A genetic map of index DNA loci on bovine chromosome 21

Sex-specific telomere redistribution and synapsis initiation in cattle oogenesis

The process of homolog pairing is well characterised in meiosis of male mammals, but much less information is available from female meiosis. We have therefore studied telomere dynamics by FISH and synapsis formation by immunostaining of synaptonemal complex proteins (SCP3, SCP1) on ovarian sections from 15 bovine fetuses, which covered the entire female prophase I. Telomeres displayed a dispersed intranuclear distribution in oogonia and relocated to the nuclear periphery during the preleptotene stage. Tight telomere clustering (bouquet formation) coincided with synapsis initiation at the leptotene/zygotene transition. Clustering of telomeres persisted during zygotene and even into the pachytene stage in a subset of nuclei, while it was absent in diplotene/dictyotene stage nuclei. Thus, the bouquet stage in the bovine female lasts significantly longer than in the male. Further, we observed that synapsis in the female initiated both terminally and interstitially in earliest zygotene stage oocytes, which contrasts with the predominantly terminal synapsis initiation in early zygotene spermatocytes of the bovine male. Altogether, our data disclose a sex-specific difference in telomere dynamics and synapsis initiation patterns in male and female bovine germ cells that may be related to the sex-specific differences in recombination rates observed in this and other mammalian species.

Physical and linkage mapping of the bovine genome with cosmids

We have initiated a mapping strategy using cosmid clones to chromosomally anchor a high-resolution bovine genetic linkage map. Ten cosmids containing microsatellites were assigned to bovine chromosomes by fluorescence in situ suppression hybridization (FISH). Four cosmid clones, three of which contain an informative microsatellite, were assigned to autosomes 5, 13, 24, and 28. The assignment to autosome 13 anchors bovine syntenic group U11. Two additional cosmid clones, each containing informative microsatellites, are assigned to autosomes 9 and 29, anchoring bovine linkage groups U2 and U8, respectively. Four cosmid clones, three of which contain informative microsatellites, also provide the first assignment to autosome 25, anchoring bovine syntenic group U7 and orienting the corresponding linkage group relative to the centromere.

Sequence conservation of microsatellites between Bos taurus (cattle), Capra hircus (goat) and related species. Examples of use in parentage testing and phylogeny analysis

A panel of 70 bovine microsatellites was tested for amplification from goat DNA. Forty-three could be successfully amplified by PCR, 20 of which were tested for polymorphism. Three were applied for parentage testing in goat families and their exclusion probability evaluated. Fourteen were cloned and sequenced from goat DNA, and goat and bovine sequences were compared to evaluate interspecific conservation. Correlation between the structure of the dinucleotide repeat and the number of alleles was studied and indicated that interruption(s) in the repeat could explain the difference in the levels of polymorphism between the two species. This study provides a valuable in vivo clue to the mechanism generating polymorphism in microsatellites. Sequence conservation was also observed for several microsatellites with two wild species of Bovidae, Nilgaï (Boselaphus tragocamelus) and Himalayan Tur (Capra cylindricornis), and with one species of Cervidae, the fallow deer (Cervus dama). This study showed that an estimated 40 per cent of the microsatellites isolated from cattle will prove useful to study the caprine genome and to characterize economically important genetic loci in this species. Moreover, bovine microsatellites were shown to constitute very useful tools for the study of genetic diversity of the Artiodactyla.

Chromosomal localization of the callipyge gene in sheep (Ovis aries) using bovine DNA markers

A mutation causing muscular hypertrophy, with associated leanness and improved feed efficiency, has been recently identified in domestic sheep (Ovis aries). Preliminary results indicate that an autosomal dominant gene may be responsible for this economically advantageous trait. We have exploited the conservation in sequence and chromosomal location of DNA markers across Bovidae to map the corresponding callipyge locus to ovine chromosome 18 using a battery of bovine chromosome 21 markers. Chromosomal localization of the ovine callipyge locus is the first step toward positional cloning of the corresponding gene.