its transmembrane receptors that are expressed by myocytes. Expression of ET converting enzyme 1, which produces a biologically active ET ligand, begins in cardiac endothelia, both arterial and endocardial, at initiation of conduction cell differentiation and continues throughout heart development. Yet, the ability of cardiomyocytes to convert their phenotype in response to ET declines as embryos mature. Therefore, the loss of responsiveness to the inductive signal appears not to be associated with the level of ET ligand in the heart. This study examines the role of ET receptors in this age-dependent loss of inductive responsiveness and the expression profiles of three different types of ET receptors, ETA, ETB and ETB2, in the embryonic chick heart. Whole-mount in situ hybridization analyses revealed that ETA was ubiquitously expressed in both ventricular and atrial myocardium during heart development, while ETB was predominantly expressed in the atrium and the left ventricle. ETB2 expression was detected in valve leaflets but not in the myocardium. RNase protection assays showed that ventricular expression of ETA and ETB increased until Purkinje fiber differentiation began. Importantly, the levels of both receptor isotypes decreased after this time. Retrovirus-mediated overexpression of ETA in ventricular myocytes in which endogenous ET receptors had been downregulated, enhanced their responsiveness to ET, allowing them to differentiate into conduction cells. These results suggest that the developmentally regulated expression of ET receptors plays a crucial role in determining the competency of ventricular myocytes to respond to inductive ET signaling in the chick embryo.

Osteocyte-specific monoclonal antibody MAb OB7.3 is directed against Phex protein

Osteocytes are the most abundant cells in bone; however, relatively little is known about their properties and functions. The development of monoclonal antibody MAb OB7.3 directed against chicken osteocytes enabled us to purify osteocytes from enzymatically isolated bone cells. Cultures of purified osteocytes were used to gain better insight into the role of osteocytes in bone metabolism. Until now, the antigen of MAb OB7.3 has not been elucidated. In this study, we examined the antigen to which this osteocyte-specific antibody is directed. Immunoprecipitation and purification of the protein, followed by amino acid sequence analysis of two isolated peptides, revealed that the antigen has high homology to human and murine PHEX/Phex protein sequences (PHosphate-regulating gene with homology to Endopeptidases on the X chromosome). The OB7.3 antigen was therefore identified as chicken Phex protein. In addition, using suppression subtractive hybridization, we obtained a complementary DNA (cDNA) sequence of 502 base pairs (bp) with high homology to the human and murine PHEX/Phex genes. This method was applied to identify genes, which are differentially expressed in osteocytes compared with osteoblasts. The results also suggest that Phex is expressed at higher levels in chicken osteocytes compared with osteoblasts. Reverse-transcription polymerase chain reaction (RT-PCR) and Northern blot analyses supported these findings. The function of Phex is not completely understood. However, it is known that the gene is preferentially expressed in bone and that mutations in PHEX/Phex lead to X-linked hypophosphatemia and bone mineralization abnormalities. Our findings suggest that osteocytes play an important role in the Phex-regulated phosphate handling in the kidney and in bone.

Transient expression of TIP60 protein during early chick heart development

Screening of an embryonic chick cDNA library revealed a gene product termed chick TIP60 (cTIP60) due to its homology with human TIP60, a founding member of the "MYST" family of proteins that possess functional motifs, including chromo, zinc finger, and histone acetyltransferase domains. cTIP60 expression was assessed during early chick embryogenesis, at the RNA level by using reverse transcriptase-polymerase chain reaction (RT-PCR) and at the protein level by using Western blotting and immunohistochemistry. RT-PCR indicated that cTIP60 transcripts in whole embryos are present as early as Hamburger-Hamilton (HH) stage 5, diminishing after HH10. Western blotting of total embryonic protein revealed that cTIP60 was present in uniform quantities between HH3 and HH25. By contrast, Western blotting of protein from isolated hearts revealed that cTIP60 protein was strongly expressed at the earliest stages of heart development (HH11-13), diminishing thereafter. This finding was corroborated by immunohistochemistry, which revealed that cTIP60 protein was selectively expressed at high levels in the myocardium between HH 10-14. Considered in the context of its functional domains, these findings suggest that cTIP60 modulates transcriptional processes which regulate terminal cell differentiation, proliferation, or both, during early myocardial development.

Cloning and characterization of a chicken platelet-derived growth factor B-chain cDNA

Avian thrombocytes are nucleated blood cells homologous in function to mammalian platelets. In the present study, we obtained a cDNA from chicken thrombocyte polyadenylated RNA [Poly(A)+RNA], which coded for the chicken PDGF-B chain. The sequence was 1083-bp long and had an open reading frame (ORF) of 753-bp. At the amino acid level, the predicted mature protein showed 69% homology with the processed coding region of human PDGF-B. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that PDGF-B mRNA was expressed at high levels in thrombocytes and in the lung. The expression of PDGF-B chain mRNA in thrombocytes reached its maximum level 12h following type 1 collagen treatment. These results suggest that chicken PDGF-B chain may play an important role in the vascular system and in healing wounded tissue.

The extracellular ATP receptor, cP2Y(1), inhibits cartilage formation in micromass cultures of chick limb mesenchyme

We have investigated the function of the G protein-coupled receptor for extracellular ATP, chick P2Y(1) (cP2Y(1)) during development of the chick limb. cP2Y(1) is strongly expressed in undifferentiated limb mesenchyme cells but appears to be lost from cells as they differentiate, raising the possibility that the function of this receptor may be to inhibit cell differentiation. This pattern of expression was particularly striking surrounding areas of cartilage formation. We tested whether cP2Y(1) was able to regulate cartilage formation by using an in-vitro micromass model of chondrogenesis. Because limb cells in micromass culture lose expression of cP2Y(1), we have used a gain-of-function approach to demonstrate that cP2Y(1) expression can inhibit cartilage differentiation. We also demonstrate that early limb mesenchyme cells release ATP into the extracellular medium and have mechanisms to breakdown extracellular ATP. These results suggest that extracellular ATP, signaling through cP2Y(1), can modulate the differentiation of limb mesenchyme cells in vitro, and the expression pattern of cP2Y(1) suggests that this type of signaling could play a similar role in ovo.

Effects of active immunization with inhibin alpha subunit on reproductive characteristics of turkey hens

The hypothesis for the present study is that the active immunization of female turkeys with inhibin (INH) would neutralize endogenous INH, and increase levels of circulating follicle stimulating hormone (FSH) and the number of preovulatory follicles, and subsequently enhance egg production. Two experiments were conducted with female turkeys in their first (30 wk of age) and second (62 wk of age) laying cycles. Treatment groups included control turkeys immunized with keyhole limpet hemocyanine (KLH) and experimental turkeys immunized with recombinant turkey inhibin alpha conjugated to KLH (rtINH), vasoactive intestinal peptide (VIP) conjugated to KLH or rtINH+VIP. Egg production increased (P < 0.05) in VIP and rtINH+VIP immunized birds, but not in rtINH immunized hens in comparison with a control group. A similar number of ovarian follicles, arranged in the follicular hierarchy of laying hens, was observed in all experimental groups. However, there was a larger number of nongraded yellow follicles in rtINH-immunized (62.5%) and rtINH+VIP-immunized (73.5%) groups compared with that of controls, suggesting overstimulation by FSH. Anterior pituitary FSH beta subunit, LH beta subunit, and prolactin (PRL) mRNA contents were determined by Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) in laying hens at the end of the experimental period. Hens immunized with rtINH showed increased FSH beta subunit mRNA content, but no change in the content of LH beta subunit or PRL mRNA. Hens immunized with VIP or rtINH+VIP had significant increases in both pituitary LH beta subunit and FSH beta subunit mRNA contents, accompanied by a decline in PRL mRNA abundance. The magnitude of the increase in FSH beta subunit to INH immunoneutralization was greater in first-cycle hens than in second-cycle hens. These data suggest that active immunization of female turkeys with INH neutralizes endogenous INH and increases both circulating FSH and the number of preovulatory follicles. However, no significant increase in egg production was observed in INH-immunized hens. The data confirm previous reports that VIP immunoneutralization increases egg production in turkey hens and shows for the first time that it also increases FSH beta subunit and LH beta subunit gene expression.

Retinoic acid combined with neurotrophin-3 enhances the survival and neurite outgrowth of embryonic sympathetic neurons

Both nerve growth factor (NGF) and neurotrophin-3 (NT-3) are necessary for the survival of embryonic sympathetic neurons in vivo. All-trans retinoic acid (atRA) has been shown to promote neurite outgrowth and long-term survival of chick embryonic sympathetic neurons cultured in the presence of NGF. The present study shows that atRA can also potentiate the survival and neurite outgrowth-promoting activities of NT-3. This was accomplished by enhancing the survival of existing neurons, as cell proliferation was unaffected by exposure to atRA. atRA also enhanced neurite outgrowth of the NT-3-treated cells; however, the neurites appeared thicker and less branched than cells treated with atRA in combination with NGF. Using a quantitative PCR assay, trkA and p75(NTR) mRNAs, but not trkC mRNA, were increased ( approximately 1.5- to 2-fold) after 72 and 48 hr of exposure of the cultures to atRA, respectively. The atRA-induced increase in trkA mRNA may play a role in the enhanced survival of neurons cultured in the presence of either NGF or NT-3, as both neurotrophins have been shown to signal through this receptor. The time course of these mRNA changes would indicate that atRA does not regulate the neurotrophin receptor mRNA directly, rather, intervening gene transcription is required. Thus, during development, atRA may play a role in fine-tuning embryonic responsiveness to both NT-3 and NGF.

Chicken interleukin-6. cDNA structure and biological properties

Suppression subtractive hybridization technology was used to identify differentially expressed genes in spleens of chickens that had been treated with the synthetic immune modifier S-28463. One induced chicken gene encoded a protein with about 35% sequence identity to human interleukin-6 (IL-6). It consists of 241 amino acids including a putative N-terminal signal peptide of 47 residues. Bacterially expressed chicken IL-6 (ChIL-6) carrying a histidine tag in place of the signal peptide was biologically active: it induced proliferation of the IL-6-dependent murine hybridoma cell line 7TD1. The concentration of ChIL-6 required for half-maximal proliferative response was approximately 60 pg.mL-1. When injected intravenously into adult chickens, purified recombinant ChIL-6 induced an increase in serum corticosterone levels. Supernatants of chicken LMH and monkey COS-7 cells transiently transfected with a ChIL-6 expression construct induced proliferation of 7TD1 cells, demonstrating that recombinant ChIL-6 from eukaryotic cells is also active.

Characterization and expression of three forms of cDNA encoding chicken platelet-derived growth factor-A chain

Platelet-derived growth factor (PDGF) affects cell proliferation and differentiation during mammalian embryogenesis. In a number of avian species, PDGF-alpha receptors and PDGF-A chain (PDGF-A) are present during chicken limb and lens development. However, little is understood about the chicken PDGF-A gene. The present study identified short form type 1 (S1), long form (L) and short form type 2 (S2) cDNA clones encoding chicken PDGF-A chain (PDGF-A). These clones were isolated from a chicken hepatoma cell line (LMH) mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA library cloning. Genomic sequencing and Southern blotting revealed that these forms were generated by alternative splicing. The mRNAs of S1 and L contained two transcription start sites on one exon. At the amino acid level, the mature protein encoded by the L clone showed 90 and 85% homology with the processed coding regions of the long form of human and Xenopus PDGF-A, respectively. The putative mature peptides of all forms of chicken PDGF-A encompassed the eight cysteine residues conserved in all known forms of PDGF. We examined the expression of the three forms in chicken tissues and cells using RT-PCR. Expression of these forms varied among tissues and cells. Levels of PDGF mRNAs were very low in chicken thrombocytes, which are analogous to mammalian platelets. However, the level of PDGF-A chain mRNA expression in chicken thrombocytes peaked 4 h after exposure to type 1 collagen or thrombin, and then decreased gradually with continued incubation. These results suggest that chicken PDGF in thrombocytes plays an important role in the vascular system and in healing damaged tissue.

Role of FK506-binding protein 12 in development of the chick embryonic heart

A cDNA encoding chicken FK506-binding protein 12 (FKBP12) was isolated and sequenced. The predicted amino acid sequence of the chicken protein shows high homology to those of FKBP12 proteins of other species ranging from human to frog. The possible role of FKBP12 in chick embryonic cardiac development was examined. Northern blot analysis revealed that FKBP12 mRNA is distributed widely in chick embryos, being especially abundant in the heart; the amount of FKBP12 mRNA in the embryonic heart decreased with time. Administration of FK506 to chick embryos at 7 to 9 days resulted in marked cardiac enlargement. FK506 also reduced the expression of myosin, induced a more elongated cell morphology, and impaired network formation in cultured chick embryonic cardiomyocytes. These results suggest that FKBP12 is important in the regulation of contractile function and phenotypic expression in chick cardiomyocytes during embryonic development.

Occurrence of ovalbumin in ovarian yolk of chicken during oogenesis

Yolk specimens from chicken ovaries during oogenesis gave a positive signal for ovalbumin as analyzed by Western blotting, indicating that the ovarian yolk contains ovalbumin. Northern blotting and reverse transcriptase-polymerase chain reaction gave a negative signal for ovalbumin mRNA in the liver and other organs except oviduct, whereas the laying hen serum was found to indicate immunologically the presence of ovalbumin. It was therefore assumed that ovalbumin synthesized in the oviduct might partly be secreted into the blood circular system, from which it is taken up into the oocyte.

Screening from a subtracted embryonic chick hindbrain cDNA library: identification of genes expressed during hindbrain, midbrain and cranial neural crest development

The vertebrate hindbrain is segmented into a series of transient structures called rhombomeres. Despite knowing several factors that are responsible for the segmentation and maintenance of the rhombomeres, there are still large gaps in understanding the genetic pathways that govern their development. To find previously unknown genes that are expressed within the embryonic hindbrain, a subtracted chick hindbrain cDNA library has been made and 445 randomly picked clones from this library have been analysed using whole mount in situ hybridisation. Thirty-six of these clones (8%) display restricted expression patterns within the hindbrain, midbrain or cranial neural crest and of these, twenty-two are novel and eleven encode peptides that correspond to or are highly related to proteins with previously uncharacterised roles during early neural development. The large proportion of genes with restricted expression patterns and previously unknown functions in the embryonic brain identified during this screen provides insights into the different types of molecules that have spatially regulated expression patterns in cranial neural tissue.

Autocrine regulation of norepinephrine transporter expression

The norepinephrine transporter (NET) is a neurotransmitter scavenger and site of drug action in noradrenergic neurons. The aim of this study was to identify mechanisms that regulate NET expression during the development of quail (q) sympathetic neuroblasts, which develop from neural crest stem cells. Neurotrophin-3 (NT-3) and transforming growth factor beta1 (TGF-beta1) cause an increase of qNET mRNA levels in neural crest cells. When combined, the growth factors are additive in increasing qNET mRNA levels. Both NT-3 and TGF-beta1 are synthesized by neural crest cells. Onset of NET expression precedes the onset of neural crest stem cell emigration from the neural tube. In older embryos, qNET is expressed by several crest-derived and noncrest tissues. The data show that qNET expression in presumptive sympathetic neurons is initiated early in embryonic development by growth factors that are produced by neural crest cells themselves. Moreover, the results support our previous observations that norepinephrine transport contributes to the regulation of the differentiation of neural crest stem cells into sympathetic neurons.

The autoregulation of retinal ganglion cell number

The development of the nervous system is dependent on a complex set of signals whose precise co-ordination ensures that the correct number of neurones are generated. This regulation is achieved through a variety of cues that influence both the generation and the maintenance of neurones during development. We show that in the chick embryo, stratified retinal ganglion cells (RGCs) are themselves responsible for providing the signals that control the number of RGCs that are generated, both by inhibiting the generation of new ganglion cells and by killing incoming migratory ganglion cells. Selective toxicological ablation of RGCs in the chick embryo resulted in the achronic generation of ganglion cells, which eventually led to the repopulation of the ganglion cell layer and a large decrease in the physiological cell death affecting postmitotic migratory neurones. Interestingly, the application of exogenous NGF reversed the effects of ganglion cell ablation on ganglion cell death. Because the only source of NGF in the retina is that produced by the stratified ganglion cells, we infer that these differentiated neurones regulate their own cell number by secreting NGF, a neurotrophin that has previously been shown to be responsible for the death of migrating ganglion cells.

Programmed cell death in the developing somites is promoted by nerve growth factor via its p75(NTR) receptor

Neurotrophins control neuron number during development by promoting the generation and survival of neurons and by regulating programmed neuronal death. In the latter case, the cell death induced by nerve growth factor (NGF) in the developing chick retina is mediated by p75(NTR), the common neurotrophin receptor (J. M. Frade, A. Rodriguez-Tebar, and Y.-A. Barde, 1996, Nature 383, 166-168). Here we show that NGF also induces the programmed death of paraxial mesoderm cells in the developing somites. Both NGF and p75(NTR) are expressed in the somites of chick embryos at the time and the place of programmed cell death. Moreover, neutralizing the activity of endogenous NGF with a specific blocking antibody, or antagonizing NGF binding to p75(NTR) by the application of human NT-4/5, reduces the levels of apoptotic cell death in both the sclerotome and the dermamyotome by about 50 and 70%, respectively. Previous data have shown that Sonic hedgehog is necessary for the survival of differentiated somite cells. Consistent with this, Sonic hedgehog induces a decrease of NGF mRNA in somite explant cultures, thus showing the antagonistic effect of NGF and Sonic hedgehog with respect to somite cell survival. The regulation of programmed cell death by NGF/p75(NTR) in a mesoderm-derived tissue demonstrates the capacity of neurotrophins and their receptors to influence critical developmental processes both within and outside of the nervous system.

Requirement for BMP and FGF signaling during cardiogenic induction in non-precardiac mesoderm is specific, transient, and cooperative

We previously reported that combined treatment with bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor-4 (FGF-4) induces cardiogenic events culminating in full cardiac differentiation of non-precardiac mesoderm explanted from stage 6 avian embryos (Lough et al. [1996] Dev. Biol. 178:198-202.). To elucidate the respective functions of BMP and FGF in initiating and maintaining the cardiogenic process, we have used these ectopic cells as a cardiac specification model to ascertain requirements for growth factor specificity and extent of application, as well as induction of cardiac transcription factors. The inability of some BMP isoforms to replace the inductive activity of BMPs-2/4 indicated a specific requirement for this signaling pathway; moreover, neither activin-A nor insulin, which support terminal differentiation of precardiac mesoderm, nor leukocyte inhibitory factor (LIF), which promotes hypertrophy in cardiac myocytes, could replace BMP's cardiogenic activity. A similarly specific requirement for FGF-2/4 signaling was revealed since neither FGF-7, activin-A nor insulin could replace this activity. The effect of both factors was concentration-dependent; maximal incidence of explant differentiation for each occurred at 50 ng/ml. Surprisingly, the majority of explants treated with high BMP levels (250 ng/ml) exhibited a non-cardiac phenotype that was characterized by intense expression of alkaline phosphatase, suggesting differentiation toward an alternative mesodermal phenotype. Experiments to assess the duration of exposure to each factor that was required revealed that while exposure to BMP and FGF during only the initial 30 min of a 48-hr culture period was sufficient to induce cardiogenesis in a significant percentage of explants, 100% incidence of explant differentiation was obtained only when FGF treatment was restricted to the first 30 min and BMP was continuously present during the 48-hr culture period. Treatment with both growth factors was required to induce the cardiac transcription factors cNkx-2.5 and SRF; neither mRNA was induced by BMP or FGF alone. These findings indicate that: (1) specific members of the BMP and FGF families are required to induce cardiogenesis in non-precardiac mesoderm; (2) BMPs-2/4 may function as a morphogen; (3) brief application of both factors can induce cardiogenesis in a modest number of explants whereas (4) 100% incidence of explant differentiation can only be attained by brief FGF treatment combined with continuous BMP treatment and (5) both factors are necessary to induce downstream cardiac transcription factors. These findings are interpreted in terms of these factors' possible roles during cardiac specification and differentiation.

Cyclic AMP signaling functions as a bimodal switch in sympathoadrenal cell development in cultured primary neural crest cells

Cells of the vertebrate neural crest (crest cells) are an invaluable model system to address cell fate specification. Crest cells are amenable to tissue culture, and they differentiate to a variety of neuronal and nonneuronal cell types. Earlier studies have determined that bone morphogenetic proteins (BMP-2, -4, and -7) and agents that elevate intracellular cyclic AMP (cAMP) stimulate the development of the sympathoadrenal (SA, adrenergic) lineage in neural crest cultures. To investigate whether interactive mechanisms between signaling pathways influence crest cell differentiation, we characterized the combinatorial effects of BMP-2 and cAMP-elevating agents on the development of quail trunk neural crest cells in primary culture. We report that the cAMP signaling pathway modulates both positive and negative signals influencing the development of SA cells. Specifically, we show that moderate activation of cAMP signaling promotes, in synergy with BMP-2, SA cell development and the expression of the SA lineage-determining gene Phox2a. By contrast, robust activation of cAMP signaling opposes, even in the presence of BMP-2, SA cell development and the expression of the SA lineage-determining ASH-1 and Phox2 genes. We conclude that cAMP signaling acts as a bimodal regulator of SA cell development in neural crest cultures.

Capsid-targeted viral inactivation can eliminate the production of infectious murine leukemia virus in vitro

Capsid-targeted viral inactivation (CTVI), a promising gene-based antiviral strategy against retroviruses, was designed to disrupt the retroviral life cycle by incorporating a degradative enzyme (e.g., nuclease) into viral particles during assembly, thereby reducing or eliminating the production of infectious virus. The experimental system used to develop the CTVI strategy for retroviruses is designed to block the production of infectious Moloney murine leukemia virus (Mo-MLV). Two nucleases, Escherichia coli ribonulease HI and Staphylococcus nuclease, have been shown to be tolerated by the cell as Mo-MLV Gag-nuclease fusion polyproteins and still be active in the viral particles. The goal of this study was to determine what cellular and viral factors limit CTVI in cultured cells. The avian DF-1 cell line greatly expanded our ability to test the antiviral efficacy of CTVI in long-term assays and to determine the mechanism(s) of CTVI action. The CTVI antiviral effect is dependent on the level of Mo-MLV Gag-nuclease fusion polyprotein expressed. The Mo-MLV Gag-nuclease polyproteins produce a long-term prophylactic antiviral effect after a low- or high-dose Mo-MLV challenge. The Mo-MLV Gag-nuclease fusions have a significant therapeutic effect ( approximately 1000-fold) on the production of infectious Mo-MLV. The therapeutic CTVI effect can be improved by a second delivery of the CTVI fusion gene. Both the prophylactic and the therapeutic CTVI antiviral approaches can virtually eliminate the production of infectious Mo-MLV in vitro and are only limited by the number of cells in the population that do not express adequate levels of the CTVI fusion polyprotein.

Expression of five steroidogenic genes including aromatase gene at early developmental stages of chicken male and female embryos

In the course of avian embryo development, estrogen has been indicated to play a key role in gonadal differentiation by the inhibition of aromatase (P-450arom) that synthesizes estrogen from androgen. Biosynthesis of estrogen requires not only P-450arom but also other enzymes for a steroidogenic pathway. To elucidate gonadal differentiation, the steroidogenic pathway should be studied comprehensively in the early developmental stages including that of sex differentiation. Therefore, in the present study, the expressions of the steroidogenic genes, P-450scc, 3beta-HSD, P-450c17, 17beta-HSD and P-450arom, were measured at the developmental stages (days 2-9 of incubation) of chicken embryos by quantitative RT-PCR. Transcripts for all the genes studied, except for P-450arom were detected in all the developmental stages examined, indicating that mRNAs for the steroidogenic enzymes required to convert cholesterol to androgens are present in the avian embryo before gonadal differentiation. In contrast, P-450arom mRNA was detected in female embryos during days 5-9 of incubation but not in male embryos throughout incubation. The onset of P-450arom gene expression at day 5 coincides with the stage of gonadal differentiation, corroborating the role of estrogen in the process of gonadal differentiation in chicken.

Soluble forms of the subgroup A avian leukosis virus [ALV(A)] receptor Tva significantly inhibit ALV(A) infection in vitro and in vivo

The interactions between the subgroup A avian leukosis virus [ALV(A)] envelope glycoproteins and soluble forms of the ALV(A) receptor Tva were analyzed both in vitro and in vivo by quantitating the ability of the soluble Tva proteins to inhibit ALV(A) entry into susceptible cells. Two soluble Tva proteins were tested: the 83-amino-acid Tva extracellular region fused to two epitope tags (sTva) or fused to the constant region of the mouse immunoglobulin G heavy chain (sTva-mIgG). Replication-competent ALV-based retroviral vectors with subgroup B or C env were used to deliver and express the two soluble tv-a (stva) genes in avian cells. In vitro, chicken embryo fibroblasts or DF-1 cells expressing sTva or sTva-mIgG proteins were much more resistant to infection by ALV(A) ( approximately 200-fold) than were control cells infected by only the vector. The antiviral effect was specific for ALV(A), which is consistent with a receptor interference mechanism. The antiviral effect of sTva-mIgG was positively correlated with the amount of sTva-mIgG protein. In vivo, the stva genes were delivered and expressed in line 0 chicken embryos by the ALV(B)-based vector RCASBP(B). Viremic chickens expressed relatively high levels of stva and stva-mIgG RNA in a broad range of tissues. High levels of sTva-mIgG protein were detected in the sera of chickens infected with RCASBP(B)stva-mIgG. Viremic chickens infected with RCASBP(B) alone, RCASBP(B)stva, or RCASBP(B)stva-mIgG were challenged separately with ALV(A) and ALV(C). Both sTva and sTva-mIgG significantly inhibited infection by ALV(A) (95 and 100% respectively) but had no measurable effect on ALV(C) infection. The results of this study indicate that a soluble receptor can effectively block infection of at least some retroviruses and demonstrates the utility of the ALV experimental system in characterizing the mechanism(s) of viral entry.

Cotransport of glyceraldehyde-3-phosphate dehydrogenase and actin in axons of chicken motoneurons

1. To study proteins transported with actin in axons, we pulse-labeled motoneurons in the chicken sciatic nerve with [35S]methionine and, 1-20 days later, isolated actin and its binding proteins by affinity chromatography of Triton soluble nerve extracts on DNase I-Sepharose. The DNase I-purified proteins were electrophoresed on two-dimensional gels and the specific activity of the radioactively labeled protein spots was estimated by fluorography. 2. In addition to actin, which binds specifically to DNase I, a small number of other proteins were labeled, including established actin monomer binding proteins and a protein of 36 kDa and pI 8.5. On the basis of its molecular mass, pI, amino acid composition, and immunostaining, the unrecognized protein was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). 3. The high-affinity binding of GAPDH to actin was confirmed by incubation of Triton-soluble nerve extracts with either mouse anti-GAPDH (or antiactin) and indirect immunomagnetic separation with Dynabeads covalently linked to sheep anti-mouse antibody. Analysis by one-dimensional gel electrophoresis and immunoblotting showed that actin and GAPDH were the main proteins isolated by these methods. 4. Analysis of labeled nerves at 12 and 20 days after pulse labeling showed that GAPDH and actin were transported at the same rate, i.e., 3-5 mm/day, which corresponds to slow component b of axonal transport. These proteins were not associated with rapidly transported proteins that accumulated proximal to a ligation 7 cm from the spinal cord 9 hr after injection of radioactivity. 5. Our results indicate that GAPDH and actin are transported as a complex in axons and raise the possibility that GAPDH could act as a chaperone for monomeric actin, translocating it to intraaxonal sites for exchange with or assembly into actin filaments. Alternatively, actin could be involved in translocating and anchoring GAPDH to specialized sites in axons and nerve terminals that require a source of ATP by glycolysis.

Chicken histone deacetylase-2 controls the amount of the IgM H-chain at the steps of both transcription of its gene and alternative processing of its pre-mRNA in the DT40 cell line

Histone deacetylases (HDACs) are involved in the deacetylation of core histones, which is an important event in transcription regulation in eukaryotes through alterations in the chromatin structure. We cloned cDNAs and genomic DNAs encoding two chicken HDACs (chHDAC-1 and -2), which are preferentially localized in nuclei. Treatment with trichostatin A reduced the HDAC activities in immunoprecipitates obtained with anti-chHDAC-1 and -2 antisera. Using gene targeting techniques, we generated homozygous DT40 mutants, DeltachHDAC-1 and -2, devoid of two alleles of the chHDAC-1 and -2 genes, respectively. The protein patterns on two-dimensional PAGE definitely changed for DeltachHDAC-2, and the amounts of the IgM H- and L-chains increased in it. Of the two IgM H-chain forms, the secreted form mu(s) increased in DeltachHDAC-2, but the membrane-bound form mu(m) decreased. The IgM H-chain gene was transcribed more in DeltachHDAC-2 than in DT40 cells. In the mutant, the alternative processing of IgM H-chain pre-mRNA preferentially occurred, resulting in an increase in the amount of mu(s) mRNA, whereas the stability of the two types of mRNA, mu(s) and mu(m), was unchanged. In DT40 cells, treatment with trichostatin A increased both the amounts of IgM H-chain mRNAs and the switch from mu(m) to mu(s) mRNAs. Based on these results, we propose a model for a role of chHDAC-2 in both the transcription and alternative processing steps, resulting in control of the amount of the mu(s) IgM H-chain in the DT40 cell line.

Hypothalamic neuropeptide Y mRNA is increased after feed restriction in growing broilers

As part of an approach to uncover the brain mechanisms underlying the regulation of energy balance in broiler chickens, we investigated the possible role of neuropeptide Y (NPY). The NPY gene expression was measured in the hypothalamus of birds from a standard Ross male line and a Ross relaxed line. Both lines are derived from the same founder stock, but the relaxed line has not been selected for rapid growth since 1976. Birds of each line consumed feed either ad libitum or according to a standard commercial restricted feeding program. All groups of birds were killed at an average body weight of 2.4 kg. The NPY mRNA levels were significantly increased (P < 0.0001) in feed-restricted birds of both lines relative to ad libitum controls. No significant differences were detected between the lines. These results show that NPY gene expression in the broiler hypothalamus is sensitive to changes in energetic status, as it is in mammals. However, the maintenance of selection pressure for high growth rate is not associated with altered hypothalamic NPY mRNA levels in the ad libitum or restricted state.

Recombinant duck interferon gamma inhibits duck hepatitis B virus replication in primary hepatocytes

Interferon gamma (IFN-gamma), which has been cloned in several mammalian species and recently in birds, plays a critical role in modulating immune system function. IFN-gamma and tumor necrosis factor alpha (TNF-alpha) have been shown to be crucial in the pathogenesis of viral hepatitis and in the transient disappearance of hepatitis B virus (HBV) from the liver after adoptive transfer of HBV-specific cytotoxic T lymphocytes into HBV-transgenic mice. Similar studies in the natural animal hosts of related hepadnaviruses have been limited because the corresponding probes and recombinant cytokines were not available. For this reason, we initiated studies to clone and characterize cytokines from the duck, the natural host of the duck hepatitis B virus (DHBV). We describe here the cDNA cloning and initial characterization of the IFN-gamma homologue of ducks (DuIFN-gamma). The DuIFN-gamma cDNA codes for a predicted mature protein of 145 amino acids with a molecular mass of 16.6 kDa. The precursor protein has 67% identity with the previously cloned chicken IFN-gamma and 21 to 34% identity with mammalian IFN-gamma. Recombinant DuIFN-gamma induces the transcription of several IFN-inducible genes including IFN regulatory factor 1 and guanylate-binding protein, and it exhibits antiviral activity that protects duck cells from vesicular stomatitis virus-mediated lysis. Importantly, treatment of primary duck hepatocytes with recombinant DuIFN-gamma inhibits DHBV replication in a dose-dependent fashion. Time course analysis revealed that IFN-gamma treatment does not affect initial covalently closed circular DNA (cccDNA) conversion but inhibits the synthesis of progeny cccDNA by amplification.

Interferon-induced human MxA GTPase blocks nuclear import of Thogoto virus nucleocapsids

Interferon-induced human MxA protein belongs to the dynamin superfamily of large GTPases. It exhibits antiviral activity against a variety of RNA viruses, including Thogoto virus, an influenza virus-like orthomyxovirus transmitted by ticks. Here, we report that MxA blocks the transport of Thogoto virus nucleocapsids into the nucleus, thereby preventing transcription of the viral genome. This interaction can be abolished by a mAb that neutralizes the antiviral activity of MxA. Our results reveal an antiviral mechanism whereby an interferon-induced protein traps the incoming virus and interferes with proper transport of the viral genome to its ultimate target compartment within the infected cell.

Selective expression of purinoceptor cP2Y1 suggests a role for nucleotide signalling in development of the chick embryo

Responses to extracellular nucleotides (e.g., ATP, ADP, etc.) have been demonstrated in a number of embryonic cell types suggesting they may be important signalling molecules during embryonic development. Here the authors describe for the first time the expression of a G-protein-coupled receptor for extracellular ATP, chick P2Y1 (cP2Y1), during embryonic development of the chick. During the first 10 days of embryonic development, cP2Y1 is expressed in a developmentally regulated manner in the limb buds, mesonephros, brain, somites, and facial primordia, suggesting that this receptor may have a role in the development of each of these systems.

Expression of chicken steroidogenic factor-1 during gonadal sex differentiation

The orphan nuclear receptor, steroidogenic factor-1 (SF-1), regulates steroidogenic enzyme expression and is essential for gonadal and adrenal development in mammals. We have examined expression of the chicken homologue, cSF-1, during gonadal sex differentiation using whole mount in situ hybridisation and RNase protection assays (RPA). In the youngest embryos examined (day 3.5; stages 21-22), cSF-1 transcripts were already detectable by in situ hybridisation in the undifferentiated genital ridge of both sexes. Expression continued in the gonads of both sexes at the time of sexual differentiation (days 5.5-6.5; stages 28-30). Expression then became higher in developing ovaries compared to testes at days 6.5-8. 5 (stages 30-35). At day 13.5 (stage 40), when the gonads are well differentiated, both ovaries and testes showed cSF-1 expression, with higher levels of expression in the left ovary compared to the right (regressing) gonad in females and compared to testes. RPA analysis of isolated gonads confirmed higher expression of SF-1 in differentiating ovaries relative to testes. Expression of cSF-1 in the developing adrenal gland was similar for both sexes at all stages examined. In tissue sections of day 8.5 whole mount gonads, cSF-1 expression was localised in the medulla of the ovary and was weakly detectable in the testis. These observations indicate that SF-1 has a conserved role in early gonadal and adrenal development in vertebrates. However, upregulation of cSF-1 expression during ovarian differentiation is opposite to the pattern seen in mammals, in which SF-1 is downregulated in females. This difference between the birds and mammals may reflect differences in steroidogenic activity of the embryonic ovary versus the testis in the two groups.

Several novel transcripts of glyceraldehyde-3-phosphate dehydrogenase expressed in adult chicken testis

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in addition to being a classic glycolytic enzyme, is a multifunctional protein involved in relevant cell functions such as DNA replication, DNA repair, translational control of gene expression, and apoptosis. Although the multifunctional nature of GAPDH suggests versatility in the mechanisms regulating its expression, no major qualitative changes and few quantitative changes in the GAPDH transcripts have been reported. While studying the expression of GAPDH during spermatogenesis, we detected alternative initiations to TATA box and alternative splicings in the 5' region of the pre-mRNA, resulting in at least six different types of mRNAs. The amount and the polyadenylation of the GAPDH transcripts increased in mature testis in relation to immature testis and further increased when cell suspensions from mature testis were exposed to heat shock. These results suggest that alternative initiation, alternative splicing, and polyadenylation could provide the necessary versatility to the regulation of the expression of this multifunctional protein during spermatogenesis.

Determination by modified RT-PCR of transcript amounts from genes involved in sex-steroid synthesis in chicken organs including brain

Sex steroid hormones in mammals have shown to be synthesized not only in gonads but also in non-steroidogenic organs such as the brain. Steroid hormones in the brain were indicated to be involved in sex behavior and brain differentiation. In avian species, an experimental injection of androgen into the brain suggested the existence of a steroidogenic pathway. However, no studies have demonstrated the expression of genes involved in such a steroidogenic pathway in the brain, or in other non-steroidogenic organs of birds such as the liver and kidney. In this study, we have modified the RT-PCR procedure to analyze the expression of the steroidogenic genes, P-450scc, 3beta-HSD, P-450c17, 17beta-HSD and P-450arom in non-steroidogenic organs of chicken including the brain. The RT-PCR has demonstrated the presence of mRNAs from genes in non-steroidogenic as well as steroidogenic organs of chicken. The amounts of mRNAs from these genes (except for P-450c17) among the non-steroidogenic organs were found to be greatest in the brain.

Vaccinia virus-encoded cytokine receptor binds and neutralizes chicken interferon-gamma

To counteract the host immune response, poxviruses have evolved secreted factors that bind cytokines and thereby neutralize their biological activities. The vaccinia virus B8R gene encodes a protein that neutralizes interferon-gamma (IFN-gamma) from several mammals including man, cow, rat, and rabbit but not mice. We now report that the activity of the B8R gene product is not restricted to cytokines of mammals: it also efficiently neutralized chicken IFN-gamma. B8R blocked chicken IFN-gamma-mediated induction of guanylate binding protein RNA in the chicken fibroblast cell line CEC-32 and secretion of nitric oxide in HD-11 cells. Radiolabeled baculovirus-expressed B8R efficiently bound to immobilized recombinant chicken IFN-gamma. Scatchard analysis revealed a binding constant of chicken IFN-gamma to B8R of approximately 0.5 nM. A mutant form of chicken IFN-gamma which lacks the 18 C-terminal amino acids and which has lost more than 99% of its biological activity was able to block the IFN-gamma-neutralizing effect of B8R. Binding studies showed that the mutant protein bound radiolabeled B8R only about threefold less well than wild-type chicken IFN-gamma but failed to compete with wild-type chicken IFN-gamma for binding to the cellular receptor. These results suggest that the extreme C terminus of chicken IFN-gamma is crucial for binding to its cellular receptor but less important for recognition by the viral cytokine receptor.

Expression pattern of messenger ribonucleic acid for follistatin and the inhibin/activin subunits during follicular and testicular development in gallus domesticus

The expression of mRNA for follistatin and the inhibin/activin subunits was investigated in the follicles of laying hens and the testes of immature and mature roosters. Total RNA was isolated from immature and mature testes and from individual granulosa layers of the F1 through F5 follicles, from a pool of the F6-F8 follicles, from the small yellow follicles, and from the combined granulosa and theca layers of the large white follicles. Northern blot analysis was performed, and a follistatin mRNA transcript of approximately 2. 4 kilobases (kb) was detected in immature testes and in the following follicles: F5, the pool of F6-F8, and small yellow and large white follicles. The greatest expression of follistatin occurred in the small yellow follicles, and in this tissue two minor transcripts of approximately 1.7 and 3.7 kb were also detected. The inhibin alpha subunit was expressed in both testes samples and in all of the follicles except the large white follicles. Expression of the alpha subunit was greatest in the F5 follicle, and expression decreased with follicle maturity. As previously reported, the inhibin/activin ssA subunit was found in the greatest abundance in the F1 follicle, with lesser amounts detected in the other hierarchical follicles and immature testes. In contrast to the ssA subunit, the inhibin/activin ssB subunit was not detected in the four largest hierarchical follicles but was expressed in greatest abundance in the pool of F6-F8 and small yellow follicles. This represents the first report, to our knowledge, of the detection of follistatin mRNA in the hen ovary and rooster testes. The restriction of follistatin mRNA expression to the small follicles suggests that follistatin, by regulating activin and/or inhibin availability, may play a critical role in early follicular development.

Borna disease virus-induced neurological disorder in mice: infection of neonates results in immunopathology

Borna disease virus (BDV) is a neurotropic nonsegmented negative-stranded RNA virus that persistently infects warm-blooded animals. In horses and other natural animal hosts, infections with BDV cause meningoencephalitis and behavioral disturbances. Experimental infection of adult mice takes a nonsymptomatic course, an observation previously believed to indicate that this animal species is not suitable for pathogenesis studies. We now demonstrate that BDV frequently induces severe neurological disease in infected newborn mice. Signs of neurological disease were first observed 4 to 6 weeks after intracerebral infection. They included a characteristic nonphysiological position of the hind limbs at an early stage of the disease and paraparesis at a later stage. Histological examination revealed large numbers of perivascular and meningeal inflammatory cells in brains of diseased mice and, unexpectedly, no increase in immunoreactivity to glial fibrillar acidic protein. The incidence and severity of BDV-induced disease varied dramatically among mouse strains. While only 13% of the infected C57BL/6 mice showed disease symptoms, which were mostly transient, more than 80% of the infected MRL mice developed severe neurological disorder. In spite of these differences in susceptibility to disease, BDV replicated to comparable levels in the brains of mice of the various strains used. Intracerebral infections of newborn beta2-microglobulin-deficient C57BL/6 and MRL mice, which both lack CD8+ T cells, did not result in meningoencephalitis or neurological disease, indicating that the BDV-induced neurological disorder in mice is a cytotoxic T-cell-mediated immunopathological process. With this new animal model it should now be possible to characterize the disease-inducing immune response to BDV in more detail.

Expression and conservation of apolipoprotein AIV in an avian species

In birds, intestinally derived lipoproteins are thought to be secreted directly into the portal vein rather than to enter the circulation via the lymphatic system as in mammals. Hepatic clearance of these so-called portomicrons must be rapid, but the protein(s) mediating their catabolism, presumably analogues of the 36-kDa mammalian apolipoprotein E, have not been identified. In searching for such a mediator(s), we have isolated a hitherto unknown 38-kDa protein from chicken serum, which we identified by microsequencing and molecular cloning as a counterpart to mammalian apolipoprotein AIV (apoAIV). Mature chicken apoAIV consists of 347 amino acids, lacks cysteine residues, and displays 57% sequence identity with human apoAIV and, to a significantly lesser extent, with apoAIVs of rodents. This first nonmammalian apoAIV characterized is the smallest homologue reported so far, because of the lack of repeated motifs at the carboxyl terminus with the consensus sequence Glu-Gln-Glu/Ala-Gln, a hallmark of mammalian apoAIVs. Chicken apoAIV (isoelectric point, 4.65) is also considerably more acidic than its human counterpart. Agarose gel electrophoresis revealed that unlike human apoAIV, which migrates to a pre-alpha-position, chicken apoAIV shows fast alpha migration. Functional characterization demonstrated that the avian protein is able to activate the enzyme lecithin:cholesterol acyltransferase. Roosters and hens express apoAIV predominantly in the gut, one-fifth as much in the liver, and no other sites of expression are identifiable by Northern blot analysis. Although pronounced intestinal synthesis is common to apoAIVs, the features of the avian protein support the notion that it represents a prototype of an apoprotein that evolved to acquire possibly distinct functions in mammals and birds.

Kainic acid, tetrodotoxin and light modulate expression of brain-derived neurotrophic factor in developing avian retinal ganglion cells and their tectal target

Increasing evidence underlies the importance of neurotrophins as neuron-derived trophic signals in the developing visual system, although their precise roles are still undefined. Here we show that brain-derived neurotrophic factor messenger RNA is simultaneously expressed in a subpopulation of retinal ganglion cells and in their target during late embryogenesis. Moreover, light as well as the excitotoxin; kainic acid, induced an increase of the brain-derived neurotrophic factor messenger RNA, which could be blocked by the sodium-channel blocker; tetrodotoxin. Messenger RNA for trkB, a receptor for brain-derived neurotrophic factor, was found in the retinal ganglion cells expressing brain-derived neurotrophic factor showing that certain retinal ganglion cells express messenger RNA both for brain-derived neurotrophic factor and trkB. Furthermore, trkB messenger RNA was found in tectum, in the same layers as the brain-derived neurotrophic factor messenger RNA. These findings suggest that brain-derived neurotrophic factor expression is regulated in an activity-dependent manner during the phase of development when neuronal activity plays an important role.

Induction and characterization of metallothionein in chicken epiphyseal growth plate cartilage chondrocytes

Following exposure to cadmium or zinc, chickens were sacrificed and the liver, kidney, and bone epiphyseal growth plates harvested. When cytosolic extracts of the growth plate cartilage were fractionated by gel filtration chromatography, a protein with high metal-binding capacity and low ultraviolet (UV) absorbance eluted in the same position as liver metallothionein (MT) and a MT standard. Cd or Zn treatment resulted in a 25-fold or 5-fold induction in growth plate MT, respectively. In liver the greatest level of MT induction was seen with short-term Cd exposures. In contrast, MT levels in the growth plate increased as the duration of Cd exposure increased. Induction of MT in growth plate chondrocyte cell cultures was observed for media Cd concentrations of > or = 0.1 microM and Zn concentrations of > or = 100 microM. Basal and inducible levels of MT declined through the culture period and were lowest in the terminally differentiated mineralized late stages of the culture. Alkaline phosphatase activity was also lowest in the late-stage cultures, while total cellular protein increased throughout the culture period. Treatment of chondrocytes with Zn prior to Cd exposure resulted in a protective induction of MT. Pre-treatment of chondrocytes with dexamethasone resulted in suppressed synthesis of MT upon Cd exposure and greater Cd toxicity. Both Cd and Zn resulted in significantly increased levels of MT mRNA in chondrocyte cell cultures. Dexamethasone treatment resulted in an approximate 2- to 3-fold increase in MT mRNA. This is contrary to the finding that MT protein levels were decreased by dexamethasone. The findings suggest that an increased rate of MT degradation in dexamethasone-treated and late-stage chondrocyte cultures may be associated with the terminally differentiated phenotype.

One allele of the major histone gene cluster is enough for cell proliferation of the DT40 chicken B cell line

Thirty-nine of the 44 chicken histone genes are located in a major histone gene cluster of 110 kb, the others residing in four separate regions. We generated a heterozygous chicken DT40 mutant, 1/2 delta110 kb, devoid of one allele of the cluster, using gene targeting techniques. Analyses of the mutant revealed that the growth rate of DT40 cells was unchanged even in the absence of one allele of the cluster. Moreover, analyses involving a RNase protection assay, SDS-PAGE or Triton-acid-urea-PAGE revealed not only that in the 1/2 delta110 kb mutant the steady-state levels of total mRNAs of gene families H1, H2A, H2B, H3 and H4 remained constant, but also that the amounts of histones H1, H2A, H2B, H3 and H4 were not changed. A comparison by 2D-PAGE revealed no changes in total cellular protein patterns of the mutant. These observations demonstrate that all the histone gene families have the inherent ability to compensate for the disruption of one allele of the gene cluster, with no influence on cell functions.

Hierarchy of lens proteins requiring protection against heat-induced precipitation by the alpha crystallin chaperone

Gel filtration of the water-soluble extract from bovine lens yields a group of proteins, emerging between the peaks of beta H and beta L crystallins, which show a considerably greater sensitivity to heat-induced aggregation/precipitation than the far more abundant beta and gamma crystallins. However, the small heat shock protein: alpha crystallin was effective in protecting these trace constituents of the lens from precipitating out of solution at 55 degrees C (measured under the standard conditions in a pH 7.5 buffer containing 50 mM sodium phosphate, 100 mM NaCl, 1 mM EDTA and 0.05% NaN3). Prominent components of the precipitate, formed in the absence of a recombinant alpha B crystallin chaperone could be resolved by one- and two-dimensional electrophoresis. Identification by amino acid sequencing revealed that the heat-sensitive group of lens proteins comprised glyceraldehyde-3-phosphate dehydrogenase (M(r) approximately 39 kDa), enolase (approximately 48 kDa), leucine aminopeptidase (approximately 52 kDa) and aldehyde dehydrogenase (approximately 53 kDa). These findings indicate for the first time that the aggregation of such minor lens constituents could possibly contribute to initiating the process of opacification in the development of cataracts.

Identification of a chicken homologue in the Brn-3 subfamily of POU-transcription factors

Among the many transcription factors thus far identified several are found to be expressed almost exclusively in the nervous system. The Brn-3 subfamily of POU-transcription factors constitutes a highly conserved group of such factors showing expression predominantly in sensory neurons. We now describe the nucleotide sequence and proposed amino acid sequence of a chicken homologue to the murine and human Brn-3 genes. Furthermore we characterise the early embryonic expression pattern of this chicken Brn-3 gene and show it to be expressed in peripheral sensory ganglia as well as in retinal ganglion cells. Based on these findings we conclude that the chicken homologue to the murine and human Brn-3a genes has been cloned. We have begun to examine possible regulatory pathways of Brn-3a by stimulating chick embryonic peripheral ganglia with trophic factors and assaying resulting levels of Brn-3a with a quantitative PCR approach. Trigeminal and dorsal root ganglia stimulated in culture by NGF and NT-3 embryonic day 9 (E9) produce neurites without raising the Brn-3a mRNA levels.

Biological properties of recombinant chicken interferon-gamma

Supernatants of the chicken T cell line 855 contain antiviral and macrophage activating factor activity and strongly activate transcription of the guanylate binding protein (GBP) gene in chicken cells. To characterize the cytokine responsible for the GBP-inducing activity, we chose a cDNA expression cloning strategy in COS cells. Sequencing a positive clone revealed that it encode chicken interferon-gamma (ChIFN-gamma). Histidine-tagged ChIFN-gamma was expressed in Escherichia coli and purified by nickel chelate affinity chromatography. ChIFN-gamma from COS cells and E. coli both potently induced GBP RNA synthesis but were rather poor antiviral agents. In macrophages, recombinant ChIFN-strongly stimulated secretion of nitric oxide and enhanced expression of major histocompatibility complex class II antigen. A rabbit antiserum to E. coli derived ChIFN-gamma effectively neutralized the macrophage-activating factor activity secreted by concanavalin A-induced spleen cells and various T cell lines, suggesting that IFN-gamma is the major macrophage-activating factor of the chicken.