Association of Xmv-10 and the non-agouti (a) mutation explained by close linkage instead of causality

In a previous survey of endogenous proviruses among inbred mouse strains, the Xmv-10 provirus was found only in strains that carried the non-agouti (a) mutation (Frankel et al. J. Virol. 63: 1763–1774, 1989). To determine whether insertion of Xmv-10 caused the a mutation, we cloned a portion of Xmv-10 and its insertion site. Using a fragment of flanking cellular DNA as a Southern hybridization probe, we found that the Xmv-10 provirus was still present in revertant alleles of a to a ^tor A W.A restriction fragment length variant (RFLV) in cellular DNA at the Xmv-10 insertion site was found to be correlated with the presence or absence of the provirus among inbred strains of laboratory mice regardless of their agouti allele. This correlation did not extend to wild mice, however, in which none of the samples contained Xmv-10, yet one, Mus domesticus poschiavinus, contained the insertion site RFLV correlated with Xmv-10 in laboratory mice. Analysis of an intersubspecific backcross with RFLVs at the insertion sites of Xmv-10 and Emv-15 (an endogenous provirus associated with A ^y)revealed the following genetic map information: cen-A-0.31±0.31 cM-Emv-15-0.62±0.27 cM-Xmv-10-tel. Haplotype analysis of inbred strains in which a was not associated with Xmv-10 and in which A ^ywas not associated with Emv-15 demonstrated that these exceptions were explained most simply by a single recombination that disturbed the linkage relationships evident in most inbred strains. These results demonstrate that Xmv-10 did not cause the a mutation, suggest that insertion of Xmv-10 occurred recently in the evolution of laboratory mice, and show that the associations between agouti alleles and endogenous proviruses are due to linkage disequilibrium.     

Inheritance of coat colour in the German Pinscher dog

The two primary colour varieties of the German Pinscher breed are the red and the black and tan. Respectively, these are produced by the dominant yellow allele A ^y and the black and tan allele a ^t of the agouti locus. The dilute gene d is present in the breed at a low frequency and produces the rarer isabella and blue and tan colours, with the genotypes A ^y -dd and a ^t dd, respectively.     

Prediction of hybrid performance in maize using molecular markers and joint analyses of hybrids and parental inbreds

The identification of superior hybrids is important for the success of a hybrid breeding program. However, field evaluation of all possible crosses among inbred lines requires extremely large resources. Therefore, efforts have been made to predict hybrid performance (HP) by using field data of related genotypes and molecular markers. In the present study, the main objective was to assess the usefulness of pedigree information in combination with the covariance between general combining ability (GCA) and per se performance of parental lines for HP prediction. In addition, we compared the prediction efficiency of AFLP and SSR marker data, estimated marker effects separately for reciprocal allelic configurations (among heterotic groups) of heterozygous marker loci in hybrids, and imputed missing AFLP marker data for marker-based HP prediction. Unbalanced field data of 400 maize dent × flint hybrids from 9 factorials and of 79 inbred parents were subjected to joint analyses with mixed linear models. The inbreds were genotyped with 910 AFLP and 256 SSR markers. Efficiency of prediction (R ²) was estimated by cross-validation for hybrids having no or one parent evaluated in testcrosses. Best linear unbiased prediction of GCA and specific combining ability resulted in the highest efficiencies for HP prediction for both traits (R ² = 0.6–0.9), if pedigree and line per se data were used. However, without such data, HP for grain yield was more efficiently predicted using molecular markers. The additional modifications of the marker-based approaches had no clear effect. Our study showed the high potential of joint analyses of hybrids and parental inbred lines for the prediction of performance of untested hybrids.     

Genetic interaction between Non-MHC T- and B-cell alloantigens in response to rous sarcomas in chickens

Chickens of Regional Poultry Research Laboratory (RPRL) inbred line 6₃ regress sarcomas induced by Bryan high-titer Rous sarcoma virus to a greater extent than chickens of line RPRL 100, although these lines are identical for the major histocompatibility B complex. They differ, however, at three independent autosomal loci: Ly-4 and Th-1 determine the surface alloantigens of partly overlapping subsets of T lymphocytes, and Bu-1 determines a surface alloantigen of B lymphocytes. The association of genotypes at these loci with quantitative variation in their ability to regress Rous sarcomas was tested in segregating F₄ generation progeny derived from crosses of lines 100 and 6₃. The Ly-4 and Bu-1 genotypes showed association with Rous sarcoma regression, but the Th-1 genotype did not. Chickens of the Ly-4 ^a/Ly-4 ^a, Bu-1 ^b/Bu-1 ^b and Ly-4 ^b/Ly-4 ^b, Bu-1 ^a/Bu-1 ^a genotypes had a significantly higher regressor ability than the other two double homozygous genotypes. These results indicate that higher regression is associated with (1) interaction between the Ly-4 and Bu-1 loci, and (2) complementation between either the line 6 Ly-4 ^a allele and the line 100 Bu-1 ^b allele, or the line 100 Ly-4 ^b allele and the line 6 Bu-1 ^a allele.     

Genetics of an esterase in Aedes aegypti

Zymograms of single individuals of Aedes aegypti were obtained by means of starch gel electrophoresis, using alpha-naphthyl acetate as substrate. Inbred lines gave consistently homogeneous patterns; earlier results from random-breeding laboratory strains had shown considerable variability. Six distinct bands were observed. The furthest moving band, designated Esterase 6, showed differential migration in two inbred lines. Reciprocal crosses between these lines gave F₁ progeny showing both bands. Backcrosses of F₁ to either parental line gave a 1:1 segregation. These results are consistent with the hypothesis that the two forms of Esterase 6 are controlled by a single pair of codominant alleles at a single gene locus (Est 6 ^a and Est 6 ^b). Linkage tests with marker genes have demonstrated that Est 6 is on linkage group 2, with the following alignment: spot-abdomen (9.0±1.0) yellow-larva (17.4±1.3) Est 6. Crosses with another inbred line demonstrated a third band with intermediate mobility, designated Est 6 ^c. An additional electrophoretic variant which seems to have a simple Mendelian basis was found in esterase band 1.This work was supported by NIH Research Grant No. A1-02753.     

Influence of non-MHC T lymphocyte alloantigens on regression of rous sarcomas in the chicken

Chickens of Regional Poultry Research Laboratory (RPRL) inbred line 63 regress sarcomas induced by Bryan high-titer Rous sarcoma virus to a greater extent than chickens of line 7₂, although these lines are identical for the major histocompatibility complex (MHC, B complex). They differ, however, at two independent autosomal loci, Ly-4 and Th-1, which determine surface alloantigens of partly overlapping subsets of T lymphocytes. Association of genotypes at these loci with quantitative variation in ability to regress Rous sarcomas was tested in segregating progeny derived from crosses of lines 6₃ and 7₂. In the F4 generation chickens of the Ly-4 ^a /Ly-4 ^a , Th-1 ^a /Th-1 ^a genotype (symbolized aa/aa) had significantly higher regressor ability than any of the other three double homozygous genotypes. In F5, all nine genotypes formed by combinations of homozygotes and heterozygotes were tested, and higher regressor ability was shown by the aa/aa, ab/aa, and aa/ab genotypes. These results indicate that higher regression is associated with: (1) interaction between the line 6₃ Ly-4 ^a and Th-1 ^a alleles in homozygous form; and (2) dominance x dominance interaction, in that the a allele at each locus is dominant for higher regression only within the homozygous aa genotype at the other locus.     

Characterizations of candidate genes for IDD susceptibility from the diabetes-prone NOD mouse strain

The nucleotide sequences of the NOD and C57BL/6J alleles of Glut-2, Sod-2, and Il-2 were determined by RT-PCR sequencing. Each of these loci is located in intervals that strongly correlated with susceptibility to diabetes in an (NOD/Uf x C57BL/6J)F₁ x NOD/Uf backcross. No significant variations in the alleles of Glut-2 at 16 cM on Chromosome (Chr) 3 or Sod-2 at 8 cM on Chr 17 were detected. However, the Il-2 allele in NOD at 20 cM on Chr 3 was found to differ from that in C57BL/6J by a complex mutation involving the contraction of a simple sequence repeat (SSR). Il-2 in NOD differs from the allele in C57BL/6J via a complex mutation involving a deletion of four CAG codons from the SSR together with a length-compensatory four-codon duplication of a segment 5 from the SSR. Two nonsynonymous mutations in the coding region 5 to the SSR were also detected. Only these two allelic forms of Il-2 were detected in a survey of 13 standard inbred lines and 4 wild mouse strains. We propose to designate these alleles as Il-2 ^a (for alleles such as C57BL/6J that contain 12 CAG repeats) and Il-2 ^b (for alleles such as NOD), which occurred in a variety of standard inbred strains and in all four wild Mus musculus domesticus tested. The distribution of these Il-2 alleles among inbred strains correlated with the detection of Chr 3 as an interval effecting diabetes susceptibility in three separate genetic crosses. However, functional characterizations of the quantity and functional characteristics of Il-2 produced by Il-2 ^a and Il-2 ^b failed to reveal any allele-specific variations.     

Tissue microenvironment and the genetic control of hair pigment patterns in mice

This study was conducted to assess microenvironmental variability within integumental tissue of genetically identical mice with respect to a specific cellular response: cyclic synthesis of yellow and black pigment by hair bulb melanocytes. Crosses were performed within and between inbred strains of mice that were isogenic with the exception of a single gene substitution at the agouti locus. Agouti locus genes included the A^vy, A^w, A, a^td, a^t, a^x, a^m, and a alleles. The pigment patterns of dorsal, flank, and ventral hairs of the first and third hair generations and of hairs growing in special integumentary areas such as the pinna, tail, and hind foot were studied. It was found that the amount of yellow pigment synthesized by hair bulb melanocytes within genetically identical mice is both agedependent and conditioned by the integumentary environment. Furthermore, the special integumentary regions produce hairs with a variety of pigment patterns in which the distribution and relative amounts of black and yellow pigments do not necessarily conform to dominance relationships expected among agouti locus alleles as judged by their effects on the pigmentation of the dorsal pelage. We conclude that within genetically uniform integumental tissues, microenvironmental differences occur and are reflected as alterations in the metabolic pattern of differentiated cells.     

Tests of association of immunoglobulin allotype genes and viral oncogenesis in chickens

Chickens from Regional Poultry Research Laboratory (RPRL) inbred line 6₃ are resistant to virally-induced Marek's disease (MD) and lymphoid leukosis (LL) and are relatively strong regressors of virally-induced Rous sarcomas. In contrast, RPRL line 100 chickens are highly susceptible to MD and LL and are weaker regressors of Rous sarcomas than line 6₃. RPRL lines 100 and 6₃ differ for alleles at the IgG-1 (G-1) allotype locus, but have identical IgM-1 (M-1) allotype alleles. To test the possible association of the G-1 locus with variations in resistance to virally-induced tumors, homozygous and heterozygous genotypes among F₃ crosses were infected. F₃ chickens with different G-1 types were comparable in their resistance to MD tumors following inoculation with the JM strain of the MD virus, and for their ability to regress Rous sarcoma tumors induced by the Rous sarcoma virus (RSV) RAV-1. However, following RAV-1 virus infection a smaller proportion of G-1 ^a /G-1 ^a F₃ or F₄ birds developed LL tumors than G-1 ^a /G-1 ^e and G-1 ^e /G-1 ^e birds. Genes determining immunoglobulin heavy chains were therefore associated with a recessive resistance to B-cell lymphomagenesis in chickens.Deceased     

Mitomycin C induces genomic rearrangements involving transposable elements in Drosophila melanogaster

Summary Mitomycin C was injected into the abdomen of male flies of the y ² sc¹ w^aG strain of Drosophila melanogaster. They were mated with females bearing attached-X chromosomes, and the male offspring (F₁) were analysed for the appearance of mutations in the X chromosome. We observed y ¹ and sc ⁺ reversions induced either by excision of mdg4 (gypsy) with retention of one long terminal repeat (LTR) or by insertion of a foreign sequence into mdg4, partial reversion of the w ^aG mutation, w ^aGw ^aGd, and unstable f mutations. The overall mutation frequency was considerably higher than in control flies of the y ² sc¹ w^aG strain. Possible mechanisms of genomic rearrangements induced by Mitomycin C, in particular the role of homologous recombination, are discussed.     

Effects of chimaerism for two T/t complex mutations on sperm function

Mouse chimaeras produced by aggregation of embryos heterozygous for two different recessive mutations at the T/t complex have been analyzed by breeding to explore the basis for the phenomena of male transmission ratio distortion and sterility associated with these genes. Whereas males of genotype t^w2/t^w5 are always sterile, male chimaeras of the type +/t^w2 ? +/t^w5 are normally fertile; furthermore, they transmit each t mutation to the same very high extent seen in ordinary (+/t) heterozygotes. Since spermatogenic cells derived from either the +/t^w2 and +/t^w5 genotypes thus function quite independently of one another in mosaic testes, it can be concluded that sterility, and presumably distorted transmission ratio as well, depends on specific interactions between T/t alleles in diploid spermatogenic cells or their individual meiotic descendants.     

Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses

Four loci seem responsible for the dilution of the basic coat colours in horse: Dun (D), Silver Dapple (Z), Champagne (CH) and Cream (C). Apart from the current phenotypes ascribed to these loci, pearl has been described as yet another diluted coat colour in this species. To date, this coat colour seems to segregate only in the Iberian breeds Purebred Spanish horse and Lusitano and has also been described in breeds of Iberian origin, such as Quarter Horses and Paint Horse, where it is referred to as the ‘Barlink Factor’. This phenotype segregates in an autosomal recessive manner and resembles some of the coat colours produced by the champagne CH^CH and cream C^Cr alleles, sometimes being difficult to distinguish among them. The interaction between compound heterozygous for the pearl C^prl and cream C^Cr alleles makes SLC45A2 the most plausible candidate gene for the pearl phenotype in horses. Our results provide documented evidence for the missense variation in exon 4 [SLC45A2:c.985G>A; SLC45A2:p.(Ala329Thr)] as the causative mutation for the pearl coat colour. In addition, it is most likely involved as well in the cremello, perlino and smoky cream like phenotypes associated with the compound C^Cr and C^prl heterozygous genotypes (known as cream pearl in the Purebred Spanish horse breed). The characterization of the pearl mutation allows breeders to identify carriers of the C^prl allele and to select this specific coat colour according to personal preferences, market demands or studbook requirements as well as to verify segregation within particular pedigrees.     

Effect of environmental factors on in vitro and in situ interactions between atoxigenic and toxigenic A. flavus strains and control of aflatoxin contamination of maize

Abstract

The potential of three atoxigenic strains from different geographical origins in Africa were examined for in vitro and in situ competitiveness against two toxigenic strains of Aspergillus flavus and subsequent inhibition of aflatoxin B₁ (AFB₁) production under different environmental conditions. Temperature, water activity (a _w) and substrate influenced the types of interaction between the three AFL^? and two AFL⁺ strains. The competitiveness and AFB₁ reduction ability of the three atoxigenic strains when interacting with the two toxigenic strains were evaluated by inoculation of 100, 25:75, 50:50, 75:25 and 100% ratios of mixed spore suspensions in vitro on malt extract and milled maize agars over 28 days and in situ on stored maize grain for 14 days, respectively at 0.99, 0.96 and 0.90 a _w. For all the treatments, the effect of a _w and inoculum ratio and their interaction was highly significant. Toxin inhibition was >80% in vitro at both 0.99 and 0.96 a _w. In situ AFB₁ reduction was influenced by the toxigenic strain assayed, a _w and the inoculum ratio. Where control was achieved, it was more variable at 0.96 a _w, while with more stringent water stress conditions (0.90 a _w) the percentage inhibition was up to 77.2%. The study shows the importance of including environmental factors in screening and identifying effective atoxigenic strains for control of AFs (aflatoxins).     

Identification of opaque-2 genotypes in segregating populations of Quality Protein Maize by analysis of restriction fragment length polymorphisms

Quality Protein Maize (QPM) is a name given to genetically modified opaque-2 maize with hard endosperm. The opaque-2 mutation conditions a reduction in the amount of zein seed storage protein; zeins are deficient in the essential amino acids lysine and tryptophan, and mutant seed have a higher nutritional value. To utilize the potential of opaque-2 maize, elite inbreds can be converted to o2/o2 forms and subsequently to hard endosperm opaque-2. Since opaque-2 is recessive and endosperm specific, conventional backcross procedures to convert elite inbreds to opaque-2 forms are inefficient. To alleviate this problem, a marker-assisted selection procedure was developed for the Texas A&M University Quality Protein Maize breeding program. Hybridization of an O2 cDNA probe to blots of DNA from plants carrying O2 and o2 alleles showed that restriction fragment length polymorphisms (RFLPs) exist between the W64A o2 allele and O2 alleles of Mo17 and TX5855 inbred lines. To identify the opaque2 genotypes in segregating populations, an RFLP marker assay combining the O2 cDNA probe and HindIII-digestion of genomic DNA was developed. The effectiveness of the O2 RFLP marker assay was tested under field conditions using F₂ and backcross populations of several hard endosperm opaque-2 lines. A comparison of the genotypes identified by RFLP analysis with the seed phenotypes of the next generation indicated that this procedure is accurate and can be used for identifying O2/O2, O2/o2, and o2/o2 genotypes of individual juvenile plants in breeding populations.     

Agouti-Related Maturation and Tissue Distribution of oc-Melanocyte Stimulating Hormone in Wild-Type (AwJ/AwJ) and Mutant (Ay/a,a/a) Mice

Because of ectopic overproduction of agouti protein, yellow alleles (A^y and A^vy) of the murine agouti gene may secondarily modulate the synthesis, maturation (i.e., acetylation), and/or tissue deployment of α-Melanocyte Stimulating Hormone (MSH). We used HPLC to test the hypothesis that A^y/a mice exhibit altered concentrations of desacetyl-, monoacetyl-, and diacetyl-α-MSH in pituitaries, sera, and telogen hair bulbs when compared to black (a/a) mice. We also used RIA to measure total MSH in those same tissues of A^y/a, a/a, and white-bellied agouti (A^wJ/A^wJ) mice (Strain C57BL/6J). We found no evidence that A^y/a mice possessed an imbalance of des-, mono-, and diacetylated α-MSH species. However, radioimmunoassay (RIA) analyses of total MSH suggest that wild-type agouti mice (A^wJ/A^wJ) exhibited significantly decreased (P < 0.05) tissue levels of total α-MSH in pituitaries, sera, and regenerating hair bulbs when compared to those of mutant A^y/a and a/a mice.     

A deletion spanning the promoter and first exon of the hair cycle-specific ASIP transcript isoform in black and tan rabbits

Black and tan animals have tan-coloured ventral body surfaces separated by sharp boundaries from black-coloured dorsal body surfaces. In the a^t mouse mutant, a retroviral 6 kb insertion located in the hair cycle-specific promoter of the murine Asip gene encoding agouti signalling protein causes the black and tan phenotype. In rabbits, three ASIP alleles are thought to exist, including an a^t allele causing a black and tan coat colour that closely resembles the mouse black and tan phenotype. The goal of our study was to identify the functional genetic variant causing the rabbit a^t allele. We performed a WGS-based comparative analysis of the ASIP gene in one black and tan and three wt agouti-coloured rabbits. The analysis identified 75 a^t-associated variants including an 11 kb deletion. The deletion is located in the region of the hair cycle-specific ASIP promoter and thus in a region homologous to the site of the retroviral insertion causing the a^t allele in mice. We observed perfect association of the genotypes at this deletion with the coat colour phenotype in 49 rabbits. The comparative analysis and the previous knowledge about the regulation of ASIP expression suggest that the 11 kb deletion is the most likely causative variant for the black and tan phenotype in rabbits.     

The histocompatibility-2 system in wild mice

The I-region gene products of 29 wild-derivedH-2 haplotypes on a B10 background (B10.W congenic lines) were typed with alloantisera which detect 17 inbred I-region antigens. Five new I-region antigens were defined by expanding the inbred line panel ofH-2 haplotypes to includeH-2 ^u , H-2^v, andH-2 ^j . Based on serological analyses of the inbred and B10.W lines, the polymorphism of theIA gene (or genes) is estimated to be at a minimum of 15 alleles and theIE gene (or genes) at a minimum of 4 alleles. These results indicate that theIA subregion is more polymorphic than theIE subregion. By combining the I-region typing data with theH-2K andH-2D region typing data reported previously, a total of 11 new natural recombinants of inbredH-2 alleles were detected among the B10.W lines.     

The causes of competition between two cell lines ofDaucus carota in mixed culture

Summary Observations were made of the changes in frequency of two genetically different culture lines ofDaucus carota (designated DBB and DSL) during successive subcultures of mixed cultures. Under conditions of phosphate limited growth, one line (DSL) had a competitive advantage over the other. Under other cultural conditions, this competitive interaction was removed or reversed. Detailed comparisons of the growth patterns and phosphate uptake rates of the two culture lines grown separately allowed prediction of their behaviour in mixed cultures. Deviations of observed from predicted behaviour in mixed cultures demonstrated that the dominant culture line (DSL) could compete more effectively for the available phosphate, thereby modifying the growth of line DBB and causing its elimination from mixed cultures. It is concluded that the phosphate limited medium in which these culture lines were initiated had selected genotypes differing in their efficiencies of phosphate utilisation.     

The production of callus capable of plant regeneration from immature embryos of numerous Zea mays genotypes

In the summer of 1983, immature embryos from 101 selfed inbred lines and germplasm stocks of Zea mays L. were examined for their ability to produce callus cultures capable of plant regeneration (regenerable cultures) using a medium with which some limited success had previously been obtained. Forty-nine of the genotypes (49%) produced callus which visually appeared similar to callus previously cultured and shown to be capable of plant regeneration. After five months, 38 of these genotypes were alive in culture and plants were subsequently regenerated from 35 (92%) of them. No correlation was observed between plant regeneration and callus growth rate, the vivipary mutation (genes vp1, 2, 5, 7, 8 and 9), or published vigor ratings based on K⁺ uptake by roots. When F₁ hybrid embryos were cultured, 97% of the hybrids having at least one regenerable parent also produced callus capable of plant regeneration. No regenerable cultures were obtained from any hybrid lacking a parent capable of producing a regenerable callus culture.In the summer of 1984, immature embryos from 218 additional inbred lines and germplasm stocks were plated and examined for their ability to produce regenerable callus cultures on media containing altered micronutrient concentrations, 3,6-dichloro-o-anisic acid (dicamba), glucose, and elevated levels of vitamin-free casamino acids and thiamine. Of these genotypes 199 (91%) produced callus that was regenerable in appearance. In the 1984 study, plant regeneration was noted in many commercially important inbreds, including B73, Mo17, B84, A632, A634, Ms71, W117, H99³H95 and Cm105. Thus tissue-culture techniques are now available to obtain callus cultures capable of plant regeneration from immature embryos of most maize genotypes.Abbreviations trade names 2,4-D 2,4-dichlorophenoxyacetic acid - dicamba 3,6-dichloro-o-anisic acid     

Inheritance patterns of new genetic markers and occurrence of spontaneous mosaicism in the monogenic blowfly Chrysomya rufifacies (Diptera: Calliphoridae)

 Four new genetic markers for Chrysomya rufifacies, a fly with maternal sex determination, were characterized. The markers include one body colour mutant, black body (bl), and three eye colour mutants, brown eye (br), apricot eye (ap), and red eye (w ^r ). Two of the latter, br and w ^r , turn out to be sex linked, the others behave as autosomal genes belonging to different linkage groups. w ^r is a hypomorphic and w an apomorphic mutation of the white gene, w/w is epistatic to br/br and to ap/ap. A preliminary genetic linkage map with the sex realizer F′/f  and the loci br and w residing in homomorphic sex chromosomes is established. Evidence is presented that crossing over is absent in the male sex. The possible causes of the spontaneous appearance of mosaics for eye colour observed among individuals heterozygous for recessive genes are discussed. Received: 18 March 1996/Accepted: 9 August 1996