Abstract
Caenorhabditis briggsae is emerging as an attractive model organism not only in studying comparative biology against C. elegans, but also in developing novel experimentation avenues. In particular, recent identification of a new Caenorhabditis species, C. sp.9 with which it can mate and produce viable progeny provides an opportunity for studying the genetics of hybrid incompatibilities (HI) between the two. Mapping of a specific HI locus demands repeated backcrossing to get hold of the specific genomic region underlying an observed phenotype. To facilitate mapping of HI loci between C. briggsae and C. sp.9, an efficient mapping method and a genetic map ideally consisting of dominant markers are required for systematic introgression of genomic fragments between the two species. We developed a fast and cost-effective method for high throughput mapping of dominant loci with resolution up to 1 million bps in C. briggsae. The method takes advantage of the introgression between C. briggsae and C. sp.9 followed by PCR genotyping using C. briggsae specific primers. Importantly, the mapping results can not only serve as an effective way for estimating the chromosomal position of a genetic locus in C. briggsae, but also provides size information for the introgression fragment in an otherwise C. sp.9 background. In addition, it also helps generate introgression line as a side-product that is invaluable for the subsequent mapping of HI loci. The method will greatly facilitate the construction of a genetic map consisting of dominant markers and pave the way for systematic isolation of HI loci between C. briggsae and C. sp.9 which has so far not been attempted between nematode species. The method is designed for mapping of a dominant allele, but can be easily adapted for mapping of any other type of alleles in any other species if introgression between a sister species pair is feasible.
Highlights
C. briggsae, a close relative of C. elegans has gained increasing attention in biomedical research in recent years
Overall mapping strategy To facilitate rapid mapping of dominant loci in C. briggsae, we developed a straightforward mapping method that took advantage of introgression between C. briggsae and its sister species C. sp.9 followed by genotyping with single worm PCR using C. briggsae specific primers (Figure 4)
Given the fact that a substantial portion of the hybrid progeny between C. briggsae and C.sp.9 are viable [14], we reasoned that if we cross a C. briggsae dominant marker into C. sp.9 and repeatedly backcross the hybrid progeny expressing the marker with C. sp.9 for multiple generations, only a minimal amount of C. briggsae genomic fragment that is closely linked to the marker will be retained in an otherwise C. sp.9 background due to recombination
Summary
C. briggsae, a close relative of C. elegans has gained increasing attention in biomedical research in recent years. Most of these new species are more related to C. briggsae than to C. elegans in the phylogenetic analysis One of these species, C. sp. is able to mate and produce hybrid viable progeny with C. briggsae [14], hereafter termed as its sister species, providing an unprecedented opportunity for studying the genetic and molecular mechanisms of hybrid incompatibility (HI) between the nematode species. In Drosophila species, flagging and mapping of a chromosomal fragment are primarily achieved by a combination of P element transposes with a dominant and visible white gene as a marker [17] The former allows the random insertion of a transgene into a Drosophila genome while the latter permits the selection of the transgenic animals from those without transgene insertion
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