Variability in the resistance of four chicken lines to experimental intravenous infection with Salmonella enteritidis phage type 4

The capacity of four chicken lines (Y11, L2, B13, PA12) to control Salmonella enteritidis (SE) phage type 4 (PT4) systemic colonization was investigated. Thirteen-week-old chickens were intravenously inoculated with 10(6) SE colony-forming units, and the levels of SE colonization were determined at various time intervals after inoculation in liver, spleen, genital organs, and ceca. The course of SE infection showed a rapid contamination of liver, spleen, and genital organs, whereas the ceca were infected later. A significant (P < 0.001) effect of the chicken line on levels of SE was detected on day 3 postinoculation (PI) in liver and ceca, on day 10 PI in ceca, and on day 15 PI in spleen. Because an early control of systemic Salmonella infection by the Ity/Nramp1 gene has been demonstrated in mice, we aimed to study the early resistance of chickens to SE. As a consequence, we then focused our study on the between- and within-line variabilities of SE levels on day 3 PI. According to the SE levels in liver on day 3 PI, the chicken lines could be classified as susceptible (Y11 and L2) or resistant (PA12 and B13). This early variability was explored in resistant B13 and susceptible L2 lines. Differences between these two lines were confirmed in liver but not in ceca. A large within-line variability was observed in all organs of these two lines. The genetic origin of this variability will have to be determined as a prerequisite to an eventual selection.

Genetic analysis of a selection experiment on increased body weight and breast muscle weight as well as on limited abdominal fat weight

1. Genetic parameters of body weight (BW), breast meat weight or yield (BRW, BRY) and abdominal fat weight or yield (FTW, FTY) were estimated in males and females originated from an experimental line selected for improving broiler carcase quality and its control line. 2. Mean heritabilities over both sexes of BW, FTW and FTY were 0.43, 0.56 and 0.63 respectively. Those of BRW and BRY were 0.53 and 0.65 respectively. 3. BW was unfavourably correlated with FTW (rg of 0.40) and to a lesser extent with FTY (rg of 0.12). BW was, as expected, highly correlated with BRW (rg 0.77), but a poor correlation was obtained with BRY (rg of 0.15). Selection for more breast yield should not reduce the leanness of the birds, with a genetic correlation between BRY and FTY of -0.15. 4. The variance explained by the maternal effects accounted for a rather small part of the total phenotypic variance (from 3% to 8% according to the trait), but ignoring these effects led to a significant overestimation of the heritabilities (by 11% to 19%). 5. Except for BRY, the heritability estimates differed between sexes, only moderately for BW but more for BRW, FTW and FTY. However, estimated genetic correlations between sexes were high (between 0.94 and 0.99) and in turn heritabilities of sexual dimorphism of the various traits very low (between 0.02 and 0.07). 6. A significant improvement of the genetic level for growth and carcase composition had been obtained in the selected line, with a mean genetic gain per generation of 0.12 sigma g, 0.13 sigma g and -0.30 sigma g for BW, BRY and FTY respectively.

Role of ferritin in the control of the labile iron pool in murine erythroleukemia cells

In vitro studies have shown that ferritin iron incorporation is mediated by a ferroxidase activity associated with ferritin H subunits (H-Ft) and a nucleation center associated with ferritin L subunits (L-Ft). To assess the role played by the ferritin subunits in regulating intracellular iron distribution, we transfected mouse erythroleukemia cells with the H-Ft subunit gene mutated in the iron-responsive element. Stable transfectants displayed high H-Ft levels and reduced endogenous L-Ft levels, resulting in a marked change in the H:L subunit ratio from 1:1 in control cells to as high as 20:1 in some transfected clones. The effects of H-Ft overexpression on the labile iron pool were determined in intact cells by a novel method based on the fluorescent metallosensor calcein. H-Ft overexpression resulted in a significant reduction in the iron pool, from 1.3 microM in control cells to 0.56 microM in H-Ft transfectants, and in higher buffering capacity following iron loads. A fraction of the H-Ft-associated iron was labile, available to cell-permeant, but not cell-impermeant, chelators. The results of this study provide the first in vivo direct demonstration of the capacity of H-Ft to sequester cell iron and to regulate the levels of the labile iron pool.

Estimated heritability of the resistance to cecal carrier state of Salmonella enteritidis in chickens

Previously, we have shown differences in susceptibility to the cecal carrier state in chicks orally infected with Salmonella enteritidis (SE) at 1 wk of age for four outbred lines: L2, B13, PA12, and Y11. The egg-type line L2 was one of the most susceptible lines and presented a large variability in cecal SE colonization. The heritability (h2) of the resistance to SE colonization in ceca was estimated in L2 chickens to determine whether genetic factors might be involved in its control. In three independent trials, a total of 819 L2 chicks produced from 88 sires and 232 dams were challenged orally with SE at 1 wk of age. Each week after inoculation, the frequency of cecal colonization was estimated. When this value had fallen to 50%, all the remaining animals were killed. The extent of cecal colonization by SE was estimated directly by counting the viable organisms in organs and determining the numbers of positive ceca. Enrichment culture was used in Trials 2 and 3. The effects of trial, of room within trial, and of cage within room on the frequency of SE contaminated ceca were often significant. No significant effect of sex was observed. Estimation of h2 using the frequency of SE positive ceca was low, 0.06 +/- 0.07, when results of direct culture were considered. In contrast, when considering the frequency obtained after enrichment, the h2 was estimated at 0.20 +/- 0.12. This result suggests a genetic basis for the expression of the resistance to colonization. An experiment of selection for resistance to SE carrier state in the chicken ceca should definitively confirm the genetic origin of the resistance.

Analysis of ferritins in lymphoblastoid cell lines and in the lens of subjects with hereditary hyperferritinemia-cataract syndrome

Hereditary hyperferritinemia-cataract syndrome (HHCS) is an autosomal and dominant disease caused by heterogeneous mutations in the iron responsive element (IRE) of the 5' untranslated flanking region of ferritin L-chain mRNA, which reduce the binding to the trans iron regulatory proteins and make L-chain synthesis constitutively upregulated. In the several families identified so far, the serum and tissue L-ferritin levels are fivefold to 20-fold higher than in nonaffected control subjects, iron metabolism is apparently normal, and the only relevant clinical symptom is early onset, bilateral cataract. Some pathogenetic aspects of HHCS remain obscure, with particular reference to the isoferritins produced by HHCS cells, as well as the mechanism of cataract formation. We analyzed lymphoblastoid cell lines obtained from two nonaffected control subjects and from HHCS patients carrying the substitution A40G (Paris-1), G41C (Verona-1), and the deletion of the residues 10-38 (Verona-2) in the IRE structure. Enzyme-linked immunosorbent assays specific for the H- and L-type ferritins showed that L-ferritin levels were up to 20-fold higher in HHCS than in control cells and were not affected by iron supplementation or chelation. Sequential immunoprecipitation experiments of metabolically-labeled cells with specific antibodies indicated that in HHCS cells about half of the L-chain was assembled in L-chain homopolymers, which did not incorporate iron, and the other half was assembled in isoferritins with a high proportion of L-chain. In control cells, all ferritin was assembled in functional heteropolymers with equivalent proportion of H- and L-chains. Cellular and ferritin iron uptake was slightly higher in HHCS than control cells. In addition, we analyzed the lens recovered from cataract surgery of a HHCS patient. We found it to contain about 10-fold more L-ferritin than control lens. The ferritin was fully soluble with a low iron content. It was purified and partially characterized. Our data indicate that: (1) in HHCS cells a large proportion of L-ferritin accumulates as nonfunctional L-chain 24 homopolymers; (2) the concomitant fivefold to 10-fold expansion of ferritin heteropolymers, with a shift to L-chain-rich isoferritins, does not have major effects on cellular iron metabolism; (3) L-chain accumulation occurs also in the lens, where it may induce cataract formation by altering the delicate equilibrium between other water-soluble proteins (ie, crystallins) and/or the antioxidant properties.

Transient overexpression of human H- and L-ferritin chains in COS cells

The understanding of the in vitro mechanisms of ferritin iron incorporation has greatly increased in recent years with the studies of recombinant and mutant ferritins. However, little is known about how this protein functions in vivo, mainly because of the lack of cellular models in which ferritin expression can be modulated independently from iron. To this aim, primate fibroblastoid COS-7 cells were transiently transfected with cDNAs for human ferritin H- and L-chains under simian virus 40 promoter and analysed within 66 h. Ferritin accumulation reached levels 300-500-fold higher than background, with about 40% of the cells being transfected. Thus ferritin concentration in individual cells was increased up to 1000-fold over controls with no evident signs of toxicity. The exogenous ferritin subunits were correctly assembled into homopolymers, but did not affect either the size or the subunit composition of the endogenous heteropolymeric fraction of ferritin, which remained essentially unchanged in the transfected and non-transfected cells. After 18 h of incubation with [59Fe]ferric-nitrilotriacetate, cellular iron incorporation was similar in the transfected and non-transfected cells and most of the protein-bound radioactivity was associated with ferritin heteropolymers, while H- and L-homopolymers remained iron-free. Cell co-transfection with cDNAs for H- and L-chains produced ferritin heteropolymers that also did not increase cellular iron incorporation. It is concluded that transient transfection of COS cells induces a high level of expression of ferritin subunits that do not co-assemble with the endogenous ferritins and have no evident activity in iron incorporation/metabolism.

A point mutation in the bulge of the iron-responsive element of the L ferritin gene in two families with the hereditary hyperferritinemia-cataract syndrome

The molecular basis for the recently described hereditary hyperferritinemia-cataract syndrome is the presence of a mutation in the iron-responsive element (IRE) of the L ferritin gene, located on chromosome 19q13.3-13.4. Two mutations have been reported so far, altering adjacent nucleotides in the IRE loop, in a region that has been extensively studied in vitro and shown to mediate high affinity interaction with the iron-responsive protein. In this report, we describe two families with a new mutation in the bulge of the IRE stem, and we show that this mutation alters the protein-binding affinity of the IRE in vitro to the same extent as the loop mutation. In addition, we present evidence that some variability in the age of onset of cataract can be associated with this genetic syndrome, probably because of additional genetic or environmental factors that modulate the penetrance of the L ferritin defect in the lens. We confirm that the patients do not have increased iron stores despite the persistence of elevated serum ferritin levels and that, accordingly, they do not tolerate well venesection therapy. Further studies will be necessary to elucidate the mechanism responsible for the onset of cataract.

Function and regulation of transferrin and ferritin

Iron represents a paradox for living systems by being essential for a wide variety of metabolic processes (oxygen transport, electron transport, DNA synthesis, etc) but also having the potential to cause deleterious effects. Because of Iron's virtual insolubility and potential toxicity under physiological conditions, specialized molecules for the acquisition, transport, and storage of iron in a soluble, nontoxic form have evolved to meet cellular and organismal iron requirements. Physiologically, the majority of cells in the organism acquire iron from a well-characterized plasma glycoprotein, transferrin. Iron uptake from transferrin is reasonably well understood, and involves the binding of transferrin to the transferrin receptor, internalization of transferrin within an endocytic vesicle by receptor-mediated endocytosis, and the release of iron from the protein by a decrease in endosomal pH. Most of the transferrin-bound iron is used for the synthesis of hemoglobin by developing erythroid cells. Senescent erythrocytes are internalized by the macrophages that liberate hemoglobin iron and release it back to plasma transferrin at a rate that normally matches the rate of iron transport for erythropoiesis. Unfortunately, the mechanisms and controls involved in the release of iron from macrophages have not been defined. After iron release from transferrin within endosomes, iron passes through the endosomal membrane by ill-understood mechanisms and then enters the poorly characterized intracellular labile pool. Iron in the labile pool that exceeds requirement for the synthesis of functional heme and nonheme iron-containing proteins is stored within the iron-storage protein, ferritin. Evidence in vitro indicates that relatively soluble ferrous iron can enter or be released from ferritin. However, we know virtually nothing about the exchange of iron with ferritin in intact cells, and some evidence indicates that the degradation of the ferritin protein may be an important mechanism for the release of iron within the cell. Cellular iron uptake and storage are coordinately regulated through a feedback control mechanism mediated at the post-transcriptional level by cytoplasmic factors know as iron-regulatory proteins 1 and 2. These proteins "sense" levels of iron in the transit pool and, when iron in this pool is scarce, they bind to stem-loop structures known as iron-responsive elements on the 5' untranslated region of the ferritin mRNA and 3' untranslated region of the transferrin mRNA. Such a binding inhibits translation of ferritin mRNA and stabilizes the mRNA for transferrin receptors. The opposite scenario develops when iron in the transit pool is plentiful. This remarkable regulatory mechanism prevents the expansion of a catalytically active intracellular iron pool, while maintaining sufficient concentrations of the metal for metabolic needs.

Genetic parameters of survival to the different stages of embryonic death in laying hens

Heritabilities and genetic correlations of fertility (FERT) as well as of susceptibilities to early (EEM), medium (MEM), and late (LEM) embryonic mortalities conditional on fertility and survival to earlier stage(s) of embryonic mortality were estimated with a general linear model using a logistic link function on 59,794 eggs obtained from 6,480 hens issued from 228 sires and 1,053 dams. Estimated heritabilities of FERT, EEM, MEM, and LEM were, when estimated from sire and dam components, respectively, equal to 0.09 and 0.31, 0.09 and 0.25, 0.07 and 0.20, and 0.05 and 0.18; whereas estimated heritabilities of hatchability of fertile eggs were 0.05 and 0.15, respectively, when estimated from the sire or dam components. Most genetic correlations between FERT, EEM, MEM, and LEM were favorable with the exception of correlations between FERT and MEM and between EEM and MEM when estimated from the sire component. These results show the theoretical interest of distinguishing the three stages of mortality.

Differences in frequency, level, and duration of cecal carriage between four outbred chicken lines infected orally with Salmonella enteritidis

Four chicken lines, L2, B13, PA12 (egg-type), and Y11 (meat-type), were tested for experimental carrier state of Salmonella enteritidis (SE) in two identical trials. After oral inoculation of SE at 1 wk of age with 5 x 10(4) SE colony-forming units (CFU), 10 chickens per line were necropsied weekly for 6 wk and then every 8 or 15 days until the 12th week postinoculation (PI). Liver, spleen, ovary, and ceca were examined for level of SE colonization. Numbers of positive livers and spleens and levels of the challenge strain in these organs differed little between the four chicken lines. Only three positive ovaries were detected. According to the chicken line, ceca exhibited generally significant (P < 0.05) differences in the number of positive organs during weeks 5-11 PI, in the SE CFU levels (P < 0.05) in the first 5 wk PI and during weeks 8 and 10 PI, and in the duration of colonization. L2 and B13 chickens generally carried SE in their ceca at higher levels, in more animals, and for a longer time than PA12 and Y11 chickens. Y11 chickens were the most resistant to SE cecal colonization.

Expression of H and L ferritin mRNAs in mouse small intestine

Regulation of iron absorption occurs mainly at the level of duodenal enterocytes. Several proteins including ferritin, the iron-storing molecule, have been implicated in the uptake, cellular processing, and transfer of iron by the mucosal cells. H and L ferritin subunits assemble in various proportions to form a 24-subunit protein shell which can store up to 4500 iron atoms. Although tissue-specific distribution of H and L ferritin mRNAs has been widely described, little is known of ferritin gene expression in duodenal cells. In this study, we performed quantitative measurements of H and L ferritin mRNAs levels in mouse duodenum, ileum, and liver by ribonuclease protection assay. In addition, we assessed the relative subcellular distribution of these two mRNAs in mouse duodenal and ileal sections by in situ hybridization. The results show that in duodenal cells, the level of H ferritin mRNA is higher than the L ferritin level (H/L ratio of about 5). Moreover, expression of the H mRNA is regulated along both axes of the small intestine: the level increases sharply from the crypt to the apex of the villus, thus following the general differentiation pathway of these cells, and decreases from the proximal to the distal small intestine. In contrast, the L ferritin mRNA level does not change along the cryptovillus axis and increases in value in the ileum. These results suggest that expression of the H ferritin gene is dependent on the differentiation of the enterocytes but, as yet, the regulatory elements remain to be identified.

Line differences in resistance to Salmonella enteritidis PT4 infection

1. Four groups of hens, each of a different line, were inoculated at peak of lay, per os in the crop with 1 ml of a suspension containing 10(9) cfu/ml Salmonella enteritidis PT4 (SE). The kinetics of SE contamination in the environment, egg shell and yolk were studied during the first 28 d post inoculation. On the day of slaughter, intestines, caeca, spleen, liver, ovary, oviduct and content were investigated for SE contamination. 2. The commercial egg-type line L2 was found to be the most susceptible to SE. It laid many SE-positive yolks (13.8%) and internal and faecal organs were frequently infected. 3. Certain lines are found to exhibit a degree of resistance to SE; the cause of which is unknown and might be attributed to major genes.

Novel properties of L-type polypeptide subunits in mouse ferritin molecules

Properties of the L- and H-type polypeptide subunits forming ferritin 24-mer molecules in mice were investigated, using the products of in vitro transcription and translation from the two cloned genes, and recombinant ferritin molecules (H24L0 or H0L24) produced by transformation in Escherichia coli. Several different conditions for analytical electrophoresis reproducibly show that the relative migration position of the two mouse ferritin subunits is reversed from that reported for ferritin H- and L-subunits in all other mammals; since mouse and human H-polypeptides almost co-migrate, this unusual relative mobility is due largely to novel properties of the murine L-subunit. This unusual electrophoretic property of the mouse L-subunit has led to conflicting reports about the subunit composition of natural mouse ferritin. Here, we show that the single major electrophoretic band given by liver ferritin purified from mice having a short-term iron overload matches that produced by the genetically defined L-polypeptide and that some bona fide H-subunits are also detected. In conclusion, it is reasonable to assume that, when mouse ferritin samples will be analyzed under the same conditions as those described here, the slower species will correspond to the L-type subunit. However, when dealing with ferritin from species other than human or mouse, it should be kept in mind that upon electrophoretic analysis of ferritin polypeptide, the designation of an electrophoretic band as being H- or L-type subunits will be very uncertain without corroboration from genetic, immunological, or amino acid sequencing data.

Overexpression of the ferritin H subunit in cultured erythroid cells changes the intracellular iron distribution

To test the hypothesis that variations in H- and L-subunit composition in the ferritin shell affect intracellular iron metabolism, we established stable transfectants of mouse erythroleukemia cells overexpressing the H-ferritin subunit. Analyses were performed on individual clones of transfected cells induced to differentiate with hexamethylenbisacetamide (HMBA). The results showed that there was a reduction in the amount of hemoglobin produced, in inverse relationship with the level of H-subunit overexpression. Incorporation of [2-14C]glycine into heme was reduced by 20% t0 30% in the clones overexpressing H-ferritin subunit compared with control clone. However, the reduction in hemoglobin production was not reversed by addition of heme precursors (delta-aminolevulinic acid or iron) or by hemin itself. A reduced accumulation of beta-globin mRNA was also observed, which could account for the impaired hemoglobin synthesis. Furthermore, synthesis of the endogenous L-ferritin subunit was greatly repressed. Gel retardation assays performed on cytoplasmic extracts of transfected cells using an iron-responsive element (IRE) as a probe revealed that in overexpressing cells, the iron-regulatory protein (IRP) had a conformation with a high RNA-binding affinity, thus leading to translational repression of the endogenous L-ferritin synthesis. These data suggest that an increased formation of H-rich isoferritins leads to a rapid chelation of the regulatory iron pool. While the mechanism underlying the reduction in beta-globin mRNA remains to be elucidated, this study provides direct evidence for the role of IRP-mediated regulation of ferritin expression in erythroid cell metabolism.

Modulation of the phenotype in dominant erythropoietic protoporphyria by a low expression of the normal ferrochelatase allele

Erythropoietic protoporphyria (EPP) is a monogenic inherited disorder of the heme biosynthetic pathway due to ferrochelatase (FC) deficiency. EPP is generally considered to be transmitted as an autosomal dominant disease with incomplete penetrance, although autosomal recessive inheritance has been documented at the enzymatic and molecular level in some families. In the dominant form of EPP, statistical analysis of FC activities documented a significantly lower mean value in patients than in asymptomatic carriers, suggesting a more complex mode of inheritance. To account for these findings, we tested a multiallelic inheritance model in one EPP family in which the enzymatic data were compatible with this hypothesis. In this EPP family, the specific FC gene mutation was an exon 10 skipping (delta Ex10), resulting from a G deletion within the exon 10 consensus splice donor site. The segregation of all FC alleles within the family was followed using the delta Ex10 mutation and a new intragenic dimorphism (1520 C/T). mRNAs transcribed from each FC allele were then subjected to relative quantification by a primer extension assay and to absolute quantification by a ribonuclease protection assay. The data support the hypothesis that in this family the EPP phenotype results from the coinheritance of a low output normal FC allele and a mutant delta Ex10 allele.

Mutation in the iron responsive element of the L ferritin mRNA in a family with dominant hyperferritinaemia and cataract

The synthesis of ferritin, the iron-storing molecule, is regulated at the translational level by iron through interaction between a cytoplasmic protein, iron regulatory protein (IRP), and a conserved nucleotide motif present in the 5' non-coding region of all ferritin mRNAs--the iron responsive element (IRE). This region forms a stem-loop structure and when the supply of iron to the cells is limited, the IRP is bound to IRE and represses ferritin synthesis. Ferritin is composed of a 24-subunit protein shell surrounding an iron core. The two types of subunit, H and L, are encoded by two genes located on chromosomes 11q13 and 19q13.1, respectively. Both genes are ubiquitously expressed but transcriptional regulation mediates tissue-specific changes in the H/L mRNA ratio and isoferritin profiles. We now report the identification of a single point mutation in the IRE of the L-ferritin mRNA in members from a family affected with dominantly inherited hyperferritinaemia and cataract. This mutation consists of an A to G change in the highly conserved CAGUGU motif that constitutes the IRE loop and mediates the high-affinity interaction with the IRP. We show that this mutation abolishes the binding of IRP in vitro and leads to a high constitutive, poorly regulated L-ferritin synthesis in cultured lymphoblastoid cells established from affected patients. This is, to our knowledge, the first mutation affecting the IRP-IRE interaction and the iron-mediated regulation of ferritin synthesis. We suggest that excess production of ferritin in tissues is responsible for the hyperferritinaemia and that intracellular accumulation of ferritin leads to cataract.