Mapping of Char10, a novel malaria susceptibility locus on mouse chromosome 9

Abstract

Resistance to blood-stage malaria in AcB55 and AcB61 is caused by a loss of function mutation in pyruvate kinase (Pklr I90N ). Likewise, pyruvate kinase (PK) deficiency in humans is protective against Plasmodium replication in vitro. We identified a third AcB strain, AcB62 that also carries the Pklr I90N mutation. However, AcB62 mice were susceptible to P.chabaudi infection and showed high levels of parasite replication (54-62% peak parasitemia). AcB62 mice showed the hallmarks of PK deficiencyassociated anemia similar to AcB55/61 with reticulocytosis, splenic red pulp expansion, tissue iron overload, and increased expression of iron metabolism proteins. This suggests that malaria susceptibility in AcB62 is not because of absence of PK deficiency-associated pathophysiology. To map novel genetic factors affecting malaria susceptibility in AcB62, we generated an informative F2 population using AcB62 (Pklr I90N ) and CBA-Pk slc (Pklr G338D ) as progenitors and identified a novel locus on chromosome 9 (Char10; LOD ¼ 7.24) that controls peak parasitemia. A weaker linkage to the Pklr region of chromosome 3 (LOD ¼ 3.7) was also detected, a finding that may reflect the segregation of the two defective Pklr alleles. AcB62 alleles at both loci are associated with higher peak parasitemia. These results identify Char10 as a novel locus modulating severity of malaria in the context of PK deficiency.

The contribution of Plasmodium chabaudi to our understanding of malaria

“…These regions are located on chromosomal regions named chabaudi resistance ( Char ) loci [25,26]. Ten Char loci have been defined to date, and these regions include genes encoding proinflammatory cytokines and signaling pathways as well as immune cell adhesion molecules.…”

The mouse Char10 locus regulates severity of pyruvate kinase deficiency and susceptibility to malaria

“…Char10 was previously shown to regulate parasitemia levels at the peak of infection in pyruvate kinase deficient [AcB62xCBA/Pk] F2 mice, and was mapped to the proximal portion of chromosome 9[19]. This cross segregates two Pklr mutations, the Pklr I90N allele from AcB62 and the more severe Pklr G338D mutation from CBA/Pk[27].…”

“…The LOD trace was adapted from Min-Oo et al . 2010[19]. The schematic representation of the recombinant chromosome 9 is shown below for the Char10C incipient congenic line and for parental CBA/Pk and AcB62.…”

“…Linkage analysis identified a major locus on chr 9 controlling parasitemia in infected animals, that we designated Char10 (LOD = 10.8; 95% confidence interval 51.3Mb-68.3Mb). There was an additional effect on chr 3 (LOD = 3.8; near Pklr ), due to Pklr mutant alleles of different severity segregating in this cross[19,27]. Hence the Char10 locus is a modifier of the malaria-protective effective effect of PK-deficiency.…”

“…Yet, AcB62 is susceptible to P . chabaudi with high peak parasitemia (~60%) compared to AcB55/61 (~35%) and to C57BL/6J resistant controls (~35%), suggesting the presence of a genetic modifier of the Pklr I90N malaria-protective effect in this strain[19]. A genome scan in PK-deficient [AcB62 X CBA/Pk]F2 mice infected with P .…”