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L B Crittenden

Publications and source records attributed to L B Crittenden.

At least 19 recordsLinked to original sources
PubMed2000

A consensus linkage map of the chicken genome.

A consensus linkage map has been developed in the chicken that combines all of the genotyping data from the three available chicken mapping populations. Genotyping data were contributed by the laboratories that have been using the East Lansing and Compton reference populations and from the Animal Breeding and Genetics Group of the Wageningen University using the Wageningen/Euribrid population. The resulting linkage map of the chicken genome contains 1889 loci. A framework map is presented that contains 480 loci ordered on 50 linkage groups. Framework loci are defined as loci whose order relative to one another is supported by odds greater then 3. The possible positions of the remaining 1409 loci are indicated relative to these framework loci. The total map spans 3800 cM, which is considerably larger than previous estimates for the chicken genome. Furthermore, although the physical size of the chicken genome is threefold smaller then that of mammals, its genetic map is comparable in size to that of most mammals. The map contains 350 markers within expressed sequences, 235 of which represent identified genes or sequences that have significant sequence identity to known genes. This improves the contribution of the chicken linkage map to comparative gene mapping considerably and clearly shows the conservation of large syntenic regions between the human and chicken genomes. The compact physical size of the chicken genome, combined with the large size of its genetic map and the observed degree of conserved synteny, makes the chicken a valuable model organism in the genomics as well as the postgenomics era. The linkage maps, the two-point lod scores, and additional information about the loci are available at web sites in Wageningen (http://www.zod.wau.nl/vf/ research/chicken/frame_chicken.html) and East Lansing (http://poultry.mph.msu.edu/).

Animals↗
PubMed1998

Genetic mapping of the cloned subgroup A avian sarcoma and leukosis virus receptor gene to the TVA locus.

A chicken gene conferring susceptibility to subgroup A avian sarcoma and leukosis viruses (ASLV-A) was recently identified by a gene transfer strategy. Classical genetic approaches had previously identified a locus, TVA, that controls susceptibility to ASLV-A. Using restriction fragment length polymorphism (RFLP) mapping in inbred susceptible (TVA*S) and resistant (TVA*R) chicken lines, we demonstrate that in 93 F2 progeny an RFLP for the cloned receptor gene segregates with TVA. From these analyses we calculate that the cloned receptor gene lies within 5 centimorgans of TVA, making it highly probable that the cloned gene is the previously identified locus TVA. The polymorphism that distinguishes the two alleles of TVA in these inbred lines affects the encoded amino acid sequence of the region of Tva that encompasses the viral binding domain. However, analysis of the genomic sequence encoding this region of Tva in randomly bred chickens suggests that the altered virus binding domain is not the basis for genetic resistance in the chicken lines analyzed.

Amino Acid Sequence↗
PubMed1995

Chicken genome mapping: a new era in avian genetics.

More than 460 loci representing either expressed or anonymous sequences have been mapped on to the first comprehensive molecular genetic linkage map of the chicken genome. Here, we review the current status of poultry genome mapping and discuss some of the new opportunities this provides.

Animals↗
PubMed1995

Influence of the alv6 recombinant avian leukosis virus transgene on production traits and infection with avian tumor viruses in chickens.

The biological costs of the alv6 recombinant transgene that in chickens induces dominant resistance to the subgroup A avian leukosis virus (ALV), in terms of effects on production traits, were studied. Four generations of White Leghorn chickens of Line TR, segregating for alv6 but free of endogenous viral genes, as well as two generations of crosses between TR and Ottawa Line WG (WGTR) were tested under a specific-pathogen-free environment. In the birds studied, the transgene appeared unchanged compared to the original alv6: No major changes in alv6 DNA were detected by restriction analysis, the transgene did not express the group-specific antigen of ALV, and its presence was associated with absence of immune response to ALV. In most test years, and both TR and WGTR genomic backgrounds, alv6 was associated with delayed sexual maturity by 4 to 6 d, reduced egg production to 497 d of age by 20 to 46 eggs, and a 3.6 to 15% decline in egg production rate. No consistent effects on other traits, including mortality, were detected. When inoculated with the AC-1 isolate of Marek's disease virus in a separate experiment, TR birds with alv6 had a significantly lower body weight gain to 10 d of age than their sibs without the transgene. Thus, transgenesis has biological costs that have to be assessed against desirable effects of transgenes.

Animals↗
PubMed1995

Development of a genetic map of the chicken with markers of high utility.

Microsatellites are tandem duplications with a simple motif of one to six bases as the repeat unit. Microsatellites provide an excellent opportunity for developing genetic markers of high utility because the number of repeats is highly polymorphic, and the assay to score microsatellite polymorphisms is quick and reliable because the procedure is based on the polymerase chain reaction (PCR). We have identified 404 microsatellite-containing clones of which 219 were suitable as microsatellite markers. Primers for 151 of these microsatellites were developed and used to detect polymorphisms in DNA samples extracted from the parents of two reference populations and three resource populations. Sixty, 39, 46, 49, and 61% of the microsatellites exhibited length polymorphisms in the East Lansing reference population, the Compton reference population, resource population No. 1 (developed to identify resistance genes to Marek's disease), resource population No. 2 (developed to identify genes involved in abdominal fat), and resource population No. 3 (developed to identify genes involved in production traits), respectively. The 91 microsatellites that were polymorphic in the East Lansing reference population were genotyped and 86 genetic markers were eventually mapped. In addition, 11 new random amplified polymorphic DNA (RAPD) markers and 24 new markers based on the chicken CR1 element were mapped. The addition of these markers increases the total number of markers on the East Lansing genetic map to 273, of which 243 markers are resolved into 32 linkage groups. The map coverage within linkage groups is 1,402 cM with an average spacing of 6.7 cM between loci. The utility of the genetic map is greatly enhanced by adding 86 microsatellite markers. Based on our current map, approximately 2,550 cM of the chicken genome is within 20 cM of at least one microsatellite marker.

Animals↗
PubMed1994

Microsatellite markers for genetic mapping in the chicken.

Microsatellite markers have been found to be abundant, evenly distributed, and highly polymorphic in a number of eukaryotic genomes. The objective of this study was to determine the utility of (TG)n microsatellites in the chicken. A chicken library enriched for (TG)n repeats was generated and 42 unique clones containing (TG)n microsatellites were identified and sequenced. The number of uninterrupted TG repeats ranged from 4 to 14 with an average of 7.8, which was considerably less than the number of repeats found in mammalian species. When primers designed to amplify across the (TG)n microsatellites were used in polymerase chain reactions (PCR) containing genomic chicken DNA, 19 of the 33 primer sets examined yielded polymorphisms in at least one of the three sets of chicken families: 15, 11, and 11 primer sets detected polymorphisms in the East Lansing (EL) reference population, the Compton (C) reference family, and between Line 63 and Line 72 chickens, respectively. The polymorphic microsatellite markers in the EL and C reference families were genetically mapped. Nine and seven mapped markers in the EL and C reference families, respectively, are polymorphic between Line 63 and Line 72, indicating that microsatellite markers will greatly enhance the ability to genotype specific loci of any chicken population.

Animals↗
PubMed1993

Genetic map of the chicken Z chromosome using random amplified polymorphic DNA (RAPD) markers.

Commercially important traits of domestic animals have often been genetically linked to sex chromosomes, such as the Z chromosome of chickens. Using a backcross mapping population between two divergent, inbred lines and random-amplified polymorphic DNA (RAPD)-PCR markers, a genetic map of the chicken Z chromosome has been generated. Thirteen Z-linked RAPD markers were identified, mapped, and linked to two RFLPs and one phenotypic marker. The protocol used also generated RAPD markers for the W chromosome. The linkage distances obtained suggest that the RAPD markers are widely distributed throughout the Z chromosome and are likely to be linked to most or all traits of interest on this chromosome. The map provides a preliminary estimate of genetic to physical distance of about 0.5 Mb per centimorgan for the Z chromosome in chickens (male-specific recombination). A similar approach should be applicable to facilitate the mapping and analysis of sex-linked traits in other domestic animals.

Animals↗
PubMed1993

A new defective retroviral vector system based on the Bryan strain of Rous sarcoma virus.

We have constructed a helper cell line and vector system based on the Bryan high titer (BH) strain of Rous sarcoma virus (RSV). BH-RSV is a defective virus which lacks an env gene; however, if env is supplied in trans, it replicates to a very high titer. Like BH-RSV, the vector contains gag and pol genes and lacks an env gene. The helper cell line supplies env in trans and permits the production of infectious virions. To construct the helper cell line the subgroup A env gene from the Schmidt-Ruppin-A (SRA) RSV was stably transfected into Qt6 cells, a chemically transformed quail fibroblast line. To minimize homology between the vector and helper cell line, transcription of the env gene is driven by a MuLV LTR, and 3' processing is controlled by the simian virus 40 (SV40) polyadenylation signal. This combination of vector and helper cells can be used to produce high-titer viral stocks in which recombinant replication-competent virus have not been detected even when the stocks were used to inoculate chickens. This system should be useful for developing transgenic chickens, studying cell lineage, and introducing genes into cultured cells.

Animals↗
PubMed1993

Sequence-tagged microsatellite sites as markers in chicken reference and resource populations.

Two chicken genomic libraries were screened for the presence of poly(TG/AC) microsatellite tracts. The number of positive clones was low, confirming the low frequency of such microsatellites in the chicken genome relative to mammalian genomes. Polymorphism of 29 microsatellite tracts, comprising 11 from the library screening and 18 obtained from GenBank, was examined in the East Lansing and Compton reference families, in a resource population formed by a cross between a single White Rock broiler and inbred Leghorn females, and in a panel of birds from five layer stocks. Twenty microsatellites, primarily of the poly(TG/AC) type, were polymorphic in at least one of the populations. Thirteen of the microsatellites were polymorphic in the East Lansing reference family and 13 were also polymorphic in the resource population, confirming that the genetic distance between White Rock and White Leghorn is about as great as between Jungle fowl and White Leghorn. Only six microsatellites were polymorphic in the Compton reference family, formed by a cross between two White Leghorn strains. Twelve of the microsatellites were mapped in the East Lansing and/or Compton reference families. These were well dispersed among the various linkage groups and did not show any indications of terminal clustering.

Animals↗
PubMed1992

A transgene, alv6, that expresses the envelope of subgroup A avian leukosis virus reduces the rate of congenital transmission of a field strain of avian leukosis virus.

A major mode of transmission of avian leukosis virus (ALV) is from a dam that is viremic with and immunologically tolerant to ALV, through the egg to the progeny. The authors have produced a line of chickens transgenic for a defective ALV provirus that expresses envelope glycoprotein, but not infectious virus, and is very resistant to infection with Subgroup A ALV. In the present experiment the authors sought to prevent or reduce congenital transmission by mating viremic-tolerant hens to males carrying the inserted provirus, thus introducing a gene for resistance into the progeny. Mature viremic females were mated with males hemizygous for the transgene to produce over 80 progeny each with and without the transgene. The chicks were hatched and maintained for 36 wk and observed for viremia, antibody, and the incidence of bursal lymphomas. Over 90% of the transgene-negative controls remained viremic through 36 wk of age and 51% developed bursal lymphomas. In contrast, 27% of the transgene-positive birds remained viremic and 18% died with bursal lymphomas. Thus, expression of Subgroup A envelope protein in the developing embryo reduced but did not eliminate congenital infection.

Analysis of Variance↗
PubMed1991

Experimentally introduced defective endogenous proviruses are highly expressed in chickens.

We have previously described the experimental introduction of recombinant subgroup A avian leukosis viruses (ALV) with Rous-associated virus 0 long terminal repeats into the germ line of line 0 chickens and the generation of 23 transgenic lines. Two of these transgenic lines, alv6 and alv11, do not produce infectious virus. Both of these lines contain defective proviruses but do express the gag and/or env protein. We have measured viral RNA expression in tissues derived from alv6, alv11, and the parental line 0. Total RNA was prepared from 9-day embryo, 16-day embryo, 1-day chicken, and 28-day chicken tissues. Viral RNA was detected by Northern RNA transfer analysis. The results indicate that both alv6 and alv11 chickens express viral RNA in all tissues tested regardless of the stage of development. No viral transcripts were detected in any line 0 (C/E; ev-negative) tissue. The levels of biologically active env glycoprotein correlates with the env RNA levels in both lines. In an in vivo interference assay, alv6, alv11, and line 0 chickens were infected with Rous-associated virus 1 and monitored for viremia, antibody against Rous-associated virus 1, and ALV-induced pathogenesis from 4 to 21 weeks. None of the 61 alv6 chickens contained detectable virus or produced antibody against subgroup A ALV. Virus and/or antibody against subgroup A ALV was detected in 34 of the 43 alv11 chickens, whereas 51 of 52 line 0 birds were viremic and/or produced antibody. ALV-induced pathogenesis was observed predominantly in line 0 chickens (10 of 59), whereas very little ALV-induced pathogenesis was seen in either alv6 (1 of 62) or alv11 (1 of 44) chickens. Presumably the mechanism for the increased resistance of alv6 and alv11 chickens was subgroup-specific receptor interference. These results clearly demonstrate that experimentally introduced endogenous proviruses can be expressed at high levels in the avian system.

Animals↗
PubMed1991

Endogenous viral genes: association with reduced egg production rate and egg size in White Leghorns.

Endogenous viral (ev) genes are DNA sequences residing permanently in the genome of most chickens that have a high degree of homology to avian leukosis viruses (ALV). Association of ev genes with production trait differences was studied in White Leghorns free of exogenous ALV. The Cornell Strain K and S chickens used in Experiment 1 had multiple ev genes. In each of four lines of chickens in Experiment 2, there was a 1:1 segregation of full-sibs free of ev genes and those carrying one ev gene: ev-12 that produces the complete endogenous virus, ev-3 or ev-6 that express certain viral antigens, or ev-1, a silent gene. In Experiment 1, the presence of genes ev-10 or ev-19, known to produce the complete virus, was associated with a 9% reduction in the annual egg production rate (P less than .05) in Strain S. Similarly, the presence of the virus-producing ev-12 in Experiment 2 was associated with an 8% reduction of annual egg production rate (P less than .05), a 2.2-g reduction in egg weight (P less than .01), and a .003 reduction in egg specific gravity (P less than .01). No significant effects of ev genes on age at first egg, Haugh unit score, percentage of eggs with blood spots, and body weight of hens were observed. It was concluded that ev genes producing complete endogenous virus are associated with production trait differences similar to those associated with subclinical infections with exogenous ALV.

Animals↗
PubMed1991

The influence of ev6 on the immune response to avian leukosis virus infection in rapid-feathering progeny of slow- and rapid-feathering dams.

Endogenous virus (EV) locus ev6 encodes only virus envelope glycoprotein. The influence of ev6 on the immune response to contact infection with hatchmates infected with avian leukosis virus (ALV) was compared in replicate hatches. The ALV Subgroup E-resistant, rapid-feathering (RF) female chickens produced by slow-feathering (SF) and RF dams with and without ev6 were exposed at hatch to hatchmates infected with ALV Subgroup A (Strain RPL-40). The RPL-40 viremia, shedding, and virus neutralizing antibodies were measured among pullets from two hatches at 22 wk of age. Although significant (P less than .05) differences between hatches in the immune response to contact infection were noted among ev6+ pullets, significantly fewer ev6+ pullets seroconverted than their ev6- hatchmates. At 22 wk of age, significantly more lymphomas were also found among ev6+ pullets than among ev6- hatchmates. In flocks wherein both parents and progeny were homozygous resistant to Subgroup E virus, there was no deterimental maternal effect on RF progeny from SF dams that carried ev21. These results also confirm that selection for genetic cellular resistance to Subgroup E ALV infection eliminates congenital transmission of EV21.

Animals↗
PubMed1990

Interactions between endogenous virus loci ev6 and ev21. 1. Immune response to exogenous avian leukosis virus infection.

The effects of ev6, ev21, sex, and hatch, were studied with respect to avian leukosis virus (ALV) viremia, cloacal shedding, and antibody response among RPL-40 virus-infected White Leghorns that carried ev6 and ev21 in all combinations. Among the four possible ev genotypes, chickens that carried only ev21 were the most immunologically tolerant to RPL-40 infection. Incidence of RPL-40 viremia was lowest among hatchmates that lacked both ev genes. Analysis of variance indicated significant interactions between ev6 and ev21 with respect to all responses. Among ev21+ slow-feathering (SF) chickens, the incidence of viremia and shedding of RPL-40 was reduced in the presence of ev6 when compared with ev6- hatchmates. Conversely, among ev21- rapid-feathering (RF) chickens, ev6 significantly enhanced the incidence of RPL-40 viremia when compared with ev6- hatchmates. The endogenous virus, ev6, markedly reduced recovery of the endogenous virus (EV21) from plasmas of slow-feathering chickens. When both flocks were terminated at 21 wk of age, significantly more ev21+ SF females had died from or developed RPL-40-induced tumors than ev21- hatchmates.

Animals↗
PubMed1990

Interactions between endogenous virus loci ev6 and ev21. 2. Congenital transmission of EV21 viral product to female progency from slow-feathering dams.

The influence of the endogenous virus ev6 on congenital transmission of EV21, the infectious viral product encoded by locus ev21, and the immune response to exogenous avian leukosis virus (ALV) infection was studied in rapid-feathering (RF) female progeny from four classes of slow-feathering (SF) (ev21+ and RF (ev21-) dams with and without ev6. Apart from transmitting infectious EV21 and ev6 to progency, dam ev genotype did not influence the immune response or shedding of RPL-40. The endogenous virus envelope glycoprotein encoded by ev6, however, completely restricted shedding and congenital transmission of infectious endogenous virus EV21, from SF dams. After 19 wk of exposure to ALV strain RPL-40 infected cage mates, only 11% of the congenitally infected female progeny mounted neutralizing antibodies against RPL-40, whereas 73% of their noncongenitally infected sisters seroconverted. More ev6+ female progeny, however, were shedders of RPL-40 and developed tumors than ev6- sisters. Among progeny from the four classes of dams, EV21 congenitally infected hens had the highest incidence (31%) of RPL-40-induced tumors.

Animals↗
PubMed1990

Expression of retroviral genes in transgenic chickens.

The development of transgenic technology in poultry has lagged behind that in mammals because of the unique reproductive system of birds. Therefore, we chose to use wild-type and recombinant replication-competent avian leukosis viruses to determine whether these retroviruses could be artificially introduced into the germ line by injecting them near the blastoderm of fertile eggs just before incubation. We generated 23 proviral inserts that were stably inherited through two generations. Twenty-one inserts coded for complete avian leukosis virus. Two interesting inserts failed to produce complete virus. One coded for envelope glycoprotein only and the other coded for the group-specific antigen and envelope glycoprotein. Cell culture and animal studies showed that one of these inserts was very resistant to infection and oncogenesis by subgroup A field strains of avian leukosis virus. Therefore, this represents a model system for introducing genes from the pathogen into the host to induce host resistance to the pathogen. Future studies should be aimed at developing more efficient systems for introducing replication-defective retroviral vectors or cloned DNA into the germ line of poultry so that the regulation of gene expression can be studied and transgenic technology can be applied to the improvement of this highly reproductive group of farm animals.

Animals↗
PubMed1989

Expression of avian reticuloendotheliosis virus envelope confers host resistance.

We constructed two reticuloendotheliosis virus (REV) envelope gene expression plasmids, one containing the REV-A envelope gene, the other the spleen necrosis virus (SNV) envelope gene. Cell lines were generated by transfecting each of the REV envelope plasmids into D17 cells, a canine cell line. The levels of REV envelope glycoprotein in the cell lines were assayed by immunoprecipitating the envelope glycoproteins from lysates of cells that were labeled with [35S]methionine. Virological challenge assays determined the degree of resistance of each of the cell lines to REV-A or SNV infection. The expression of either envelope gene protected the cells from infection by either REV-A or SNV virus. Several cell lines were significantly more resistant to REV infection than the parental D17 cells, and two lines were 25,000-fold more resistant, approaching the resistance of REV-infected D17 cells to reinfection. The resistant cell lines were not able to confer resistance to susceptible cells by cocultivation. The level of resistance was correlated with the uniformity of expression of the REV envelope glycoproteins by the individual cells in a cell line and not with the absolute level of expression by the population of cells.

Animals↗