A Genetic Linkage Map of the Apicomplexan Protozoan Parasite Eimeria tenella

Abstract

Apicomplexan protozoan parasites have complex life cycles that involve phases of asexual and sexual reproduction. Some genera have intermediate insect hosts, for example, Plasmodium spp. (the cause of malaria), but related genera such as Eimeria spp. (causative agents of coccidiosis in poultry) have a direct life cycle occurring in only a single host. Mechanisms that regulate the life cycles of apicomplexan parasites are unknown, but the intracellular growth of avian Eimeria spp. is easily shortened by serial selection for the first parasites to complete the transition from asexual to sexual reproduction (to yield so-called precocious lines). To investigate the genetic basis of such an abbreviated life cycle, we have used the species E. tenella and analyzed the inheritance of 443 polymorphic DNA markers in 22 recombinant cloned progeny derived from a cross between parents that had selectable phenotypes of precocious development or resistance to an anticoccidial drug. The markers were placed in 16 linkage groups (which defined 12 chromosomes) and a further 57 unlinked groups. Two linkage groups showed an association (P = .0105) with the traits of precocious development or drug-resistance and were mapped to chromosome 2 (ca 1.2 Mbp) and chromosome 1 (ca 1.0 Mbp), respectively. The map provides a framework for further studies on the identification of genetic loci implicated in the regulation of the life cycle of an important protozoan parasite and a representative of a major taxonomic group.[A table with the segregation data is available as an online supplement at http://www.genome.org.]

Allelic segregation and independent assortment in T. brucei crosses: Proof that the genetic system is Mendelian and involves meiosis

“…However, given the small number of available progeny clones generated from each cross, it has not been possible to prove Mendelian inheritance. The importance of determining the mechanism of genetic exchange in T.brucei lies in understanding this fundamental biological process of the parasite, providing a framework for the analysis of the population genetics and opening up the possibility of using genetic analysis as a tool for gene discovery, as has undertaken in Plasmodium falciparum [17,18], Plasmodium chabaudi chabaudi [19,20,21], Toxoplasma gondii [22] and Eimeria tenella [23]. In contrast to these haploid apicomplexan parasites, T.brucei is diploid and so the progeny of a cross would be expected to be heterozygous for markers that are homozygous and different between the parents but would inherit only one allele from each locus that is heterozygous in the parents.…”

Recent Advances in Biology and Immunobiology ofEimeriaSpecies and in Diagnosis and Control of Infection with These Coccidian Parasites of Poultry

“…within host cells are not known. However, through study of precocious and drug-resistant lines of E. tenella (86,87), two linkage groups associated with these traits have been identified and mapped to parasite chromosomes 1 and 2. This information may help identify other genetic loci involved in regulating the life cycle of E. tenella.…”

Designing strategies for the control of coccidiosis in chickens on poultry farms using modern diagnostic tools

“…Nevertheless, initial PCR efforts were focused on finding variations in genome sequences or organization. Blake et al 38 and Shirley and Harvey 39 were some of the first to use random primers in an amplified fragment length polymorphism technique to produce restriction fragments from genomic DNA (gDNA) and construct genetic lineage maps of Eimeria species. This high-stringency fingerprinting technique is useful because it does not require previous knowledge of the genome sequence; however, it cannot be used to detect mixed-species infections, because of an overlap between the species-specific bands on electrophoretic gels.…”