Marie-Françoise Mahé

A Mendelian polymorphism underlying quantitative variations of goat αs1-casein

Using SDS-polyacrylamide gel electrophoresis and rocket immunoelectrophoresis, 3 new alleles, designated a,,-Cn’-, &alpha; s1 -Cn F and &alpha; s1 -Cn o, were identified at the goat a!-Cn locus, in addition to alleles <2,j-Cn!, as!-Cn° and <2,j-Cn! previously reported by BOULANGER et al. (1984). Alleles a,,Cn’, a,,-Cn’ and <2,j-Cn! are associated with a high content of a,,-casein (approximate mean contribution of each allele being 3.6 g/I) compared to (Y,,-Cn’ with a low content (0.6 g/I) and a,,Cn° with an intermediate content (1.6 g/1) ; a,,-Cn° appears to be a true null allele. In a sample of 213 Alpine females from 49 flocks in West Central France, the frequencies of the 6 alleles

Polymorphisme des caséines αs1 et αs2 de la chèvre (Capra hircus)

Contrairement à ce qui paraissait acquis depuis le travail de RICHARDS ON& CREAMER (1975), le lait de chèvre contient de la caséine asi ; on y retrouve donc les quatre mêmes espèces de caséine que dans le lait de vache (a.,[, a,2, ! (i et x). Les caséines as1 et a82 , dont les fractions sont en partie superposées après électrophorèse en gel d’amidon à pH 8,6, sont par contre bien séparées après électrophorèse en gel d’amidon à pH 3.

High-resolution comparative mapping among man, cattle and mouse suggests a role for repeat sequences in mammalian genome evolution

BackgroundComparative mapping provides new insights into the evolutionary history of genomes. In particular, recent studies in mammals have suggested a role for segmental duplication in genome evolution. In some species such as Drosophila or maize, transposable elements (TEs) have been shown to be involved in chromosomal rearrangements. In this work, we have explored the presence of interspersed repeats in regions of chromosomal rearrangements, using an updated high-resolution integrated comparative map among cattle, man and mouse.ResultsThe bovine, human and mouse comparative autosomal map has been constructed using data from bovine genetic and physical maps and from FISH-mapping studies. We confirm most previous results but also reveal some discrepancies. A total of 211 conserved segments have been identified between cattle and man, of which 33 are new segments and 72 correspond to extended, previously known segments. The resulting map covers 91% and 90% of the human and bovine genomes, respectively. Analysis of breakpoint regions revealed a high density of species-specific interspersed repeats in the human and mouse genomes.ConclusionAnalysis of the breakpoint regions has revealed specific repeat density patterns, suggesting that TEs may have played a significant role in chromosome evolution and genome plasticity. However, we cannot rule out that repeats and breakpoints accumulate independently in the few same regions where modifications are better tolerated. Likewise, we cannot ascertain whether increased TE density is the cause or the consequence of chromosome rearrangements. Nevertheless, the identification of high density repeat clusters combined with a well-documented repeat phylogeny should highlight probable breakpoints, and permit their precise dating. Combining new statistical models taking the present information into account should help reconstruct ancestral karyotypes.

A first generation bovine BAC-based physical map

A first generation clone-based physical map for the bovine genome was constructed combining, fluorescent double digestion fingerprinting and sequence tagged site (STS) marker screening. The BAC clones were selected from an Inra BAC library (105 984 clones) and a part of the CHORI-240 BAC library (26 500 clones). The contigs were anchored using the screening information for a total of 1303 markers (451 microsatellites, 471 genes, 127 EST, and 254 BAC ends). The final map, which consists of 6615 contigs assembled from 100 923 clones, will be a valuable tool for genomic research in ruminants, including targeted marker production, positional cloning or targeted sequencing of regions of specific interest.

A second generation radiation hybrid map to aid the assembly of the bovine genome sequence

BackgroundSeveral approaches can be used to determine the order of loci on chromosomes and hence develop maps of the genome. However, all mapping approaches are prone to errors either arising from technical deficiencies or lack of statistical support to distinguish between alternative orders of loci. The accuracy of the genome maps could be improved, in principle, if information from different sources was combined to produce integrated maps. The publicly available bovine genomic sequence assembly with 6× coverage (Btau_2.0) is based on whole genome shotgun sequence data and limited mapping data however, it is recognised that this assembly is a draft that contains errors. Correcting the sequence assembly requires extensive additional mapping information to improve the reliability of the ordering of sequence scaffolds on chromosomes. The radiation hybrid (RH) map described here has been contributed to the international sequencing project to aid this process.ResultsAn RH map for the 30 bovine chromosomes is presented. The map was built using the Roslin 3000-rad RH panel (BovGen RH map) and contains 3966 markers including 2473 new loci in addition to 262 amplified fragment-length polymorphisms (AFLP) and 1231 markers previously published with the first generation RH map. Sequences of the mapped loci were aligned with published bovine genome maps to identify inconsistencies. In addition to differences in the order of loci, several cases were observed where the chromosomal assignment of loci differed between maps. All the chromosome maps were aligned with the current 6× bovine assembly (Btau_2.0) and 2898 loci were unambiguously located in the bovine sequence. The order of loci on the RH map for BTA 5, 7, 16, 22, 25 and 29 differed substantially from the assembled bovine sequence. From the 2898 loci unambiguously identified in the bovine sequence assembly, 131 mapped to different chromosomes in the BovGen RH map.ConclusionAlignment of the BovGen RH map with other published RH and genetic maps showed higher consistency in marker order and chromosome assignment than with the current 6× sequence assembly. This suggests that the bovine sequence assembly could be significantly improved by incorporating additional independent mapping information.

Identification of the two common alleles of the bovine κ-casein locus by the RFLP technique, using the enzyme Hind III

As could be predicted from a comparison of the cDNA sequences established by STEWART et al. (1984) and GORODETSKIY & KALEDIN (1987) the two common alleles of the bovine K-casein locus, K-Cn’ and K-Cn’, can be identified by the restriction fragment length polymorphism (RFLP) technique using either Hind III or Taq I. The latter endonuclease also detects a polymorphism of the DNA strand carrying the allele K-Cn’. However, for determination of both alleles, the use of Hind III is preferable because, according to the data of the above authors, the RFLP detected by that enzyme is specific for the amino-acid substitution responsible for the difference in charge of the two K-casein variants. When DNA is prepared from blood leucocytes, the occurrence of chimaerism in twins may cause difficulties in interpretation.

A genetic and biochemical analysis of a polymorphism of bovine alpha S2-casein.

Using gel electrophoresis a genetic polymorphism of alpha S2-casein (Cn) was discovered in individual milk samples from 2 bovine breeds of the eastern part of France (Vosgienne and Montbéliarde). The 3 observed phenotypes (Plate 1) are determined by 2 co-dominant alleles at an autosomal locus. The alpha S2-Cn A variant was the only one known up to now in European breeds (reference variant) and alpha S2-Cn D is a new variant, whose bands overlap the beta-casein A band at pH 8.6, and migrate faster than alpha S2-Cn A at pH 3.0. The sequence of the polypeptide chain alpha S2-Cn D differs from that of alpha S2-Cn A by the deletion of a very acidic nonapeptide, which includes a cluster of 3 phosphoseryl residues. Due to the characteristics of the reference sequence, this deletion cannot be exactly located but it involves residues 50-58, or 51-59, or 52-60. A genetic analysis shows that locus alpha S2-Cn is closely linked to the cluster alpha S1-Cn--beta-Cn--kappa-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.

Localisation, dans la partie NH2-terminale de la caséine αs1 bovine, d'une délétion de 13 acides aminés différenciant le variant a des variants B et C

The A variant of bovine αs1 casein is devoid of the segment of 13 amino acid residues which occupies the 14th to 26th position from the NH2‐terminal in the polypeptide chain (198 residues) of the B and C variants.

Comparaison du polymorphisme génétique des lactoprotéines du zébu et des bovins

77 8 lactosérums et 586 solutions de caséines préparés à partir de laits individuels de zébus malgaches ont été examinés par électrophorèse en gel d’amidon ou d’acrylamide dans le but d’analyser le polymorphisme génétique des protéines du lait de zébu (Bos indicus), et de le comparer à celui du lait bovin (Bos taurus). Les loci de structure des cinq principales lactoprotéines (x-lactalbumine, [3-lactoglobuline, caséines as l. fi et x) sont tous bialléliques et déterminent les variants classiques suivants : La A et B ; Lg A et B ; as l B et C ; [3 A I et A2 ; x A and B. Les variants [3B et fiD n’ont pas été trouvés au cours de cette étude. Les fréquences alléliques observées dans l’échantillon, ainsi que les fréquences des combinaisons alléliques contrôlées par l’unité génétique formée des trois loci, as l Cn, p-Cn et x-Cn, sont indiquées dans le tableau i. La comparaison des fréquences alléliques observées dans les cinq sous-échantillons géographiques les plus importants indique que la population de zébus considérée présente une certaine homogénéité génétique. Les substitutions d’acides aminés responsables des différences de mobilité électrophorétique entre les variants as l B et C, [3A I et A2 et xA et B, ont été caractérisées en suivant, en général, les méthodes précédemment appliquées par notre équipe à l’étude des variants des caséines bovines. Elles sont toutes identiques aux substitutions trouvées chez les bovins, y compris lorsque les variants as l C et [3A I sont commandés par la combinaison allélique asl CnC-(3-CnA’ [substitutions 192 Glu (as l B) Gly (as l C), 67 Pro (gA 2) -! His ([3A’) et 14 8 Asp (xA) Ala (xB)], Par ailleurs, l’étude d’un échantillon de caséine [3B, préparé à partir du lait d’un zébu Choa (République Tchadienne), indique que ce variant diffère de [3A I, comme chez les bovins, par la substitution m2 Ser ([3A I) Arg ([3B), ce qui rend discutable l’utilisation d’une notation particulière (pBz) pour désigner le variant [3B du zébu. Selon toute vraisemblance, et pour chacun des trois loci, le polymorphisme commun à Bos taurus et à Bos indicus dérive de mutations uniques, antérieures à la divergence phylogénétique de ces deux rameaux du genre Bos, qui s’est produite, selon EpSTE iN(1971 ), en Asie du sud-ouest, vers les quatrième et troisième millé-

Localisation des substitutions d'acides aminés différenciant les variants a et b de la caséine × bovine

Comme le suggéraient les résultats de WOYCHIK et al. (19 66), DE KoNirrc et al. (19 66) et HILL et al. (1970 ), les caséinomacropeptides des variants A et B de la caséine x bovine diffèrent par deux substitutions d’acides aminés : Ala (xB) Asp (xA) et Ile (xB) Thr (xA). Ces substitutions affectent respectivement la 22 e et la 34 e position à partir de l’extrémité COOH-terminale du caséinomacropeptide, qui est également celle de la caséine x. D’un point de vue génétique, les deux variants de la caséine x assurent donc le marquage de la partie terminale du locus x-Cn.