Oil bodies isolated from the mature seeds of rape (Brassica napus L.), mustard (Brassica juncea l.), cotton (Gossypium hirsutum L.), flax (Linus usifafis simum), maize (Zea mays L.), peanut (Arachis hypogaea L.), and sesame (Sesamum indicum L.) had average diameters that were different but within a narrow range (0.6-2.0 fim), as measured from electron micrographs of seria1 sections. Their contents of triacylglycerols (TAC), phospholipids, and proteins (oleosins) were correlated with their sizes. The correlation fits a formula that describes a spherical particle surrounded by a shell of a monolayer of phospholipids embedded with oleosins. Oil bodies from the various species contained substantial amounts of the uncommon negatively charged phosphatidylserine and phosphatidylinositol, as well as small amounts of free fatty acids. These acidic lipids are assumed to interact with the basic amino acid residues of the oleosins on the surface of the phospholipid layer. lsoelectrofocusing revealed that the oil bodies from the various species had an isoelectric point of 5.7 to 6.6 and thus possessed a negatively charged surface at neutra1 pH. We conclude that seed oil bodies from diverse species are very similar in structure. In rapeseed during maturation, TAC and oleosins accumulated concomitantly. TAC-synthesizing acyltransferase activities appeared at an earlier stage and peaked during the active period of TAC accumulation. l h e concomitant accumulation of TAC and oleosins is similar to that reported earlier for maize and soybean, and the finding has an implication for the mode of oil body synthesis during seed maturation.Seeds store TAG as food reserves for germination and postgerminative growth of the seedlings. The TAG are present in small, discrete intracellular organelles called oil bodies (Yatsu and Jacks, 1972; Appelquist, 1975; Stymne and Stobart, 1987; Huang, 1992). Isolated oil bodies have a spherical shape and possess diameters ranging from about 0.5 to 2.0 pm. They contain mostly TAG and small amounts of PL and proteins called oleosins. It is generally agreed that the oil body has a matrix of TAG surrounded by a layer of PL embedded with oleosins. The PL form a monolayer such that the acyl moieties of the molecules face inward to interact with the hydrophobic TAG in the matrix, and the hydrophilic PL head groups are exposed to the cytosol. The embedded oleosin molecule is composed of three structural domains: an N-terminal amphipathic domain, a central hydrophobic domain, and a C-terminal amphipathic a-helical domain (Vance and Huang, 1987; Qu and Huang, 1990; Murphy et al., 1991; Tzen et al., 1992). It is predicted that the hydrophobic portion Supported by U.S. Department of Agriculture grant 91-01430 (A.H.C.H.).* Corresponding author; fax 1-714-787-4437. 267 of the oleosin molecule penetrates the PL layer into the TAG matrix, and its amphipathic portion resides on the PL layer or protrudes to the exterior. The structure of an oil body as described in the preceding paragraph implies that the relative...

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-A bovine artificial chromosome (BAC) library of 105 984 clones has been constructed in the vector pBeloBAC11 and organized in 3-dimension pools and high density membranes for screening by PCR and hybridization. The average insert size, determined after analysis of 388 clones, was estimated at 120 kb corresponding to a four genome coverage. Given the fact that a male was used to construct the library, the probability of finding any given autosomal and X or Y locus is respectively 0.98 and 0.86. The library was screened for 164 microsatellite markers and an average of 3.9 superpools was positive for each PCR system. None of the 50 or so BAC clones analysed by FISH was chimeric. This BAC library increases the international genome coverage for cattle to around 28 genome equivalents and extends the coverage of the ruminant genomes available at the Inra resource center to 15 genome equivalents. bovine / BAC library / mapping

A French sheep case control study has been organised to estimate the effects of the PrP haplotypes on resistance to atypical scrapie. The ALHQ and AFRQ haplotypes are significantly more susceptible than the others.

-A bovine artificial chromosome (BAC) library of 105 984 clones has been constructed in the vector pBeloBAC11 and organized in 3-dimension pools and high density membranes for screening by PCR and hybridization. The average insert size, determined after analysis of 388 clones, was estimated at 120 kb corresponding to a four genome coverage. Given the fact that a male was used to construct the library, the probability of finding any given autosomal and X or Y locus is respectively 0.98 and 0.86. The library was screened for 164 microsatellite markers and an average of 3.9 superpools was positive for each PCR system. None of the 50 or so BAC clones analysed by FISH was chimeric. This BAC library increases the international genome coverage for cattle to around 28 genome equivalents and extends the coverage of the ruminant genomes available at the Inra resource center to 15 genome equivalents. bovine / BAC library / mapping

A series of 31 marker genes (one per chromosome) were localized precisely to both Q- and R-banded bovine chromosomes by fluorescence in situ hybridization (FISH), as a contribution to the revised chromosome nomenclature of the three major domestic bovidae (cattle, sheep and goat). All marker genes except one (LDHA) are taken from the Texas Nomenclature of the cattle karyotype published in 1996. Homologous probes for each marker gene were obtained by screening a bovine BAC library by PCR with specific primer pairs. After labeling with biotin, each probe preparation was divided into two fractions and hybridized to bovine chromosomes identified either by Q or R banding. Clear signals and good quality band patterns were observed in all cases. Results of the two series of hybridizations are totally concordant both for Q and R band chromosome numbering and precise band localization. This work permits an unambiguous correlation between the Q/G- and R-banded 31 bovine chromosomes, including chromosomes 25, 27 and 29 which remained unresolved in the Texas Nomenclature (1996). Hybridization of the chromosome 29 marker gene to metaphase spreads from a 1;29 Robertsonian translocation bull carrier showed a positive signal on the short arm of this rearranged chromosome, confirming that the numbering of this long-known translocation in cattle is correct when referring to the Texas Nomenclature (1996). Taking into account that cattle, goat and sheep have very similar banded karyotypes, the data presented here will help to establish a definite and complete reference chromosome nomenclature for these species.

Although susceptibility to scrapie is largely controlled by the PRNP gene, we have searched for additional genomic regions that affect scrapie incubation time in sheep, using two half-sib families with a susceptible PRNP genotype and naturally infected by scrapie. Quantitative trait loci were detected on OAR6 and OAR18.

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.