Integrating genetics and genomics to identify new leads for the control ofEimeriaspp.

Abstract

Eimerian parasites display a biologically interesting range of phenotypic variation. In addition to a wide spectrum of drug-resistance phenotypes that are expressed similarly by many other parasites, the Eimeria spp. present some unique phenotypes. For example, unique lines of Eimeria spp. include those selected for growth in the chorioallantoic membrane of the embryonating hens egg or for faster growth (precocious development) in the mature host. The many laboratory-derived egg-adapted or precocious lines also share a phenotype of a marked attenuation of virulence, the basis of which is different as a consequence of the in ovo or in vivo selection procedures used. Of current interest is the fact that some wild-type populations of Eimeria maxima are characterized by an ability to induce protective immunity that is strain-specific. The molecular basis of phenotypes that define Eimeria spp. is now increasingly amenable to investigation, both through technical improvements in genetic linkage studies and the availability of a comprehensive genome sequence for the caecal parasite E. tenella. The most exciting phenotype in the context of vaccination and the development of new vaccines is the trait of strain-specific immunity associated with E. maxima. Recent work in this laboratory has shown that infection of two inbred lines of White Leghorn chickens with the W strain of E. maxima leads to complete protection to challenge with the homologous parasite, but to complete escape of the heterologous H strain, i.e. the W strain induces an exquisitely strain-specific protective immune response with respect to the H strain. This dichotomy of survival in the face of immune-mediated killing has been examined further and, notably, mating between a drug-resistant W strain and a drug-sensitive H strain leads to recombination between the genetic loci responsible for the specificity of protective immunity and resistance to the anticoccidial drug robenidine. Such a finding opens the way forward for genetic mapping of the loci responsible for the induction of protective immunity and integration with the genome sequencing efforts.

Sequence analysis of the PIP5K locus in Eimeria maxima provides further evidence for eimerian genome plasticity and segmental organization

“…By scrutinizing genetic codes in the genomes and unraveling the complex biochemical and genetic mechanisms that underlie host-parasite interactions, potential targets for novel anticoccidial drugs and vaccines can be recognized (Shirley et al, 2004). Among the potential target proteins, phosphatidylinositol 4-phosphate 5-kinase (PIP5K) has previously been reported to play important roles in diverse biological processes, including signal transduction, cell secretion, vesicular trafficking, and regulation of cytoskeleton assembly (Kunz et al, 2000).…”

Eimeria maxima phosphatidylinositol 4-phosphate 5-kinase: locus sequencing, characterization, and cross-phylum comparison

“…are a group of obligate intracellular parasites belonging to the phylum Apicomplexa and are responsible for causing coccidiosis among livestock such as chickens, turkeys, cattle, and sheep (Shirley et al 2004a). Eimerian infection can cause severe intestinal enteritis, leading to poor absorption of nutrients, weight loss, retarded growth rates, lowered egg production, diarrhea, and increased mortality rates in poultry (Shirley et al 2007).…”

Análise da expressão diferencial em três fases da esporulação de oocistos de Eimeria maxima.

“…poderia ser o resultado do pareamento dos cromossomos homólogos não duplicados e a variação individual era devido à combinação aleatória dos cromossomos (Canning e Anwar, 1968). Porém mais tarde, após o mapeamento de ligação gênica em E. tenella foi demonstrado que há recombinação durante a meiose (Shirley e Harvey, 2000;Shirley et al, 2004a).…”

“…Em paralelo, os cromossomos 1 e 2 de E. tenella foram totalmente sequenciados e apresentam uma complexidade de 1Mpb e 1,2Mpb respectivamente (Ling et al, 2007). O cromossomo 1 possui uma organização genômica incomum segmentada em regiões R (feature-rich), ricas em repetições, apresentando elementos similares a transposons e repetições teloméricas, confirmando estudos preliminares que apontavam para uma distribuição frequente de regiões repetitivas no genoma de Eimeria tenella (Shirley, 2000;Shirley et al, 2004a). Também apresenta segmentos livre de repetições P (feature-poor) (Ling et al, 2007).…”